JPS6237835B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor laser having a buried heterostructure.

In order to operate a semiconductor laser continuously at high temperatures, optical energy and injection must be applied to specific areas that provide the best thermal path to remove heat from the junction, while minimizing light loss and wasteful recombination. Embedded semiconductor lasers with current confinement have emerged. In this structure, the active layer region is complementarily surrounded by a low refractive index material, ie, in the case of a GaAs active layer, by an AlGaAs layer, giving it a strong optical waveguide effect. Although the results were quite good, the refractive index difference had to be larger than necessary, and as a result, although fundamental mode oscillation occurred within a stripe width of 1 μm,
When the stripe width becomes wider than that, it becomes difficult to avoid mixing of higher-order modes. Furthermore, if the stripe width is narrow, it is unavoidable that the optical output is limited to several mW or less, but the optical output is still too small. A striped buried type semiconductor laser has been proposed for the purpose of improving the various drawbacks and problems of low output of the buried type. In this striped buried structure, as described below, an optical waveguide layer is provided separately from the active layer, and only the active layer is surrounded by a semiconductor with a low refractive index to completely confine the injection carrier and allow light to propagate through the optical waveguide layer. This aims to weaken the optical waveguide effect, prevent higher-order mode oscillation, and maintain single mode oscillation over a large current region.

This striped embedded semiconductor laser should be mentioned as the prior art prior to the present invention, and below we will briefly explain with drawings the manufacturing method and structure of this type, which should be solved by the present invention. Explain. FIG. 1 is a cross-sectional view showing the outline thereof. FIG. 3 is a diagram showing the important manufacturing process.

First, an n-type Al _0.3 Ga _0.7 As layer 2 and an n-type Al _0.3 Ga _0.7 As layer 2 are sequentially grown on a semiconductor substrate 1 made of n-type GaAs shown in FIG.
Al _{0.1 Ga 0.9} As layer ₃ , p-type GaAs active layer 4, p-type
An Al _{0.3 Ga 0.7} AS layer ₅ is grown (FIG. 3B). At this point, the growth is temporarily stopped, and selective etching is performed from the surface of the p-type Al _0.3 Ga _0.7 As layer ₅ to form an n-type layer _.
A striped mesa shape as shown in FIG _{. 3C reaching the Al 0.1 Ga 0.9 As} layer 3 is formed. After that, the p-type is grown by a second liquid phase epitaxial growth step.
Al ₀ . ₃ Ga ₀ . ₇ As layer 6, p-GaAs 7, n-
By growing Al ₀ . ₄₅ Ga ₀ . ₅₅ As8 (Fig. 3D), n
- Mesa-etch Al _{0. 45} Ga _{0. 55} As8 again and p
- Place the electrode so that a part of the GaAs 7 is exposed and the current is injected into the mesa-shaped active layer 4 from here.
9.10 is attached to fabricate a striped embedded semiconductor laser (Fig. 1).

When a forward bias is applied to this semiconductor laser, the GaAs active layer oscillates. However, n
-As a result of providing the Al _{0.1 Ga 0.9} As optical waveguide layer ₃ , the laser light largely seeps into the optical waveguide layer side as well. Therefore, although the effective refractive index difference in the lateral direction of the active layer becomes small, carrier confinement has a two-dimensional effect as in the conventional embedded type. As a result, the light confinement effect is weakened, and stable fundamental mode oscillation can be obtained over a wide current range even with a laser with a wide stripe width.In this point, the drawbacks of conventional buried type semiconductor lasers have been greatly improved. It can be said that the mold was an innovative proposal.

However, this striped embedded type had problems in that it was very complicated to manufacture and required new technology.

In particular, the second liquid phase epitaxial growth is n-type.
Growth layers will be stacked on three sides of the Al ₀ . ₁ Ga ₀ . ₉ As layer. At this time _, the n-type Al _0.1 Ga _0.9 As layer is once exposed to _the atmosphere prior to the second liquid phase epitaxial growth step. As a result, even if the Al composition is low, the surface is still slightly oxidized.

This oxide film becomes a source of growth inhibition, and greatly impairs the uniformity and reproducibility of the second liquid phase epitaxial growth. In other words, there is p-type on the surface of _the Al _0.1 Ga _0.9 As layer _.
It becomes difficult to uniformly grow the Al _{0.3 Ga 0.7} As layer over the entire surface of the crystal _.

As a solution to this problem, when mesa-etching _{the active layer, the GaAg active layer is etched only slightly, without etching until the Al 0.1 Ga 0.9 As surface is} completely exposed.
For example, the etching is finished leaving about 200 Å left, and the second liquid phase epitaxial growth is performed thereon.

According to this method, the disadvantage of non-uniform growth of the second liquid phase epitaxial growth described above is eliminated. On the other hand, a different problem arose. In the etching process, it is necessary to mesa-etch a very thin GaAs active layer, leaving it uniformly over the entire surface of the crystal.
To achieve this, advanced etching control, uniformity of the thickness of the growth layer to be etched, and its Al
It is a necessary condition that the composition be uniform. At present, it is extremely difficult to fully satisfy these manufacturing conditions. Therefore, this etching process significantly impairs economic efficiency, mass productivity, and reliability. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a striped embedded semiconductor laser which does not have the above-mentioned drawbacks of the conventional methods, has high productivity, and can be easily realized.

The gist of this invention is to grow another layer on top of the layer that will become the active region in the first stage of growth, to ensure that the upper part is buried, and to form narrow grooves parallel to both sides of the striped active layer. Then, prior to the second stage of growth, the surface of the growing crystal is cleaned with a solution containing an element that has a strong reduction reaction, the oxide film is removed, and then the grown layer is deposited on the groove again, and the side surface is This is an attempt to complete the embedding.

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

FIG. 2 is a schematic sectional view when the present invention is implemented;
FIG. 4 is a schematic process diagram showing the manufacturing process of each main part.

First, on a semiconductor substrate made of n-type GaAs 11 shown in FIG. 4A, an _{n-type Al 0.3 Ga 0.7} As layer ₁₂ and an n-type
Al ₀ . ₁ Ga ₀ . ₉ As 13, p-type GaAs active layer 14, p-type
An Al _{0.3 Ga 0.7} As layer ₁₅ is grown by a first liquid phase epitaxial growth (FIG. 4B). then p type
A mesa etching mask was prepared in _which a 20 μm wide groove was selectively etched on both sides of a 5 μm wide band-like region on the upper surface side of the Al _{0 .} 3 _Ga 0 . _{The p-type Al 0.3 Ga 0.7} As layer ₁₅ is etched. This 20 μm wide groove is n-type
The depth is set to reach the Al _{0.1 Ga 0.9} As layer ₁₃ , and only this portion _{of the Al 0.1 Ga 0.9} As layer ₁₃ is exposed, thereby preparing the crystal shown in FIG. 4C. After removing the photoresist film and thoroughly cleaning the crystal surface, a second stage of liquid phase epitaxial growth is performed. _{The crystal to be grown is an n-type Al 0.3 Ga 0.7} As layer ₁₆ . The n-type
Prior to the growth of the Al ₀ . ₃ Ga ₀ . ₇ As layer 16, the p-type
Elements such as Al, Mg, and Be _, which have a composition similar to that of the growth solution used for the Al 0 . ₃ Ga ₀ . ₇ As layer 15 and whose standard redox potential (hereinafter referred to as E ₀ value) is negative, are used. The containing cleaning solution is brought into contact with the crystal growth surface of FIG. 4C. The cleaning solution is placed simultaneously with the growth solution in the growth _{boat in which the n-type Al 0.3 Ga 0.7} As layer ₁₆ is grown. Since this cleaning solution has the function of removing the oxide film attached to the surface of the crystal, the oxide film is completely removed by passing the grown crystal under the cleaning solution. After this, _{an n-type Al 0.3 Ga 0.7 As layer 16}
grow.

As shown in FIG. 4D, a flat crystal surface can be obtained by appropriately controlling the growth temperature, cooling rate, and growth time. For example, if the growth time is short, the groove portion becomes concave. A part of the n-type Al _0.3 Ga _0.7 As layer ₁₆ grown in this way is converted into _a p-type region 17 by Zn diffusion, and a p-type electrode 19 is formed on its surface.
are formed through the SiO ₂ film 18, and an n-type electrode 20 is formed on the back side of the base 11, thereby completing the intended striped embedded semiconductor laser.

Typical _{thickness of each layer is 20 mm for n-type Al 0.3 Ga 0.7 As layer} 12 _.
μm, n-type Al _{0.1 Ga 0.7} As layer 13 is 1.0 μm, p _- type
GaAs layer 14 is 0.2 μm, p _{-type Al 0.3 Ga 0.7} As _layer 15
is 0.5 μm, and the n-type Al _0.3 Ga _0.7 As layer ₁₆ is 1.0 μm _.

By the way, according to the manufacturing method described above in FIG. 4 of this embodiment, prior to the growth in the second liquid phase epitaxial growth step, the crystal surface is cleaned with the previous cleaning solution to remove the The remaining oxide film is removed. Therefore, unlike the conventional method, the n-type Al _0.3 Ga _0.7 As layer ₁₆ grows uniformly over the entire _surface of the crystal.

The cleaning solution used in this example had a composition containing Al at a molar ratio of 0.05 (Ga, GaAs, Al, Mg). Elements such as Al, Mg, Be, etc. mixed into the cleaning solution do not need to be present in large amounts, and their effects can be fully demonstrated with very small amounts. Furthermore, the smaller the E ₀ value of these elements, the more likely the reduction reaction will occur, and the greater the effect will be. If the E ₀ value is greater than -1, the effects of the present invention cannot be expected to be very effective. By the way,
Regarding Al, Mg, and Be, Mg (−2.363) has the largest effect, followed by Be (−1.85) and Al (−
1.662). Note that, considering that the chemical reaction rate is generally proportional to the concentration, it goes without saying that the effect will be even better if the amount of the above elements in the cleaning solution is increased.

Removal of the oxide layer is included in the cleaning solution.
It is thought that Al, Mg, Be, etc. cause a reduction reaction with the oxide, and the oxide dissolves into the cleaning solution.

Further in accordance with the practice of the present invention, n-type Al _{0.3 Ga 0.7 As}
Since the layer 6 and the growth substrate interface are almost completely crystallized, an epitaxial layer without lattice defects is formed.

When forming a groove in the etching process, even if the etching depth goes into the n-type Al _0.3 Ga _{0.9 As} layer ₁₃ , the characteristics of the semiconductor laser will not be deteriorated. Rather, this is a factor that improves the yield.

As described above, according to the semiconductor laser shown in FIG. 2 obtained by the manufacturing method according to the embodiment of the present invention, the semiconductor laser shown in FIG. omitted.

The present invention provides a long-life semiconductor laser that has the same excellent characteristics as described above in FIG. provide.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a conventional striped buried semiconductor laser, FIG. 2 is a schematic sectional view of a striped buried semiconductor laser obtained by an embodiment of the present invention, and FIG. 3 is a schematic diagram showing a conventional manufacturing method. A linear process diagram and FIG. 4 each show a schematic process diagram showing a manufacturing method of an embodiment of the present invention. In the figure, 1, 11... n-type GaAs substrate, 2,
12...n-type _Al0.3Ga0.7As layer, _{3,13 ...} n _- type
Al ₀ . ₁ Ga ₀ . ₉ As layer, 4, 14...active layer, 5, 6, 1
5...p _{-type Al0.3Ga0.7As layer} , _{7 ...} p-type GaAs layer, 8
_... n _- type _{Al0.45Ga0.55As} layer, 9,20 _... n-type electrode,
10, 19...p- _{type electrode, 16...n-type Al 0.3 Ga 0.7 As}
17 shows a p-type Zn diffusion region, and 18 shows a SiO ₂ film.

Claims (1)

[Claims] 1. On a first conductivity type semiconductor substrate, at least a first conductor layer of a first conductivity type, a second semiconductor layer of a first conductivity type having a refractive index higher than that of the first semiconductor layer, and a refractive index higher than that of the second semiconductor layer. a first liquid phase epitaxial growth step of forming a substrate crystal by sequentially providing an active layer with a high refractive index and a fourth semiconductor layer of a second conductivity type with a lower refractive index than the second semiconductor layer; a selective etching step of etching the substrate crystal from the fourth semiconductor layer side to a depth reaching the second semiconductor layer so that the semiconductor layer and the active layer remain in a band shape; and second semiconductor layer growth or fourth semiconductor layer growth. The surface of the substrate crystal provided with the etching grooves is cleaned with a cleaning solution that has a composition similar to that of the growth solution used in the process and contains an element whose standard redox potential is negative and whose absolute value is 1 or more. a structure in which a fifth semiconductor layer having a refractive index lower than at least the active layer and exhibiting a first conductivity type is formed on the substrate crystal surface, and a side surface of the active layer is covered with the fifth semiconductor layer; a second liquid phase epitaxial growth step comprising: a second liquid phase epitaxial growth step;