JPS59147478A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce the width of an active layer remarkably by making the width of the upper end of a clad layer on the semiconductor substrate side larger than that of the lower end of a clad layer immediately above the active layer. CONSTITUTION:An N-clad layer 2, an N-light guide layer 3, an active layer 4, a P-clad layer 5 and a P-cap layer 6 are grown on an N-substrate 1 in succession. The refractive indices of the layer 2 and the layer 5 are set to values smaller than that of the layer 4 at that time. The refractive index of the layer 3 is set to a value smaller than that of the layer 4 and larger than that of the layer 2. Each layer is etched in the direction of a trapezoid of which the upside is smaller than the downside in a sectional shape. Only the layer 2 and the layer 5 are etched selectively. The exposed section of the exposed layer 4 is removed through etching. Accordingly, since a mesa stripe is formed in the direction of the trapezoid of which the upside is smaller than the downside in the sectional shape, the width of the layer 5 is made narrower than that of the layer 2, and the width of the layer 4 can be reduced extremely.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a buried hetero type semiconductor laser device and a manufacturing method thereof.

[Prior art]

Many proposals have been made to try to increase the output of semiconductor laser devices. Typical examples include providing a so-called optical guide layer in contact with the active layer and making the output end face of the laser beam transparent, but it cannot be said that a sufficiently high output has been achieved yet.

[Purpose of the invention]

The present invention has been made in view of the actual state of the prior art as described in "-", and its purpose is to make it possible to make the active layer width extremely small, thereby increasing the output power and stabilizing the transverse mode at high output. The objective is to provide a semiconductor laser device that can achieve this goal and a method for manufacturing the same.

[Summary of the invention]

That is, in the semiconductor laser device of the present invention, after growing each layer (the so-called first cladding layer, optical guide layer, active layer second cladding layer, etc.), the cross-sectional shape is such that the -1- side is smaller than the lower side. A mesa stripe of the laminated semiconductor layers is formed along a direction in which a trapezoidal shape is formed. After that 2
The device is manufactured by selectively etching two cladding layers, and the width of the light guide layer on the active layer side is wider than the width of the cap layer on the substrate side, and the width of the light guide layer on the substrate side is wider than the width of the active layer side. or become wider. Therefore, the width of the upper end of the cladding layer on the semiconductor substrate side is wider than the width of the lower end of the cladding layer directly adjacent to the active layer, so that the width of the active layer can be made very small.

In addition, the properties IIt of each clathode layer, active layer, and optical guide layer
'1 is selected as follows.

The refractive index of the first and second cladding layers is set smaller than the refractive index of the active layer. The refractive index of the light guide layer is set to be smaller than the refractive index of the active layer and larger than the refractive index of the cladding layer. Furthermore, the forbidden band widths of both the cladding layer and the optical guide layer that are in contact with the active layer are set to be wider than that of the active layer.In this way, photons are confined in both the active layer and the optical guide layer, and on the other hand, The carriers will be confined in the active layer.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be explained in detail with reference to FIGS. 2 and 3.

FIRST EMBODIMENT FIG. 1 is a cross-sectional view showing each step of a method for manufacturing a semiconductor laser device according to a first embodiment when the present invention is applied to a GaAtAs semiconductor laser device. Note 2
The figure is a cross-sectional view taken in a direction perpendicular to the radiation direction of laser light.

(a) As shown in the figure, an n-GaAs substrate 1''-
n-Ga (+55A
Ag4s As crat layer 2 (thickness 0.8-2 μm
), n-Gao, 74 AAo, 26 As optical guide layer 3 (0.4-3 μm), undoped GELo86
Al-0 As active layer 4 (0.04~0.47'rn
) + p-Gao, 5sAto, <5As cladding layer 5
(0.8-2 μm), and p-Gao, B At
0.2 As key 1' Sequential growth of bulge layer 6 (05 to 1 μm). Note that at this time, the refractive index of the n-cladding layer 2 and the p-cladding layer 5 is set to be smaller than the refractive index of the active layer 4. Furthermore, the refractive index of the light guide layer 3 is the same as that of the active layer 4.
The refractive index of the n-cladding layer 2 is smaller than the refractive index of the n-cladding layer 2.
Although an As layer is used, in this example, the purpose is not to epitaxially grow a mesa stripe in the subsequent step of buried growth, and to make it as easy as possible to make ohmic contact. B /V, o, 2 As layer.

Next, each layer shown in Figure 1 (a) is etched along the direction so that the cross-sectional shape becomes a trapezoid with one side smaller than the bottom side, and Form a mesa strip.In this mesa formation, the mesa depth is
In order to facilitate the subsequent step of buried growth, Ga
Make sure that it reaches the As substrate 1. In the semiconductor laser device of the present invention, it is necessary that the width of the optical guide layer 3 be wider than the width of the active layer 4.

Note that etching such that the cross-sectional shape becomes trapezoidal is realized using a so-called reaction rate-limiting etching solution. For example, in the case of a GaAs substrate, the 9 surfaces are (
100) surface, and the area to be left in the form of a mesa is
Live etching mask < o i 1. ＞
Provided in the direction. Then, etching is performed using an etching solution consisting of a mixture of sulfuric acid, hydrogen peroxide, and ethylene glycol. In this way, a mesa portion having a trapezoidal cross section is realized. The same concept can be used for other materials as well.

Next, as shown in Figure (C), only the n-cladding layer 2 and the p-cladding layer 5 are selectively etched by about several 11 meters from both sides. Here, HF is used as the 9-selection etching solution.

Thereafter, the exposed portion of the active layer 4 exposed by this selective etching is removed using an H3po-based etching solution to form a cross-sectional structure as shown in FIG.
) As shown in the figure, the entire mesa stripe was grown by liquid phase epitaxial growth with p-aao, 55 Aj-0,4
5As layer 7 and naaO, 55AZo, ll! l
Fill with As layer 8. That is, since the bias is reversed outside the mesa stripe region, the current flows only in the mesa stripe region. Note that these buried layers 7 and 8 are high-resistance semiconductor layers, for example, +Ga0.55 At0.45
An As high resistance layer may also be used.

Finally, after performing selective diffusion 9 or full-surface diffusion of Zn on the mesa strip, ohmic electrodes 10° 11 are formed, and an element having a final cross-sectional view as shown in the figure ([) is completed.

As described in 1-, in this example, after forming each layer on the substrate, the mesa stripes are formed along the direction such that the cross-sectional shape becomes a trapezoid whose sides are smaller than the bottom sides. The semiconductor laser device manufactured through the subsequent selective etching of the cladding layers 2 and 5 has a width on the active layer 4 side of the optical guide layer 3 wider than a width on the substrate 1 side of the cap layer 6, and a width on the active layer 4 side of the optical guide layer 3. The width of the substrate 1 side is wider than the width of the active layer 4 of
The width of the active layer 4 can be made very small (for example: bzm).

Further, according to the ninth embodiment, since the mesa depth reaches the substrate 1, the optical guide layer 3 (Ga-x Azx As
) even if the AAAs concentration is large (for example, X = 0.26)
, it is possible to form a structure that allows easy buried growth and high output even in the visible range of nine oscillation wavelengths.

In this example, a stable device with a single transverse mode was obtained with an oscillation wavelength of 780 nm and an optical output of 5 QmW. The transverse mode is stable up to an optical output that is about 3 to 5 times higher than that of a normal visible semiconductor laser device.
It has excellent device characteristics.

Second Embodiment FIG. 2 is a cross-sectional view of a semiconductor laser device according to a second embodiment of the present invention. In contrast to FIG. The cross-sectional structure in the direction of the laser optical axis is shown in FIG.

In the second embodiment shown in FIG. 2, the end face is made transparent to the laser beam (a material with a narrow band gap may be used). After forming a mesa stripe as shown in FIG.
, qc+, s5A/Lo, l5As end face portion of crat layer 5 and active layer 4 +2. ]2' only is removed by selective etching. Thereafter, the outside of the mesa stripe is buried with a GaAtAs layer of the same type as in the buried growth in the first embodiment (FIG. 1(C)). Note that the width of the buried regions 12, 12' of the two light emitting end faces is often about 10 μm to 3011 m.

If it is too thin, it will be difficult to manufacture, so a thickness of several μm to 5 μm is practical. On the other hand, if it is too thick (but the light will be diffused etc.)
The dot becomes larger.

In the device of the second embodiment made in this way,
The optical guide layer 3 is located at the reflective end face of the laser resonator, and the end face of the active layer 4 is located inside the reflective end face.

In this example, the 5 oscillation wavelength is 780 nm and the optical output is 50 nm.
mW single transverse mode and maximum optical output J, W ii
A J-view semiconductor laser was obtained. In other words, it can be seen that this embodiment is quite effective in increasing the output and stabilizing the transverse mode at high output.

In addition, 1. the present invention is as follows. In addition to the composition shown in the second embodiment, X of each Ga]-xAtxAs layer is Q<x
Applicable within the range of ≦1. Furthermore, it can be applied not only to GaAtAs-based semiconductor laser devices but also to quaternary-based semiconductor laser devices such as InGaAsP. Furthermore, a p-type substrate may be used, in which case all the conductivity types of the epitaxial layers need only be set to the opposite conductivity type to that in the first embodiment.

〔Effect of the invention〕

As explained below, in the present invention, the mesa stripe is formed in a direction such that the cross-sectional shape is trapezoidal with one side smaller than the lower side, so that p- Since the cladding layer width is relatively narrow with respect to the n-cladding layer width, the active layer width can be made very small. Therefore, according to the present invention, a semiconductor laser device capable of achieving high output and transverse mode stabilization at high output can be obtained with a high yield.

FIG. 3 is a sectional view showing a comparative example to the present invention. The figure shows only the mesa stripe section. In the figure, 1 is an n-GaAs substrate, 2 is an n-GaAAAs cladding layer, 3 is an n-GaΔAAAs optical guide layer 4 is a GaAs
tAs active layer, 5 a p-GaAtAs cladding layer.

(i is the p-GaAtAs camp layer. By the way,
In this ``1'' conductor laser device, after growing each of the above layers, when forming these layers as a whole into a mesa shape, the cross-sectional shape of the completed mesa stripe or the 1-side is lower than the lower side. The mesa stripe is formed along a direction that forms an inverted trapezoid shape.Then, only the two cladding layers 2 and 5 are selectively edged to obtain a mesa shape as shown in FIG. However, in a semiconductor laser device formed in this manner and having a mesa shape as shown in the figures, the width of one end of the n-cladding layer 2 is wider than the width of the lower end of the p-cladding layer 5. becomes narrow, and if two selected edges are continued, one end of the n-cladding layer 2 becomes very narrow and may break.

, the width of the active layer 4 directly under the i&p-cladding layer 5 is several μ.
It would be difficult to make it smaller than m. Therefore, there are undesirable disadvantages in stabilizing the transverse mode of a high-power 11-conductor laser device.

The present invention satisfactorily solves these problems.

[Brief explanation of the drawing]

FIG. 1 +al~([) is a sectional view showing each step of the manufacturing method of the semiconductor laser device according to the first embodiment of the present invention, and FIG. 2 is a laser of the semiconductor laser device according to the second embodiment of the present invention. A sectional view taken along a plane parallel to the optical axis, and FIG. 3 is a sectional view of a stripe portion showing a comparative example. 1...Substrate 2,5...Clad layer 3...
- Light guide layer 4... Active layer 6... Cap layer 7, 8... Buried layer 9... Zn diffusion layer] 0. H... Ohmic Electrode Representative Patent Attorney Junnosuke Nakatoshi 3 Figure -415-

Claims (6)

[Claims] (1) A first . Second. The third and fourth semiconductor layers have a small optical confinement region formed by stacking layers in contact with each other, and the third semiconductor layer has a larger refractive index than the second and fourth semiconductor layers. , fiif, the refractive index of the second semiconductor layer is smaller than that of the third semiconductor layer, and 1.1 is larger than that of the first semiconductor layer, and the forbidden band width of the third semiconductor layer is smaller than that of the third semiconductor layer. In a semiconductor laser device having a structure in which a side portion of the optical confinement region having a surface substantially parallel to the traveling direction of the laser beam is embedded with a semiconductor layer, the side portion of the optical confinement region is set to be smaller than that of the fourth semiconductor layer. , the third semiconductor layer and the fourth semiconductor layer have substantially the same width on their contact surfaces, -1-1, the width of the fourth semiconductor layer has the third width
A semiconductor laser device characterized in that a width on a surface opposite to the semiconductor layer is larger than a width on a surface in contact with the semiconductor layer. (2) The semiconductor laser device according to claim 1, wherein the semiconductor layer filling the side surface of the optical confinement region reaches the substrate. (3) The second semiconductor layer is present up to the end face of the stacked semiconductor layers, and the third semiconductor layer has a small end face (one of which is located inside the end face of the stacked semiconductor layers); A semiconductor laser device according to claim 1 or 2, characterized in that: (4) Claims 1 to 3, characterized in that a semiconductor layer is further laminated on the fourth semiconductor layer.
3. The semiconductor laser device according to any one of the items. (5) "Predetermined substrate" is small in two parts (both 1st, 2nd and 3rd)
and a step of sequentially stacking and forming a fourth semiconductor layer. Processing the laminated semiconductor layers into a trapezoidal stripe shape with a cross-sectional shape that is wide on the side of the substrate and narrow on the side opposite to the substrate. Selectively etching the first and fourth semiconductor layers to make the widths of both semiconductor layers narrower than the width of the second semiconductor layer] Step 2. 2. At least a portion of the exposed portion of the third semiconductor layer exposed by the selective etching is removed by etching. 11. embedding at least one semiconductor layer in a side portion of the striped semiconductor stack having a surface substantially parallel to the traveling direction of the laser beam; 11. Said third
11. The semiconductor layer has a larger refractive index than the second and fourth semiconductor layers, and the second semiconductor layer has a smaller refractive index than the third semiconductor layer. larger than that of the first semiconductor layer. A method for manufacturing a semiconductor laser device, characterized in that the forbidden band width of the third semiconductor layer is set smaller than that of the second and fourth semiconductor layers. (6) Prior to burying the sidewalls of the striped semiconductor stack with at least -. semiconductor layers. 6. The method of manufacturing a semiconductor laser device according to claim 5, further comprising a step of removing at least one of the ends of the light emitting surface of the third semiconductor layer.