JPS587894A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To oscillate a semiconductor laser in a stable fundamental lateral mode by forming a V-shaped groove on a multilayer semiconductor layer and forming an active region therein, thereby preventing the leakage current. CONSTITUTION:Three clad layers, i.e., an n type buffer layer 11, a P type block layer 12 and a current reducing n type clad layer 13 are sequentially grown on an n type InP substrate 10. Thereafter, a V-shaped groove is formed in the clad layers formed of the three layers. The depth of the groove is formed to the degree to produce only the fundamental lateral mode in the length (the width of the active region 15) of the bottom side of an inverted triangular active region 15 formed on the bottom of the groove to coincide with the surface of the layer 12, i.e., the boundary between the layers 12 and 13 to the surface. Subsequently, a P type clad layer 16 and a cap layer 17 are continuously grown, a Cd diffused region 18 is formed, thereby obtaining the desired semiconductor laser.

Description

[Detailed description of the invention] The present invention relates to a semiconductor laser.

Long-wavelength lasers using crystal materials such as 111P/InGaAsP are attracting attention as light sources for optical fibers (with low transmission loss), and their practical use is progressing. For practical use, a semiconductor laser is required that exhibits stable single-transverse mode oscillation over a wide range of operating currents and exhibits excellent dynamic characteristics with suppressed relaxation oscillations. In order to meet these requirements, various striped structures have been proposed and prototyped.

Among them, Hirao et al.
ied Physics), Vol. 51, pp. 4539-4
InP/InGaAsP B reported on page 540
The active region of the H semiconductor laser is InGaAsP (λ
= 1.3 μm) layer is surrounded by InP which has a low refractive index and serves as a cladding layer, and a '1 current injection region is provided in a part of the cladding region adjacent to the active region, and both ends of the cladding region are Since the BH conductor laser has cladding layers not only in the vertical direction of the active region but also in the horizontal direction, rectangular refraction based on the difference in refractive index occurs. Not only does it continue to maintain stable induration mode oscillation with a constant rate distribution, but the active region and current confinement region coincide, the @ value 'gi is small, and it exhibits dynamic characteristics with suppressed relaxation oscillations. You can expect the same characteristics.

However, if the active region remains embedded in the cladding layer, current leaks from the cladding layer adjacent to the active region and serves as a current injection region to the cladding layers adjacent to both ends of the cladding layer, which effectively injects current into the active region. However, it has disadvantages such as an increase in threshold current and poor temperature characteristics. To overcome this drawback, a clad 1@ having the same electrical characteristics as the current injection region for leakage WttIL is usually provided at both ends of the active region and used as a blocking layer. However, when the block layer becomes thick and comes into contact with the cladding layer serving as the current injection region, current flows from the current injection region to the block layer having the same electrical characteristics, and the leakage current increases rapidly. Also, on the other hand, it is necessary to grow the block layer so that the surface of the hot water with a thin block layer coincides with the surface of the active region.
Controlling this growth is extremely difficult, and it has been impossible to produce it with good reproducibility. In order to obtain fundamental transverse mode oscillation in BH conductor lasers, it is necessary to create an active region with a width of 2 μm or less by etching, and in order to facilitate the growth of brick layers, buried cladding layers, etc., the etching depth must be increased. It was necessary to control the shape and shape, and the process was extremely complicated. Furthermore, the thickness of the blocking layer is approximately 0.2 μm, which is equivalent to the thickness of the active region, and thus it is impossible to completely block leakage current.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, completely block leakage current, have a current confinement region in the horizontal and horizontal directions of the active region, and not only have a low threshold current but also reduce the refractive index of the entire active region in the vertical and horizontal directions. The semiconductor laser of the present invention, which is embedded with a small material and emits extremely stable fundamental transverse mode oscillation, has a semiconductor layer with a multilayer structure including at least a blocking layer and a current confining cladding layer adjacent to the blocking layer. V #l is formed from the cladding layer side, and in this V groove (the growth surface is on the surface of the block M (i.e., the block layer and one layer).
It has a structure in which an active region is formed so as to coincide with the interface with the cladding layer for four current confinement, and a semiconductor layer consisting of one layer or multiple layers is formed adjacent to the active region and the cladding layer for current confinement. There is.

The principle of the present invention is to apply the technology of forming grooves by etching and etching and growing crystals inside the grooves.According to the present invention, three cladding layers, namely a buffer layer, a blocking layer and a cladding layer for current confinement, are sequentially formed. Make it grow. At this time, the conductivity type of the block layer is opposite to that of the other two layers. After this, #I is formed in the cladding layer composed of the above three layers. ■
The depth of the groove is determined by the block layer surface, that is, the block layer and
The length of the base of the inverted triangular active region formed at the bottom of the trench so that the surface coincides with the interface with the current confining cladding layer (the width of the active region) is such that only the fundamental transverse mode occurs. . In this case, although the conductivity types are different, the three layers have the same composition, so they can be controlled (etching can be performed, and the shape of the formed 6IIl is constant and can be made into a centrally symmetrical V-groove. For example, taking the InGaAsP/InP system as an example, zl-I
When an n-InP layer, a p-jnP layer, and an n-InP layer are grown sequentially on the (100) plane of an nP substrate, if a groove is formed in the (Oll) direction, the etching rate of the (111) plane is faster and a V-groove is formed. Ru. At this time, the angle of the V-shape of the V-groove formed by the two (111) planes will always be constant once the semiconductor material, process, and tinda liquid are determined, so the shape next to the V is the length of the widest part of the V-groove. It is uniquely determined by Therefore, the shape of the groove is V@
This is determined by the stripe width formed in the mask for etching and etching, and by selecting this stripe width, it is possible to form a hole of any depth. Moreover, once a V-groove is formed at one end, even if further machining or etching is performed, the etching will not occur.
It does not progress any further and the shape remains constant. Therefore, it is possible to form grooves of the same shape on the entire surface of the wafer with good reproducibility without uneven etching.

Since the formed v4s have the same shape, it becomes easy to control the crystal growth within the groove (1) to be performed next. Furthermore, crystal growth within v1# has the following advantages. In other words, in the case of liquid phase growth, the growth rate within the groove is about 4 times faster than the growth on the ml (100) plane outside, so it is possible to form active regions mainly within the V groove. be. At this time, the active layer grown on the external plane may be extremely thin, but the current flow from the cap layer can be regulated and the electric current flt can be concentrated in the V-groove, so that it does not cause any problem in terms of laser characteristics.

Also, when performing liquid phase growth in the groove, the growth rate will be slow if the melt amount is small and the cooling rate is slow and the supersaturation ratio is small, so the growth thickness should be controlled (formation ◎ Therefore, as described above, ◎ the effect that the shape of the groove is centrally symmetrical also works, and the active region can be formed with good control up to the thickness of the block layer.

The active region is formed at the bottom of the active region so that its surface coincides with the layer surface, that is, the boundary between the block layer and the current confinement cladding layer formed on the block layer. Since the active region is formed at the bottom of v#l, it is easy to narrow the width of the active region. That is, the width of the active region can be easily changed by controlling the depth of the V-groove, and manufacturing is simple, but the center-symmetrical effect also works to allow the active region to grow in a well-controlled manner up to the thickness of the Glock layer. I can do things.

Next, fill the groove and the current confinement cladding layer with a conductive type cladding layer (top cladding layer) adjacent to the active region and the current confinement cladding layer and opposite to the current confinement cladding layer, and then form a cap layer. and obtain a semiconductor laser. In particular, if the conductivity of the cap layer is opposite to that of the adjacent top cladding layer and the current injection port is formed above V@ by diffusion, etc., the injection IIC flow in the cladding layer can be improved. Since the lateral spread is small, it is effective to apply vLf only within vTs.
L can be compiled.

In particular, in conventional structures, the striped regions formed by etching tend to be asymmetrical, and it is extremely difficult to form uniform striped regions over the entire wafer. There was no connection (which would increase the leakage current), and the yield was extremely poor and the reproducibility was poor.

On the other hand, in the structure of the present invention, the shape of the V-groove formed in the cladding layer is fixed and can be formed uniformly over the entire surface of the growth wafer, making it easy to control the growth of the active layer. It can be formed adjacent to the block layer and has excellent yield and reproducibility. Furthermore, to maintain fundamental transverse mode oscillation, the active region width should be approximately 2 μm.
In the conventional structure, the width of the active layer in the striped region is 2 μm or less at 11° or less, and by simply controlling the growth thickness of the sub-active region, an active region with an active layer thickness of 2 μm or less can be easily formed. I can do that.

In addition, in the present invention, the blocking layer can be made thicker, and since the current confinement region is formed adjacent to the active region, oscillation is possible with no leakage and an extremely low threshold current. In particular, when a guide layer is formed in V@ and an active layer is formed adjacent to the guide layer and the block layer (in this case, the active region is composed of the guide layer and the active layer).

), the fundamental transverse mode oscillation can be maintained even if the width of the active region is widened, so the block layer can be made thicker as desired, which is more effective.

The cross section of the active region of the semiconductor laser formed according to the present invention is triangular, and the active region is surrounded by a cladding layer with a lower refractive index, so it has a refractive index guiding mechanism and has a concentric circle. It is possible to obtain a point light source that increases the coupling rate with the fiber.

Furthermore, even when a guide layer is provided adjacent to the active layer, light seeps into the guide layer, and the spread angles of light in the horizontal and vertical directions of the active region are approximately the same, making it possible to obtain a concentric point light source. can.

That is, the semiconductor laser according to the present invention has the following effects. ■The present invention has a structure in which a V-groove is formed and an active region is formed inside it. V-grooves of the same shape can be formed with good reproducibility and high yield, and narrow active regions can be easily grown with good control. It is easy to manufacture and has excellent reproducibility. (2) Since the blocking layer is thick and adjacent to both ends of the active region, it can not only block leakage current, but also has a current confinement mechanism formed adjacent to the active region, allowing oscillation with an extremely low threshold current. ■Since the active region is surrounded by layers with a low refractive index, it has a refractive index guiding mechanism and can maintain stable fundamental transverse mode oscillation. ■Active area The spread angle of light in both vertical and horizontal directions is the same!
[1] It is possible to increase the coupling efficiency with the fiber to a point light source close to equicentric circles.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a cross-sectional view of the semiconductor laser of the present invention during the manufacturing process. First, (100) plane n-InP substrate 10
1 fi layer of n-InP buffer layer on top by liquid phase growth
ms p-I nP 9 rad layer 12 is 1 μm, n-
Inpit #: 8i0z on the cladding layer 13 after which the cladding layer 13 for narrow nitrogen is continuously grown to a thickness of 1.5 μm.
@ Attach 14 and add 4μ to (011) using photoresist method.
Remove the M stripe and etch it using a Br methanol etching bath. (111) plane is etched and V
A groove 100 is formed. The structure obtained through the steps up to this point is shown in FIG. At this time, the V groove is symmetrical with respect to the center line, and the angle between one side of the V groove and the center line is always 35 degrees 16
The present inventors have found that the Therefore, in the case of the thickness of each layer and the width of the etching mask shown above, the depth of the groove is 2.8 μm, and the tip of the inner groove in layer 1 of the n-InP buffer layer; 1.01 has a depth of 0.3 μm. reach

- The inventors of the present invention have also discovered that once the supporting grooves are formed, etching does not proceed any further. In this way, grooves of a constant shape are formed on the wafer with good reproducibility (the first
figure). Next, remove the 5iQz film and undope Jn in the groove.
QaAsP (λ = 1.3 pm) active layer 15 (this active layer becomes the active region) is 1.3 μm deep, p-InP
71116 with n-InP current confinement cladding N113
The V-groove is grown to a thickness of 2.5 μm on top, and n-InGaAsP (2m1.1.c<m
) The layers 1' and 7 are continuously grown in a liquid phase. Thus, the active region growth plane coincides with the growth plane of the block layer 12,
Furthermore, the width of the growth surface of the active region is 1.8 μm, making it possible to maintain fundamental transverse mode oscillation. An 8i02 film is deposited on the growth surface of the cab layer 17, a striped window with a width of 3 μm is opened above the groove using a photoresist method, and the film is sealed together with a CdzPs diffusion source in a vacuum quartz container. When this is heated at 566° C. for 1 hour, Cd is diffused and the diffusion tip 102 reaches a depth Q of about 2 μm in the p-InpH 16 (Cd diffusion region 1B). Next, the 8i0z film is removed and a p-type ohmic contact 19 is attached to the substrate, an n-type ohmic contact 20 is attached to the substrate, and a semiconductor laser having the structure shown in FIG. 2 is obtained. In the thus obtained semiconductor laser, both ends of the active region are surrounded by a 1 μm thick blocking layer, so there is no leakage, and the injected current is effectively injected into the trench through the Cd diffusion region. The effects of the current confining layers on the upper layer are combined to produce an extremely low threshold value of 11LfI! Figure 3 shows another example in which a p-InP block layer 12 and an n-InPg cladding layer 13 are successively grown on an InP substrate 10. A groove is formed deep into the substrate. Next ■
n-InGaAsP (λ= , 1.1 pm
) Guide layer 21. The active layer 15 is grown continuously. In this case, the active region is composed of an active layer and a guide layer. At this time, the growth surface of the active layer is controlled so as to coincide with the growth surface of the block layer. Further, a p-InP cladding layer 16 and a cap/fi 17 are successively grown by liquid phase growth, and Cd diffusion and ohmic contact are formed in the same manner as in the previous embodiment to obtain a semiconductor laser.

In any of the above embodiments, the cap layer is omitted and I
The object of the present invention can also be achieved by forming electrodes directly on the nP substrate 10. In this case, the characteristics are slightly inferior to those of the previous example.

In the above embodiments, p-type and n-type may be repelled, and composition diffusion materials such as InGaAsP in each layer thickness are not limited to those mentioned above. Although the above embodiment describes an InP-InGaAsP dove heterojunction crystal material, other materials such as G
aAs8b-AI GaAsSb etc.QJlti&
It can be applied to material R.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a semiconductor laser according to an embodiment of the present invention, which is in the process of being manufactured. That is, an InP substrate is coated with a P layer, a P layer, a P layer, a P layer, a P layer, a P layer, a P layer, a P layer, a P layer, a P layer, a 111 T II 1. 2 is a cross-sectional view of one embodiment of the semiconductor laser formed according to the present invention, and FIG. 3 is a cross-sectional view of another embodiment of the semiconductor laser formed according to the present invention. FIG. 2 is a cross-sectional view of a semiconductor laser in which a guide layer is formed adjacent to an active layer (in this case, active region=active layer+guide layer) in one example of the embodiment. In the figure, 10... n-type InP substrate, 11...
・N-type InP buffer layer. 12--- p-type InP Oy 9 Ml. 13・----El type InP crack P layer. 14...5iQz film. 15・----Undoped InGaAsP (λ=1
．． 3 μm) active chain ring. 16...p-type InP cladding layer. 17-----n-type InGaAsP (λ= 1.1
μm) Cap layer. 18...Cd diffusion region. 19...P-type ohmic contact. 20...N-type ohmic contact. 21...-n type 1nQaAsP (2-1, 1ttm
) Guide layer. 100... V groove, 101...
...The tip of v#1. 102-... Tip of Cd diffusion. are shown respectively. Figure 1 +00 01 Figure 2 Figure 3

Claims (1)

[Claims] The current lI! - A groove with a V-shaped cross section is formed from the rad layer side to the back layer side of the Q cracking layer, and an active region is formed in this V-shaped groove so that the growth surface coincides with the growth surface of the block layer. A semiconductor laser characterized in that it has a structure in which a single or multi-layer semiconductor layer is formed adjacent to the active region and the current cladding layer.