JPH041514B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a semiconductor laser, and particularly to a striped semiconductor laser with stabilized transverse mode. Semiconductor lasers are small, highly efficient, and capable of direct modulation, and are therefore being considered for a variety of uses as light sources for optical communications, optical information processing, and optical integrated circuits.
In particular, lasers capable of single transverse mode oscillation have become increasingly important, and various semiconductor lasers have been developed. However, if the stripe width is made extremely narrow, there are drawbacks such as an extremely increased threshold current density and oscillation of many axial modes instead of a single axial mode. In optical integrated circuits, the size of the semiconductor laser itself is a serious problem, and narrow stripes cannot be avoided. The present inventors have also filed a patent application for a three-terminal semiconductor laser suitable for optical integrated circuits (Japanese Unexamined Patent Publication No. 78180/1989; Semiconductor Laser). A three-terminal semiconductor laser is a device that integrates a bipolar mode electrostatic induction transistor and a semiconductor laser, and the principle thereof will be explained with reference to FIG. 1, which is a typical example. FIG. 1 is a perspective view of a typical example. GaAs,
A specific example will be described in which GaAlAs is used as the semiconductor layer. 1 is a P ⁺ GaAs crystal substrate, 2 is a second semiconductor layer
p ⁺ Ga _1-x Al _x As, 3 is the first semiconductor layer Ga _1-y Al _y
As, 4 is the third semiconductor layer nGa _1-x Al _x As, and 5 is the fourth semiconductor layer nGaAs, and they have a relationship of 0y<x<1. 6 is p ⁺ region, 7 is n ⁺ region, 8,
9 and 10 are metal electrodes. 9 is an anode, 8 is a cathode, and 10 is a gate. Electrode 9 and Electrode 8
The function of the semiconductor laser shown in FIG. 1 is to control the current flowing during this time with high efficiency and high speed by the voltage applied to the gate 10. Although it varies depending on the carrier concentration of the third semiconductor layer, if you want to control it efficiently by applying a voltage to the gate, the gate spacing W should be set to about twice the diffusion distance L _A of holes flowing from the gate. must be done. When the carrier concentration in region 4 is about 1×10 ¹⁵ cm ⁻³ , the gate interval is preferably 3 μm or less. That is, the current path becomes a very narrow stripe, which also has the drawbacks of the narrow stripe described above. SUMMARY OF THE INVENTION An object of the present invention is to improve the drawbacks of semiconductor lasers with narrow stripes and to provide a three-terminal semiconductor laser having a single transverse mode, low threshold current density, and a control electrode with low power consumption. It is. FIG. 2 is an embodiment according to the present invention. 1 in the diagram
10 are the same as those in FIG. 1, and 21 indicates a convex portion of the second semiconductor layer. 22 is for example
The sixth semiconductor layer is made of n ⁺ GaAs, has a conductivity type opposite to that of the substrate and the first semiconductor layer, and has a higher refractive index than layer 2. In order to stabilize the mode, it is necessary to increase the refractive index of the optical waveguide portion, but in the structure shown in FIG. 1, there is no refractive index distribution in the direction parallel to the pn junction. There are two ways to effectively increase the refractive index. One is to provide a portion with a high refractive index or a portion with a large light propagation loss in the stripe from the beginning by selecting the material and structure. In other methods, when a place with a high optical gain is provided for optical waveguide, the refractive index of that place becomes effectively high. A high gain region can be achieved by concentrating the injection current and creating a population inversion of carriers in the semiconductor. That is, in the structure shown in FIG. 1, no refractive index distribution is structurally provided in the lateral direction. Further, the flow of electrons injected from the cathode 7 is restricted by the gate 6, but then expands. In addition, the anode electrode is usually provided over the entire surface, and the thickness of the substrate 1 is usually about 100 μm, so that the current spreads as shown by the arrow in FIG. 1, and the active layer 3 cannot contain the current in the lateral direction. Since the threshold current increases and the current cannot be concentrated, it is impossible to stabilize the transverse mode. In FIG. 2, two structures are adopted that provide a substantial internal refractive index difference. First, as a first structure, the second semiconductor layer has a thick region 21 corresponding to the light emitting region, and a thin region in other parts. That is, the thickness of either or both of the second and third semiconductor layers is made to have a step difference at least at the boundary between the light-emitting region and the portion corresponding to the other region, and the semiconductor layer is made to seep outside of the thinner region. A layer is provided that changes the effective complex refractive index of the emitted light. FIG. 3 shows the intensity distribution of light in the direction perpendicular to each layer when the active layer 3 is GaAs with a thickness of 0.1 μm and the outside thereof is a Ga _1-x Ax _x As semiconductor layer (x=0.3). The horizontal axis is the vertical distance d (μm), the vertical axis is the relative light intensity RI, and the active layer thickness d ₁ = 0.1 μm is shown in the figure.
It shows m. In other words, it shows the amount of light seeping out from the active layer _d1 , and it is well understood that a considerable amount of light seeps out of the active layer.
Furthermore, in the Ga _0.7 Al _0.3 As layer, at least
If the thickness is less than about 0.6 μm, light will seep out to the outside, resulting in increased loss. Taking the laser structure shown in FIG. 2 as an example, if the thickness d ₂ is made thinner than 0.6 μm and the thickness of the region 21 is made thicker than about 1 μm, there will be a large loss outside the groove width a. Within the groove width a, the loss is small and the laser beam can be confined within the groove. The waveguide characteristics of light are determined by the complex refractive index difference Δn between the grooved part and the grooved part. δn〓
can be written as δn〓=△n+i1/2K ₀ α ^~ . Here, Δn is the effective refractive index, α〓 is the effective absorption coefficient, and K ₀ is the wave number of the laser beam in vacuum. Δn is approximately proportional to α〓, and by determining α〓 from the structure, the waveguide characteristics of light can be described. d ₁ = 0.1 μm, d ₂ = 0.6 μm
Therefore, α=≒40cm ^-1 and △n≒4×10 ^-4 . As d ₁ increases, light seepage in Figure 3 decreases, so to set α = 40 cm ^-1 , if d ₁ = 0.15 μm, d ₂ 0.5 μm (△n = 3 × 10 ^-4 ) d ₁ = 0.2 μm, d ₂ is 0.45 μm (△n≒2×10 ⁻⁴ ).
Although the effective refractive index is a little small, if we try to keep △n≧1×10 ^-3 , d ₁ = 0.1 μm, d ₂ 0.45 μm (α〓≒
200cm ^-1 ) d ₁ = 0.15 μm, d ₂ 0.35 μm (α = 300 cm
^-1 ), d ₁ =0.2 μm, and d ₂ 0.25 μm (α=500 cm ⁻¹ ). In that case, the loss α〓 becomes very large. On the other hand, as a second structure, a semiconductor layer of a conductivity type opposite to that of the substrate 1 and the second semiconductor layer or a layer of high resistance is provided in the region 22 of FIG. As a result, the current path is also narrowed on the semiconductor substrate side, and the spread of the current can be suppressed almost exclusively to the laser emitting portion. For example, the current flows as shown by the arrow in Figure 2, and the current effect in the active layer of the semiconductor laser becomes very good.As a result, mode confinement improves, and the overall threshold current also becomes substantially smaller. Become. The relationship between the electron density injected into the active layer and the gain △g of the optical waveguide is as follows based on the threshold current equation (experimental equation) for a GaAs-Ga _1-x Al _x As double heterostructure laser. is expressed in △g=eηΓ/20τsn−225Γ (cm ^-1 ) ...(1) where, e≒1.602×10 ^-19 coulombs, η: internal quantum efficiency, τ _s : carrier lifetime, Γ: light confinement coefficient, n= The carrier density is cm ^-3 . x=0.3,
Assuming d=0.1μm, τs=1nsec, η=1, x=0.3
If we set Γ≒0.28 from d=0.1 μm, then △g=2.24×10 ^-16 n-63 (cm ^-1 )...(2). On the other hand, the loss (αtotal) is as follows. αtotal=α _i +1/2L (ln1/R ₁ +ln1/R ₂ ) ...(3) where, α _i : scattering and absorption loss in the semiconductor, L:
Length of semiconductor laser, R ₁ , R ₂ : Reflectance of mirror. In this case, gain begins to occur when n is 2.8×10 ¹⁷ cm ⁻³ and laser oscillation occurs when Δg=αtotal. α _i =10cm ^-1 , L = 100μm, R ₁ = R ₂ = 0.31
(GaAs), αtotal=127cm ^-1 , and nth=
Laser oscillation occurs at 8.5×10 ¹⁷ cm ^-3 (Jth=1360A/cm ² ). The internal gain is then gnet = 117cm ^-1
There is some gain. Figure 4a shows the spread of the current in the lateral direction of the stripe. FIG. 4b shows the distribution of the net gain gnet across the stripe. Figure 4a
The horizontal axis is the stripe width direction x (μm), with the center of the stripe being 0, and the vertical axis is the injected electron density n (cm ^-3 ).
It shows. In the example, the stripe width is S = 6 μm. In the figure, 41 indicates the current spread in the active layer of the semiconductor laser as shown in Fig. 1, and 42 indicates the current narrowing structure on the substrate side of the structure shown in Fig. 2. This shows the current spread when introduced. The effect of current throttling is very large, and the threshold current can be reduced. In particular, in semiconductor lasers with a stripe width of 2 to 3 μm or less, the current spread becomes even larger and the threshold current becomes extremely large. This generates heat and causes mode instability. Therefore, the narrower the stripes, the more important is the structure that prevents current spread. In Fig. 4b, the horizontal axis is the stripe width direction x (μm),
The center of the stripe is set to 0, and the vertical axis is the net gain gnet after subtracting absorption and scattering loss inside the semiconductor laser.
It is. In the figure, 43 and 44 are gains corresponding to the electron density distributions 41 and 42 in FIG. 4a. Equation (2) is used for calculation. 45 and 46, in the light seepage structure, the loss in parts other than the optical waveguide is
It shows the change from 43 and 44 when it is about 100 cm ^-1 . By using the two methods, it becomes easy to greatly increase the optical amplification gain only in the stripe width, and it is possible to further reduce the threshold current and improve the transverse mode stability. The complex refractive index difference in the horizontal direction of the stripe width can be expressed by δn = Δn + i1/2K ₀ (α = ~g) using the loss and gain described above. The real part Δn and the imaginary part 1/2K ₀ (α〓~g) can be related by the Kramer-Kronig relationship, and if (α〓−g) is known, Δn can be derived. From the gain and loss described above, Δn is usually about Δn≒10 ⁻³ even if it is increased. As the stripe width becomes narrower and the wavelength of the transmitted light wave becomes an issue, propagation gain may decrease or higher-order modes may occur unless the relationship between stripe width and active layer thickness is set to an appropriate value. Occurs. Considering the case of a rectangular dielectric line, if it is rectangular, the internal refractive index at width W and thickness d is n ₁ and the surrounding refractive index is all n ₂ , and the conditions for transmitting only a single fundamental mode are shown in Table 1. become that way. In Table 1, λ:
It is the free space wavelength, and the value in the table is the maximum size that propagates only the fundamental mode.

[Table] Therefore, if the value is larger than this value, higher-order modes will propagate, but conversely, as the size is smaller than this value, the propagation loss will increase. for example,
For GaAs-based lasers, n ₁ = 3.6; for Inp-based lasers, n ₁ =
3.3, and since n ₁ /n ₂ =1.05 is normal, the dimensions are shown in Table 2.

[Table] When the stripe width W is set to about 1 μm, the propagation loss becomes smaller when the active layer thickness is set to the value shown in Table 2 d. Furthermore, the Inp-based semiconductor laser must be larger in size, which is disadvantageous for narrow stripe formation. However, in many semiconductor lasers, n ₁ /n ₂ = about 1.001 outside the stripe width, and the thickness of the active layer can be made thinner than the above-mentioned dimensional limitations. However, the buried heterojunction DH semiconductor laser (BH
(laser), the above conditions apply as is. Narrow striping will be explained in more detail using a model. FIG. 5 is a cross-sectional view of the optical waveguide model. It is composed of surrounding regions 98 and 99 surrounding the optical waveguide region 100. The refractive index n ₁ of the area is 100, the refractive index n ₂ is 99, and the refractive index n ₃ is 98, and n ₁ >n ₂ and n ₃ are satisfied. The region 100 corresponds to the active region of the semiconductor laser, the waveguide width a corresponds to the stripe width, and the waveguide thickness b corresponds to the active layer thickness of the laser. The shaded area is ignored using the approximation that there is no light. FIG. 6 shows the dispersion characteristics of the optical waveguide in FIG. 5. However, assuming that △n ₁ = n ₁ - n ₂ / n ₁ = 5 × 10 ^-2 is constant, △n ₂ = n ₁ - _{n 3} / n ₁ and n ₁ related to the thickness b of the optical waveguide and the wavelength input. The parameter is b/λ. The horizontal axis is n ₁ a/λ corresponding to the optical waveguide width a and wavelength λ, and the vertical axis is (K ² 〓−K ₂ ² )/(K ₁ ² −K _Z ² ). K is a wave number, K ₁ =2πn ₁ /λ, and K ₂ =2πn ₂ /λ. λ is the free space length. K〓 is the propagation wave number of the mode propagating in the waveguide. (K ₂ 〓−K ₂ ² )/
The fact that (K ₁ ² − K ₂ ² ) approaches 0 means that K = K ₂ , and the waveguide light propagates at the wave number of the cladding layer and spreads over a wide space. , it can be seen that the losses have become very large. Conversely, when (K〓 ² − _{K 2} ² )/(K ₁ ² − _{K 2} ² ) approaches 1,
K = K ₁ , and most of the light is confined within the waveguide, and its wave number is determined only by the refractive index n ₁ . The closer the value is to 1, the better the waveguide characteristics are. In Figure 5, for n ₁ b/λ = 0.5, 1, 1.5, the variance when △n ₂ = n ₁ − _{n 3} /n ₁ = 10 ^-3 , 10 ^-2 , 5×10 ^-2 It shows the characteristics. However, it is shown for the basic mode (TEoo, TMoo). As n ₁ b / λ increases, the waveguide characteristics improve, but when n ₁ b / λ = 1.5 or more, higher-order modes begin to propagate, and the laser threshold value increases. Since the current will also increase, it cannot be made too large.
In order to keep the threshold current low, in the case of GaAs, d is usually selected to be 0.1 to 0.2 μm in the case of a short resonator. In other words, it is preferable that 0.4<n ₁ b/λ<0.8. Furthermore, for the width a of the optical waveguide, △n ₂ =
When 10 ^-3 , it is almost constant regardless. This means that light is not trapped in the lateral direction very effectively. As △n ₂ = 10 ^-2 and 5 × 10 ^-2 , the dependence on the optical waveguide width becomes more pronounced, and at n ₁ a/λ, it rapidly decreases around 2 to 3, and the waveguide width becomes more pronounced. Characteristics deteriorate. Since we cannot clearly determine the limit of narrow stripes from this dispersion characteristic alone, we will try to find the confinement coefficient of the optical waveguide. FIG. 7 shows the relationship between the confinement coefficient p and n ₁ a/λ, which corresponds to the stripe width. The confinement coefficient p is the amount of light present in the area (a×b) within the optical waveguide with respect to the total amount of light intensity in the entire area. When Γ is close to 1, it means that most of the light is concentrated in the core region, that is, in the active layer region. △n ₂ = 5×10 ^-2
Then, n ₁ a/λ can be narrowed to between 1 and 2, but when △n ₂ = 10 ^-2 , the limit of n ₁ b/λ is about 2 to 3, and when △n ₂ = 10 ^-3 , n ₁ Even if a/λ is set to 5 to 6, the confinement coefficient does not increase. Good light propagation characteristics cannot be obtained unless Δn ₂ is increased to a certain extent, and the threshold current density cannot be lowered. The effect of Γ is shown in equation (1), and if Γ is smaller than 1, the internal loss,
The mirror loss appears to be large. Because a double heterostructure is introduced, in the direction perpendicular to the heterojunction, carrier confinement is sufficient if the band gap of the active layer is made somewhat smaller than that of the cladding layer, but normally in the direction parallel to the heterojunction, There is not enough carrier confinement. Buried Hetero (BH)
This has only been done using TJS and TJS lasers. In order to confine carriers in the stripe width direction, it is possible to confine carriers by introducing a heterostructure in the lateral direction or by creating barriers of opposite conductivity type. An outline of the structure shown in FIG. 2 will be described below. Impurity density of p ⁺ GaAs substrate 1, which is an anode: 1×10 ¹⁸ ~2
×10 ¹⁹ cm ^-3 , 21 is a groove provided in the substrate 1 (depth is e.g. 1 to 1.5 μm), 2 is a p-Ga _1-x Al _x As layer (x ~ 0.3 , p=~1×
10 ^17-3 ) 22 is n- of the opposite conductivity type to substrate 1 and layer 2.
GaAs layer thickness and impurity density: 0.1-1.5μm, 1
×10 ¹⁶ to 1 × 10 ¹⁸ cm ^-3 , thickness of GaAs active layer 3, impurity density, approximately 0.05 to 1 μm, and 1 × 10 ¹⁴ to 1 ×
10 ¹⁷ cm ^-3 , the thickness and impurity density of n-Ga _1-x Al _x As (e.g. x = 0.3) 4 are about 0.5 to 3 μm and 1×
The thickness of the n-GaAs layer 5 is about 10 ¹³ to 1×10 ¹⁶ cm ^-3 .
Approximately 0.5 to 2μm, impurity density 1×10 ¹³ to 1×10 ¹⁶ cm
^-3 , the impurity density of p ⁺ gate region 6 is 1×10 ¹⁷
The impurity density of the n ⁺ source region 7 is about 1×10 ^{17 to} 5× ^{10 19 cm −3} . The gate-to-gate spacing (channel width) is approximately 0.3 to 3 μm. Also, the conductivity type of each part is completely opposite,
Even if 1, 2, and 6 are n-type and the others are p-type (the active layer can be either), region 1 is an anode and region 6 is
is called a gate, and region 7 is called a source. For example, p ⁺
By ion implantation into the substrate, Te, S, Se,
N-type ions such as Si are implanted at about 1×10 ¹⁶ to 1×10 ¹⁸ cm ^-3 in an AsH ₃ atmosphere of about 1 to 3 Torr at 800 m
After annealing at ~900°C, stripe-shaped grooves are dug in the substrate by etching, and layers 2, 3,
This can be achieved by epitaxially growing layers 4 and 5 successively, and forming high concentration regions again in regions 6 and 7 by diffusion or ion implantation. For the p ⁺ region, Be, Cd, etc. are used for ion implantation.
Impurities such as Zn are used for diffusion. Forming an optical waveguide can be achieved by various structures. The structure shown in FIG. 2 is not the only one. In other words, it is sufficient to create a portion having a higher refractive index than the surrounding area in a portion where light propagates. Broadly speaking, the refractive index changes stepwise (step structure), and the light propagates while reflecting at the boundaries.The refractive index is high at the center of the optical waveguide, similar to a convex lens, and decreases as it goes to the periphery. It can be divided into cases in which light propagates in a meandering manner due to a decrease in (focusing structure). The portion 21 in FIG. 2 can be roughly divided into a step structure. FIG. 8 shows various shapes of the optical waveguide section and the current throttle section in the present invention. A to d have a step structure, and e to h have a focusing structure. Without being limited to these shapes, for example, the optical waveguide may be trapezoidal, triangular, or other polygonal, as long as it has a substantially high refractive index and a current concentration portion. In FIG. 2, gate region 6 is formed across layers 4 and 5, but layers 4 and 5 are a heterojunction;
Since the bandgap of layer 4 is larger, the hole injection at the p-n junction in the gate region of layer 4 is smaller than the hole injection from the gate p-n junction of layer 5, which reduces the current gain due to the characteristics of the device. (gm=△I _D /△I _G ) is not good. FIG. 9 shows an embodiment in which the current gain is increased by forming the gate region 6 in the layer 5 by making the layer 5 thick and the layer 4 thin. Furthermore, the layer 5 is essentially unnecessary since it is formed to lower the ohmic contact resistance of the electrodes 8, 10, etc. without affecting the laser threshold current or the like. Figure 10 eliminates layer 5,
This is an example in which layer 4 is thickened and a gate region is formed therein. In GaAs and GaAlAs-based double heterostructure semiconductor lasers, the layer 5 for ohmic reduction described above is formed, but in InP and InGaPAs-based double heterostructure semiconductor lasers, the structure is usually as shown in FIG. 10, for example, p ⁺ InP. Substrate 1, n ⁺ InGaAsP layer 2
2, P-InP layer 2, InGaPAs active layer 3, n-InP
Layer 4 is formed by p ⁺ InP region 6 . In _1-x
InP has an active layer of Ga _x PyAs _1-y .
Various compositions can be realized while achieving lattice matching with the crystal grains of 1.0 to 1.7 μm.
However, in the case of InGaPAs, when the composition is λ1.4 μm or more, a buffer layer may be provided between the active layer 3 and the cladding layer 4 due to meltback during growth when formed using liquid phase growth. The same applies to other embodiments, but 71 in FIG.
By forming a high-resistance region by proton irradiation or the like, the injection of carriers into the extra region is reduced and the current gain is increased, and the capacitance of the gate region is reduced and the modulation frequency is increased. The structure according to the present invention is not necessarily limited to three-terminal semiconductor lasers, but can also be applied to ordinary two-terminal semiconductor lasers. 11 and 12 show examples of two-terminal semiconductor lasers. As mentioned above, this is particularly effective when the stripes are narrow, and the effect is particularly effective when the stripe width W is 5 μm or less. Furthermore, when W≦2 to 3 μm or less, semiconductor lasers with conventional structures exhibit significant mode instability and threshold increases, but the structure of the present invention significantly improves various characteristics. In FIG. 11, the region 81 is made of n-type GaAs, for example.
82 is a p ⁺ region formed by diffusion, ion implantation, etc. 81 and 82
The interface of layer 4 becomes reverse biased and no current flows.
Current flows only in the area where the two are in contact. By forming V-grooves, narrow stripes can be easily achieved. Furthermore, in FIG. 12, a region 80 is also made n-type, for example, made of n-type GaAlAs, and the V-groove is deepened so that the region 82 extends beyond the active layer 3 and reaches the layer 2. Then, because of the heterojunction,
The region where current flows is almost concentrated in the junction between region 82 and layer 3, resulting in extremely high efficiency. Although the transverse mode can be stabilized in the semiconductor laser of the present invention, the axial mode is not necessarily stabilized.
In particular, multiplicity of longitudinal modes occurs in narrow stripes, and a stable semiconductor laser with a single emission wavelength can be realized by using a structure as shown in FIG. 13.
FIG. 13 shows an embodiment of a semiconductor laser in which transverse mode and axial mode are stabilized. FIG. 13a is a surface view, b is a cross-sectional view taken along the line A-A', and FIG. 13c is a cross-sectional view taken along the line B-B'. Each region will be explained using an InP-InGaAsP semiconductor laser as an example. 101:
p ⁺ InP substrate, 102: p ⁺ -InP growth layer, 103:
InGaPAs active layer, 104: n ^- -InP layer, 105:
n ⁺ -InP region, 106: p ⁺ -InP region, 107:
Cathode electrode, 108: Gate electrode, 109: Anode electrode, 110: Insulating film such as Si ₃ N ₄ or Al ₂ O ₃ , 111: n ⁺ InGaPAs layer. The period in the laser emission direction of the p ⁺ gate is m・λ/2n (λ: free space wavelength, n: refractive index of the active layer, m: integer 1, 2
…) will be done. As m becomes larger than 1, mode selection becomes less efficient. For example, λ=
If 1.5 μm, n=3.3, and m=1, it becomes 0.23 μm.
When m=3, it is about 0.69 μm. In this structure, the current flows periodically only in the vicinity where the electric field strength of the axial standing wave of the laser beam is maximum, so the axial mode tends to oscillate in a single mode. , and operates in single-axis mode even when the current value is significantly larger than the threshold current. Similarly, DFB (Distributed−
(feedback) It can also be applied to DH structure semiconductor lasers. In this way, a semiconductor laser that operates completely in a single mode in axial mode, longitudinal mode, and transverse mode maintains single wavelength operation even when direct modulation is performed to modulate the injection current of the semiconductor laser. When used for communications, etc., the entire system is stable and extremely effective. All of the semiconductor lasers described above are single-channel type semiconductor lasers, but multi-channel semiconductor lasers can be easily manufactured. The cross-sectional structure of the embodiment in the direction perpendicular to the laser resonator direction is shown in the 14th, 15th, and 16th sections.
As shown in the figure. FIG. 14 shows a three-terminal multichannel semiconductor laser in which a gate region 6 is embedded in a semiconductor region 4. FIG. 12 shows a surface gate type multi-channel three-terminal semiconductor laser manufactured by surface diffusion or ion implantation. 14th
In other words, the figure is suitable for a high-output semiconductor laser in which all spots emit laser light at the same time.
If the gate is configured as a buried region as shown in FIG. 14, the current flowing through the gate required to flow the same current between the cathode and anode becomes large, resulting in a small current gain. In the semiconductor laser shown in FIG. 16, each spot can emit light at the same time, or each spot can be controlled. Furthermore, when all light emitting regions emit light at the same time, the phase relationship of light is also important. For example, in FIG. 16, GaAlAs,
By using a GaAs laser and making the layer 4 3 μm thick, the cathode stripe width 3 μm, the diffusion depth 2 μm, and the stripe center spacing approximately 10 μm or less, and introducing a waveguide coupling structure, laser light emission with the phase of each laser emission spot synchronized can be obtained. It will be done. The spacing between the laser emitting regions depends on the lateral diffusion distance of the carrier, the seepage distance of the laser beam, and the waveguide coupling structure, and varies depending on the material, structure, etc. When it is desired to control each laser region independently, as shown in FIG. 16, by providing a high resistance region 71 by irradiating protons or helium between every other gate, each element can be controlled independently by the voltage of each gate. can. Further, element isolation may be performed by etching the region 71, but of course, after etching, light irradiation may be performed.
Si ₃ N ₄ or AlN may be deposited by CVD. The spacing between the light emitting regions should not be too narrow. or,
The gate is not limited to the above structure, and may be a cut gate or the like. In the above description, the channel region is of only one conductivity type, but a portion of the channel region may include a layer of the opposite conductivity type. Figures 17a and 17b show cross-sectional views of the laser. A p layer indicated at 171 is inserted in figure a. In figure b, the cathode region 105 and the gate region 106 are separated by an insulating region 172.
Further, in order to reduce the contact resistance between the semiconductor and the electrode, a layer 173 of a material having a smaller band gap than the material of the channel layer 104 is laminated on the layer 104. By providing the p region 171, the potential barrier becomes higher, and the channel length (between the cathode and the anode) can be made shorter than that of a single conductivity type laser. It goes without saying that the structure of the semiconductor laser of the present invention is not limited to that described here. Although the above embodiment uses a p ⁺ substrate, an n ⁺ substrate may be used, and the conductivity type of the other regions may be completely opposite to that of the embodiment. The laser emitting part has not only the structure explained here, but also a BH (Buried
Heterostructire), PCW (Plano-Convex)
It goes without saying that it is possible to introduce structures such as Waveguide (Waveguide) and BC (Buried Crescent) structure. Material too
It is not limited to GaAs, GaAlAs, and InP-InGaPAs, and heterostructures using other - group, - group, - group compound semiconductors, and mixed crystals thereof may also be used. With other semiconductors, the refractive index, carrier diffusion length, etc. change, so the dimensions must be designed for each. As described above, the present invention makes the optical waveguide portion (within the stripe width) substantially different from its surroundings in optical waveguide gain and loss, and also in refractive index, as well as lateral diffusion of current. By attaching an opposite conductivity type or high resistance portion to the substrate side to suppress this, it is possible to stabilize the transverse mode and the axial mode even in a narrow stripe laser. In short, a gate region is introduced to control the current flowing through the semiconductor laser, and the current flows in a confined manner between the gates formed by the introduced high impurity density regions. It has a structure in which the waveguide structure is also carried in the direction parallel to the junction plane in the active region where laser light is actually emitted, and the gate-to-gate interval and the width of the optical waveguide are approximately equal or slightly narrower. All you have to do is stay there. By doing this, the current flows in a concentrated manner only in areas where the laser light intensity is strong, resulting in extremely high light emission efficiency. Furthermore, by providing gates periodically in the laser emission direction, single wavelength, single transverse mode, and single longitudinal mode can be achieved over a wide range of current, and the emission wavelength can also be stabilized during optical modulation. has been realized and is extremely effective in various fields. Furthermore, the application range is expanded by multi-channeling, and the present application is of extremely high industrial value.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a conventional three-terminal semiconductor laser, Fig. 2 is an embodiment of the present invention, Figs. 3 to 7 are diagrams for explaining the present invention, and Figs. FIG. 13 shows an embodiment in which a periodic structure is introduced into the gate, FIGS. 14 to 16 show an embodiment in which a multi-channel structure is used, and FIG. 17 shows another embodiment of the present invention. 1...p ⁺ -GaAs substrate, 2...p-GaAlAs,
3...GaAs active layer, 4...n ^- -GaAlAs layer, 5
...n ^- -GaAs, 6...p ⁺ region gate part, 7...
n ⁺ GaAs cathode section, 8... cathode electrode, 9...
...Anode electrode, 10...Gate electrode, 21...
Convex portion, 22...n-GaAs layer.

Claims (1)

[Claims] 1. An anode region of a first conductivity type consisting of a high impurity density region, an active layer provided adjacent to the anode region and having a higher refractive index and a narrower forbidden band width than the surroundings, and a high resistance region adjacent to the active layer. a channel region of a second conductivity type opposite to the first conductivity type, and surrounding at least a part of the channel region and a region of the second conductivity type consisting of a high impurity density region at one end of the channel region; the effective refractive index in the laser emitting region in the direction parallel to the heterojunction;
A region having a structure that increases effective gain and having a second conductivity type for current concentration is formed between the anode and the active layer along the outside of the laser emission region at a distance equal to the gate interval. , a plurality of the gate regions are arranged periodically in the laser emission direction, and the width of the channel region sandwiched between the gates is 3 μm.
In the following, a semiconductor laser is characterized in that the width is equal to or smaller than the width of the region having a high effective refractive index in the laser emission region.