JP4415440B2 - Manufacturing method of semiconductor laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser and a method for manufacturing the same, and is particularly suitable for application to a semiconductor laser having a ridge structure using a nitride III-V compound semiconductor.
[0002]
[Prior art]
In recent years, research and development of semiconductor lasers using nitride-based III-V compound semiconductors such as AlGaInN as active semiconductor lasers capable of emitting light from the blue region to the ultraviolet region, which are necessary for increasing the density of optical disks, have been actively conducted. It has been broken. The realization of a writable optical disk requires an optical output of at least 20 mW, but Nakamura et al. Reported on the production of a high-power laser using this material system (Appl. Phys. Lett., 72 (1998) 2014, Jpn. J. Appl. Phys., 37 (1998) L627).
[0003]
FIG. 14 shows a conventional ridge type GaN semiconductor laser. This GaN semiconductor laser has an SCH (Separate Confinement Heterostructure) structure.
[0004]
As shown in FIG. 14, in this GaN-based semiconductor laser, an n-type GaN contact layer 103, an n-type AlGaN cladding layer 104, and an n-type GaN are formed on a c-plane sapphire substrate 101 via an undoped GaN buffer layer 102. Optical waveguide layer 105, for example, undoped Ga _1-x In _x N / Ga _1-y In _y An active layer 106 having an N multiple quantum well structure, a p-type AlGaN cap layer 107, a p-type GaN optical waveguide layer 108, a p-type AlGaN cladding layer 109, and a p-type GaN contact layer 110 are sequentially stacked.
[0005]
Upper layer portion of n-type GaN contact layer 103, n-type AlGaN cladding layer 104, n-type GaN optical waveguide layer 105, active layer 106, p-type AlGaN cap layer 107, p-type GaN optical waveguide layer 108, and p-type AlGaN cladding layer 109 Has a mesa shape with a predetermined width. A ridge-shaped stripe having a predetermined width extending in one direction is formed in the upper layer portion of the p-type AlGaN cladding layer 109 and the p-type GaN contact layer 110 in the mesa portion.
[0006]
There are SiO on both sides of this stripe. ₂ The film 111 is embedded, and the p-side electrode 112 has a structure in contact only with the p-type GaN contact layer 110 on the upper surface of the stripe. An n-side electrode 113 is provided on the n-type GaN contact layer 103 adjacent to the mesa portion.
[0007]
[Problems to be solved by the invention]
However, as mentioned above, SiO ₂ In a GaN-based semiconductor laser in which the film 111 is embedded on both sides of the stripe, SiO 2 ₂ The refractive index (1.5) of GaN is very small compared to the refractive index of GaN (2.55), so the effective refractive index difference in the lateral direction is too large and the transverse mode confinement is too strong. For this reason, the single mode property of the laser beam becomes high. For example, when it is used in an optical pickup of an optical disc recording apparatus, there is a drawback that the laser beam interferes with the return light and generates strong noise.
[0008]
Therefore, the problem to be solved by the present invention is to provide a semiconductor laser capable of multimode oscillation and reducing the return light noise, and a method for manufacturing the same.
[0009]
[Means for Solving the Problems]
This inventor earnestly examined in order to solve the above problems which conventional technology has. The outline will be described below.
[0010]
Now, in GaN semiconductor lasers, SiO ₂ Consider the case of embedding a GaN layer instead of embedding a film. By embedding the GaN layer in this way, the effective refractive index difference in the lateral direction is reduced to 1 × 10. ^-3 To 3 × 10 ^-3 The transverse mode confinement can be moderately weakened. Therefore, multimode oscillation (or pulsation oscillation) is possible, and a semiconductor laser with little return light noise can be realized.
[0011]
In general, selective growth is used for embedding the GaN layer. That is, as shown in FIG. 1, in a manufacturing process of a GaN-based semiconductor laser, after growing up to a p-type AlGaN cladding layer 1 and a p-type GaN contact layer 2, striped SiO2 is formed on the p-type GaN contact layer 2 ₂ A film 3 is formed and this SiO ₂ The film 3 is used as a mask to etch the p-type AlGaN cladding layer 1 to a middle depth to form stripes, and then SiO 2 ₂ Using the film 3 as a mask, the GaN layer 4 is selected and selected at the buried portion and buried. However, even if the GaN layer 4 is selectively grown in this way, it is difficult to completely bury the GaN layer 4 due to the level difference on both sides of the stripe. In addition, depending on the shape of the stripe, a plane orientation may appear during the growth of the GaN layer 4, so that voids may be formed in the GaN layer 4.
[0012]
As a result of studying the cause of these problems, the present inventor has found that when the stripe is formed by etching, the width of the embedded portion formed on both sides thereof is almost equal to the width of the laser chip, and is usually 200 μm or more. We came to the conclusion that big is one of the major factors. That is, since the width of the buried part is very large in this way, Ga atoms and N atoms participating in the selective growth of the GaN layer 4 in the portions on both sides of the stripe are SiO 2 on the stripe. ₂ Most of them are supplied onto the film 3 and migrate to the buried part by lateral diffusion. For this reason, the selective growth rate of the GaN layer 4 is slow, and the embedding shape is poor, making it difficult to perform flat embedding.
[0013]
The burying property of the GaN layer 4 can be improved to some extent by extending the growth time. However, when the growth is performed for a long time as described above, the InGaN semiconductor used as the active layer of the GaN semiconductor laser has a high temperature. Because of its weak thermal history, the active layer is greatly damaged during the growth, leading to a problem of deterioration of laser characteristics.
[0014]
In order to solve these problems, the present inventor intentionally significantly narrows the width of the buried portion on both sides of the stripe so that Ga atoms and N atoms are supplied to the buried portion from both sides. Found that it was effective. That is, as shown in FIG. 2, if the width W of the buried portion on both sides of the stripe is set to a limited width and selective growth of the GaN layer 4 is performed, Ga atoms and Ga atoms and Since N atoms are supplied, the selective growth rate of the GaN layer 4 is increased, the embedding shape is improved, and uniform and flat embedding can be performed.
[0015]
The present inventor further examined to what extent the width of the embedding sites on both sides of the stripe should be narrowed so that good embedding can be performed in a shorter time. For this purpose, SiO 2 is deposited on the GaN layer 11 as shown in FIG. ₂ A film 12 is formed and this SiO 2 ₂ The width of the film 12 is W ₁ , W ₂ , W _Three ... (W ₁ <W ₂ <W _Three <...) and the changed stripe-shaped opening 12a is formed. ₂ Using the film 12 as a growth mask, an experiment was conducted in which the GaN layer 13 was selectively grown on the opening 12a by, for example, a low pressure metal organic chemical vapor deposition (MOCVD) method. As a result, it was found that the growth rate of the GaN layer 13 grown on the opening 12a depends on the width of the opening 12a, and the growth rate tends to increase as the width of the opening 12a decreases. FIG. 4 schematically shows changes in the growth rate of the GaN layer 13 with respect to the width W of the opening 12a. The growth rate also changes depending on the pitch of the openings 12a, and the growth rate tends to increase as the pitch increases.
[0016]
As a result of further investigation based on the experimental results, the present inventor has found that the GaN layer, more generally, a nitride-based III-V compound semiconductor layer, can be embedded in the embedded portions on both sides of the stripe in a shorter time. In order to carry out well, the conclusion has been reached that the width of the implantation site should be 50 μm or less, preferably 30 μm or less, more preferably 20 μm or less.
[0017]
The present invention has been devised based on the above examination by the present inventors.
[0018]
That is, in order to solve the above problem, the first invention of the present invention is:
In a semiconductor laser using a nitride III-V compound semiconductor having a ridge-shaped stripe,
The width of the embedded portion on both sides of the stripe is 50 μm or less,
A buried semiconductor layer made of a nitride III-V compound semiconductor is buried in the buried portion.
It is characterized by this.
[0019]
The second invention of this invention is:
In a method for manufacturing a semiconductor laser using a nitride III-V compound semiconductor having a ridge-shaped stripe,
Forming a stripe and forming embedded portions with a width of 50 μm or less on both sides of the stripe;
And a step of selectively growing a buried semiconductor layer made of a nitride III-V compound semiconductor at a buried portion.
It is characterized by this.
[0020]
In the present invention, from the viewpoint of shortening the growth time of the buried semiconductor layer and making the buried semiconductor layer flatter, the width of the buried portion is preferably selected to be 30 μm or less, more preferably 20 μm or less.
[0021]
In the present invention, the stripe is typically formed in the p-type semiconductor layer including at least the p-type cladding layer, but in some cases, the stripe may be formed in the n-type semiconductor layer including the n-type cladding layer. The embedded semiconductor layer may be n-type, p-type, or i-type, and is selected as necessary. Here, for example, silicon (Si) can be used as the n-type impurity, and magnesium (Mg) can be used as the p-type impurity. The embedded semiconductor layer may be either a single layer or a multilayer. When the embedded semiconductor layer has a multilayer structure, for example, a stacked structure of the same or different semiconductor layers can be used as necessary, and the conductivity type of each layer may be different.
[0022]
For example, the stripe is formed in a p-type semiconductor layer including at least a p-type cladding layer, and the embedded semiconductor layer is an n-type semiconductor layer. Alternatively, the stripe is formed in a p-type semiconductor layer including at least a p-type cladding layer, and the embedded semiconductor layer includes an n-type semiconductor layer and a p-type semiconductor layer thereon.
[0023]
The embedded semiconductor layer is, for example, In _x Ga _1-X N (0 ≦ x ≦ 1), Al _x Ga _1-X N (0 ≦ x ≦ 1) or the like.
[0024]
In the present invention, in order to further increase the effective refractive index difference in the lateral direction, a material having a band gap equal to or lower than the photon energy corresponding to the oscillation wavelength is used for a part of the embedded semiconductor layer. Specifically, for example, the stripe is formed in a p-type semiconductor layer including at least a p-type cladding layer, and the active layer is In. _x Ga _1-x N (where 0 ≦ x ≦ 1), and the embedded semiconductor layer is In _y Ga _1-y A first semiconductor layer made of N (where 0 ≦ y ≦ 1 and x ≦ y) and Al _z Ga _1-z And a second semiconductor layer made of N (where 0 ≦ z ≦ 1).
[0025]
In the present invention, typically, a growth mask is formed on the surface of the portion other than the buried region, and the buried semiconductor layer is selectively grown using the growth mask. The growth mask is, for example, SiO. ₂ It can be formed by a film, a SiN film, or the like.
[0026]
In the present invention, from the viewpoint of improving the embedding property, for example, the initial growth temperature of the selective growth of the embedded semiconductor layer is set to 400 ° C. or higher and lower than 800 ° C. Thus, the buried semiconductor layer grown at a relatively low temperature is in an amorphous state that does not depend on the plane orientation, so that the buried portion can be buried well in the early stage of selective growth. The thickness of the amorphous part is set to 200 nm or less, for example. Note that this amorphous portion is crystallized during growth at a high temperature to be performed later.
[0027]
In the present invention, the nitride-based III-V compound semiconductor includes at least one group III element selected from the group consisting of Ga, Al, In, B, and Tl, and at least N, and optionally further As or It consists of a V group element containing P. Specific examples of the nitride III-V group compound semiconductor include GaN, AlGaN, AlN, GaInN, AlGaInN, InN, and the like.
[0028]
For the growth of the buried semiconductor layer, a metal organic chemical vapor deposition (MOCVD) method, a hydride vapor phase epitaxial growth or a halide vapor phase epitaxy (HVPE) method, a molecular beam epitaxy (MBE) method, or the like can be used.
[0029]
In the present invention, the semiconductor laser can be a real refractive index guided semiconductor laser.
[0030]
According to the present invention configured as described above, the embedded semiconductor layer made of a nitride III-V compound semiconductor is embedded in the embedded portions on both sides of the stripe, so that SiO 2 is formed on both sides of the stripe. ₂ Compared with conventional semiconductor lasers with embedded films, the effective refractive index difference in the lateral direction can be made sufficiently small, especially when the embedded semiconductor layer is made of a GaN-based semiconductor. For example, 1 × 10 ^-3 To 3 × 10 ^-3 Can be set to In addition, since the width of the buried portion on both sides of the stripe is 50 μm or less, when a buried semiconductor layer is grown in this buried portion by selective growth, the growth rate becomes, for example, several times larger than the conventional case. The growth time can be significantly shortened, the embedding can be performed well, and the surface of the embedded semiconductor layer can be planarized. In particular, by setting the initial growth temperature of the selective growth of the embedded semiconductor layer to 400 ° C. or higher and lower than 800 ° C., the embedded semiconductor layer becomes amorphous, so that the embedded portion can be embedded uniformly and flatly in the initial stage of growth, As a result, the layer grown thereon can be made uniform and flat.
[0031]
In addition, since the growth time of the embedded semiconductor layer can be significantly shortened as described above, the thermal history at a high temperature of 600 ° C. or higher that the active layer receives during the selective growth can be shortened, and the damage generated in the active layer. Can be minimized.
[0032]
Further, from the viewpoint of eliminating the kink in the optical output-current characteristics and reducing the return optical noise, it is preferable that a nitride system having a band gap equal to or lower than the photon energy corresponding to the oscillation wavelength in a part of the embedded semiconductor layer. By using a III-V compound semiconductor and adjusting its thickness, composition, impurity concentration, etc., the effective refractive index difference in the lateral direction is further increased. For example, a part of the embedded semiconductor layer may include In _y Ga _1-y By using N (where 0 ≦ y ≦ 1 and x ≦ y), the effective refractive index difference in the lateral direction is 3 × 10 ^-3 To 7 × 10 ^-3 And can be set larger.
[0033]
Further, since the impurity of the p-type layer or the n-type layer can be activated simultaneously with the growth of the buried semiconductor layer, it is not necessary to provide a separate step for activating the impurity. In particular, when a stripe is formed in a p-type semiconductor layer including at least a p-type cladding layer and the buried semiconductor layer is an n-type semiconductor layer, the n-type semiconductor layer is grown simultaneously with the growth in the p-type layer. A p-type impurity such as Mg can be activated. This is considered to be because the n-type semiconductor layer can prevent the intrusion of hydrogen atoms, which is the cause of inactivation of p-type impurities.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts are denoted by the same reference numerals.
[0035]
FIG. 5 shows a GaN-based semiconductor laser having a ridge structure according to the first embodiment of the present invention. This GaN-based semiconductor laser has an SCH structure.
[0036]
As shown in FIG. 5, in this GaN-based semiconductor laser, for example, an n-type GaN contact layer 53, an n-type AlGaN cladding are formed on a c-plane sapphire substrate 51 having a thickness of 400 μm via an undoped GaN buffer layer 52. Layer 54, n-type GaN optical waveguide layer 55, for example, undoped Ga _1-x In _x N / Ga _1-y In _y An active layer 56 having an N multiple quantum well structure, a p-type AlGaN cap layer 57, a p-type GaN optical waveguide layer 58, a p-type AlGaN cladding layer 59, and a p-type GaN contact layer 60 are sequentially stacked.
[0037]
The GaN buffer layer 52 has a thickness of, for example, 30 nm. The n-type GaN contact layer 53 has a thickness of 4 μm, for example, and is doped with, for example, silicon (Si) as an n-type impurity. The n-type AlGaN cladding layer 54 has a thickness of 0.7 μm, for example, and is doped with, for example, Si as an n-type impurity. The n-type GaN optical waveguide layer 55 has a thickness of, for example, 0.1 μm and is doped with, for example, Si as an n-type impurity. Undoped Ga _1-x In _x N / Ga _1-y In _y The active layer 56 having an N multiple quantum well structure has, for example, a well layer thickness of 3 nm and a barrier layer thickness of 4 nm.
[0038]
The p-type AlGaN cap layer 57 has a thickness of 20 nm, for example, and is doped with, for example, magnesium (Mg) as a p-type impurity. The p-type AlGaN cap layer 57 has an Al composition of 0.2, for example. This p-type AlGaN cap layer 57 prevents In from diffusing and deteriorating from the active layer 56 during the growth of the p-type GaN optical waveguide layer 58, the p-type AlGaN cladding layer 59, and the p-type GaN contact layer 60. In addition, the carrier overflow from the active layer 56 is prevented. The p-type GaN optical waveguide layer 58 has a thickness of 0.1 μm, for example, and is doped with, for example, Mg as a p-type impurity. The p-type AlGaN cladding layer 59 has a thickness of 0.7 μm, for example, and is doped with, for example, Mg as a p-type impurity. The p-type GaN contact layer 60 has a thickness of 0.3 μm, for example, and is doped with, for example, Mg as a p-type impurity.
[0039]
Upper layer portion of n-type GaN contact layer 53, n-type AlGaN cladding layer 54, n-type GaN optical waveguide layer 55, active layer 56, p-type AlGaN cap layer 57, p-type GaN optical waveguide layer 58 and p-type AlGaN cladding layer 59 Has a mesa shape with a predetermined width. In addition, a stripe having a predetermined width extending in one direction is formed in the upper layer portion of the p-type AlGaN cladding layer 59 and the p-type GaN contact layer 60 in the mesa portion, and grooves 61 are formed on both sides thereof. The extending direction of the stripe is, for example, the <11-20> direction, and the width is, for example, 2 to 3 μm. An n-type GaN buried layer 62 is buried in the groove 61. The n-type GaN buried layer 62 also serves as a current confinement layer.
[0040]
A p-side electrode 63 is provided on the p-type GaN contact layer 60 in the stripe portion and the n-type GaN buried layers 62 on both sides thereof. The p-side electrode 63 has a Ni / Pt / Au structure in which, for example, a Ni film, a Pt film, and an Au film are sequentially stacked. The thicknesses of these Ni film, Pt film, and Au film are, for example, 10 nm, 100 nm, and 300 nm. An n-side electrode 64 is provided on the n-type GaN contact layer 53 adjacent to the mesa portion. The n-side electrode 64 has a Ti / Al / Pt / Au structure in which, for example, a Ti film, an Al film, a Pt film, and an Au film are sequentially stacked. The thickness of these Ti film, Al film, Pt film, and Au film The lengths are, for example, 10 nm, 100 nm, 100 nm, and 300 nm, respectively.
[0041]
FIG. 6 shows changes in the effective refractive index difference Δn with respect to the distance between the active layer 56 and the bottom surface of the groove 61 in this GaN-based semiconductor laser, in other words, the total thickness d of the p-type layer on both sides of the stripe. As shown in FIG. 6, in this GaN-based semiconductor laser, the stripe is embedded by the n-type GaN buried layer 63, so that the effective refractive index difference Δn in the lateral direction is 1 × 10. ^-3 ~ 3x10 ^-3 And can be set small. Further, d has a very large influence on laser characteristics, but it is generally difficult to control the value at the time of device fabrication. On the other hand, in this GaN-based semiconductor laser, Δn is 1 × 10 × in the range of d to 0.2 to 0.5 μm. ^-3 ~ 3x10 ^-3 Therefore, even if d varies somewhat, Δn can be easily set within these ranges.
[0042]
Next, a method for manufacturing the GaN-based semiconductor laser according to the first embodiment configured as described above will be described.
[0043]
In order to manufacture this GaN-based semiconductor laser, first, as shown in FIG. 7, an undoped GaN film is formed on a c-plane sapphire substrate 51 whose surface has been previously cleaned by thermal cleaning or the like at a temperature of about 520 ° C., for example, by MOCVD. After the buffer layer 52 is grown, the substrate temperature is raised to a predetermined growth temperature, and the n-type GaN contact layer 53, the n-type AlGaN cladding layer 54, and the n-type GaN optical waveguide are formed on the GaN buffer layer 52 by MOCVD. Wave layer 55, for example undoped Ga _1-x In _x N / Ga _1-y In _y An active layer 56 having an N multiple quantum well structure, a p-type AlGaN cap layer 57, a p-type GaN optical waveguide layer 58, a p-type AlGaN cladding layer 59, and a p-type GaN contact layer 60 are sequentially grown. Here, the n-type GaN contact layer 53, the n-type AlGaN cladding layer 54, the n-type GaN optical waveguide layer 55, the p-type AlGaN cap layer 57, the p-type GaN optical waveguide layer 58, and the p-type AlGaN, which are layers not containing In. The growth temperature of the cladding layer 59 and the p-type GaN contact layer 60 is, for example, about 1000 ° C. and is a layer containing In. _1-x In _x N / Ga _1-y In _y The growth temperature of the active layer 56 having the N multiple quantum well structure is set to 700 to 800 ° C., for example. The growth raw material of these GaN-based semiconductor layers is, for example, trimethylgallium ((CH _Three ) _Three Ga, TMG) is a trimethylaluminum ((CH _Three ) _Three Al, TMA) is a trimethylindium ((CH _Three ) _Three In, TMI) is used as a raw material for N which is a group V element. _Three ) Is used. As the carrier gas, for example, hydrogen (H ₂ ) And nitrogen (N ₂ ) And a mixed gas. As for the dopant, examples of the n-type dopant include monosilane (SiH _Four ) As a p-type dopant, for example, bis = methylcyclopentadienylmagnesium ((CH _Three C _Five H _Four ) ₂ Mg) or bis = cyclopentadienylmagnesium ((C _Five H _Five ) ₂ Mg) is used.
[0044]
Next, the c-plane sapphire substrate 51 on which the GaN-based semiconductor layer is grown is taken out from the MOCVD apparatus. Next, as shown in FIG. 8, for example, a 0.4 μm thick SiO. ₂ After forming the film 65, this SiO ₂ A resist pattern (not shown) having a predetermined shape is formed on the film 65 by lithography, and using this resist pattern as a mask, for example, wet etching using a hydrofluoric acid-based etchant or CF _Four And CHF _Three SiO by RIE method using etching gas containing fluorine such as ₂ The film 65 is etched to have a stripe shape. Next, this SiO ₂ Using the film 65 as a mask, a stripe is formed by etching to a predetermined depth in the thickness direction of the p-type AlGaN cladding layer 59 by, for example, the RIE method, and grooves 61 are formed on both sides of the stripe. The width of the groove 61 is set to 50 nm or less, preferably about 20 to 30 nm. As this RIE etching gas, for example, a chlorine-based gas is used.
[0045]
Next, as shown in FIG. 9, by the MOCVD method, for example, at a growth temperature of 400 to 1000 ° C., SiO 2 ₂ Using the film 65 as a mask, an n-type GaN buried layer 62 is selectively grown to fill the trench 61.
[0046]
Next, the c-plane sapphire substrate 51 on which the n-type GaN buried layer 62 is grown is taken out from the MOCVD apparatus. Next, as shown in FIG. 10, for example, a 0.4 μm thick SiO. ₂ After the film 66 is formed, this SiO ₂ A resist pattern (not shown) having a predetermined shape is formed on the film 66 by lithography, and using this resist pattern as a mask, for example, wet etching using a hydrofluoric acid-based etchant or CF _Four And CHF _Three SiO by RIE method using etching gas containing fluorine such as ₂ The film 66 is etched to have a predetermined shape.
[0047]
Next, as shown in FIG. ₂ Etching is performed until the n-type GaN contact layer 53 is exposed by, for example, the RIE method using the film 66 as a mask, so that the upper layer portion of the n-type GaN contact layer 53, the n-type AlGaN cladding layer 54, the n-type GaN optical waveguide layer 55, The active layer 56, the p-type AlGaN cap layer 57, the p-type GaN optical waveguide layer 58, the p-type AlGaN cladding layer 59, and the p-type GaN contact layer 60 are patterned into a mesa shape.
[0048]
Next, SiO ₂ The film 66 is removed by etching. Next, a resist pattern (not shown) having a predetermined shape is formed on the surface of the substrate, and a Ti film, an Al film, a Pt film, and an Au film are sequentially formed on the entire surface of the substrate by vacuum deposition or the like, and then the resist pattern is formed thereon. The Ti film, Al film, Pt film and Au film are removed together (lift-off). As a result, an n-side electrode 64 is formed on the n-type GaN contact layer 53 in a portion adjacent to the mesa portion, as shown in FIG. Next, an alloy process for making the n-side electrode 64 ohmic contact is performed. In the same process, the p-side electrode 63 is formed on the p-type GaN contact layer 60 in the mesa portion and the n-type GaN buried layers 62 on both sides thereof. Next, an alloy process for making the p-side electrode 63 in ohmic contact with the p-type GaN contact layer 60 is performed.
[0049]
Thereafter, the c-plane sapphire substrate 51 having the laser structure formed as described above is processed into a bar shape by cleaving or the like to form both resonator end faces, and further, end face coating is applied to these resonator end faces. Then, this bar is chipped by cleaving or the like. As described above, the target buried ridge structure and SCH structure GaN-based semiconductor laser are manufactured.
[0050]
As described above, according to the first embodiment, by embedding the n-type GaN buried layer 62 on both sides of the stripe, the effective refractive index difference in the lateral direction is reduced to 1 × 10. ^-3 To 3 × 10 ^-3 And can be set small. Therefore, multimode oscillation is possible, and a GaN-based semiconductor laser with little return light noise can be realized. Further, since the buried portion where the n-type GaN buried layer 62 is buried, that is, the width of the groove 61 is set to 50 μm or less, the growth time of the n-type GaN buried layer 62 is greatly reduced to, for example, about 1/20 of the conventional one. And a flat shape. In addition, since the time for selective growth of the n-type GaN buried layer 62 can be greatly shortened in this way, high-temperature heat of 600 ° C. or higher received by the active layer 56 during the selective growth of the n-type GaN buried layer 62. The history can be greatly shortened, damage to the active layer 56 can be minimized, and deterioration of laser characteristics can be suppressed.
[0051]
Further, according to the first embodiment, the following advantages can be obtained. That is, in general, in the growth of GaN-based semiconductors, there is a problem that the p-type impurities in the growth layer are inactivated by hydrogen in the growth atmosphere, and therefore it is necessary to perform post-annealing in a nitrogen atmosphere after the growth of the p-type layer. There is. However, in the first embodiment, during the selective growth of the n-type GaN buried layer 62, hydrogen can be prevented from entering which causes inactivation of Mg in the p-type layer. At the same time, Mg in the p-type layer can be activated. Therefore, it is possible to activate the p-type impurity in the p-type layer during the selective growth of the n-type GaN buried layer 62 without performing post-annealing.
[0052]
Next explained is the second embodiment of the invention. In the second embodiment, the selective growth of the n-type GaN buried layer 62 is performed in two stages in the manufacture of the GaN-based semiconductor laser according to the first embodiment. That is, first, the n-type GaN buried layer 62 is grown to a predetermined thickness, for example, a thickness of 200 nm or less, at a relatively low temperature of 400 ° C. or higher and lower than 800 ° C. Since the n-type GaN buried layer 62 grown at such a low temperature becomes amorphous, the buried portion can be buried uniformly and flatly without forming a void. Next, as the second growth, the remaining n-type GaN buried layer 62 is grown at a high temperature, for example, a growth temperature of 800 to 1000 ° C. During the growth at the high temperature, the amorphous portion grown at the low temperature is recrystallized. Since other things are the same as those of the first embodiment, description thereof is omitted.
[0053]
According to the second embodiment, the same advantages as those of the first embodiment can be obtained, and the embeddability of the n-type GaN buried layer 62 can be further improved. .
[0054]
Next explained is the third embodiment of the invention. In the third embodiment, as shown in FIG. 12, the buried semiconductor layer has a two-layer structure including an n-type GaN buried layer 62 and a p-type GaN buried layer 67 thereon. The p-type GaN buried layer 67 is in contact with the p-type GaN contact layer 60 on the side surface of the stripe portion. The p-side electrode 63 is in ohmic contact with both the p-type GaN contact layer 60 and the p-type GaN buried layer 67 in the stripe portion. Since other things are the same as those of the first embodiment, description thereof is omitted.
[0055]
According to the third embodiment, the same advantages as those of the first embodiment can be obtained, and the following advantages can be obtained. That is, since the p-side electrode 63 is in ohmic contact not only with the p-type GaN contact layer 60 in the stripe portion but also with the p-type GaN buried layer 67, the contact area of the p-side electrode 63 with respect to the p-type layer increases. Therefore, the contact resistance of the p-side electrode 63 can be reduced by that amount. For this reason, the operating voltage of the GaN-based semiconductor laser can be reduced. This is very effective because the operating voltage of a GaN-based semiconductor laser is originally high.
[0056]
Next explained is the fourth embodiment of the invention. In the fourth embodiment, as shown in FIG. 13, the buried semiconductor layer has a two-layer structure including an n-type InGaN buried layer 68 and an n-type GaN buried layer 62 thereon. The band gap of the n-type InGaN buried layer 68 is not more than the photon energy corresponding to the oscillation wavelength. The thickness of the n-type InGaN buried layer 68 is, for example, 300 nm or less. Since other things are the same as those of the first embodiment, description thereof is omitted.
[0057]
According to the fourth embodiment, the same advantages as those of the first embodiment can be obtained, and the following advantages can be obtained. That is, considering the use as a light source for writing on an optical disk, if the effective refractive index difference in the lateral direction is set small as in the GaN-based semiconductor laser according to the first embodiment, light output by so-called hole burning is obtained. A kink occurs in the current characteristics. On the other hand, in the fourth embodiment, since the band gap of the n-type InGaN buried layer 68 constituting a part of the buried semiconductor layer is equal to or less than the photon energy corresponding to the oscillation wavelength, this n-type InGaN. By adjusting the thickness, composition, impurity concentration, etc. of the buried layer 68, the effective refractive index difference in the lateral direction is reduced to 3 × 10. ^-3 To 7 × 10 ^-3 Thus, kink does not occur in the light output-current characteristic. For this reason, the optical output-current characteristic can be kept linear up to the optical output with a high recording level of the optical disc.
[0058]
As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.
[0059]
For example, the numerical values, structures, shapes, substrates, raw materials, processes, and the like given in the above-described embodiments are merely examples, and different numerical values, structures, shapes, substrates, raw materials, processes, etc. are used as necessary. May be.
[0060]
In the above-described embodiment, the extending direction of the ridge stripe is the <11-20> direction of the c-plane sapphire substrate 1, but the extending direction of the ridge stripe may be the <1-100> direction.
[0061]
In the above-described embodiment, the c-plane sapphire substrate is used as the substrate, but other substrates such as a SiC substrate, a Si substrate, and a spinel substrate may be used as necessary.
[0062]
Furthermore, in the above-described embodiment, the case where the present invention is applied to a GaN semiconductor laser having an SCH structure has been described. However, the present invention may be applied to a GaN semiconductor laser having a DH (Double Heterostructure) structure, for example. Good.
[0063]
【The invention's effect】
As described above, according to the present invention, the width of the buried portion on both sides of the stripe is set to 50 μm or less, and the buried semiconductor layer made of a nitride III-V group compound semiconductor is buried in this buried portion. The return light noise can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining the principle of the present invention;
FIG. 2 is a schematic diagram for explaining the principle of the present invention.
FIG. 3 is a schematic diagram for explaining the principle of the present invention;
FIG. 4 is a schematic diagram for explaining the principle of the present invention;
FIG. 5 is a cross-sectional view showing a ridge-based GaN semiconductor laser according to the first embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the total thickness d of the p-type layers on both sides of the stripe and the effective refractive index difference Δn in the GaN semiconductor laser according to the first embodiment of the present invention.
7 is a cross-sectional view for explaining the method of manufacturing the GaN-based semiconductor laser according to the first embodiment of the invention. FIG.
FIG. 8 is a cross-sectional view for explaining the method for manufacturing the GaN-based semiconductor laser according to the first embodiment of the invention.
FIG. 9 is a cross-sectional view for explaining the method for manufacturing the GaN-based semiconductor laser according to the first embodiment of the invention.
10 is a cross-sectional view for explaining the method of manufacturing the GaN-based semiconductor laser according to the first embodiment of the invention. FIG.
11 is a cross-sectional view for explaining the method of manufacturing the GaN-based semiconductor laser according to the first embodiment of the invention. FIG.
FIG. 12 is a sectional view showing a GaN-based semiconductor laser having a ridge structure according to a third embodiment of the present invention.
FIG. 13 is a sectional view showing a GaN-based semiconductor laser having a ridge structure according to a fourth embodiment of the present invention.
FIG. 14 is a perspective view showing a GaN-based semiconductor laser having a conventional ridge structure.
[Explanation of symbols]
51... C-plane sapphire substrate, 53... N-type GaN contact layer, 54... N-type AlGaN clad layer, 55... N-type GaN optical waveguide layer, 56. P-type GaN optical waveguide layer, 59... P-type AlGaN cladding layer, 60... P-type GaN contact layer, 61... Groove, 62. Electrode, 64 ... n-side electrode, 67 ... p-type GaN buried layer, 68 ... n-type InGaN buried layer

Claims (9)

Forming a mask having a predetermined shape formed of a SiO ₂ film on a p-type semiconductor layer including at least a p-type cladding layer;
Etching the p-type semiconductor layer using the mask to form a ridge-shaped stripe in the p-type semiconductor layer and forming a groove having a width of 50 μm or less on both sides of the stripe;
A method of manufacturing a semiconductor laser using a nitride III-V compound semiconductor, comprising: selectively growing a buried semiconductor layer made of a nitride III-V compound semiconductor using the mask; and embedding the groove . After selectively growing the amorphous embedded semiconductor layer at an initial growth temperature of 400 ° C. or higher and lower than 800 ° C., the remaining embedded semiconductor layer is selected at a growth temperature of 800 to 1000 ° C. 2. The method of manufacturing a semiconductor laser according to claim 1, wherein the semiconductor laser is grown, and the amorphous embedded semiconductor layer is recrystallized. The n-type semiconductor layer and a p-type semiconductor layer thereon are selectively grown as the embedded semiconductor layer, and a p-side electrode is formed so as to be in ohmic contact with both the stripe and the p-type semiconductor layer. 3. A method for producing a semiconductor laser according to 2. The method for manufacturing a semiconductor laser according to claim 1, wherein the groove has a width of 30 μm or less. The method for manufacturing a semiconductor laser according to claim 1, wherein the groove has a width of 20 μm or less. The buried semiconductor layer is In _x Ga _1-x The method for manufacturing a semiconductor laser according to claim 1, comprising N (0 ≦ x ≦ 1). The embedded semiconductor layer is made of Al. _x Ga _1-x The method for manufacturing a semiconductor laser according to claim 1, comprising N (0 ≦ x ≦ 1). Active layer is In _x Ga _1-x N (where 0 ≦ x ≦ 1), and the embedded semiconductor layer is In _y Ga _1-y A first semiconductor layer made of N (where 0 ≦ y ≦ 1 and x ≦ y) and Al _z Ga _1-z 2. The method of manufacturing a semiconductor laser according to claim 1, comprising a second semiconductor layer made of N (where 0 ≦ z ≦ 1). 9. The method of manufacturing a semiconductor laser according to claim 1, wherein the semiconductor laser is a real refractive index guided semiconductor laser.

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