JPS6017980A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser which can generate a large light output, and has relatively ready manufacture and excellent reliability by disposing an active layer in a striped structure adjacent to a thick guide layer in a groove region. CONSTITUTION:The entire striped region is surrounded by a clad layer 15 of a high resistance layer, a guide layer 16 and a clad layer 17. A current introduced into the striped region at the center with a wider width than a zinc diffused region 19 is not leaked, but effectively introduced into an active layer 12, and contributed to an oscillation. The emitted light is introduced into the narrow width striped region adjacent to the wide width striped region without loss and propagated. Since the layer 12 of the narrow width striped region is adjacent to the layer 16 of the region of a groove 22, the light is introduced and propagated into the guide layer near the both reflecting surfaces. The layer 16 is formed in the shape near a semicircular shape of cross section, the other portion than the flat part of the grown surface is formed in an opticalwaveguide buried with the clad layers 15, 17 having smaller refractive index than the guide layer, and the light is condensed in the guide layer, and propagated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to semiconductor lasers, particularly high optical output semiconductor lasers.

Recently, visible light semiconductor lasers using crystalline materials such as AlGaAs/GaAs are suitable as light sources for optical digital audio disks (DAD) because they can perform continuous oscillation at room temperature with a low threshold and high efficiency. As such, its practical application is progressing. At the same time, visible light semiconductor lasers are in high demand as light sources for optical writing in optical printers and the like, and to meet this demand, research and development of visible light semiconductor lasers that can withstand large optical output oscillations is underway. In order to be used for these purposes, there is a need to develop a semiconductor laser that has improved coupling efficiency with an optical system and whose active layer has equal spread angles in the horizontal and vertical directions.

Among semiconductor lasers, Tsukada Yoshi M, magazine 'Journ'
alof Applied Physlcs' 45th
What is reported in Vol. 4899-4906 is a so-called Buried Heteroator (BH) which has a structure in which the active layer is surrounded by a cladding layer and carriers can be effectively injected only into the active layer by a combination of pH junctions.
) With a laser, the horizontal and vertical directions of the active layer are
A nearly circular light source with an equal spread angle to the ′ direction.・Dust,
It has excellent characteristics of performing highly efficient laser oscillation with a low threshold current. However, since the spot size of a normal BT laser is extremely small (about 2 to 3 μm), the room temperature continuous wave (CW) optical output is 2 to 3 mW, and the pulse operation (
100 ns width) The optical output is at the operating limit of about 1 On#, and if more optical output is emitted, the reflective surface will be easily destroyed. This phenomenon is known as optical damage, and the critical optical output density for CW operation is around 1. On the other hand,
As a method to prevent optical damage and obtain high optical output, a BOG structure in which a guide layer is provided adjacent to the active layer (13uried
0ptical Guid6 B II) The laser is
Dig Japanese Jour by Nakajima et al.
nal of Applied Physics” 1st
It is reported in Volume 9, pages L591-E, page 594. This structure embeds the active layer and the guide layer with a cladding layer,
The idea is to allow some of the light from the active layer to seep into the adjacent guide layer to increase the level of optical damage.

Although this method depends on the amount of light seeping into the guide layer, the maximum optical output that can be used reliably is limited to around 10 mW.

In addition, B) An attempt to bury the vicinity of the reflective surface of the f structure with a cladding layer with a larger bandgap than the active layer to achieve large optical output oscillation was reported by Watanabe et al. It is reported on page 161 (Spring 1982). However, with this method, the laser beam spreads as it propagates through the cladding layer near the reflective surface, which lowers the amount of light that is reflected by the reflective surface and enters the active region and is reexcited (coupling efficiency). It has the disadvantage of increasing current and decreasing external differential quantum efficiency.

According to this report by Watanabe et al., the threshold current is twice that of a normal BH semiconductor laser, and the external differential quantum efficiency is only 11.
．． Only 8% was obtained. Furthermore, when forming this structure, since the region that will become the reflective surface is buried by etching after crystal growth, crystal defects are likely to occur at the interface between the buried cladding layer region and the active layer, which poses a problem in terms of reliability. It had some drawbacks, such as:

The purpose of the present invention is to eliminate these drawbacks, to achieve not only low-threshold, high-efficiency oscillation, but also high optical output oscillation by fundamental transverse mode oscillation, relatively easy manufacture, high reproducibility, and high reliability. Our goal is to provide excellent semiconductor lasers.

That is, the present invention uses a double heterojunction semiconductor material sandwiched between first and second cladding layers made of a material whose refractive index is smaller than that of the active layer, and has a width in the center along the longitudinal direction. A striped structure consisting of a wide area and narrow areas formed adjacent to both ends of the striped structure is provided, and a surface forming a boundary between the wide striped area and the adjacent narrow striped area is provided. has a total reflection angle with respect to the laser beam, and the groove region formed near the internal reflection surface adjacent to the stripe-like region with narrow ridge width and the region outside the stripe-like structure are combined into a third cladding layer, a cladding layer. With the guide layer made of a material whose refractive index is larger than that of the active layer and smaller than that of the active layer, and the fourth cladding layer is continuously buried, the guide jΔ is made thick in the groove region and thin in the other buried regions. , a semiconductor laser characterized in that the active layer in the striped structure is adjacent to the guide layer in the groove region in the longitudinal direction.

Embodiments of the present invention will be described in detail below using the drawings.

In FIG. 6, n-type GaA with the (100) plane as the plane
On the s-substrate 10, an n-type Alo, 4Gao, 6As first cladding layer 11 of 1°08 m1 is then deposited with undoped Al (,
,1,Ga0.8. The As active layer 12 has a thickness of 0.07 μm and P
Type Al (,,=Gao, 6As second cladding layer 1
3 was successively grown to a thickness of 1°5 μm. Next, Sin! Membrane 1
This is the longitudinal direction of the resonator to be formed by photoresist method and etching method after coating the entire surface in step 4 (O1
After opening a window with a width of 3μ7π and a length of 20μm in the vicinity of the internal reflection surface with a width of 300μm in the central portion in the [l] direction, etching is performed to a depth of 1.0μm. In contact with both ends of the groove formed by this, and in the longitudinal direction, the center of the groove and 5LO
The width is 5 μm and the length is 220 μ so that the center of the n film 14 coincides with the center of the film 14.
A strip-like 5ins film 14 with a width of 3 μm and a length of 40 μm is left at both ends of the central portion, and the rest is an n-type G
The entire surface is uniformly etched until it reaches the aAa substrate 10 (Fig. 7). At this time, the etching progresses at the same time in the area near the internal reflective surface where the grooves were initially formed, and a narrow deep area is formed near the internal reflective surface. A groove 22 with a diameter of 1 μm is formed in the other etched areas, and a striped area is left in the form of an island in the center (Fig. 8), and a wide striped area in the center and adjacent areas are left in the center. At the boundary with the narrow striped region, the angle 0 (FIG. 8) formed by each extra surface with the longitudinal direction of the resonator to be formed is such that i-θ is larger than the critical angle.

That is, the critical angle ψ is sinψ=111 (,,; refractive index of the dishing layer, n!;
(Refractive index of active layer) At this time, θ is 0 and θ(T −5i11 (refractive index)). In the case of the embodiment of the present invention, the buried layer is p-type Al, 4Ga, as described below. , As becomes the third cladding layer, so it is desirable to set O〈θ (21 degrees).In this way, among the light emitted from the wide striped region and propagating in the longitudinal direction of the resonator, the light that hits the slope will be The light is totally reflected by this slope and travels within an adjacent narrow stripe-shaped region.

1 to 5, next, the 5tO2 film 14 is left and the tp-type A1o, 4Gao, 6As third cladding layer 1 is shown.
5 by 1°5/'d. Parts of the first cladding layer 11, the active layer 12, and the second cladding layer 13 of the striped region are adjacent to the third cladding layer 15 grown on the flat part of the outer region of the striped region. At this time, the groove 22 is the third
It is buried with the cladding layer 15, and the surface of this groove region has a curved concave shape with a depth of about 1 μm relative to the other buried regions. Then successively p-type Al o, azQao, a
The sh guide layer 16 is grown to completely fill the concave shape of the groove region and become flat as a whole. In general, the growth rate of the concave area is faster than that of the flat area, so it is desirable to use this to fill the concave area and grow the layer to a thickness of 0.1 to 0.2 μm and 8 degrees in the flat area. At this time, the position of the active layer in the striped region is such that after growing the third cladding layer 15, it is at the center of the groove concave in the vertical direction, and when the guide layer 16 is grown, it is located at the center of the groove in the longitudinal direction of the resonator. The active layer in the narrow striped region is adjacent to the guide layer near the internal reflection surface. Furthermore, n-type Alo, Ga. , the entire surface is buried with a fourth cladding layer 17 of As.

At this time, since no crystal growth occurs on the sio film 4, the groove portion and the entire outside of the striped region are buried. In the above, it is desirable that the third cladding layer 15, the guide layer 16, and the fourth cladding layer 17 are high resistance layers. Further, it is more desirable to adjust the growth thickness of the fourth cladding layer 17 so that the surface becomes flat.

Next, after removing SiO, J[14, the entire surface is coated with a 5ill film 18, and a wide stripe-like area in the center is coated with a width of 3
A window with a length of 200 μm is opened and zinc is diffused halfway into the second cladding layer 13 (zinc diffusion region 19). Next, a p-type ohmic contact 20 is placed in the zinc-diffused region and an n-type ohmic contact 21 is placed on the substrate side. When formed, a semiconductor laser having the structure of the present invention is obtained.

In the structure of the present invention, since the entire striped region is surrounded by the third cladding layer 15, the guide layer 16, and the fourth cladding layer 17, which are high resistance layers, the wide central striped region is formed through the zinc diffusion region 19. The current injected into the region effectively enters the active layer 12 without leaking and contributes to oscillation. The light emitted from the wide striped area in the center travels in the longitudinal direction of the cavity, but the boundary surface adjacent to the wide striped area has a total internal reflection angle for the light traveling in the longitudinal direction of the cavity. Since a narrow stripe-like region with a width of . Since the active layer 12 in this narrow striped area is adjacent to the guide layer 16 in the groove area, light enters and travels within the guide layer in the groove area near the internal reflection surface. The guide layer 16 in this groove region has a nearly semicircular cross-section, and except for the flat portion of the growth surface, the other portions are covered with third and fourth guide layers having a smaller refractive index than this guide layer. It is embedded in a cladding layer to form an optical waveguide, and light travels while condensing within this guide layer without spreading out.

In the case of the composition of the guide layer 16 described above as an example of the present invention, the band gap of the guide layer is wider than 230 meV with respect to the laser oscillation light, so the light traveling through the guide layer will not suffer any absorption loss. do not have. In addition, the guide layer near the internal reflection surface is connected to the growth layer in the area where the growth surface is flat, but since the layer thickness between the guide layer and the guide layer is extremely thin, light is effectively transmitted through the thick layer where the refractive index is high. There is only a small amount of leaves that advance within the guide layer in the groove area and leak into the flat area. In this way, a part of the light that has traveled within the guide layer near the reflective surface is reflected by the reflective surface, returns to the guide layer in the groove region that has an optical waveguide function without loss, and enters the active layer where it is re-excited. Therefore, laser oscillation can be performed with low threshold and high efficiency. As mentioned above, the structure of the present invention is as follows.
The structure of the present invention is completely different from the edge-embedded BH laser reported by Watanabe et al. on page 161 of the proceedings of the Joint Conference on Applied Physics, but the structure of the present invention has dramatically increased coupling efficiency and a low threshold value. It has this without sacrificing the basic characteristics of a BE structure laser, which is high efficiency.

Furthermore, in the structure of the present invention, the vicinity of the internal reflection surface serves as a guide layer with a wide bandgap for the laser oscillation light.
The light output level at which optical damage (COD) occurs can be significantly increased. That is, in a normal semiconductor laser, the end face of the active layer, which serves as an excitation region due to carrier injection, is exposed as a reflective surface, where surface recombination occurs and forms a depletion layer, reducing the band gap. Therefore,
When a large optical power is oscillated, light is absorbed by this narrowed bandgap, which generates heat and rises in temperature to near the melting point, eventually causing optical damage.

In contrast, in the structure of the present invention, not only is the area near the internal reflection surface a non-excitation region, but also the laser oscillation light is oscillated by passing through a layer with a wide band gap difference of 230 meV or more. There is no light absorption, optical damage is less likely to occur, and large optical output oscillation is possible.

Further, in the structure of the present invention, the size of the transverse mode of the laser beam is defined by the width of the narrow striped region and the guide layer of the groove region adjacent thereto. Therefore, if this width is set to a size that can maintain the fundamental transverse mode, the optical output can be increased and the primary transverse mode can be maintained in the longitudinal direction of the resonator even if spatial hole burning occurs in the central wide striped region. Since the loss is large, the carriers work to fill up the hole burning, and the fundamental transverse mode oscillation is maintained.

Furthermore, as the light travels through the optical waveguide mechanism near the internal reflection surface, it spreads throughout this area, but the laser light emitted from the end face is limited to the width and thickness of the guide layer that forms this mechanism. Coupling with an external optical system becomes easy and efficiency can be increased.

According to the semiconductor laser according to the present invention as described above, compared to a normal semiconductor laser in which the excitation region is directly exposed to the reflective surface, chemical reactions with the outside are less likely to occur, and deterioration due to optical reactions on the reflective surface is prevented. It can also be manufactured in the same manufacturing process as a normal BH laser.

The dimensions and composition of each region are not limited to those in the above embodiments. Furthermore, although the present embodiment has been described with reference to the AlGaAs/CaAg double-petero junction crystal material, other crystal materials, such as InGaAsP/InGaP*InGaP/A
IInP rInGaAsP/TnP # AlGaA
It can be applied to many crystalline materials such as sSb/GaAsSb.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention, and FIG. 2 is a perspective view showing an embodiment of the present invention. Figure M3 and Figure 4 are A-A' and B-B' in Figure 1, respectively.
, C-C', FIG. 5 is a top view of FIG. 1, and FIG. 6 is a top view of FIG.
The figure is a cross-sectional view of the double heterojunction crystal grown during the manufacturing process of this example, and FIG.
Fig. 8 is a top view of Fig. 7. 10-n type GaAs substrate, 11-n type A10.4
Gao, sA8 first cladding layer, 12-... undoped AL, tiGao, m5AI! Active layer, 13-p type Al
o, 4G&o, @AS second cladding layer, 14・Sin,
membrane, 15-I) - form A1.0. Ga, ..., As third cladding layer, 16.p-type o, 5zGao, @sA3 guide layer, 17...n-1 type Alo, 4GjL 6,6
kB 4th cladding layer, 18...5i01 film, 19.
...Zinc diffusion region, 2゜...P-type ohmic contact, 21...N-type ohmic contact, 22...
Mizo patent applicant NEC Corporation Figure 1 Figure 2

Claims (1)

[Claims] (1) The active layer is made of a double heterojunction semiconductor material sandwiched between first and second cladding layers made of a material with a lower refractive index than the active layer, and the width is increased in the center along the longitudinal direction. A stripe-like structure consisting of a wide region and narrow regions formed adjacent to both ends of the stripe-like structure is provided, and the wide stripe-like region and the adjacent narrow stripe-like region form a boundary. The surface has a total reflection angle with respect to the laser beam, and a groove region formed in the vicinity of both reflecting surfaces adjacent to the narrow stripe-like region and an external region of the stripe-like structure are covered with a third cladding layer. , a guide layer made of a material having a refractive index higher than that of the cladding layer and a refractive index lower than that of the active layer, and a fourth cladding layer are continuously embedded, and the guide layer is thick in the groove region and 1. A semiconductor laser characterized in that the embedded region is thin, and the active layer in the stripe-like structure is adjacent to the guide layer in the groove region in the longitudinal direction.