JPH01115191A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain high reliability and high output by sequentially laminating a semiconductor layer and a dielectric layer from on top of a light radiating face in this order, increasing the energy gap of the semiconductor layer larger than that of an active layer, and substantially equalizing lattice constant to that of the active layer. CONSTITUTION:A semiconductor layer 4 having larger energy gap than that of an active layer 3 and lattice constant substantially equal to that of the layer 3, and a dielectric film 7 are sequentially formed in this order from on top of light irradiating face 11. In this case, the layer 4 is formed of group III-V compound containing aluminum, the layer 7 is formed of Al2O3, the layer 4 containing the aluminum is formed on a vapor atmosphere containing oxygen of 0.1-100ppm by a vapor growing method with organic metal as a starting material, and an Al2O3 film 7 is subsequently formed without exposing the layer 4 to the atmosphere. Thus, an optical absorption in an element end face region can be reduced, heat generation due to the optical absorption can be decreased, and output and reliability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a highly reliable and high output semiconductor laser and a method for manufacturing the same.

(Prior Art) Light oscillated in the active layer of a semiconductor laser is extracted to the outside from a light emitting surface of the device. In a semiconductor laser, the laser light emitting surface is formed by opening the arms, and the laser oscillation light is
It is taken from that aspect.

Since the laser light emitting surface has an extremely high photon density, the reliability and operable output of the device are limited due to destruction or oxidation of the light emitting surface. Therefore, conventionally, a structure has been adopted in which a dielectric film such as 5iot, MtOs, 5isNt, etc. is adhered to the light emitting surface to protect the light emitting surface and improve reliability and operational output. As an example of a conventional semiconductor laser, the journal
Physics (, T, Apl) 1-Phys, ) 5th
Figure 3 shows the structure published in Vol. 0, page 5150 (1979). This figure is a view of an AQGaAs semiconductor laser seen from a side surface parallel to the stripe electrodes. Laser light emitting surface 1 formed by folds at both left and right ends of the figure
It is 09. This semiconductor laser has an n-GaAs substrate 1
n AQs, aGaa, J! on top of 01! 3 clad M
102. Undoped GaAs active layer 103. p-AQ
o, aGaa, aAs cladding layer 104 and n
-Has a semiconductor multilayer structure in which semiconductor layers of the GaAs cap layer 105 are laminated in order, and has a p electrode 106 and an n electrode 1
A current is injected from 07. 5 on the laser beam emitting end face
An i0z film 108 is formed and serves as an end face protection film.

In the example shown in FIG. 3, the protective film 108 is 5ill, but Mhos, St, and am films can also be used in a similar configuration. In addition, such a protective film can be used for other semiconductor light emitting devices such as GaInPAs lasers and AQGaIn
It is similarly used for P-based visible light lasers.

(Problems to be Solved by the Invention) In the conventional method described above, since the physical properties of the dielectric film applied as a protective film and the semiconductor are significantly different, the interface state between the two is not necessarily good, and the coefficient of thermal expansion is also poor. Because they are different,
When the temperature rises during high-output operation, distortion occurs on the end face, which causes deterioration.

For this reason, it has been difficult to achieve long life with high output operation. A structure in which the light exit surface is protected with a semiconductor film having the same lattice constant as the element is also considered, but it has been difficult to obtain a high-resistance semiconductor film without shadowing the element. Further, since it is difficult to differentiate the refractive index of such a semiconductor film from that of the semiconductor film constituting the element, the conventional method has the drawbacks as described above, in which it is difficult to control the end face reflectance.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a highly reliable and high-performance semiconductor laser and its manufacturing method, which eliminates the above-mentioned drawbacks by utilizing the properties of crystal growth and the properties of materials.

(Means for Solving the Problems) The gist of the semiconductor laser of the first invention of the present application is to provide a semiconductor laser on the light emitting surface with a larger energy gap than the active layer and with substantially the same lattice constant as the active layer. The layer and the dielectric film were formed in this order. When the semiconductor layer is made of a 1-v compound containing carbon dioxide, or the dielectric film is AQ t Os, the first invention of the present application can be applied to a semiconductor laser made of a 1-v compound semiconductor, and the effect is remarkable. Also, Al
The ■-■ compound semiconductor layer containing
Formed in a gas phase atmosphere containing in the range of from to 1100 pp,
Without exposing this semiconductor layer to the atmosphere, AQ,
o.

The structure of the first invention of the present application can be easily manufactured and realized with remarkable effects by the second invention of the present application in which a film is formed. The ■-■ compound semiconductor layer containing Al may be any material as long as it satisfies the conditions that the energy gap is larger than that of the active layer of the semiconductor laser and the lattice constant is approximately equal to that of the active layer, such as AQGaAs or AQInP.
, AQGaSb, A11) GaInP, etc.

Furthermore, the semiconductor layer does not need to be made of a ■-■ compound containing Al, and the dielectric film is made of M, 0. Even if this is not the case, the first invention of the present application is still effective.

(Function) A film or region formed on the end face of a semiconductor laser element to protect the end face has three main functions. They increase the energy gap near the end face, reduce light absorption in this region, and prevent end face destruction due to heat generation due to light absorption (
Function 1) Prevents chemical changes on the end face by not directly exposing the end face of the excited semiconductor element to the atmosphere (Function 2)
There are three functions: controlling the reflectance of the element end face to reduce the photon density inside the light emitting end face to prevent end face destruction and deterioration (Function 3). Although conventional structures satisfy some of these three functions, none fully satisfies all of them. By adopting the structure of the first invention of the present application, first, a semiconductor layer having a larger energy gap than the active layer of the semiconductor laser is provided on the device end face in contact with the active layer, thereby reducing light absorption in the device end face region. can be reduced,
Heat generation due to light absorption can be reduced.

At this time, if the lattice constant of the semiconductor layer provided on the element end face is different from the lattice constant of the semiconductor material that constitutes the active layer and eventually the semiconductor laser, distortion will occur at the interface with the semiconductor layer provided on the element end face. This causes deterioration of the device. This point can be solved by making the lattice constant of the semiconductor layer provided at the device interface approximately match that of the active layer of the semiconductor laser.
Simply providing the semiconductor layer described above on the end face satisfies the aforementioned function 1, but does not have sufficient effect on function 29 and function 3. Function 2 and Function 3 are satisfied by forming the semiconductor layer thickly, and Function 2 is satisfied by covering the semiconductor end face with a dielectric film to prevent the semiconductor layer from being exposed to the atmosphere.

By controlling the dielectric film thickness and dielectric refractive index, the end face reflectance can be controlled, and Function 3 is satisfied.

The semiconductor film provided on the end face of the element described above is required to have high electrical resistance. In other words, when the resistance of the film is low, the efficiency of the device decreases due to leakage current. Utilizing the ■-■ compound containing AQ as the semiconductor film has the following advantages. First, compounds containing Al easily become high in resistance when oxygen is added during formation. Second, in a II-V compound containing only Ga or both AQ and Ga, by replacing Ga and Al, the band gap can be increased with almost no change in the lattice constant. Therefore, if a III-v compound containing Al is used as the semiconductor film provided on the end face of the device, the effect of the first invention of the present application is remarkable.

Further, a dielectric film of M, 0. Then, after forming the above-mentioned Al-containing compound 1--2, it is easy to continue forming the compound in the same apparatus without taking out the sample into the atmosphere. Therefore, AQ*Os is used as a dielectric film.
In addition to the above-mentioned effects, the use of the above-described method has the advantage of ease of manufacture and further improvement in reliability.

As a method for forming a ■-■ compound layer containing Al, a vapor phase epitaxy method (MOVPE method) using an organic metal is one of the excellent methods. When using this method, if grown in a normal high-purity atmosphere, it is difficult to provide insulation even when undoped. On the other hand, if oxygen is mixed into the growth atmosphere, the I[-4 compound layer containing Al will have high resistance. However, if a large amount of oxygen is included, the crystal will deteriorate and cause surface roughness, making it unsuitable for protecting the light exit surface. However, if the oxygen concentration during growth is reduced to 0. When a ■-v compound containing Al is grown while controlling it within the range of 1 ppm to 1100 ppm, a high-resistance crystal can be obtained while maintaining crystal quality. Therefore, Al
A ■−■ compound semiconductor layer containing
When formed in a gaseous atmosphere containing oxygen in the range of 0.1 ppm to 1100 ppm, an ideal semiconductor layer having a larger energy gap than the active layer and approximately the same lattice constant as the active layer can be obtained.

Further, after forming a ■-v compound semiconductor layer containing Al, M! By forming 08, the cause of deterioration can be eliminated without contaminating the interface between the semiconductor and the dielectric film.

(Example) Next, an example of the present invention will be shown. Fig. 1 shows a schematic perspective view of a semiconductor laser which is an example of the first invention of the present application.
An example of an AQGaInP visible light semiconductor laser that oscillates in the 600 nm band is shown in FIG. Components pointing to the same locations in both drawings are given the same numbers.

FIGS. 2(a) and 2(b) are cross-sectional views of a wafer for manufacturing elements;
FIG. 2(c) is a plan view of the wafer shown in FIG. 2(b) seen from above.
o, aGa*, s) a, 1Ino, iP cladding layer 2° undoped Gas, 5Ina, sP active layer 3
, p - (AQ, .

Gas, a) o, sIn*, aP clad Fa 4
, p-GaAs cap layer 5 is sequentially formed (second
Figure (a)). The growth method may be MOVPE method or molecular beam epitaxial method (CMBE method).
A groove 12 for forming a groove 12 is formed. Thereafter, AQo, 5Ins, and gP layers 6 are formed by MOVPE. At this time, oxygen is added in a range of 0.1 ppm to 1100 ppm to a mixed raw material gas consisting of trimethylaluminum (TMAQ), trimethylindium (TMIn), 'Pt(s) and hydrogen used as a carrier gas.

In this way, the oxygen concentration in the gas phase atmosphere during growth is Q, lp
From pm to 1100pp. AQ e, gIns
, without exposing the sample to the atmosphere after forming the sP.
Subsequently, M gos is formed (FIG. 2(b)). To form this AQ tOs film, AQ*, 11n
＠, TMA in the same apparatus in which the aP film was formed.
Q and oxygen should be passed in the same way, and the substrate should be heated to about 400°C.
The injection stripe window 8 is formed by forming an AQ x Os film 7 and an AQ
o, aIn-, -P layer 6. Etching solutions include HF buffer for AQ t Os, AQs, g
Selective etching can be performed for Ins and aP by using dilute hydrochloric acid. After that, pttO is deposited by vapor deposition and again by photolithography, as shown in Fig. 2(c).
The structure shown in FIG. 1 is obtained by forming the n-electrode 10 selectively as shown in FIG. The device thus obtained has superior reliability during high-output operation compared to semiconductor lasers of conventional structure. In the embodiment, a stripe laser in which a stripe injection region is formed with an insulating film is shown, but the invention of the present application can be applied to any structure as long as it is a semiconductor laser whose light emitting end is the end face of a semiconductor laser element. . Also, Al
AQs, gIns, iP are shown as ■-v compounds containing (AQxGas-x) o, 1Ins, sP
(0<x<1). Also, Ga, , 5In
AQ, G with larger energy gap than e, aP
A similar effect can be obtained with a, -, and As. Furthermore, although this embodiment has been described using AQGaAs-based materials, the present invention can also be applied to other materials such as AQGaAs-based and AQGaSb-based materials. From the viewpoint of the magnitude of the effect and the ease of production, a ■-v compound storage dielectric film containing Al as a semiconductor layer attached to the light emitting surface is also used.■0. Although the first invention of the present application has been explained using other materials, the effects of the invention can be obtained even if other materials are used.

(Effects of the Invention) As described above, according to the present invention, it is possible to reduce heat generation due to light absorption at the end face, reduce photon density at the end face, and protect the end face from the atmosphere at the same time and in an easy-to-manufacture method.

In addition, the attached end face protection film can be made of high quality, which also makes the present invention more reliable and more reliable than before.
A high-output semiconductor laser can be realized.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing an embodiment of the first invention of the present application, FIG. 2 is a diagram showing a method for manufacturing the semiconductor laser of FIG. 1 according to an embodiment of the second invention of the present application, FIG. 3 is a schematic cross-sectional view of a conventional semiconductor laser. 1, 101-n-GaAs substrate, 2-rl-(A
Q, , , Ga8. ,). 5Ina, iP cladding layer, 3... undoped Ga*, aIn@,
IP active layer, 4-op (AQs, 4Gam, a)e
, 5In1. , P cladding layer, 5, 105...p-
GaAs key layer, 6...high resistance AQ, sIn
,, sP layer, 7-u*os film, 8... current injection stripe region, 9, 106... = p as pole, 10° 107
...n electrode, 11, 109...laser light emitting end face, 102"' n AQ a , aGas, i
As layer, 103...-GaAs active layer, 104-...p
-AQ a, aGas, sAs layer, 108”・
SiOx protective film. Figure 1, 5p-GaAs (a) (b) Figure 2

Claims (4)

[Claims] (1) A semiconductor characterized in that a semiconductor layer and a dielectric layer are laminated in this order on a light emitting surface, and the semiconductor layer has a larger energy gap than the active layer and a lattice constant approximately equal to that of the active layer. laser. (2) The semiconductor laser according to claim 1, wherein the semiconductor layer is a III-V compound containing Al. (3) The semiconductor laser according to claim 2, wherein the dielectric film is Al_2O_3. (4) A method for manufacturing a semiconductor laser, wherein a semiconductor layer and a dielectric layer are laminated in this order on a light emitting surface, and the semiconductor layer has a larger energy gap than the active layer and a lattice constant substantially equal to that of the active layer, As the semiconductor layer, Al
A III-V compound semiconductor layer containing 0.1 ppm to 100 ppm of oxygen is formed by a vapor phase growth method using an organic metal as a raw material.
The dielectric layer is formed in a gaseous atmosphere containing A within the range of A, without exposing this semiconductor layer to the atmosphere.
A method for manufacturing a semiconductor laser, comprising forming an l_2O_3 film.