JP3742203B2 - Semiconductor laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a semiconductor laser using a compound semiconductor material.To theIn particular, semiconductor lasers using InGaAlBN-based materialsTo theRelated.
[0002]
[Prior art]
In recent years, a semiconductor laser using an InGaAlN-based material has been developed as a short wavelength light source required for increasing the density of an optical disk. A semiconductor laser made of this kind of material can be focused to a small beam by shortening the wavelength, and is expected as a light source for high-density information processing such as an optical disk. As a structure realizing oscillation by current injection in this material system, a semiconductor laser using a multiple quantum well structure has been reported (for example, the following document).
[0003]
1) S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, H. Kiyoku and Y. Sugimoto: "InGaN-based multi-quantum-well-structure laser diodes", Jpn J. Appl. Phys., 35 (1996) pp.L74-L76.
2) S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, H. Kiyoku and Y. Sugimoto: "InGaN multi-quantum-well-structure laser diodes with cleaved mirror facets" , Jpn.J.Appl.Phys., 35 (1996) pp.L217-L220.
It is known that a multiple quantum well structure using a thin film active layer with respect to a bulk active layer can significantly reduce the threshold value. However, InGaAlN-based materials still have a high threshold current density and a high operating voltage, and thus there are many problems to realize continuous oscillation.
[0004]
One of the causes of the high operating voltage in InGaAlN-based materials is that the p-type contact resistance is extremely large. In the already reported electrode stripe structure, the voltage drop in the p-type electrode stripe is large, the operating voltage becomes high, and the generation of heat in this region cannot be ignored. In order to reduce the contact resistance, the electrode area may be increased. However, in the above electrode stripe structure, the threshold current value increases as the electrode area is increased, and the fundamental transverse mode oscillation is also suppressed due to the large current injection region. It becomes possible.
[0005]
In applications such as optical disk systems, the fundamental transverse mode oscillation is indispensable because the outgoing beam of the semiconductor laser needs to be focused to a very small spot, but a transverse-mode control structure is realized with an InGaAlN laser. It has not been. In the conventional material system, for example, only an InGaAlP-based ridge stripe type SBR laser has been reported (the following document).
[0006]
3) M. Ishikawa et al .: Extended Abstracts, 19th Conf. Solid State Devises and Materials, Tokyo (1987) pp. 115-118.
However, since the material system of the InGaAlN laser is different from that of the SBR laser, this structure cannot be applied as it is. As a current confinement structure in an InGaAlN laser,
4) Japanese Patent Laid-Open No. 8-111558 (semiconductor laser element)
In addition, a structure using GaN as a current confinement layer is disclosed. With this structure, current confinement is possible, but since there is no light confinement effect, it is difficult to obtain a high-quality outgoing beam without astigmatism.
[0007]
In general, in order for the current confinement layer provided in the cladding layer to also act as a light confinement layer, it is necessary to set the composition, thickness, distance from the active layer, and the like to predetermined values. In particular, in an InGaAlN laser, since the oscillation wavelength is short, even if the composition is the same, the waveguide mechanism is completely different depending on the thickness and position. For this reason, a stable fundamental transverse mode oscillation cannot be obtained simply by providing a current confinement layer.
[0008]
In addition, in the InGaAlN-based crystal growth, when a layer containing Al such as GaAlN is grown thick, there is a problem that cracks occur in the layer containing Al because the lattice constant differs from that of the underlying GaN. For this reason, the transverse mode confinement in the layer direction (vertical direction) is not performed well, and the threshold value increases, or in some cases, the waveguide mode itself cannot exist.
[0014]
[Problems to be solved by the invention]
  Thus, in the conventional InGaAlN-based semiconductor laser, it is difficult to create a transverse mode control structure, and it is difficult to realize a laser that continuously oscillates in the fundamental transverse mode..
[0018]
  An object of the present invention is to provide an InGaAlBN-based semiconductor laser that can continuously oscillate in a fundamental transverse mode and can obtain a high-quality outgoing beam free of astigmatism suitable for a light source such as an optical disk system.TheIt is to provide.
[0023]
[Means for Solving the Problems]
In order to achieve the above object, in the semiconductor laser according to the present invention, an optical confinement layer having a refractive index larger than that of the cladding layer is provided, and the transverse mode is controlled by the loss waveguide effect or the anti-waveguide effect. Enables continuous oscillation in the fundamental transverse mode which is low and stable.
[0024]
That is, the present invention is a double heterostructure part comprising a group III-V compound semiconductor containing nitrogen and having an active layer part sandwiched between a first conductive type cladding layer and a second conductive type cladding layer having a striped ridge. And a light confinement layer formed at least in a region other than the ridge portion in contact with the second conductivity type cladding layer side of the double heterostructure portion, wherein the light confinement layer contains nitrogen. And a refractive index of the optical confinement layer is larger than a refractive index of the cladding layer of the second conductivity type.
[0025]
Further, the present invention provides a first conductivity type In_xGa_yAl_zB_1-xyzSecond conductivity type In having a clad layer made of N (0 ≦ x, y, z, x + y + z ≦ 1) and a striped ridge_uGa_vAl_wB_1-uvwA double hetero structure part sandwiching the active layer part with a clad layer made of N (0 ≦ u, v, w, u + v + w ≦ 1), and at least in contact with the second conductivity type clad layer side of the double hetero structure part A semiconductor laser including a light confinement layer formed in a region other than the ridge portion, wherein the light confinement layer is In_pGa_qAl_rB_1-pqrN (0 ≦ p ≦ 1, 0 ≦ q <1, 0 ≦ r ≦ 1, 0 <p + r ≦ 1, 0 <p + q + r ≦ 1), and the refractive index of the optical confinement layer is a second conductivity type cladding. It is characterized by being larger than the refractive index of the layer.
[0026]
Here, preferred embodiments of the present invention include the following.
[0027]
(1) The active layer is at least In_aGa_bAl_cB_1-abcA well layer composed of N (0 ≦ a, b, c, a + b + c ≦ 1) and In_eGa_fAl_gB_1-efgA single quantum well or multiple quantum wells composed of a barrier layer made of N (0 ≦ e, f, g, e + f + g ≦ 1).
[0028]
(2) The thickness of the barrier layer should not exceed the thickness of the well layer.
[0029]
(3) For the total thickness d of the core region and the laser oscillation wavelength λ, the thickness H1 of the first conductivity type cladding layer and the thickness H2 of the second conductivity type cladding layer are:
0.18 (zd / λ)^-1/2≦ H1 / λ ≦ 0.27 (zd / λ)^-1/2
0.18 (wd / λ)^-1/2≦ H2 / λ ≦ 0.27 (wd / λ)^-1/2
It must be in a range that satisfies
[0030]
(4) Total thickness d of the well layer_actIs less than 0.5 μm.
[0031]
(5) Total thickness d of the well layer_actIs 0.045 μm or less.
[0032]
(6) Al composition of each cladding layer x_Al, Average In composition in the core region y_In, The sum of both compositions Δx (= x_Al+ Y_In), The total thickness H of the core region_coreAnd the thickness H of each cladding layer_cladFor the oscillation wavelength λ
Δx · (H_core/ Λ) ・ (H_clad/Λ)≧0.08.
[0033]
(7) The above parameters are
Δx · (H_core/ Λ) ・ (H_clad/Λ)≧0.1.
[0034]
(8) The above parameters are
Δx · (H_core/ Λ) ・ (H_clad/Λ)≦0.2.
[0035]
(9) The above parameters are
Δx · (H_core/ Λ) ・ (H_clad/Λ)≦0.15.
[0036]
(10) Al composition of each cladding layer x_AlAnd thickness H_cladIs
x_Al・ H_clad≦ 0.1 μm must be satisfied.
[0037]
(11) Al composition x of each cladding layer_AlAnd thickness H_cladIs
x_Al・ H_clad≦ 0.06μm must be satisfied.
[0038]
(12) The core region is an In formed so as to sandwich the active layer_uGa_vAl_wB_1-uvwA plurality of waveguide layers made of N (0 <u ≦ 1, 0 ≦ v <1, 0 ≦ w <1) are included. At this time, the total thickness H of the core region_coreAnd average In composition in the core region y_InIs equivalent to (y_In)^1/2・ (H_core/Λ)≧0.15.
(13)
(Y_In)^1/2・ (H_core/Λ)≧0.2.
[0039]
(14) The optical confinement layer has the same conductivity type as the second conductivity type cladding layer.
[0040]
(15) The band gap energy of the optical confinement layer is smaller than the band gap energy of the active layer portion.
[0041]
(16) The contact layer on the second conductivity type cladding layer and the optical confinement layer are made of the same material, and have a band gap intermediate between the second conductivity type cladding layer and the contact layer in the stripe region. A cap layer is provided.
[0042]
(17) A waveguide layer having a refractive index smaller than the average refractive index of the quantum well and larger than the refractive index of the cladding layer is provided between the quantum well and each cladding layer, and is in at least one of the waveguide layers or the waveguide layer. Between the quantum well and the band gap energy is larger than that of the waveguide layer._sGa_tAl_hB_1-sthAt least one carrier overflow prevention layer of N (0 ≦ s, t, h, s + t + h ≦ 1) is provided.
[0043]
(18) The Al composition h of the carrier overflow prevention layer is
0 <h <0.2
It must be in a range that satisfies
[0044]
(19) Each cladding layer of the first conductivity type and the second conductivity type is made of GaAlN, and the optical confinement layer is made of InGaN or GaAlN having a smaller Al composition than the cladding layer.
[0045]
Here, the light confinement layer can be formed as shown in any one of (i) to (iii) below. (i) The optical confinement layer is In_pGa_qAl_rB_1-pqrN (0.2 ≦ p ≦ 0.3, 0 ≦ q ≦ 0.8, 0 ≦ r ≦ 0.8, 0.2 ≦ p + q + r ≦ 1), and the refractive index of the light confinement layer is second. It is larger than the refractive index of the conductive cladding layer.
[0046]
(ii) The optical confinement layer is In_pGa_qAl_rB_1-pqrN (0 ≦ p ≦ 0.95, 0 ≦ q ≦ 0.95, 0.05 ≦ r ≦ 0.3, 0.05 ≦ p + q + r ≦ 1).
[0047]
(iii) The optical confinement layer is In_pGa_qAl_rB_1-pqrN (0 ≦ p, q, 0.05 ≦ r ≦ 0.1, 0.05 ≦ p + q + r ≦ 1), and the refractive index of the light confinement layer is larger than the refractive index of the second conductivity type cladding layer.
[0048]
(20) Use a sapphire or SiC substrate as the base substrate.
[0049]
(21) The ridge portion of the second conductivity type cladding layer is formed to protrude downward on the substrate side, or to protrude upward on the opposite side of the substrate.
[0050]
(22) Contact layer absorption loss α is
α ≧ 100cm^-1Satisfying
[0051]
(23) Contact layer absorption loss α is
α ≧ 500cm^-1Satisfying
[0058]
(Function)
According to the present invention, in an InGaAlBN semiconductor laser, a ridge portion is provided in one clad layer of a double heterostructure portion, and a region other than the ridge portion is provided with an In_pGa_qAl_rB_1-pqrN (0 ≦ p ≦ 1, 0 ≦ q <1, 0 ≦ r ≦ 1, 0 <p + r ≦ 1, 0 <p + q + r ≦ 1), and a light confinement layer having a higher refractive index than the cladding layer is provided. . This optical confinement layer provides current confinement and forms a waveguide structure with a refractive index distribution to control the transverse mode, thus reducing the threshold current density and enabling continuous oscillation in the fundamental transverse mode. Become.
[0059]
Here, the optical confinement layer as described above is considered to be impossible to selectively grow because the lattice constant is greatly different from that of the double heterostructure portion. For this reason, there is no technical idea of forming a light confinement layer other than the ridge portion of the cladding layer in the conventional InGaAlN semiconductor laser. However, based on the diligent research and experiments by the present inventors, by optimizing various conditions by the metal organic chemical vapor deposition (MOCVD) method, the molecular beam epitaxy (MBE) method, etc., the optical closure of the above materials can be achieved. It has been found that selective growth of the buried layer is possible.
[0060]
In addition, it has been clarified that in the structure in which the InGaAlBN-based optical confinement layer having an In composition larger than 0 is provided, the carrier density of the cladding layer therebelow becomes high. This is because the inactivation of the Mg acceptor due to H or the like is suppressed, and it has been found that the carrier overflow is significantly reduced as compared with the structure in which the light confinement layer is not provided. By providing the light confinement layer as in the present invention, the threshold current density can be reduced and the continuous oscillation in the fundamental transverse mode can be achieved.
[0064]
DETAILED DESCRIPTION OF THE INVENTION
The details of the present invention will be described below with reference to the illustrated embodiments.
[0065]
(First embodiment)
FIG. 1 is a cross-sectional view showing a configuration of a semiconductor laser according to the first embodiment of the present invention.
[0066]
In the figure, reference numeral 10 denotes a sapphire substrate, on which a GaN buffer layer 11, an n-type GaN contact layer 12, an n-type GaAlN cladding layer 13, an n-type GaN waveguide layer 14, an n-type GaAlN overflow prevention layer 15, An InGaN multiple quantum well (MQW) active layer 16, a p-type GaAlN overflow prevention layer 17, a p-type GaN waveguide layer 18, and a p-type GaAlN cladding layer 19 are grown. These crystal growths are performed by MOCVD method or MBE method.
[0067]
The p-type GaAlN cladding layer 19 is etched away to the middle except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the cladding layer 19. In addition to the ridge portion of the p-type GaAlN cladding layer 19, an n-type InGaN optical confinement layer 20 is selectively buried and a p-type GaN contact layer 21 is formed on the cladding layer 19 and the optical confinement layer 20. Yes. These crystal growths are also performed by the MOCVD method or the MBE method.
[0068]
The portions from the p-type GaN contact layer 21 to the n-type GaAlN cladding layer 13 are partially removed, and a part of the n-type GaN contact layer 12 is exposed. A p-side electrode 22 is formed on the p-type GaN contact layer 21, and an n-side electrode 23 is formed on the exposed portion of the n-type GaN contact layer 12.
[0069]
In this embodiment, the active layer portion (hereinafter also referred to as a core region) of the laser is In_aGa_1-aN well layer / In_eGa_1-eThe SCH structure has GaAlN overflow prevention layers 15 and 17 and GaN waveguide layers 14 and 18 provided on both sides of an active layer 16 of a multiple quantum well (MQW) made of an N barrier layer (a ≧ e). In this specification, the core region is a multilayer structure portion located between both clad layers, and specifically includes at least an active layer, and optionally includes a waveguide layer, a carrier overflow prevention layer, or both. I have.
[0070]
In this embodiment, In_xGa_yAl_zB_1-xyzSince the n-type cladding layer 13 made of an N (0 ≦ x, y, z, x + y + z ≦ 1) material does not contain In and B, Ga_1-zAl_zSince the active layer 16 does not contain Al, the well layer and the barrier layer constituting the MQW are each In._aGa_1-aN and In_eGa_1-eN. Similarly, In_uGa_vAl_wB_1-uvwSince the p-type cladding layer 19 made of an N (0 ≦ u, v, w, u + v + w ≦ 1) material does not contain In and B, Ga_1-wAl_wN.
[0071]
Next, the operation of the semiconductor laser configured as described above will be described. The lateral mode control, threshold reduction, and carrier overflow prevention will be described in this order.
[0072]
(Horizontal horizontal mode control)
In the semiconductor laser of this embodiment, since the n-type InGaN optical confinement layer 20 is close to the core region outside the stripe, the equivalent refractive index is small in the region outside the stripe, and a refractive index distribution is formed in the horizontal direction. Mode confinement.
[0073]
Here, the In composition of the n-type InGaN optical confinement layer 20 is the In composition in the active layer 16._aGa_1-aIt is set higher than the In composition of the N well layer. Therefore, the refractive index of the light confinement layer 20 is larger than the refractive index of the well layer. Further, the band gap energy of the optical confinement layer 20 is smaller than the band gap energy of the well layer.
[0074]
Further, the refractive index of the optical confinement layer 20 is larger than the refractive index of the p-type GaAlN cladding layer 19 in the stripe portion, and the band gap energy of the optical confinement layer 20 is the band gap energy of the p-type GaAlN cladding layer 19 in the stripe portion. Smaller than.
[0075]
In this way, the equivalent refractive index becomes small despite the optical confinement layer 20 having a refractive index larger than that of the stripe portion. The reason is as follows. That is, since the optical confinement layer 20 has a large absorption loss with respect to the oscillation wavelength, the attenuation of the waveguide mode is large. For this reason, the proportion of the waveguide mode distribution in the optical confinement layer 20 is extremely small. That is, since the contribution of the light confinement layer 20 to the equivalent refractive index is small, the equivalent refractive index becomes smaller than that of the stripe portion as a result.
[0076]
In summary, the semiconductor laser having the structure shown in FIG. 1 has a loss waveguide structure with a small equivalent refractive index outside the stripe and a large loss. This loss waveguide structure is extremely effective for stabilizing the fundamental transverse mode. That is, since there is a loss region outside the stripe, a high-order mode with a large squeeze has a greater loss or cut-off than the fundamental mode, and therefore only the fundamental mode can oscillate stably.
[0077]
Such a loss waveguide structure can be realized for the first time by using a material having a band gap energy smaller than that of the core region as the optical confinement layer 20. As the optical confinement layer, for example, InGaN is suitable because it has a large absorption loss.
[0078]
Next, conditions for such transverse mode control will be described.
[0079]
FIG. 2A shows an equivalent refractive index difference Δn between the stripe portion and the outside of the stripe._eq, The distance between the optical confinement layer 20 and the core region outside the stripe (distance to the p-type GaN waveguide layer 17) h_outDependence on is shown. FIG. 2 (b) shows the loss α for the fundamental mode.₀And the loss difference Δα between the primary mode and the fundamental mode, h_outDependence on is shown.
[0080]
In these figures, the layer structure of the stripe portion is represented by n-type Ga._0.85Al_0.15N / n-GaN (0.1 μm) / MQW / p-type GaN (0.1 μm) / p-type Ga_0.85Al_0.15N and the layer structure outside the stripe is n-type Ga_0.85Al_0.15N / n-type GaN (0.1 μm) / MQW / p-type GaN (0.1 μm) / p-type Ga_0.85Al_0.15N (h_outThe waveguide mechanism in the case of (μm) / n-type InGaN is analyzed.
[0081]
In the figure, MQW is In_0.18Ga_0.82N well layer (2nm) / In_0.04Ga_0.96Two configurations with 5 pairs of N barrier layers (4 nm) and 10 pairs were used.
[0082]
For stabilization of the fundamental transverse mode, it is desirable that the loss difference between the higher order mode and the fundamental mode is large. From this point of view, h_outShould be larger. But h_outIs too large_eqBecomes smaller. 10^-FourSince a change in the refractive index can be caused by the plasma effect due to carrier injection, the waveguide structure due to the refractive index distribution becomes unstable in this region. Therefore, h_outIs preferably set to 0.3 μm or less, more preferably 0.2 μm or less.
[0083]
FIG. 3 (a) shows h_out= Threshold current density J for 0.2 μm_th, The dependency on the stripe width is shown. FIG. 3 (b) shows the same h_outIn the case of₀, Δα shows the dependence on the stripe width.
[0084]
If the stripe width is large, Δα becomes small, and therefore higher order modes are likely to occur. On the other hand, if the stripe width is small, the fundamental mode loss α₀Becomes the threshold current density J_thRises. Therefore, in this case, the stripe width W is desirably set to 3 μm or more.
[0085]
Further, as shown in FIGS. 4A and 4B, the composition of the light confinement layer greatly affects the waveguide mechanism. These figures show the layer structure of the stripe portion as n-type Ga._0.85Al_0.15N / n-type GaN (0.1 μm) / MQW / p-type GaN (0.1 μm) / p-type Ga_0.85Al_0.15N and the layer structure outside the stripe is n-type Ga_0.85Al_0.15N / n-type GaN (0.1 μm) / MQW / p-type GaN (0.1 μm) / p-type Ga_0.85Al_0.15This is an analysis of the waveguide mechanism in the case of N (0.05 μm) / n-type InGaAlN. The n-type InGaAlN layer outside the stripe corresponds to the light confinement layer.
[0086]
Where MQW is In_0.2Ga_0.8N well layer (2nm) / In_0.05Ga_0.95In this configuration, five pairs of N barrier layers (4 nm) are provided.
[0087]
Here, FIG. 4A shows that the light confinement layer is In._xGa_1-xN or Ga_1-xAl_xEquivalent refractive index difference Δn inside and outside the stripe for N_eqAnd the relationship between the composition. x_InThe region of ≧ 0.2 corresponds to the loss waveguide type of the present embodiment. As shown in FIG. 4B, the loss waveguide region has a small astigmatism difference (when the stripe width is 5 μm), so that a beam characteristic suitable for optical disc application can be obtained.
[0088]
0 ≦ x_InThe region of ≦ 0.2 is a region where the vertical waveguide mode is not formed outside the stripe, and the oscillation mode becomes unstable.
[0089]
On the other hand, the optical confinement layer is Ga having a refractive index smaller than that of the waveguide layer._1-xAl_xWhen N is used, the waveguide mechanism can be classified into three regions as shown in FIG. The first region is a range in which the Al composition of the light confinement layer is larger than the Al composition of the cladding layer of the stripe portion, that is, the refractive index of the light confinement layer is smaller than the refractive index of the clad layer. It becomes a waveguide structure.
[0090]
The second region is a range in which the Al composition of the light confinement layer is close to the Al composition of the cladding layer, and a small Δn_eqTherefore, it has a gain waveguide structure and has a very large astigmatic difference as shown in the figure. Such a large astigmatic beam is not suitable for optical disc applications.
[0091]
The third region is notable in FIG. 4B, and the Al composition of the optical confinement layer is smaller than the Al composition of the cladding layer and larger than the Al composition of the waveguide layer, that is, the refractive index is high. The region is larger than the cladding layer and smaller than the waveguide layer, and has an “anti-waveguide region” in which the astigmatic difference is reduced. As shown in FIG. 4A, this anti-waveguide region has Δn_eqIs negative, and the equivalent refractive index outside the stripe is larger than the equivalent refractive index inside the stripe. An embodiment using this anti-waveguide region will be described later.
[0092]
FIG. 4B also shows that a small astigmatic difference can be obtained even in the real refractive index waveguide region in which the Al composition of the light confinement layer is larger than the Al composition of the cladding layer.
[0093]
Next, the fact that the loss waveguide structure or anti-waveguide structure according to the present invention is excellent in terms of stabilization of the fundamental transverse mode will be described.
[0094]
FIG. 5A shows the dependence of the stripe width on the astigmatic difference of the gain waveguide type, the actual refractive index waveguide type, the loss waveguide type, and the anti-waveguide type. FIG. 5B shows the dependency of the stripe width on the waveguide loss difference Δα between the primary mode and the fundamental mode for each waveguide type. A small astigmatic difference is desirable for the beam characteristics. A large mode loss difference is desirable from the viewpoint of stabilization of the fundamental transverse mode.
[0095]
As shown in the figure, the gain waveguide type has a large mode loss difference, but is extremely difficult to use in an optical disc application or the like because of a very large astigmatic difference. The real refractive index waveguide type has a small astigmatism difference, but also has a small mode loss difference. Therefore, when the stripe width is increased, a higher-order mode is likely to be generated.
[0096]
On the other hand, the loss waveguide type and the anti-waveguide type have a small astigmatic difference and can secure a large mode loss difference even with a large stripe width. A larger stripe width facilitates the fabrication process and increases the degree of freedom in design. Thus, it can be seen that the semiconductor laser according to the present invention is superior in both characteristics and ease of fabrication.
[0097]
(Vertical horizontal mode control)
By the way, the problem in InGaAlN-based crystal growth is that, for example, when a layer containing Al such as a GaAlN layer is grown thickly, the lattice constant differs from that of the underlying GaN. Therefore, the layer containing Al (GaAlN) Cracks are generated. In order to prevent this type of crack, it is necessary to reduce the Al composition or the thickness of the GaAlN layer. On the other hand, when a layer containing Al is used for the cladding layer of the laser, a refractive index difference of a certain degree or more (that is, an Al composition difference with the active layer) and a cladding layer thickness H for optical confinement._cladis required. Active layer total thickness d, cladding layer thickness H_clad, Cl composition layer-active layer Al composition difference ΔX_A1FIG. 6A and FIG. 6B show the relationship between and the waveguide mode loss α.
[0098]
As you can see, ΔX_A1Is large, H_cladIs larger, α can be smaller, but practically α is 20 cm.^-1It is enough if it can be made as small as possible. Therefore, α is 100cm^-1Smaller than 20cm^-1When a larger range is obtained, the following equation (1) is obtained.
[0099]
0.18 (ΔX_A1d / λ)^-1/2≦ H_clad/Λ≦0.27 (ΔX_A1d / λ)^-1/2... (1)
Therefore, the cladding layer thickness H_cladIn this range, a laser structure having a thickness that does not cause cracks during crystal growth and a small loss can be obtained.
[0100]
Here, another point to be considered in the InGaAlN laser of the above formula (1) is that the contact layer, which is the outer layer of the cladding layer, has a refractive index larger than the refractive index of the cladding layer, and the oscillation wavelength. It is a point transparent to. For this reason, the cladding layer thickness H_cladIs not sufficiently large, the waveguide structure in the layer direction (vertical direction) is anti-waveguided, and in some cases, the threshold value may be significantly increased, or there may be no waveguide mode.
[0101]
FIG. 7 shows the cladding layer thickness H in the SCH-MQW structure._cladAnd guide layer thickness H_guideAnd an example of the relationship between the boundary line of the waveguide mode. Here, as a layer structure, n-type GaN / n-type Ga_0.85Al_0.15N (H_cladμm) / n-type In_0.06Ga_0.94N (H_guideμm) / MQW / p type In_0.06Ga_0.94N (H_guideμm) / p-type Ga_0.85Al_0.15N (H_cladAn example of calculation in the case of μm) / n-type GaN is shown. MQW is In_0.2Ga_0.8N well layer (2nm) / In_0.05Ga_0.95The N barrier layer (4 nm) was configured to have 10 pairs. The absorption coefficient of the outermost layer GaN is 500 cm.^-1It was.
[0102]
The shaded area in FIG. 7 is an area where there is no waveguide mode. In the region where the waveguide mode exists, the anti-waveguide region is above the right-down curve and the normal refractive index waveguide region is below the upper-right curve. On the boundary curve, the optical confinement factor Γ is 0, and the threshold current density J_thBecomes infinite. This situation is shown in FIGS. 8A and 8B.
[0103]
9A and 9B show the clad layer thickness dependence of the far-field image intensity distribution. FIG. 9A shows H._guide= 0.1 μm, and FIG._guide= 0.2 μm. It can be seen that the far-field image is bimodal in the parameters of the anti-waveguide region. FIG. 10 shows the boundary of the region where the waveguide mode exists when the In composition of the well layer has other values.
[0104]
As is clear from FIGS. 8A and 8B, the cladding layer thickness H is used to reduce the threshold value._cladMust be set to a value sufficiently away from the boundary of the region where the guided mode does not exist. In this calculation, the absorption coefficient of the outermost GaN is 500 cm.^-1In practice, this value may vary depending on the impurity concentration. When the absorption coefficient is small, the anti-waveguide property is further increased, and the parameter region where no waveguide mode is present is also widened.
[0105]
FIG. 11 shows that the absorption coefficient of the outermost layer GaN is 100 cm.^-1In this case, the boundary of the guided mode existence region is shown. As can be seen from comparison with FIG. 10, the region where the waveguide mode does not exist is large. In either case, the cladding layer thickness H_cladAnd waveguide layer thickness H_guideIt is clear that it is necessary to set the values in a predetermined range. This H_cladThe condition for such as can be specified by the same mathematical expression as the expression (1). However, this condition is an approximation when equation (1) has a small active layer thickness d. In the SCH structure, the region where light is confined is a thick region including the waveguide layer. ΔX_Ald / in)^-1/2Instead of (Δx_Ald / λ)^-1A better approximation can be obtained using. Specifically, this condition can be approximated as follows from FIGS.
[0106]
Δx · (H_core/ Λ) ・ (H_clad/Λ)≧0.08 (2)
Where H_coreIs the total thickness of the core region including the waveguide layer (MQW + waveguide layer), and Δx is an amount representing the composition difference between the core region and the cladding layer, and is approximately proportional to the refractive index difference between the core and the cladding To do.
[0107]
In the example of the layer structure shown here, Δx is defined below.
[0108]
Δx = x_Al+ Y_In      ... (3)
Where x_AlIs the Al composition of the cladding layer, and y_InRepresents the average In composition of the core region. When In is contained in the cladding layer, the above x_AlX instead of_Al-X_In(X_InMay be the In composition of the cladding layer. Similarly, when Al is contained in the core region, y_InInstead of y_In-Y_Al(Y_AlMay be the average Al composition of the core region).
[0109]
N-type GaN / n-type Ga shown above_0.85Al_0.15N (H_cladμm) / n-type In_0.06Ga_0.94N (H_guideμm) / MQW / p type In_0.06Ga_0.94N (H_guideμm) / p-type Ga_0.85Al_0.15N (H_cladIn the example of μm) / n-type GaN, x_Al= 0.15, y_In= 0.069 (H_guide= 0.1 μm, 10 wells). In this case, the condition of the cladding layer thickness given by Equation (2) is H = 420 nm._clad≧ 0.244 μm. Note that the left side of equation (2) corresponds to an amount representing the degree of light confinement in the core.
[0110]
The above parameter Δx · (H_core/ Λ) ・ (H_cladThe dependence of the threshold on / λ) is shown in FIG. In this figure, the vertical axis represents the threshold value divided by the total well thickness of the active layer, J_th/ D_actIt is. As shown, J_th/ D_actIs Δx · (H_core/ Λ) ・ (H_clad/ Λ). Further, as shown in the figure, this dependency also varies depending on the magnitude of the absorption coefficient of the contact layer that is the outermost layer. Actually, since the contact layer often has a very high impurity concentration, the absorption coefficient can also change. Of course, J_thD_actAlso depends on. D for lower threshold_actIt is better to make it smaller. For example, in FIG. 12, Δx · (H_core/ Λ) ・ (H_clad/ Λ) is large enough_th/ D_act~ 2x10⁹cm^-3It becomes. Where J_th<10 kA / cm²D_act<0.05 μm is required. According to another calculation, it was found that the influence of the carrier overflow increases when the total thickness of the active layer is 0.05 μm or more.
[0111]
From the above, the InGaAlN laser can be oscillated at a low threshold by being manufactured within the following range with respect to the condition and the total thickness of the active layer shown in the equation (2).
[0112]
d_act<0.05 μm (4)
More preferably, d_actShould be in the following range.
[0113]
d_act≦ 0.045 μm (5)
As can be seen from FIG. 12, Δx · (H_core/ Λ) ・ (H_cladBy setting / λ) within the following range, a low threshold can be realized regardless of the absorption coefficient of the contact layer or the like.
[0114]
Δx · (H_core/ Λ) ・ (H_clad/Λ)≧0.1 (6)
(2) or (5) is the cladding layer thickness H_cladIs a formula that gives the lower limit of H_cladEven if this becomes too large, problems such as an increase in voltage drop in the cladding layer and the occurrence of cracks described above occur. To avoid this, H_cladIs preferably set to the following range.
[0115]
x_Al・ H_clad≦ 0.1 μm (7)
More preferably, the following range is set.
[0116]
x_Al・ H_clad≦ 0.06μm (8)
As can be seen from FIG._cladHowever, if the upper limit is set by the following equation (9) as long as it satisfies the equation (2) or (6), the voltage drop in the cladding layer can be reduced.
[0117]
Δx · (H_core/ Λ) ・ (H_clad/Λ)≦0.2 (9)
Further, from FIG. 12, a sufficiently low threshold value can be obtained even in the following range.
[0118]
Δx · (H_core/ Λ) ・ (H_clad/Λ)≦0.15 (10)
In summary, the cladding layer thickness H_cladThe lower limit is set by the formula (2), more preferably the formula (6), and the upper limit is the formula (7), more preferably the range of the formula (8), or the formula (9), more preferably (10). ) Should be set within the range of the expression.
[0119]
In addition to this, the active layer well thickness d_actIs set within the range of the equation (4), more preferably the equation (5), so that oscillation at a low threshold can be realized.
[0120]
Another point to be noted in FIGS. 7 to 11 is that when the In composition of the waveguide layer is large to some extent and the waveguide layer thickness is large, the threshold value is infinite regardless of the cladding layer thickness. It may not be. In such a case, the threshold value does not change so much even in a region where the waveguide structure changes from normal refractive index waveguide to anti-waveguide (see FIGS. 8A and 8B). Therefore, if a laser is manufactured within such a structural parameter range, the threshold value is low and the parameter tolerance is large, which is extremely effective. This range is given by the following approximate expression.
[0121]
(Y_In)^1/2・ (H_core/Λ)≧0.15 (11)
More desirably, the tolerance is greater if the following range is set.
[0122]
(Y_In)^1/2・ (H_core/Λ)≧0.2 (12)
That is, if the waveguide layer contains In and is set so as to satisfy the formula (11) or the formula (12), a laser with a low threshold and a large manufacturing tolerance can be realized.
[0123]
FIG. 13 shows an example of the layer structure design for lowering the threshold described above. In this example, the MQW structure is In_0.2Ga_0.8N well layer (2nm) / In_0.05Ga_0.95Although an example in which the N barrier layer (4 nm) is one period has been described, of course, other configurations are possible. All the examples in FIG. 13 satisfy the conditions of the expressions (2) and (5). In addition, [2] to [8] also satisfy the condition of the expression (11). [6] is an example that further satisfies the condition of the expression (12). The layer structure does not need to be symmetric, and may be asymmetric like [7] and [8].
[0124]
As can be seen by comparing FIG. 10 and FIG. 11, when the refractive index of the outer layer of the cladding layer such as the contact layer is larger than the refractive index of the cladding layer, it is desirable that the absorption coefficient is larger. The value of the absorption coefficient is expressed by the following equation (13) based on FIG.
[0125]
α ≧ 100cm^-1      ... (13)
More desirably α ≧ 500 cm^-1      ... (14)
It is good to be in the range. As a method for increasing the absorption coefficient, it is effective to use an InGaN contact layer in addition to increasing the impurity concentration. In particular, the use of InGaN having a band gap smaller than that of the well layer is also effective.
[0126]
(Threshold reduction)
The multiple quantum well (MQW) structure is effective for reducing the laser threshold. The InGaAlN-based semiconductor laser according to the present invention exhibits a remarkable threshold reduction effect by using this MQW structure together with the transverse mode control structure. This is because in addition to the threshold reduction by MQW, the effect of threshold reduction by the lateral mode control structure is added, and the contact resistance which is a big problem in the InGaAlN system can be greatly reduced.
[0127]
This effect will be described with reference to FIGS. 14 (a) to 14 (c). FIG. 14A shows a current distribution in an InGaAlN laser having a conventional electrode stripe structure. In this structure, in order to realize fundamental transverse mode oscillation by gain waveguide, it is necessary to make the electrode stripe width an extremely small value on the order of several μm. However, if the stripe width is made extremely small, the p-type contact resistance increases remarkably, and continuous oscillation at room temperature becomes almost impossible due to the generation of heat in this portion.
[0128]
In order to prevent this, the stripe width may be increased or the threshold value may be lowered. However, in the former, fundamental transverse mode oscillation cannot be obtained, and in the latter, current density is reduced due to current density reduction, and fundamental transverse mode oscillation cannot be obtained as shown in FIG. 14B.
[0129]
On the other hand, in the transverse mode control structure according to the present invention, the oscillation transverse mode is determined by the optical confinement layer, so that there is almost no influence on the mode by the current value, and the optical confinement layer also functions as a current confinement layer. Therefore, the current value can also be reduced. Due to this and the threshold reduction effect by MQW, the operating current can be greatly reduced. Furthermore, as shown in FIG. 14C, the current spreads in the p-type contact layer, so that the contact resistance can be greatly reduced and heat is not generated. Therefore, continuous oscillation at room temperature is possible only with this structure.
[0130]
(Prevents carrier overflow)
The InGaAlN system has a problem that it is difficult to obtain a p-type crystal having a high carrier concentration, in addition to the above-described problem of cracks during growth. When the carrier concentration of the p-type cladding layer is low, an overflow of electrons from the active layer to the p-type cladding layer occurs, and the threshold value is significantly increased. In particular, the cladding layer carrier concentration is 10¹⁷cm^-3At lower, this is noticeable. An actual crystal is a problem because it is difficult to obtain a particularly high carrier concentration with a crystal having a large Al composition, such as that used in a cladding layer.
[0131]
In this embodiment, carrier overflow prevention layers 15 and 17 made of GaAlN are provided between the MQW active layer 16 and the waveguide layers 14 and 18 in order to prevent carrier overflow from occurring even at a low carrier concentration. Since the overflow prevention layers 15 and 17 are very thin layers of 5 nm to 500 nm, they hardly affect the shape of the waveguide mode distribution, but they effectively prevent carrier overflow by the effect of the hetero barrier with the active layer. Can be prevented.
[0132]
This overflow prevention layer is particularly effective when the carrier concentration of the cladding layer is low. In the InGaAlN system, since an n-type GaAlN layer having a relatively high carrier concentration can be formed, there is no need for an n-side overflow prevention layer. However, in the case of reducing the carrier concentration for the purpose of improving crystal morphology, it is better to have an n-side overflow prevention layer. The same applies to the p-side carrier overflow prevention layer.¹⁷cm^-3When a p-type cladding layer having a carrier concentration of about or higher is used, the carrier overflow prevention layer is unnecessary.
[0133]
The effect of the p-side overflow prevention layer 17 when the carrier concentration of the p-type cladding layer 19 is low is shown in FIGS. FIG. 15 shows that the carrier concentration of the p-type cladding layer 19 is 1 × 10.¹⁶cm^-3The band structure and the distribution of electrons and holes are shown for the case where no overflow prevention layer is included. As is apparent from the figure, significant electron overflow occurs from the active layer to the p-type cladding layer side.
[0134]
On the other hand, FIG. 16 shows a gap between the MQW active layer 16 and the p-side waveguide layer 18._0.85Al_0.15The case where the N overflow prevention layer 17 is provided is shown. It can be seen that this layer 17 almost eliminates the overflow of electrons to the p side. In this figure, the p-side waveguide layer 18 is non-doped, and the overflow prevention layer 17 is also non-doped. The non-doped overflow prevention layer also has a remarkable effect as shown in this figure, but if the p-type is doped, the effect is even greater.
[0135]
The effect of preventing carrier overflow is that the overflow prevention layer Ga_1-hAl_hThe larger the Al composition h of N, the more pronounced it. On the other hand, when h is too large, injection of holes from the p side to the active layer is hindered, which causes an increase in operating voltage. In particular, when h exceeds 0.2, the operating voltage rises significantly. Therefore, the Al composition h of the overflow prevention layer is
0 <h <0.2 (15)
It is desirable to be in the range.
[0136]
The carrier overflow prevention layer is not limited to GaAlN, and may further contain In, or may further contain B. That is, the carrier overflow prevention layer is made of In_sGa_tAl_hB_1-sthN (0 ≦ s, t, h, s + t + h ≦ 1) may be used as long as the band gap energy is larger than that of the waveguide layer. Further, it is not necessarily provided in contact with the MQW layer, and may be provided in the middle of the waveguide layer. Furthermore, it is not necessary to provide only one layer, and a plurality of layers may be provided in multiple stages.
[0137]
As described above, according to the present embodiment, in the InGaAlBN semiconductor laser, the ridge portion of the cladding layer is formed in the double heterostructure portion, and the optical confinement layer having a higher refractive index than the cladding layer is provided on the side surface. In addition to reducing the threshold current density, continuous oscillation in the fundamental transverse mode can be realized. In addition, it is possible to obtain a high quality outgoing beam free of astigmatism suitable for a light source such as an optical disk system.
[0138]
(Second Embodiment)
FIG. 17 is a cross-sectional view showing a configuration of a semiconductor laser according to the second embodiment of the present invention.
[0139]
In the figure, reference numeral 30 denotes a sapphire substrate, on which a GaN buffer layer 31, an n-type GaN contact layer 32, an n-type GaAlN cladding layer 33, an n-type GaN waveguide layer 34, an n-type GaAlN overflow prevention layer 35, A single quantum well (SQW) active layer 36 made of InGaN, a p-type GaAlN overflow prevention layer 37, a p-type GaN waveguide layer 38, and a p-type GaAlN cladding layer 39 are grown. These crystal growths are performed by MOCVD method or MBE method.
[0140]
The p-type GaAlN cladding layer 39 is etched away to the middle except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the cladding layer 39. In addition to the ridge portion of the p-type GaAlN clad layer 39, an n-type InGaN optical confinement layer 40 is selectively embedded and formed on the clad layer 39 and the optical confinement layer 40. An InGaN contact layer 42 is grown and formed. These crystal growths are also performed by the MOCVD method or the MBE method.
The p-type InGaN contact layer 42 to the n-type GaAlN cladding layer 33 are partially removed, and a part of the n-type GaN contact layer 32 is exposed. A p-side electrode 43 is formed on the p-type GaN contact layer 42, and an n-side electrode 44 is formed on the exposed portion of the n-type GaN contact layer 32.
[0141]
The present embodiment differs from the first embodiment shown in FIG. 1 in that the active layer portion is not a multiple quantum well but a single quantum well made of InGaN. A single quantum well can be designed to reduce the threshold. In this case, since the optical confinement becomes small, the threshold value usually increases due to an increase in the waveguide loss. However, by optimizing the waveguide layer thickness, the waveguide loss can be reduced and the threshold value is also lowered. It is possible.
[0142]
In this embodiment, p-type InGaN is further used as the contact layer 42. Since p-type InGaN has a smaller band gap than p-type GaN, the Schottky barrier between the electrodes can be reduced, and the contact resistance can be further reduced.
[0143]
(Third embodiment)
FIG. 18 is a cross-sectional view showing a configuration of a semiconductor laser according to the third embodiment of the present invention.
[0144]
In the figure, reference numeral 50 denotes an n-type SiC substrate, on which an n-type ZnO buffer layer 51, an n-type GaN layer 52, an n-type GaAlN cladding layer 53, an n-type GaN waveguide layer 54, and an n-type GaAlN overflow prevention. A layer 55, an InGaN multiple quantum well (MQW active layer) 56, a p-type GaAlN overflow prevention layer 57, a p-type GaN waveguide layer 58, and a p-type GaAlN cladding layer 59 are grown. These crystal growths are performed by MOCVD, MBE, or a combination of both.
[0145]
The p-type GaAlN cladding layer 59 is etched away to the middle except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the cladding layer 59. In addition to the ridge portion of the p-type GaAlN cladding layer 59, an n-type InGaN optical confinement layer 60 is selectively buried and a p-type GaN contact layer 61 is grown on the cladding layer 59 and the optical confinement layer 60. Is formed. A p-side electrode 62 is formed on the p-type GaN contact layer 61, and an n-side electrode 63 is formed on the back surface of the n-type SiC substrate 50.
[0146]
In the present embodiment, a conductive n-type SiC substrate is used as the substrate 50. As a result, current can flow in the vertical direction, so that mounting and the like are easier, and thermal resistance is reduced.
[0147]
In the above embodiment, the case where InGaN is used as the light confinement layer has been described. However, the present invention is not limited to this, and the band gap energy is smaller than that of the active layer._pGa_qAl_rB_1-pqrN (0 <p ≦ 1, 0 ≦ q, r <1, 0 <p + q + r ≦ 1) may be used. The cladding layer is not only GaAlN but also In_xGa_yAl_zB_1-xyzN (0 ≦ x, y, z, x + y + z ≦ 1) can be used.
[0148]
As shown in FIGS. 15 and 16, the injection of electrons and holes into the MQW is generally non-uniform, which is one of the factors for increasing the threshold. This becomes more significant as the number of MQW layers increases. In order to reduce this non-uniformity, it is effective to reduce the thickness of the barrier layer. In particular, if the thickness of the barrier layer is set so as not to exceed the thickness of the well layer, relatively uniform implantation is obtained and the threshold value is reduced.
[0149]
(Fourth embodiment)
FIG. 19 is a cross-sectional view showing a configuration of a semiconductor laser according to the fourth embodiment of the present invention.
[0150]
In the figure, reference numeral 70 denotes a sapphire substrate, on which a GaN buffer layer 71, an n-type GaN contact layer 72, an n-type GaAlN cladding layer 73, an n-type GaN waveguide layer 74, an InGaN multiple quantum well 75, a p-type. A GaN waveguide layer 76, a p-type GaAlN cladding layer 77, a p-type GaN cap layer 78, and a p-type InGaN optical confinement layer 79 are formed. The p-type InGaN optical confinement layer 79 also serves as a p-type contact layer. These crystal growths are performed by the MOCVD method or the MBE method.
[0151]
The p-type GaN cap layer 78 and the p-type GaAlN cladding layer 77 are etched away to the middle of the cladding layer except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the cladding layer 77. A p-type InGaN optical confinement layer / contact layer 79 is formed thereon. This crystal growth is also performed by the MOCVD method or the MBE method.
[0152]
A portion from the p-type InGaN optical confinement layer / contact layer 79 to the n-type GaAIN cladding layer 73 is partially removed, and a part of the n-type GaN contact layer 72 is exposed. Thereafter, a p-side electrode 80 is formed on the p-type InGaN optical confinement layer / contact layer 79, and an n-side electrode 81 is formed on the exposed portion of the n-type GaN contact layer 72. For the p-side electrode 80, for example, a laminated structure of Pt / TiN / Ti / Pt / Au is used, and for the n-side electrode 81, for example, a laminated structure of Ti / Au is used.
[0153]
The active layer of this laser is In_aGa_1-aN well layer / In_eGa_1-eThe SCH structure is provided with a multiple quantum well composed of an N barrier layer (a ≧ e) and a GaN waveguide layer.
[0154]
The feature of the structure shown in FIG. 19 is that the p-type InGaN optical confinement layer 79 also serves as a contact layer. For this reason, crystal growth is required only twice, and the second regrowth need not be selective growth. Therefore, the transverse mode control structure can be realized by a very simple process. In this structure, since the InGaN layer having a large absorption coefficient with respect to the oscillation wavelength is provided outside the stripe and close to the active layer, the real part of the equivalent refractive index outside the stripe is smaller than that of the stripe portion. The transverse mode confinement is realized.
[0155]
On the other hand, current confinement in this structure is realized by a hetero barrier between the p-type GaAlN cladding layer 77 and the p-type InGaN optical confinement layer 79. That is, as shown in FIG. 20A, almost no current flows at this interface due to a hetero barrier caused by band discontinuity on the valence side at the interface between the p-type GaAlN cladding layer and the p-type InGaN contact layer. Absent. On the other hand, in the stripe portion, a p-type GaN cap layer 78 having an intermediate band gap energy between the p-type GaAlN clad layer 77 and the p-type InGaN contact layer 79 is provided, so that FIG. ), The height of the hetero barrier is reduced, and current flows easily.
[0156]
Another advantage of using the InGaN layer as the optical confinement layer / contact layer is that a high value can be realized as the carrier density of the underlying cladding layer. According to the experiments by the present inventors, it has been clarified that the carrier density of the cladding layer under the structure in which InGaAlN having an In composition larger than 0 is increased. For example, in the case of only the GaN contact layer, the carrier density of the p-type cladding layer is 1 × 10¹⁶cm^-3What was the following is that by providing an InGaN layer, 5 × 10 5¹⁶cm^-3That's it. This is due to suppression of inactivation of the Mg acceptor by hydrogen (H) or the like. As a result, it has been found that the carrier overflow is significantly reduced as compared with the structure in which the InGaAlN optical confinement layer is not provided.
[0157]
In the calculation example of FIG. 20, the p-type cladding layer has a carrier density of 5 × 10.¹⁶cm^-3Ga_0.85Al_0.15N, p-type contact layer has carrier density of 1 × 10¹⁷cm^-3In_0.15Ga_0.85N, p cap layer has carrier density of 1 × 10¹⁷cm^-3The case of GaN is shown. These combinations are not limited to this, and it is sufficient that the heterobarrier between the p-type cladding layer and the p-type contact layer has a sufficient size for current blocking.
[0158]
The p-type cladding layer and the p-type contact layer in FIG._0.85Al_0.15N (carrier density 5 × 10¹⁶cm^-3), P-type In_xGa_1-xN (carrier density 1 × 10¹⁷cm^-3) Shows the current density-voltage characteristics in FIG. The cap layer in FIG. 20B is GaN with x = 0, and in this case, laser oscillation can be obtained at a voltage of ~ 3.7 V (this voltage does not include contact resistance or the like). On the other hand, it can be seen that when the In composition x increases, the current hardly flows. The current value at an operating voltage (˜3.7 V) where x is greater than 0.1 is ½ or less, and a sufficient current confinement effect can be obtained with the structure shown in FIG.
[0159]
This current blocking effect by the hetero barrier depends not only on the band gap difference between the p-type cladding layer and the p-type contact layer but also on the carrier density of the two layers. For example, the carrier density of the p-type cladding layer is 1 × 10¹⁷cm^-3As it becomes larger, the current blocking effect is reduced. Accordingly, in order to obtain a sufficient current blocking effect due to the hetero barrier in the structure shown in FIG. 19, the carrier density of the p-type cladding layer is set to 1 × 10 6.¹⁷cm^-3Hereinafter, it is desirable that the sum of the Al composition of the p-type cladding layer and the In composition of the p-type contact layer be 0.25 or more. From the viewpoint of reducing carrier overflow, the carrier density of the p-type cladding layer should not be too low, preferably 5 × 10.¹⁶cm^-3The above is good.
[0160]
Further, the current blocking effect by the hetero barrier is not limited to the combination of p-type GaAlN / p-type InGaN. Since this material system can have a large band gap difference depending on the composition, the band discontinuity on the conduction band side also becomes large as well as the band discontinuity on the valence band side. FIG. 22 shows n-type Ga._0.85Al_0.15N (carrier density 5 × 10¹⁷cm^-3), N-type In_xGa_1-xN (carrier density 1 × 10¹⁸cm^-3) Shows the current density-voltage characteristics when C is used for the cladding layer and the contact layer, respectively. It is apparent that the current hardly flows when the In composition x of the n contact layer increases. In this case, a sufficient current blocking effect is obtained when x ≧ 0.15.
[0161]
(Fifth embodiment)
FIG. 23 is a cross-sectional view showing a configuration of a semiconductor laser according to the fifth embodiment of the present invention.
[0162]
In the figure, reference numeral 90 denotes a sapphire substrate, on which a GaN buffer layer 91, a p-type GaN contact layer 92, a p-type GaAlN cladding layer 93, a p-type GaN waveguide layer 94, an InGaN multiple quantum well 95, an n-type. A GaN waveguide layer 96, an n-type GaAlN cladding layer 97, an n-type GaN cap layer 98, and an n-type InGaN optical confinement layer 99 are formed. The n-type InGaN optical confinement layer 99 also serves as an n-type contact layer.
[0163]
The n-type GaN cap layer 98 and the n-type GaAlN cladding layer 97 are etched away to the middle of the cladding layer except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the cladding layer 97. An n-type InGaN optical confinement layer / contact layer 99 is formed thereon.
[0164]
The portion from the n-type InGaN optical confinement layer / contact layer 99 to the p-type GaAlN cladding layer 93 is partially removed, and a part of the p-type GaN contact layer 92 is exposed. Thereafter, an n-side electrode 100 is formed on the n-type InGaN optical confinement layer / contact layer 99, and a p-side electrode 101 is formed on the exposed portion of the p-type GaN contact layer 92.
[0165]
In the structure shown in FIG. 23, the n-type InGaN optical confinement layer 99 also serves as a contact layer. Therefore, as in the case of FIG. 19, the crystal growth is only required twice. The principle of the lateral mode control is the same as that in FIG. 19, and the current confinement is realized by a hetero barrier between the n-type GaAlN cladding layer 97 and the n-type InGaN optical confinement layer 99. The effect of current blocking by the hetero barrier is as shown in FIG.
[0166]
Since the current blocking effect by the hetero barrier is more remarkable as the band gap difference between the two types of materials is larger, a combination having a large composition difference is desirable. However, on the other hand, if the band gap difference is too large in the stripe portion, even if a cap layer having an intermediate band gap is provided, it may be difficult for current to flow. In order to improve this, it is preferable to provide a plurality of cap layers having an intermediate band gap and different band gap values.
[0167]
(Sixth embodiment)
FIG. 24 is a sectional view showing a configuration of a semiconductor laser according to the sixth embodiment of the present invention.
[0168]
In the figure, 110 is a sapphire substrate, on which a GaN buffer layer 111, an n-type GaN contact layer 112, an n-type Ga._0.85Al_0.15N-cladding layer 113, n-type GaN waveguide layer 114, InGaN multiple quantum well 115, p-type GaN waveguide layer 116, p-type Ga_0.85Al_0.15N clad layer 117, p-type GaN first cap layer 118, p-type In_0.07Ga_0.93N second cap layer 119, p-type In_0.15Ga_0.85An N light confinement layer 120 is formed. The p-type InGaN optical confinement layer 120 also serves as a p-type contact layer. In the figure, 121 is a p-side electrode and 122 is an n-side electrode.
[0169]
In the structure shown in this figure, p-type Ga_0.85Al_0.15N clad layer 117 and p-type In_0.15Ga_0.85Since the composition difference with the N light confinement layer 120 is large and the band gap difference is large, the current blocking effect by the hetero barrier is large. On the other hand, the p-type Ga is formed on the cladding layer of the stripe portion._0.85Al_0.15N clad layer 117 and p-type In_0.15Ga_0.85Two types of cap layers having an intermediate band gap with the N light confinement layer 120 are provided. Since the band gap becomes smaller in the order of the p-type cladding layer, the first cap layer, the second cap layer, and the optical confinement layer, the hetero barrier is reduced step by step, and the structure allows a current to flow more easily.
[0170]
In the embodiment of FIG. 24, the cap layer having an intermediate band gap is two layers. However, the cap layer is not limited to this. Further, depending on the band gap difference between the clad layer and the optical confinement layer, a multi-stage cap layer is formed. It is of course possible to introduce it.
[0171]
(Seventh embodiment)
FIG. 25 is a sectional view showing a configuration of a semiconductor laser according to the seventh embodiment of the present invention.
[0172]
In the figure, reference numeral 130 denotes a sapphire substrate, on which a GaN buffer layer 131, an n-type GaN contact layer 132, and an n-type Ga._0.85Al_0.15N clad layer 133, n-type GaN waveguide layer 134, InGaN multiple quantum well 135, p-type GaN waveguide layer 136, p-type Ga_0.85Al_0.15N first p-type cladding layer 137, p-type Ga_0.85Al_0.15N second p-type cladding layer 138, p-type GaN first cap layer 139, p-type In_0.07Ga_0.93N second cap layer 140, p-type In_0.15Ga_0.85An N light confinement layer 141 is formed. The p-type InGaN optical confinement layer 141 also serves as a p-type contact layer. In the figure, 142 is a p-side electrode, and 143 is an n-side electrode.
[0173]
The carrier density of each layer is 5 × 10 5 for the first p-type cladding layer 137.¹⁷cm^-3The second p-type cladding layer 138 is 5 × 10¹⁶cm^-3The first cap layer 139, the second cap layer 140, and the optical confinement layer / contact layer 141 are all 1 × 10.¹⁷cm^-3It was.
[0174]
The feature of the structure shown in this figure is that the carrier density of the first p-type cladding layer 137 on the active layer side is increased to reduce carrier overflow during operation, and the second p-type cladding layer in contact with the optical confinement layer 141 is The carrier density is relatively low, and the current blocking effect by the hetero barrier is ensured. The principle of current flowing in the stripe part is the same as in the case of FIG. 19, FIG. 23 and FIG.
[0175]
(Eighth embodiment)
FIG. 26 is a sectional view showing the structure of a semiconductor laser according to the eighth embodiment of the present invention.
[0176]
In the figure, reference numeral 150 denotes a sapphire substrate. On this substrate 150, a GaN buffer layer 151, an n-type GaN contact layer 152, an n-type Ga layer._0.85Al_0.15N clad layer 153, n-type GaN waveguide layer 154, InGaN multiple quantum well 155, p-type GaN waveguide layer 156, p-type Ga_0.85Al_0.15N first p-type cladding layer 157, p-type Ga_0.85Al_0.15N second p-type cladding layer 158, p-type Ga_0.85Al_0.15N third p-type cladding layer 159, p-type GaN cap layer 160, p-type In_0.1Ga_0.9An N light confinement layer 161 is formed. The p-type InGaN optical confinement layer 161 also serves as a p-type contact layer. In the figure, 162 is a p-side electrode, and 163 is an n-side electrode.
[0177]
The carrier density of each layer in this embodiment is 5 × 10 5 for the first p-type cladding layer 157.¹⁷cm^-3The second p-type cladding layer 158 is 5 × 10¹⁶cm^-3The third p-type cladding layer 159 is 5 × 10 5¹⁷cm^-3The cap layer 160 and the light confinement layer / contact layer 161 are both 1 × 10¹⁷cm^-3It is.
[0178]
The feature of the structure shown in this figure is that the carrier density of the first p-type cladding layer 157 on the active layer side is increased to reduce the carrier overflow during operation, and the second p-type cladding layer in contact with the optical confinement layer 161 is The carrier density is made relatively low to secure the current blocking effect by the hetero barrier, and the carrier density of the third p-type cladding layer in contact with the cap layer 160 is made high so that the current can flow more easily in the stripe portion. That is.
[0179]
(Ninth embodiment)
FIG. 27 is a cross-sectional view showing the configuration of the semiconductor laser according to the ninth embodiment of the present invention.
[0180]
In the figure, reference numeral 170 denotes a sapphire substrate. On this substrate 170, a GaN buffer layer 171, an n-type GaN contact layer 172, and an n-type Ga._0.85Al_0.15N clad layer 173, n-type GaN waveguide layer 174, InGaN multiple quantum well 175, p-type GaN waveguide layer 176, p-type Ga_0.85Al_0.15N first p-type cladding layer 177, p-type Ga_0.85Al_0.15N second p-type cladding layer 178, p-type Ga_0.85Al_0.15N third p-type cladding layer 179, p-type GaN cap layer 180, p-type In_0.1Ga_0.9N optical confinement layer 181, p-type In_0.1Ga_0.9An N contact layer 182 is formed. In the figure, 183 is a p-side electrode and 184 is an n-side electrode.
[0181]
The carrier density of each layer in this embodiment is 5 × 10 5 for the first p-type cladding layer 177.¹⁷cm^-3The second p-type cladding layer 178 is 5 × 10¹⁶cm^-3The third p-type cladding layer 179 is 5 × 10¹⁷cm^-3, Cap layer 180 is 1 × 10¹⁷cm^-3The light confinement layer 181 is 1 × 10¹⁷cm^-3The contact layer 182 is 5 × 10¹⁷cm^-3It is.
[0182]
The feature of the structure shown in this figure is that, in addition to the feature of the eighth embodiment shown in FIG. 26, a contact layer 182 having a higher carrier density is provided on the p-electrode side. Thereby, since the contact resistance is reduced, the operating voltage can be greatly reduced.
[0183]
Note that the structure in which such a contact layer having a high carrier density is provided is not limited to this embodiment, and it is needless to say that the structure can be applied to the structures of the fourth to seventh embodiments.
[0184]
(Tenth embodiment)
FIG. 28 is a sectional view showing the structure of a semiconductor laser according to the tenth embodiment of the present invention.
[0185]
In the figure, reference numeral 190 denotes a sapphire substrate, on which a GaN buffer layer 191, an n-type GaN contact layer 192, and a p-type InGaN optical confinement layer 193 are formed. A part of the upper portions of the p-type InGaN optical confinement layer 193 and the n-type GaN contact layer 192 is etched to form a stripe-shaped groove. On top of this, an n-type GaAlN cladding layer 194, an n-type GaN waveguide layer 195, an InGaN multiple quantum well 196, a p-type GaN waveguide layer 197, a p-type GaAlN cladding layer 198, a p-type GaN layer 199, and a p-type InGaN contact. Layer 200 is formed. That is, a convex ridge portion is formed on the n-type GaAlN cladding layer 194 on the lower side. In the figure, 201 is a p-side electrode, and 202 is an n-side electrode.
[0186]
In this embodiment, the light confinement layer 193 is located closer to the substrate than the active layer. Since the optical confinement layer 193 and the quantum well active layer 196 are close to each other on both sides of the stripe, the real part of the equivalent refractive index is reduced due to the absorption loss of the optical confinement layer 193, and the equivalent formed thereby. The transverse mode confinement in the horizontal direction is realized by the refractive index distribution. The light confinement layer 193 also functions as a current confinement layer.
[0187]
The crystal growth for producing the structure of FIG. 28 is performed by MOCVD method or MBE method for both the first growth and the second growth. This structure also has the advantage that crystal growth is only required twice.
[0188]
(Eleventh embodiment)
FIG. 29 is a sectional view showing a configuration of a semiconductor laser according to the eleventh embodiment of the present invention.
[0189]
In the figure, reference numeral 210 denotes a sapphire substrate, on which a GaN buffer layer 211, a p-type GaN contact layer 212, and a p-type InGaN optical confinement layer 213 are formed. A part of the upper portions of the p-type InGaN optical confinement layer 213 and the p-type GaN contact layer 212 is etched to form a stripe-shaped groove. On top of this, a p-type GaAlN cladding layer 214, a p-type GaN waveguide layer 215, an InGaN multiple quantum well 216, an n-type GaN waveguide layer 217, an n-type GaAlN cladding layer 218, an n-type GaN layer 219, and an n-type InGaN contact. A layer 220 is formed. In the figure, 221 is a p-side electrode, and 222 is an n-side electrode.
[0190]
In this embodiment, the conductivity type of each layer is reversed except for a part of the embodiment shown in FIG. The point that the lateral mode confinement is realized by the optical confinement layer 213 is the same as in the case of FIG. 28, but the current confinement in the embodiment of FIG. 29 is the p-type GaAlN cladding layer 214 and the p-type InGaN optical confinement layer. This is realized by a hetero barrier with H.213. This principle is the same as that shown in FIG. 19 and FIGS.
[0191]
In the embodiments so far, the case where InGaN is used as the contact layer is shown, but the material is not limited to this material, and InGaBN or InGaAlBN may be used. In particular, in the case of the p-type contact layer, a low-resistance contact layer was obtained by using p-type InGaBN or p-type InGaAlBN. In addition, InGaAlBN can be used for the other layers as long as the conditions of the present invention are satisfied.
[0192]
Also, the substrate is not limited to a sapphire substrate, and SiC, ZnO, MgAl₂O_Four, NdGaO_Three, LiGaO₂, Y_ThreeAl_FiveO₁₂(YAG), Y_ThreeFe_FiveO₁₂(YIG) or the like can be used.
[0193]
(Twelfth embodiment)
FIG. 30 is a sectional view showing the structure of a semiconductor laser according to the twelfth embodiment of the present invention.
[0194]
In the figure, reference numeral 230 denotes a sapphire substrate, and a GaN buffer layer 231, an n-type GaN contact layer 232, and an n-type Ga are formed on the substrate 230._0.85Al_0.15N clad layer 233, n-type GaN waveguide layer 234, InGaN multiple quantum well 235, p-type GaN waveguide layer 236, p-type Ga_0.85Al_0.15N-clad layer 237, p-type GaN cap layer 238, p-type InGaN contact layer 239, n-type In_0.1Ga_0.9An N light confinement layer 240 and a p-type InGaN contact layer 241 are formed. In the figure, 242 is a p-side electrode and 243 is an n-side electrode.
[0195]
The laser of this embodiment is manufactured as follows. That is, first, on the sapphire substrate 230, a GaN buffer layer 231, an n-type GaN contact layer 232, an n-type GaAlN cladding layer 233, an n-type GaN waveguide layer 234, an InGaN multiple quantum well 235, a p-type GaN waveguide layer 236, A p-type GaAlN cladding layer 237, a p-type GaN cap layer 238, and a p-type InGaN contact layer 239 are sequentially grown. On top of this SiO₂A striped ridge is formed by forming a film and removing a part of the p-type InGaN contact layer 239, the p-type GaN cap layer 238, and the p-type GaAlN cladding layer 237 by removing the stripe portion by photolithography or the like. Form.
[0196]
Next, the n-type InGaN optical confinement layer 240 and the p-type InGaN contact layer 241 are formed by the second growth. This second growth is due to the SiO2 stripe.₂This is done while leaving the film, so that SiO 2₂Crystal growth does not occur on the top, but it is performed by so-called selective growth that grows only in the region outside the stripe. The n-electrode side etching can be performed before or after the second growth.
[0197]
The feature of this embodiment is that the crystal growth is only required twice despite the seemingly complicated structure. Further, since the contact layer is also formed outside the stripe portion and the stripe portion, a full-surface electrode structure can be taken, and the current spreads to the p-type InGaN contact layer 241, thereby reducing the contact resistance. .
[0198]
(13th Embodiment)
FIG. 31 is a perspective view showing the structure of a semiconductor laser according to the thirteenth embodiment of the present invention.
[0199]
Since the layer structure in this embodiment is almost the same as that of the twelfth embodiment shown in FIG. 30, its detailed description is omitted. The difference is that p-type InGaN contact layers 239 and 241 in FIG.⁺The type GaN layers 250 and 251 are used. This layer has a higher carrier density than the p-type GaN cap layer 238 (for example, 7 × 10⁷cm^-3), The current can easily spread and the contact resistance can be reduced.
[0200]
Further, in the embodiment of FIG. 31, a symmetrical structure is provided in which n-side electrodes are provided on both sides. As a result, the current distribution in the stripe portion also has improved symmetry, and more stable fundamental transverse mode oscillation can be realized.
[0201]
(Fourteenth embodiment)
FIG. 32 is a cross-sectional view showing the configuration of the semiconductor laser according to the fourteenth embodiment of the present invention. In the figure, 260 is a sapphire substrate, on which a GaN buffer layer 261, an n-type GaN contact layer 262, and an n-type Ga._0.85Al_0.15N clad layer 263, n-type GaN waveguide layer 264, InGaN multiple quantum well (MQW) active layer 265, p-type GaN waveguide layer 266, p-type Ga_0.85Al_0.15An N clad layer 267 and a p-type GaN cap layer 268 are grown. The p-type GaN cap layer 268 and the p-type GaAlN cladding layer 267 are etched away to the middle except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the cladding layer 267. In the region other than the ridge portion of the p-type GaAlN cladding layer 267, n-type Ga_0.93Al_0.07An N light confinement layer 269 is selectively buried and a p-type GaN contact layer 270 is formed on the cap layer 268, the cladding layer 267 and the light confinement layer 269. Reference numeral 271 denotes a p-electrode, and 272 denotes an n-electrode.
[0202]
A feature of this embodiment is that GaAlN having a smaller Al composition than the cladding layer 267 is used for the light confinement layer 269. As a result, an anti-waveguide structure is formed in the horizontal direction, and the horizontal transverse mode is stabilized.
[0203]
The anti-waveguide structure is basically realized when the equivalent refractive index outside the stripe is large, but in order to obtain good beam characteristics, the absolute value of the equivalent refractive index difference with the inside of the stripe must be larger than a predetermined value. It is important to set. As can be seen from FIG. 4 described above, | Δn_eq| ≧ 2 × 10^-3By setting in this area, characteristics with small astigmatic difference can be obtained. In the example of the embodiment of FIG. 32, the Al composition of the light confinement layer is 0.05 ≦ x_AlBy setting the region to ≦ 0.1, an anti-waveguide structure having excellent beam characteristics can be realized.
[0204]
As described above, according to the present embodiment, in the InGaAlBN semiconductor laser, a ridge portion is formed in one cladding layer of the double heterostructure portion, and an optical confinement layer having a higher refractive index than the cladding layer is formed on the side surface of the ridge portion. By providing, the threshold current density is reduced and stable continuous oscillation in the fundamental transverse mode is possible.
[0205]
(Fifteenth embodiment)
FIG. 33 is a sectional view showing the structure of a semiconductor laser according to the fifteenth embodiment of the present invention. In the figure, reference numeral 280 denotes a sapphire substrate. On this substrate 280, a GaN buffer layer 281, an n-type GaN contact layer 282, an n-type Ga layer._0.85Al_0.15N-clad layer 283, n-type GaN waveguide layer 284, InGaN multiple quantum well (MQW) active layer 285, p-type GaN waveguide layer 286, p-type Ga_0.85Al_0.15An N clad layer 287 and a p-type GaN cap layer 288 are grown. The p-type GaN cap layer 288 and the p-type GaAlN cladding layer 287 are removed by etching except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the cladding layer 287. In the region other than the ridge portion of the p-type GaAlN cladding layer 287, n-type Ga_0.93Al_0.07An N light confinement layer 289 is selectively buried and a p-type GaN layer 290 and a p-type InGaN contact layer 291 are formed on the cap layer 288, the cladding layer 287 and the light confinement layer 289. 292 is a p-electrode and 293 is an n-electrode.
[0206]
This embodiment is different from the embodiment of FIG. 32 in that the light confinement layer 289 is formed in contact with the p-type GaN waveguide layer 286. It goes without saying that an anti-waveguide structure is realized even in such a structure.
[0207]
(Sixteenth embodiment)
FIG. 34 is a sectional view showing the structure of a semiconductor laser according to the sixteenth embodiment of the present invention. In the figure, reference numeral 300 denotes a sapphire substrate. On this substrate 300, a GaN buffer layer 301, an n-type GaN contact layer 302, and an n-type Ga._0.85Al_0.15N-cladding layer 303, n-type GaN waveguide layer 304, InGaN multiple quantum well (MQW) active layer 305, p-type GaN waveguide layer 306, p-type InGaN cap layer 307, p-type GaN layer 308, p-type Ga_0.85Al_0.15An N clad layer 309 is grown. The p-type GaAlN clad layer 309 and the p-type GaN layer 308 are removed by etching except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the clad layer 309. On top of this, p-type Ga_0.93Al_0.07An N light confinement layer 310 and a p-type GaN contact layer 311 are formed. 312 is a p-electrode, and 313 is an n-electrode.
[0208]
In this embodiment, since the light confinement layer 310 is p-type, crystal growth is only required twice. In this structure, p-type Ga_0.93Al_0.07Current confinement is performed by a hetero barrier between the N light confinement layer 310 and the p-type InGaN cap layer 307. That is, no current flows outside the stripe due to this hetero barrier. On the other hand, since the p-type GaN layer 308 is formed between the p-type InGaN cap layer 307 and the p-type GaAlN cladding layer 309 in the stripe portion, the hetero barrier is reduced and current flows. In addition, p-type Ga_0.93Al_0.07The refractive index of the N light confinement layer 310 is p-type Ga_0.85Al_0.15Since it is larger than the N clad layer 309, light confinement is realized by the anti-waveguide structure.
[0209]
(Seventeenth embodiment)
FIG. 35 is a sectional view showing the structure of a semiconductor laser according to the seventeenth embodiment of the present invention. In the figure, reference numeral 320 denotes a sapphire substrate. On this substrate 320, a GaN buffer layer 321, an n-type GaN contact layer 322, an n-type Ga._0.85Al_0.15N clad layer 323, n-type GaN waveguide layer 324, InGaN multiple quantum well (MQW) active layer 325, p-type GaN waveguide layer 326, p-type Ga_0.85Al_0.15N first cladding layer 327, p-type Ga_0.9Al_0.1An N second cladding layer 328 is grown. p-type Ga_0.9Al_0.1N second cladding layer 328, p-type Ga_0.85Al_0.15The N first cladding layer 327 is removed by etching except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the cladding layer. A p-type InGaN optical confinement layer 329 is selectively embedded in a region other than the ridge portion of the cladding layers 327 and 328, and a p-type GaN contact layer 330 is formed on the cladding layer 328 and the optical confinement layer 329. Has been. Reference numeral 331 denotes a p-electrode, and reference numeral 332 denotes an n-electrode.
[0210]
The waveguide mechanism of the present embodiment is a loss waveguide type as in the first embodiment, but differs from the previous embodiments in that the ridge shape is wider at the top. With such a ridge shape, the current spreads in the second cladding layer 328, so that the series resistance of the element can be reduced. This structure can be realized by using a multi-layer structure in which the cladding layer is made of GaAlN having a different Al composition and utilizing the difference in the etching rate by chemical etching.
[0211]
FIG. 36 shows an etching method for creating the structure of the above embodiment. In the figure, a reaction vessel 340 is provided with a coiled metal electrode 341 along an inner side wall, and holds a stirrer 342 and an NaOH solution 343. Here, the stirrer 342 rotates by receiving a rotating magnetic field from a controller (not shown) outside the container, and stirs the NaOH solution 343. A substrate 344 having a GaN-based multilayer structure is immersed in the NaOH solution 343.
[0212]
This substrate 344 is connected to the positive side of the DC power supply 345 outside the container. Further, the metal electrode 341 in the container is connected to the negative side of the DC power supply 345. Here, when the DC power supply 345 is turned on, the substrate 344 is electrochemically etched.
[0213]
By such electrochemical etching, the etching profile can be controlled to a shape as shown in the embodiment of FIG. That is, as shown in FIG. 37, the GaAlN with a higher Al composition has a higher etching rate, so that the shape shown in FIG. 35 is realized. In this embodiment, the p-type GaN waveguide layer 326 also serves as an etching stop layer.
[0214]
The multilayer structure for controlling the etching profile is not limited to the two-layer structure shown in FIG. 35, and may be three or more layers._0.85Al_0.15It may be a graded layer whose composition is continuously changed from N to GaN. Further, the etching solution is not limited to NaOH, but KOH, HF-based solution, HPO_ThreeEtc. can be used.
[0215]
(Eighteenth embodiment)
FIG. 38 is a sectional view showing the structure of a semiconductor laser according to the eighteenth embodiment of the present invention. In the figure, reference numeral 350 denotes a sapphire substrate. On this substrate 350, a GaN buffer layer 351, an n-type GaN contact layer 352, an n-type Ga._0.85Al_0.15N clad layer 353, n-type GaN waveguide layer 354, InGaN multiple quantum well (MQW) active layer 355, p-type GaN waveguide layer 356, p-type Ga_0.85Al_0.15N first cladding layer 357, p-type Ga_0.9Al_0.1An N second cladding layer 358 and a p-type GaN cap layer 359 are grown. p-type GaN cap layer 359, p-type Ga_0.9Al_{0. 1}N second cladding layer 358, p-type Ga_0.85Al_0.15The N first cladding layer 357 is removed by etching except for the stripe portion, whereby a stripe-shaped ridge portion is formed in the cladding layer. A p-type InGaN optical confinement layer 360 is formed in a region other than the ridge portion of the cladding layers 577 and 578. Reference numeral 361 denotes a p-electrode, and 362 denotes an n-electrode.
[0216]
The current confinement in this embodiment is p-type Ga_0.85Al_0.15This is realized by a hetero barrier between the N first cladding layer 357 and the p-type InGaN optical confinement layer 360. The etching profile control is as described above.
[0217]
(Nineteenth embodiment)
39 to 40 are manufacturing process diagrams of the semiconductor laser according to the nineteenth embodiment of the present invention. As shown in FIG. 39A, on the sapphire substrate 370, a 10-200 nm thick buffer layer 371 made of GaN and 4 μm made of Si-doped n-type GaN are formed by metal organic chemical vapor deposition (MOCVD). Thick n-type contact layer 372, Si-doped n-type Ga_0.8Al_0.2A 250 nm thick n-type cladding layer 373 made of N, a 200 nm thick waveguide layer 374 made of Si-doped n-type GaN, and an Si-doped n-type GaAlN overflow prevention layer 375 are sequentially formed.
[0218]
Subsequently, a 1.5 nm thick non-doped In layer is formed on the n-type GaAlN overflow prevention layer 375._0.25Ga_0.75N and 3 nm thick non-doped In_0.05Ga_0.95An active layer 376 having a multiple quantum well (MQW) structure configured by repeating two N types of InGaN layers for 50 periods is formed.
[0219]
On the active layer 376, a Mg-doped p-type GaAlN overflow prevention layer 377, a 200 nm-thick waveguide layer 378 made of Mg-doped p-type GaN, and an Mg-doped p-type Ga._0.8Al_0.2A p-type cladding layer 379 made of N and a cap layer 380 made of Mg-doped p-type GaN and having a thickness of 0.3 μm are sequentially formed.
[0220]
Next, SiO 2 is deposited on the p-type GaN cap layer 380 by thermal CVD.₂A 400 nm thick inorganic mask layer 381 made of a film is deposited. Subsequently, a resist (AZ4110) is applied on the inorganic mask layer 381 to a thickness of 1 μm, and a stripe pattern is transferred to the resist by an optical exposure process. After development, the wafer is held in a 120 ° C. nitrogen atmosphere oven for 20 minutes and post-paked. Then, SiO of the inorganic mask layer 381₂The film is etched to form a two-layer mask layer composed of an inorganic mask layer and a resist layer.
[0221]
Next, as shown in FIG. 39B, the p-type GaN cap layer 380 is etched in a stripe shape by reactive ion beam etching (RIBE) until the p-type GaAlN cladding layer 379 is exposed.
[0222]
Here, since the thickness of the p-type GaAlN cladding layer is as thin as about 0.3 μm, the light confinement effect is affected even if the p-type GaAlN cladding layer is slightly thinned by over-etching. For this reason, in this etching process, it is necessary to make overetching as small as possible. Therefore, in this embodiment, Cl is used as an etching gas.₂Gas and SF₆GaN and GaAlN were selectively etched by using a mixed gas.
[0223]
Microwave power 200W, ion acceleration voltage 500V, Cl₂The gas pressure is constant at 0.4 mTorr, SF₆GaN and Ga when gas is added_1-xAl_xThe change in the selection ratio of N (x = 0.2) is shown in FIG. The vertical axis represents the selectivity of GaN in etching, and the horizontal axis represents SF in the mixed gas.₆Is the partial pressure ratio.
[0224]
SF₆As the gas pressure increases, the selectivity increases. This is SF₆This is because the addition of gas produces Al chloride, which is an etching reaction product that is difficult to be detached from the surface when the GaAlN layer is etched.
[0225]
As a result, the etching rate of the GaAlN layer becomes slow, and as a result, the selectivity with GaN increases. In this embodiment, SF is added as the additive gas.₆A gas is used, but a gas containing at least F as a component, such as CF_FourEtc., the same effect can be obtained. Moreover, the selective etching is, for example, O₂, CO, CO₂As long as the gas contains at least O as a component, it can be performed. The reason is that during etching of the GaAlN layer, an oxide of Al that is difficult to desorb is generated on the surface.
[0226]
Furthermore, in order to stop etching precisely at the interface between the GaN layer 380 and the GaAlN layer 379, it is preferable to use both selective etching and in-situ observation method of the etching process. In this embodiment, the etching depth was monitored by laser interference. Specifically, the etching sample surface is irradiated with a laser beam having a wavelength of 650 nm, and the reflected light is detected. At this time, the laser light is reflected from the sample surface and the interface inside the sample, and interference occurs between these reflected lights, so that the reflected light intensity vibrates with the progress of etching. By detecting this vibration, the etching amount and the heterointerface can be observed. According to this in-situ observation method, when used together with the selective etching method, the etching rate of GaAlN is slow, so the period of oscillation of the reflected light intensity during etching of the GaN layer 380 and the reflected light intensity during etching of the GaAlN layer 379 There is a big difference with the vibration period. Therefore, if the etching is finished when the period changes, the etching can be finished with the minimum overetching amount.
[0227]
According to the above method, in this embodiment, the etching can be completed when the overetching amount of the GaAlN layer 379 is 40 nm or less. After the etching process, the wafer is H₂SO_Four: H₂O₂: H₂The resist mask and etching residues are removed by dipping in an O solution. Exposed SiO after resist mask removal₂The mask can also be used as a mask for selective growth, which is the next step.
[0228]
After the above processing, as shown in FIG. 39C, the second growth by MOCVD causes a 0.5 μm-thick optical confinement layer (current confinement layer) 382 made of Si-doped n-type GaN to p. A p-type GaAlN cladding layer 379 is formed along the side surface of the p-type GaN cap layer 380. After the second growth, the wafer is immersed in an ammonium fluoride solution and SiO 2₂The mask is removed and the p-type GaN cap layer 380 is exposed.
[0229]
Next, as shown in FIG. 40 (d), by the third growth by MOCVD, a 0.5 μm thick layer of Mg-doped p-type GaN is formed on the p-type GaN cap layer 380 and the p-type GaAlN cladding layer 379. A contact layer 383 is formed. Next, Cl₂A portion of the wafer is etched by RIBE using a gas until the n-type GaN contact layer 372 is exposed to form a mesa.
[0230]
Thereafter, as shown in FIG. 40E, an n-side electrode 384 and a p-side electrode 385 were formed, and a semiconductor laser was fabricated.
[0231]
Conventionally, in a similar laser, the n-type GaN current confinement layer 382 is grown by the first growth, and then an opening is opened in the current confinement layer 382 by dry etching, and the p-type is formed by the second growth. There is also a manufacturing method in which a GaN contact layer 380 is grown. However, in the case of this conventional method, Mg is taken into the n-type GaN current confinement layer 382 from the periphery of the MOCVD reaction tube during growth, so that the current confinement layer needs to be thickened. The p-type GaN contact layer must be thick, which increases the device resistance. Further, in the case of the conventional method, a dry etching / re-growth interface is formed at the opening portion of the current confinement layer, and a current flows through this interface.
[0232]
However, according to the present embodiment, since the n-type GaN current confinement layer 382 is stacked in the second growth, Mg is not taken in from the periphery of the MOCVD reaction tube, and the n-type GaN current confinement layer 382 is thinned. Can be formed. In addition, since no current flows through the dry etching / regrowth interface, there is no problem of leakage at the interface.
[0233]
As described above, according to the present embodiment, selective etching of the gallium nitride compound semiconductor layer can be realized. Furthermore, since the etching amount can be accurately monitored, the etching amount can be accurately controlled in the process of forming the ridge portion in the cladding layer. As a result, the distance between the current confinement layer and the active layer can be set to the designed value, so that it is possible to manufacture a semiconductor laser that realizes continuous oscillation in the fundamental transverse mode while reducing the threshold current density.
[0234]
(20th embodiment)
42 to 43 are manufacturing process diagrams of the semiconductor laser according to the twentieth embodiment of the present invention.
[0235]
This embodiment is different from the nineteenth embodiment in the following two points. First, as shown in FIG. 42B, instead of the p-type GaAlN cladding layer 379, a p-type GaAlN cladding layer 390 having a ridge and flat portions on both sides thereof is formed by dry etching. The second point is that, as shown in FIG. 42C, the ridge made of the p-type GaAlN cladding layer 390 is buried along the side portion with the n-type InGaN current confinement layer 382.
[0236]
In this structure, since the current confinement layer 382 is close to the active layer 376 on both sides of the ridge, light confinement is performed by the effective refractive index distribution in the horizontal direction caused by the influence of the absorption loss of the InGaN current confinement layer 382. At this time, the thickness of GaAlN on both sides of the ridge affects the distance between the current confinement layer 382 and the active layer 376 and must be strictly controlled from the viewpoint of stably oscillating the laser in the transverse mode.
[0237]
Therefore, as described above, after the stacking step shown in FIG. 42A, a selective etching technique and a laser interference monitor are used in combination in the ridge forming step. For etching, Cl₂Gas and SF₆And a mixed gas and RIBE method are used. Etching conditions are Cl₂Gas pressure 0.4mTorr, SF₆The gas pressure is 0.15 mTorr, the microwave power is 200 W, and the ion acceleration voltage is 500 V.
[0238]
A mask is formed on the p-type GaN cap layer 380, and etching is performed from a region other than the mask in the p-type GaN cap layer 380. The progress of etching is observed by a laser interference monitor. Under the above conditions, the selectivity of GaN / GaAlN is about 1.25, and the etching rate of GaAlN is slow. Therefore, the oscillation period of the reflection intensity of the laser light in the laser interference monitor changes at the interface between GaN and GaAlN. Etching was stopped when the oscillation period of the reflection intensity corresponds to 150 nm and the oscillation appeared 1.3 periods after the GaN / GaAlN interface was detected. As a result, as shown in FIG. 42B, the etching could be stopped leaving 100 nm as designed as the thickness of the p-type GaAlN cladding layer 390 on both sides of the ridge.
[0239]
In this dry etching process, unlike the present embodiment, the selective etching technique is not applied, and Cl₂When only gas is used, GaN and GaAIN are etched at a substantially constant rate. In this constant speed etching, since the change of the vibration period at the GaN / GaAlN interface in the laser interference monitor is slight, the detection of the interface becomes inaccurate. For this reason, the accuracy of monitoring the etching amount is insufficient.
[0240]
On the other hand, in the manufacturing method according to the present invention, the etching amount can be controlled with sufficient accuracy by using selective etching, and the semiconductor laser having the structure of the present invention can be manufactured.
[0241]
After the ridge is formed as described above, the n-type InGaN current confinement layer 382 is selectively formed by the second growth as shown in FIG. Furthermore, SiO₂After removing the mask, as shown in FIG. 43D, the p-type GaN contact layer 383 is formed by the third growth. The p-type GaN contact layer 383 is etched by dry etching until the n-type GaN contact layer 384 is exposed to form a mesa. Thereafter, as shown in FIG. 43 (e), a p-side electrode 385 is formed on the p-type GaN contact layer 383, and an n-side electrode 384 is formed on the n-type GaN contact layer 384, whereby a semiconductor laser is manufactured. .
[0242]
Here, in this embodiment, the case where the n-type InGaN layer is embedded as the current confinement layer 382 has been described, but the material of the current confinement layer 382 may be another material such as an n-type GaAlN layer.
[0243]
(21st Embodiment)
44 (a) to 44 (d) are process diagrams for fabricating a semiconductor laser according to the twenty-first embodiment of the present invention. The difference of this embodiment from the twentieth embodiment is that not the selective growth but the entire ridge is buried with an n-type InGaN current confinement layer 391 as shown in FIG.
[0244]
Even in this laser structure, after the step shown in FIG. 44A, as shown in FIG. 44B, the p-type GaAlN cladding layer 390 is formed into a shape having a ridge and flat portions on both sides thereof by dry etching. There is a need. Here, since the thickness of GaAlN on both sides of the ridge affects the distance between the current confinement layer 391 and the active layer 376, it is strictly from the viewpoint of stable transverse mode oscillation of the laser as in the twentieth embodiment. Need to be controlled.
[0245]
Also in this embodiment, the selective etching technique according to the present invention and the laser interference monitor are used in combination as in the twentieth embodiment. As a result, a semiconductor laser having a structure as shown in FIG. 44 (c) can be manufactured.
[0246]
(Twenty-second embodiment)
FIG. 45 is a sectional view showing the structure of a semiconductor laser according to the twenty-second embodiment of the present invention.
[0247]
In the figure, reference numeral 400 denotes an n-type SiC substrate. On this substrate 400, an n-type ZnO layer 401, an n-type GaN layer 402, an n-type GaAlN cladding layer 403, a GaN waveguide layer 404, In_jGa_1-jA first active layer 405 made of N and a GaN waveguide layer 406 are sequentially formed, and in addition to the first region A, the second region B includes In_kGa_1-kA second active layer 407 and a GaN waveguide layer 408 made of N are formed. In the first region A and the second region B, p-type GaAlN cladding layers 411a and b, n-type InGaN optical confinement layers 412a and b, and p-type GaN contact layers 413a and b are formed. These crystal growths are performed by MOCVD, MBE, or a combination of both. 414a and b are p-side electrodes, and 415 is an n-side electrode.
[0248]
Here, the band gap Eg of the first active layer 405₁, Thickness d1 and band gap Eg of the second active layer 407₂, Thickness d2 is
Eg₁> Eg₂        ... (16)
d1> d2 (17)
It is set to become. Specifically, the In composition j of the first active layer 405 was set to 0.05 and the thickness was 100 nm, and the In composition k of the second active layer 407 was set to 0.15 and the thickness was 10 nm. This corresponds to λ1 = 380 nm and λ2 = 410 nm at the oscillation wavelength.
[0249]
In the first region A of this laser structure, since the active layer is only the first active layer 405, the active layer 405 oscillates at a wavelength of 380 nm. On the other hand, in the second region B, the first active layer 405 and the second active layer 407 exist. However, since the band gap of the second active layer 407 is smaller, the stimulated emission recombination does not occur in the second region B. Occurs in the active layer 407. Therefore, oscillation occurs at 410 nm in this region.
[0250]
Since the active layer 405 in the first region A is relatively thick at 100 nm, the active region 405 has a structure in which self-oscillation is likely to occur, and a characteristic with little return optical noise can be obtained. On the other hand, in the second region B, since the active layer 407 is as thin as 10 nm, the optical power density can be reduced and oscillation at high output is possible. Accordingly, in the laser having this structure, the laser in the first area A can be used for reading and the laser in the second area B can be used for recording in optical disc applications.
[0251]
In addition, in this embodiment, since the optical confinement layer 412 having a band gap energy smaller than that of the active layers 405 and 407 is embedded in the side surface of the clad layer 411 forming the ridge, the laser in each region A and B is formed. The oscillation threshold current density is reduced, and continuous oscillation in the fundamental transverse mode is possible.
[0252]
The manufacturing process of the semiconductor laser shown in FIG. 45 will be described with reference to FIGS. First, as shown in FIG. 46A, on an n-type SiC substrate 400, an n-type ZnO layer 401, an n-type GaN layer 402, an n-type GaAlN cladding layer 403, a GaN waveguide layer 404, In_jGa_1-jN active layer (first active layer) 405, GaN waveguide layer 406, In_kGa_1-kAn N active layer (second active layer) 407 and a GaN waveguide layer 408 are sequentially grown.
[0253]
Next, as shown in FIG. 46B, the waveguide layer 408 and the active layer 407 in the first region A are removed by etching. At this time, since the active layer 405 is protected by the waveguide layer 406, an increase in non-light-emitting components due to interface recombination can be prevented in the final structure.
[0254]
Next, as shown in FIG. 46C, a p-type GaAlN cladding layer 411 is grown on the entire surface, and SiO 2 is grown thereon.₂A film 421 is formed by a sputtering method or the like.
[0255]
Next, as shown in FIG.₂The film 421 is patterned, and ridges are formed in the regions A and B using this as a mask.
[0256]
Next, as shown in FIG.₂With the mask attached, a light confinement layer 412 that also serves as current confinement is grown by selective growth.
[0257]
Next, as shown in FIG.₂After removing the mask, a p-type GaN contact layer 413 is grown, and a p-side electrode 414 and an n-side electrode 415 are formed. Finally, a trench is formed between the region A and the region B by dry etching and element isolation is performed, whereby the structure shown in FIG. 45 is completed.
[0258]
As described above, according to the present embodiment, since the low-power laser of the thick film active layer and the high-power laser of the thin film active layer are formed on the same substrate, a difficult process such as active layer thickness control is required. In addition, it is possible to realize the laser performance required for both reproduction / reading and erasing / recording in the optical disk system. In addition, since lasers with different wavelengths can be formed on the same substrate, the problem of incompatibility due to the difference in wavelength can be solved.
[0259]
(23rd embodiment)
FIG. 48 is a sectional view showing the structure of a semiconductor laser according to the twenty-third embodiment of the present invention. The same parts as those in FIG. 19 are denoted by the same reference numerals, and detailed description thereof is omitted.
[0260]
The structure and the manufacturing method of the present embodiment are almost the same as those of the twenty-second embodiment. However, the difference from the twenty-second embodiment is that the first active layer 405 having the film thickness d1 is used instead of the first active layer 405. A second active layer 427 having a layer 425 and having a film thickness d2 larger than the film thickness of the first active layer is provided instead of the second active layer 407.
[0261]
That is, the relationship between the film thickness d1 of the first active layer 425 and the film thickness d2 of the second active layer 427 is
d1 <d2 (18)
It is that. That is, d1 = 10 nm and d2 = 100 nm. A p-type InGaN absorption layer 428 is provided in the second region B. This absorption layer 428 functions as a saturable absorber and has a structure in which self-oscillation occurs more easily. In the case of this structure, in the optical disk application, the laser in the first area A is used for recording and the laser in the second area B is used for reading.
[0262]
(24th Embodiment)
FIG. 49 is a sectional view showing the structure of a semiconductor laser according to the twenty-fourth embodiment of the present invention.
[0263]
In the figure, reference numeral 430 denotes a sapphire substrate. On this substrate 430, a GaN buffer layer 431, an n-type GaN contact layer 432, an n-type GaAlN cladding layer 433, an n-type GaN waveguide layer 434, and a first InGaN multiple quantum well. Active layer 435, undoped GaN waveguide layer 436, second active layer 437 comprising InGaN multiple quantum wells, p-type GaN waveguide layer 438, p-type GaAlN cladding layer 439, p-type GaN cap layer 440, p-type InGaN An optical confinement layer 441 and a p-type InGaN contact layer 442 are formed. In the figure, 443 and 444 are p electrodes, and 445 is an n-side electrode.
[0264]
Here, the band gap Eg of the first multiple quantum well active layer 435₁And the band gap Eg of the second multiple quantum well active layer 437₂What is
Eg₁> Eg₂
It is set to become. Specifically, the In composition of the well layer of the first multiple quantum well active layer was 0.15, and the In composition of the second multiple quantum well active layer was 0.8. Each oscillation wavelength corresponds to blue and red. The In composition of the second multiple quantum well active layer is larger than that of a normal GaN laser. However, since the composition is close to InN, a high quality crystal can be obtained.
[0265]
Since a structure in which blue and red lasers are integrated in this way can be realized, it is extremely useful in optical disc applications. That is, in the case of a system using lasers with different wavelengths as the density increases, compatibility with a conventional system can be easily realized by using a laser like this embodiment.
[0266]
FIG. 50 shows an arrangement example of electrodes in the laser of the embodiment shown in FIG. Since the n electrode side can be made common as in this example, for example, three bonding wires are sufficient.
[0267]
(25th Embodiment)
FIG. 51 is a sectional view showing the structure of a semiconductor laser according to the twenty-fifth embodiment of the present invention.
[0268]
In the figure, reference numeral 450 denotes a sapphire substrate. On this substrate 450, a GaN buffer layer 451, an n-type GaN contact layer 452, an n-type GaAlN cladding layer 453, an n-type GaN waveguide layer 454, and a first InGaN multiple quantum well. Active layer 455, undoped GaN waveguide layer 456, second active layer 457 composed of InGaN multiple quantum wells, p-type GaN waveguide layer 458, p-type GaAlN cladding layer 459, p-type GaN cap layer 460, p⁺-Type GaN contact layer 461, n-type InGaN optical confinement layer 462, p⁺A type GaN contact layer 463 is formed. In the figure, 464 and 465 are p-side electrodes, and 466 is an n-side electrode.
[0269]
Band gap Eg1 of the first multiple quantum well active layer 455₁And the band gap Eg of the second multiple quantum well active layer 457₂What is
Eg₁> Eg₂
It is set to become. As a result, the left laser is Eg₂With a wavelength corresponding to the band gap of₁It oscillates at a wavelength corresponding to the band gap.
[0270]
(26th Embodiment)
FIG. 52 is a sectional view showing the structure of a semiconductor laser according to the twenty-sixth embodiment of the present invention.
[0271]
Since the basic layer structure of the laser is the same as that shown in FIG. 28, its detailed description is omitted. Also in this embodiment, the band gap Eg of the first multiple quantum well active layer 196₁And the second multiple quantum well active layer 470 bunt gap Eg₂Is set as described above, it is possible to oscillate at different wavelengths.
[0272]
(Twenty-seventh embodiment)
FIG. 53 is a sectional view showing the structure of a semiconductor laser according to the twenty-seventh embodiment of the present invention.
[0273]
Since the basic structure of the semiconductor laser in this embodiment is the same as the example shown in FIG. 51, detailed description thereof is omitted. In this embodiment, an example of mounting with the joint surface down is shown.
[0274]
480 in the figure is a heat sink. As the heat sink 480, it is effective to use a material having high thermal conductivity such as BN or diamond in addition to Cu. The heat sink 480 is provided with steps as shown in the figure, and metal layers (for example, Ti / Pt / Au layers) 481 to 484 formed by metallization are formed thereon. Reference numeral 490 denotes a separation groove for separating electrodes. Each metallized layer and the electrode of the semiconductor laser are pressure-bonded by solder materials 485 to 489 such as AuSn.
[0275]
By using a mount with a bonding surface down as in this embodiment, the thermal resistance of the element is reduced, and oscillation at higher temperatures is possible.
[0276]
In addition, this invention is not limited to each embodiment mentioned above, In the range which does not deviate from the summary, it can implement in various deformation | transformation.
[0277]
【The invention's effect】
As described above, according to the present invention, an InGaAlBN-based semiconductor laser that can continuously oscillate in the fundamental transverse mode and can obtain a high-quality outgoing beam free of astigmatism suitable for a light source such as an optical disk system and the like. The manufacturing method can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a semiconductor laser according to a first embodiment of the present invention.
FIG. 2 shows an equivalent refractive index difference Δn inside and outside the stripe._eq, Loss for fundamental mode α₀, The distance h between the optical confinement layer and the core region with respect to the loss difference Δα_outThe figure which shows the dependence with respect to.
FIG. 3 Threshold current density J_thLoss α₀FIG. 9 is a diagram showing the dependence on the stripe width W with respect to the loss difference Δα.
FIG. 4 is an equivalent refractive index difference Δn inside and outside the stripe._eqFIG. 6 is a diagram showing the relationship between the astigmatic difference of the beam and the composition of the light confinement layer.
FIG. 5 is a diagram showing the dependence on the stripe width with respect to astigmatism difference and loss difference Δα in each waveguide type;
FIG. 6: Active layer total thickness d, cladding layer thickness H_cladAnd Al composition difference X between the cladding layer and the active layer_A1FIG. 6 is a diagram illustrating a relationship between the waveguide mode loss α and the waveguide mode loss α.
FIG. 7 shows the cladding layer thickness in the SCH-MQW structure._cladWaveguide layer thickness H_guideThe figure which shows the relationship between and a waveguide mode.
FIG. 8: Threshold current density J_th, For the optical confinement factor Γ, the cladding layer thickness_cladWaveguide layer thickness H_guideFIG.
FIG. 9 is a diagram showing the clad layer thickness dependence of the far-field image intensity distribution.
FIG. 10 shows the clad layer thickness in the SCH-MQW structure._cladWaveguide layer thickness H_guideThe figure which shows the relationship between and the boundary line of waveguide mode.
FIG. 11 shows the cladding layer thickness in the SCH-MQW structure._cladWaveguide layer thickness H_guideThe figure which shows the relationship between and the boundary line of waveguide mode.
FIG. 12 shows threshold current density J per unit well layer thickness._th/ D_actThe amount of light confinement Δx · (H_core/ Λ) ・ (H_cladThe figure which shows the dependence with respect to / (lambda).
FIG. 13 is a view showing a design example of the layer structure of the semiconductor laser in the embodiment.
FIG. 14 is a schematic diagram for explaining a threshold reduction effect according to the present invention.
FIG. 15 is a diagram showing a band structure and an electron and hole distribution when an overflow prevention layer is not provided.
FIG. 16 is a diagram showing a band structure and distribution of electrons and holes when an overflow prevention layer is provided.
FIG. 17 is a cross-sectional view showing a configuration of a semiconductor laser according to a second embodiment of the present invention.
FIG. 18 is a cross-sectional view showing a configuration of a semiconductor laser according to a third embodiment of the present invention.
FIG. 19 is a cross-sectional view showing a configuration of a semiconductor laser according to a fourth embodiment of the present invention.
FIG. 20 is a diagram showing the principle of the current blocking effect by a hetero barrier.
FIG. 21 is a diagram showing current density-voltage characteristics in a configuration having a p-GaAlN / p-InGaN interface.
FIG. 22 is a graph showing current density-voltage characteristics in a configuration having an n-GaAlN / n-InGaN interface.
FIG. 23 is a cross-sectional view showing a configuration of a semiconductor laser according to a fifth embodiment of the present invention.
FIG. 24 is a sectional view showing a configuration of a semiconductor laser according to a sixth embodiment of the present invention.
FIG. 25 is a cross-sectional view showing a configuration of a semiconductor laser according to a seventh embodiment of the present invention.
FIG. 26 is a sectional view showing a configuration of a semiconductor laser according to an eighth embodiment of the present invention.
FIG. 27 is a sectional view showing the structure of a semiconductor laser according to a ninth embodiment of the invention.
FIG. 28 is a cross-sectional view showing a configuration of a semiconductor laser according to a tenth embodiment of the present invention.
FIG. 29 is a sectional view showing the structure of a semiconductor laser according to an eleventh embodiment of the present invention.
FIG. 30 is a sectional view showing the structure of a semiconductor laser according to a twelfth embodiment of the present invention.
FIG. 31 is a perspective view showing the configuration of a semiconductor laser according to a thirteenth embodiment of the present invention.
FIG. 32 is a sectional view showing the structure of a semiconductor laser according to a fourteenth embodiment of the present invention.
FIG. 33 is a sectional view showing the structure of a semiconductor laser according to a fifteenth embodiment of the present invention.
FIG. 34 is a sectional view showing the structure of a semiconductor laser according to a sixteenth embodiment of the present invention.
FIG. 35 is a sectional view showing the structure of a semiconductor laser according to a seventeenth embodiment of the present invention.
FIG. 36 is a schematic diagram for explaining an etching method in the embodiment;
FIG. 37 is a schematic diagram for explaining an etching method in the embodiment;
FIG. 38 is a sectional view showing the structure of a semiconductor laser according to an eighteenth embodiment of the present invention.
FIG. 39 is a manufacturing process diagram of the semiconductor laser according to the nineteenth embodiment of the present invention.
FIG. 40 is a manufacturing process diagram of the semiconductor laser according to the embodiment;
FIG. 41 is a view showing a relationship between a selection ratio and a gas composition in the same embodiment.
FIG. 42 is a manufacturing process diagram of the semiconductor laser according to the twentieth embodiment of the present invention.
FIG. 43 is a manufacturing process diagram of the semiconductor laser according to the embodiment;
44 is a manufacturing process diagram of a semiconductor laser according to the twenty-first embodiment of the present invention; FIG.
FIG. 45 is a sectional view showing the structure of a semiconductor laser according to a twenty-second embodiment of the present invention.
46 is a manufacturing process diagram of the semiconductor laser in the embodiment; FIG.
47 is a manufacturing process diagram of the semiconductor laser in the embodiment, FIG.
FIG. 48 is a sectional view showing the structure of a semiconductor laser according to a twenty-third embodiment of the present invention.
FIG. 49 is a sectional view showing the structure of a semiconductor laser according to a twenty-fourth embodiment of the present invention.
50 is a view showing an arrangement example of electrodes in the laser of the embodiment shown in FIG. 49. FIG.
FIG. 51 is a sectional view showing the structure of a semiconductor laser according to a twenty-fifth embodiment of the present invention.
FIG. 52 is a sectional view showing the structure of a semiconductor laser according to a twenty-sixth embodiment of the present invention.
FIG. 53 is a sectional view showing the structure of a semiconductor laser according to a twenty-seventh embodiment of the present invention.
[Explanation of symbols]
10, 30, 70, 90, 110, 130, 150, 170, 190, 210, 230, 260, 280, 300, 320, 344, 350, 370, 430, 450 ... sapphire substrate
11, 31, 52, 71, 91, 111, 131, 151, 171, 191, 211, 231, 261, 281, 301, 321, 351, 371, 402, 431, 451... GaN buffer layer
12, 32, 72, 112, 132, 152, 172, 192, 212, 232, 262, 282, 302, 322, 352, 372, 432, 452... N-type GaN contact layer
13, 33, 53, 73, 97, 113, 133, 153, 173, 194, 218, 233, 263, 283, 303, 323, 353, 373, 403, 433, 453 ... n-type GaAlN cladding layer
14,34,54,74,96,114,134,154,174,195,217,234,264,284,304,324,354,374,404,434,454 ... n-type GaN waveguide layer
15, 35, 55, 375... N-type GaAlN overflow prevention layer
16, 56, 75, 95, 115, 135, 155, 175, 196, 216, 235, 265, 285, 305, 325, 355, 376, 435, 437, 455, 457 ... InGaN multiple quantum well (MQW) activity layer
17, 37, 57, 377... P-type GaAlN overflow prevention layer
18, 38, 58, 76, 94, 116, 136, 156, 176, 197, 215, 236, 266, 286, 306, 326, 356, 378, 438, 458 ... p-type GaN waveguide layer
19, 39, 59, 77, 93, 117, 137, 138, 157, 158, 159, 177, 178, 179, 198, 214, 237, 267, 287, 309, 327, 328, 357, 358, 379, 390, 411a, 439, 459 ... p-type GaAlN cladding layer
20, 40, 60, 79, 99, 120, 141, 161, 181, 193, 213, 213, 240, 269, 289, 310, 329, 412a, 441, 462 ... light confinement layer
21, 41, 61, 78, 92, 118, 139, 160, 180, 199, 250, 251, 268, 270, 288, 308, 359, 360, 380, 383, 413a, 413b, 440, 460, 461 462 ... p-type GaN layer
22,43,62,80,101,121,142,183,201,221,242,271,292,312,361,362,385,414a, 414b, 443,444,464,465 ... p-side electrode
23,44,63,81,100,122,143,184,202,222,243,272,293,313,384,415,445,466 ... n-side electrode
36 ... GaN single quantum well (SQW) active layer
42,119,140,200,220,239,241,307 ... p-type InGaN layer
50, 400 ... n-type SiC substrate
51, 401 ... n-type ZnO buffer layer
98,219 ... n-type GaN layer
340 ... reaction vessel
341 ... Metal electrode
342 ... Stirrer
343 ... NaOH solution
345 ... DC power supply
381 ... Inorganic mask layer
382, 391 ... Current confinement layer
405, 407, 425, 427 ... active layer
406, 408, 436 ... GaN waveguide layer
421 ... SiO₂film
428 ... Absorbing layer
480 ... heat sink
481-484 ... Metal layer
485-489 ... Solder material
490 ... separation groove
Eg₁, Eg₂... band gap
d1, d2 ... thickness

Claims (12)

A semiconductor laser comprising a group III-V compound semiconductor containing nitrogen,
A substrate,
A first conductivity type cladding layer formed on the substrate;
A core region including at least an active layer formed on the first conductivity type cladding layer;
A second conductivity type cladding layer formed on the core region and having a striped ridge;
A double heterostructure comprising the first conductivity type cladding layer, the core region and the second conductivity type cladding layer;
A light confinement layer selectively formed along the side of the ridge on the second conductivity type cladding layer;
A second conductivity type contact layer formed on the light confinement layer and on the ridge of the second conductivity type cladding layer;
A first electrode formed on the second conductivity type contact layer;
A second electrode formed in a region different from the first conductivity type cladding layer in the substrate,
The active layer in the core region includes at least _{a well} layer made of In _a Ga _b Al _c B _{1 -abc} N (0 ≦ a, b, c, a + b + c ≦ 1) and In _e Ga _f Al _g B _{1 -efg} N A single quantum well or a multiple quantum well composed of a barrier layer composed of (0 ≦ e, f, g, e + f + g ≦ 1),
The optical confinement layer is made of a III-V group compound semiconductor containing nitrogen, and the refractive index of the optical confinement layer is larger than the refractive index of the second conductivity type cladding layer.
The band gap energy of the optical confinement layer is less than the band gap energy of the active layer,
The first conductivity type cladding layer is made of In _x Ga _y Al _z B _1-xyz N (0 ≦ x, y, z, x + y + z ≦ 1), and the second conductivity type cladding layer is In _u Ga _v Al _w B _1-uvw N (0 ≦ u, v, w, u + v + w ≦ 1)
Al composition difference ΔZ _Al (= Al composition of the first conductivity type cladding layer−Al composition of the active layer) between the first conductivity type cladding layer and the active layer, the second conductivity type cladding layer and the active layer With respect to the oscillation wavelength λ determined by the well layer, the total thickness d of the core region, and the Al composition difference ΔW _Al (= Al composition of the second conductivity type cladding layer−Al composition of the active layer) The thickness H1 of the first conductivity type cladding layer and the thickness H2 including the ridge in the second conductivity type cladding layer are:
0.18 ( ΔZ _Al d / λ) ^−1/2 ≦ H1 / λ ≦ 0.27 ( ΔZ _Al d / λ) ^−1/2
0.18 ( ΔW _Al d / λ) ^−1/2 ≦ H2 / λ ≦ 0.27 ( ΔW _Al d / λ) ^−1/2
A semiconductor laser characterized by being in a range satisfying A semiconductor laser comprising a group III-V compound semiconductor containing nitrogen,
A substrate,
A buffer layer formed on the substrate;
A first conductivity type contact layer formed on the buffer layer;
A first conductivity type cladding layer formed on the first conductivity type contact layer;
A core region including at least an active layer formed on the first conductivity type cladding layer;
A second conductivity type cladding layer formed on the core region and having a striped ridge;
A double heterostructure comprising the first conductivity type cladding layer, the core region and the second conductivity type cladding layer;
A light confinement layer selectively formed along the side of the ridge on the second conductivity type cladding layer;
A second conductivity type contact layer formed on the light confinement layer and on the ridge of the second conductivity type cladding layer;
A first electrode formed on the second conductivity type contact layer;
A second electrode formed in a region different from the first conductivity type cladding layer in the first conductivity type contact layer;
The active layer in the core region includes at least _{a well} layer made of In _a Ga _b Al _c B _{1 -abc} N (0 ≦ a, b, c, a + b + c ≦ 1) and In _e Ga _f Al _g B _{1 -efg} N A single quantum well or a multiple quantum well composed of a barrier layer composed of (0 ≦ e, f, g, e + f + g ≦ 1),
The optical confinement layer is made of a III-V group compound semiconductor containing nitrogen, and the refractive index of the optical confinement layer is larger than the refractive index of the second conductivity type cladding layer.
The band gap energy of the optical confinement layer is less than the band gap energy of the active layer,
The first conductivity type cladding layer is made of In _x Ga _y Al _z B _1-xyz N (0 ≦ x, y, z, x + y + z ≦ 1), and the second conductivity type cladding layer is In _u Ga _v Al _w B _1-uvw N (0 ≦ u, v, w, u + v + w ≦ 1)
Al composition difference ΔZ _Al (= Al composition of the first conductivity type cladding layer−Al composition of the active layer) between the first conductivity type cladding layer and the active layer, the second conductivity type cladding layer and the active layer With respect to the oscillation wavelength λ determined by the well layer, the total thickness d of the core region, and the Al composition difference ΔW _Al (= Al composition of the second conductivity type cladding layer−Al composition of the active layer) The thickness H1 of the first conductivity type cladding layer and the thickness H2 including the ridge in the second conductivity type cladding layer are:
0.18 ( ΔZ _Al d / λ) ^−1/2 ≦ H1 / λ ≦ 0.27 ( ΔZ _Al d / λ) ^−1/2
0.18 ( ΔW _Al d / λ) ^−1/2 ≦ H2 / λ ≦ 0.27 ( ΔW _Al d / λ) ^−1/2
A semiconductor laser characterized by being in a range satisfying In the semiconductor laser according to claim 1 or 2,
A thickness H _out excluding the ridge in the second conductivity type cladding layer is 0.3 μm or less. In the semiconductor laser according to claim 1 or 2,
The semiconductor laser according to claim 1, wherein a conductivity type of the light confinement layer is the same as a conductivity type of the second conductivity type cladding layer. In the semiconductor laser according to claim 1 or 2,
An intermediate between a band gap energy of the second conductivity type cladding layer and a band gap energy of the second conductivity type contact layer, formed between the ridge of the second conductivity type cladding layer and the second conductivity type contact layer. A second conductivity type cap layer having a band gap energy of a value of
The semiconductor laser, wherein the light confinement layer and the second conductivity type contact layer are one layer made of the same material. In the semiconductor laser according to claim 1 or 2,
The core region is
A plurality of waveguide layers formed so as to sandwich the active layer and having a refractive index smaller than an average refractive index of the quantum well and larger than a refractive index of each cladding layer;
Is formed between at least one of the cladding layers the active _{layer, In s Ga t Al h B} 1-sth N becomes (0 ≦ s, t, h , s + t + h ≦ 1) from the band gap of the waveguide layer A semiconductor laser comprising: a carrier overflow prevention layer having a band gap energy larger than energy. The semiconductor laser according to claim 6 , wherein
An Al composition h of the carrier overflow prevention layer is in a range satisfying 0 <h <0.2. A semiconductor laser comprising a group III-V compound semiconductor containing nitrogen,
A substrate,
A first conductivity type cladding layer formed on the substrate and made of In _x Ga _y Al _z B _1-xyz N (0 ≦ x, y, z, x + y + z ≦ 1);
A core region including at least an active layer formed on the first conductivity type cladding layer;
Formed in the core region, and the _{In u Ga v Al w B 1} -uvw N (0 ≦ u, v, w, u + v + w ≦ 1) consists, second conductivity type cladding layer having a stripe-shaped ridge,
A double heterostructure comprising the first conductivity type cladding layer, the core region and the second conductivity type cladding layer;
A second conductivity type contact layer formed on the second conductivity type cladding layer;
A first electrode formed on the second conductivity type contact layer;
A second electrode formed in a region different from the first conductivity type cladding layer in the substrate,
The active _{layer, In a Ga b Al c B} 1-abc N (0 ≦ a, b, c, a + b + c ≦ 1) consisting of a well layer and the _{In e Ga f Al g B 1} -efg N (0 ≦ e, a single quantum well or a multiple quantum well composed of a barrier layer composed of f, g, e + f + g ≦ 1),
The total thickness d _act of the well layer is less than 0.5 μm;
The Al composition x _Al of each cladding layer, the average In composition y _In of the core region, the sum Δx (= x _Al + y _In ) of both compositions, the total thickness H _{core of the} core region, and the thickness H _{clad of} each cladding layer For the oscillation wavelength λ
A semiconductor laser characterized by satisfying Δx · (H _core / λ) · (H _clad /λ)≧0.08. A semiconductor laser comprising a group III-V compound semiconductor containing nitrogen,
A substrate,
A buffer layer formed on the substrate;
A first conductivity type contact layer formed on the buffer layer;
A first conductivity type cladding layer formed on the first conductivity type contact layer and made of In _x Ga _y Al _z B _{1 -xyz} N (0 ≦ x, y, z, x + y + z ≦ 1);
A core region including at least an active layer formed on the first conductivity type cladding layer;
Formed in the core region, and the _{In u Ga v Al w B 1} -uvw N (0 ≦ u, v, w, u + v + w ≦ 1) consists, second conductivity type cladding layer having a stripe-shaped ridge,
A double heterostructure comprising the first conductivity type cladding layer, the core region and the second conductivity type cladding layer;
A second conductivity type contact layer formed on the second conductivity type cladding layer;
A first electrode formed on the second conductivity type contact layer;
A second electrode formed in a region different from the first conductivity type cladding layer in the first conductivity type contact layer;
The active _{layer, In a Ga b Al c B} 1-abc N (0 ≦ a, b, c, a + b + c ≦ 1) consisting of a well layer and the _{In e Ga f Al g B 1} -efg N (0 ≦ e, a single quantum well or a multiple quantum well composed of a barrier layer composed of f, g, e + f + g ≦ 1),
The total thickness d _act of the well layer is less than 0.5 μm;
The Al composition x _Al of each cladding layer, the average In composition y _In of the core region, the sum Δx (= x _Al + y _In ) of both compositions, the total thickness H _{core of the} core region, and the thickness H _{clad of} each cladding layer For the oscillation wavelength λ
A semiconductor laser characterized by satisfying Δx · (H _core / λ) · (H _clad /λ)≧0.08. A semiconductor laser comprising a group III-V compound semiconductor containing nitrogen,
A substrate,
A first conductivity type cladding layer formed on the substrate and made of In _x Ga _y Al _z B _1-xyz N (0 ≦ x, y, z, x + y + z ≦ 1);
A well layer made of In _a Ga _b Al _c B _{1 -abc} N (0 ≦ a, b, c, a + b + c ≦ 1) and In _e Ga _f Al _g B ₁₋ a core region including an active layer of a single quantum well or a multiple quantum well composed of a barrier layer composed of _efg N (0 ≦ e, f, g, e + f + g ≦ 1);
Formed in the core region, and the _{In u Ga v Al w B 1} -uvw N (0 ≦ u, v, w, u + v + w ≦ 1) consists, second conductivity type cladding layer having a stripe-shaped ridge,
A double heterostructure comprising the first conductivity type cladding layer, the core region and the second conductivity type cladding layer;
A second conductivity type contact layer formed on the second conductivity type cladding layer;
A first electrode formed on the second conductivity type contact layer;
A second electrode formed in a region different from the first conductivity type cladding layer in the substrate,
The core region includes a plurality of conductive layers made of In _h Ga _i Al _j B _1-hij N (0 <h ≦ 1, 0 ≦ i <1, 0 ≦ j <1) formed so as to sandwich the active layer. Including wave layers,
The total thickness H _core of the core region and the average In composition y _In of the core region satisfy (y _In ) ^1/2 · (H _core /λ)≧0.15 with respect to the oscillation wavelength λ. A semiconductor laser. A semiconductor laser comprising a group III-V compound semiconductor containing nitrogen,
A substrate,
A buffer layer formed on the substrate;
A first conductivity type contact layer formed on the buffer layer;
A first conductivity type cladding layer formed on the first conductivity type contact layer and made of In _x Ga _y Al _z B _{1 -xyz} N (0 ≦ x, y, z, x + y + z ≦ 1);
A well layer made of In _a Ga _b Al _c B _{1 -abc} N (0 ≦ a, b, c, a + b + c ≦ 1) and In _e Ga _f Al _g B ₁₋ a core region including an active layer of a single quantum well or a multiple quantum well composed of a barrier layer composed of _efg N (0 ≦ e, f, g, e + f + g ≦ 1);
Formed in the core region, and the _{In u Ga v Al w B 1} -uvw N (0 ≦ u, v, w, u + v + w ≦ 1) consists, second conductivity type cladding layer having a stripe-shaped ridge,
A double heterostructure comprising the first conductivity type cladding layer, the core region and the second conductivity type cladding layer;
A second conductivity type contact layer formed on the second conductivity type cladding layer;
A first electrode formed on the second conductivity type contact layer;
A second electrode formed in a region different from the first conductivity type cladding layer in the first conductivity type contact layer;
The core region includes a plurality of conductive layers made of In _h Ga _i Al _j B _1-hij N (0 <h ≦ 1, 0 ≦ i <1, 0 ≦ j <1) formed so as to sandwich the active layer. Including wave layers,
The total thickness H _core of the core region and the average In composition y _In of the core region satisfy (y _In ) ^1/2 · (H _core /λ)≧0.15 with respect to the oscillation wavelength λ. A semiconductor laser.   The semiconductor laser according to any one of claims 1 to 11, wherein
  The substrate is made of sapphire, SiC, ZnO, MgAl ₂ O _Four , NdGaO _Three , LiGaO ₂ , Y _Three Al _Five O ₁₂ (YAG) or Y _Three Fe _Five O ₁₂ A semiconductor laser comprising any of (YIG).

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