JPS6372177A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To realize an excellent characteristic with respect to a high output level, a basic horizontal mode and a low threshold electric current by a method wherein, after an inversely structured mesa has been formed by etching using a bromine methanol solution, a clad layer at the lower part is etched to form a stripe by means of hydrochloric acid so that the second epitaxial growth can be made. CONSTITUTION:During the first liquid phase epitaxial growth, a stripe-like pattern with a <001> crystal orientation is formed on a flat N-type InP substrate 6 in such a way that a lattice is aligned in succession, and, by means of etching using a bromine methanol solution, an active layer 4 with a width of about 2 mum is formed at the position where an inverted mesa shows the minimum width. After that, by using a mixed solution which is composed of one part of hydrochloric acid and two parts of phosphoric acid, an N-type InP layer 5 is etched almost vertically (about 2.5 mum). Then, during the second liquid phase epitaxial growth, the first buried P-type InP layer 8 is grown to the height of the active layer 4, and, after that, the second buried N-type InP layer 7 is growth. After the pattern of an SiO2 film 1 has been removed, an electrode part is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a buried semiconductor laser.

Conventional technology 1 μm band semiconductor lasers are made of InGaAsP and InGaAsP.
The main material is P, and in order to achieve low threshold current and high output, it is designed to enhance the light confinement effect and carrier confinement effect in the active layer. Buried stripe laser (Buried H) is a typical device structure.
The eterostructure La5er is hereinafter referred to as a BH laser. ) is shown in Figure 3.

In the conventional BH laser manufacturing method, a 1n
P cladding layer 15, In, Ga, -xAs, P
After growing a double heterojunction consisting of the , -y active layer 14 and the InPn tinted layer 13, and further providing the InGaAsP layer 12 as an ohmic electrode, these are etched with a bromine methanol solution to reverse the <011> crystal direction. Obtain a mesa stripe structure. Following this, in the second liquid phase epitaxial growth method, N-type and P-type InP layers 18 and 17 are successively buried and grown in the etched area to form a buried layer.The BH structure is
The double heterojunction limits the diffusion of minority carriers into the cladding layer and increases the carrier density in the active layer.
Furthermore, due to the reverse bias region generated at the boundary between the N-type and P-type of the buried layer, a current confinement structure is realized in which current flows only into the active layer. Furthermore, since the active layer is surrounded by InP having a low refractive index, laser light is effectively confined in the active layer. Moreover, fundamental transverse mode oscillation can be realized by controlling the stripe width to be narrow, and the BH laser has extremely excellent characteristics in practical use, such as low threshold current and 9 oscillation mode characteristics.

The problem that the invention seeks to solve For BH lasers manufactured using conventional manufacturing methods.

In the current-light output characteristics, characteristic curve 10.1 in Figure 2
1, the phenomenon where the light output suddenly decreases from a certain current value,
A phenomenon occurs in which the optical output becomes saturated.

It was not suitable for high output. When this phenomenon was investigated, the following facts were confirmed as the cause.

That is, the buried layers 17.18 are the cladding layers 13.
15 to form a silisk structure, and the cladding layer 1
3, when a leakage current as shown by arrow 19 is injected into the buried first layer 18, the breakover voltage decreases, even at a low bias voltage that does not normally result in an on state (conducting state). Easily turns on. As a result, the current confinement structure ceases to function, and the cyrisk current flowing along the path indicated by the arrow 20 in FIG. 3 increases as a leakage current, causing the decrease in optical output and the saturation phenomenon described above.

In order to prevent this, the leakage current from the cladding layer 13 to the buried first layer 18 is reduced, and the transistor structure consisting of the buried layer 18 and the cladding layer 15 when the buried first layer 18 is viewed as a base. The current gain of the current gain must be reduced to suppress the drop in breakover voltage. However, in order to improve the former, the contact area between the cladding layer 13 and the buried first layer 18 is narrowed (this makes the buried first layer thinner and the current gain increases, so it is more likely to turn on). On the other hand, in order to improve the latter, the buried first layer is made thicker (then the leakage current 19 increases and the optical output becomes saturated. Another method is to position the active layer above the minimum width and fill the buried first layer 1.
8 could be considered, but the active layer cannot be controlled narrowly and fundamental transverse mode oscillation cannot be obtained.As described above, in the conventional manufacturing method, the current pinching effect is It is difficult to maintain this level, and results have been unsatisfactory in response to demands for higher output.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention proposes a manufacturing method for obtaining a new reverse mesa stripe shape. After etching to form an inverted mesa structure, the lower cladding layer is etched in stripes using hydrochloric acid, and then a second epitaxial growth is performed.

According to the present invention, etching with hydrochloric acid
Only InP is etched without etching the active layer or contact layer made of sP, and the etching rate also varies depending on the crystal plane orientation.
It has the characteristic of being extremely slow on one surface, and due to this characteristic, the region below the active layer can be etched vertically, leaving a width approximately the same as that of the active layer. When a second epitaxial growth is performed on the new inverted mesa shape thus formed, the buried first layer can be made thicker while the contact area between the buried first layer and the cladding layer is reduced, and the buried layer can be grown from the buried layer to the cladding layer. It is possible to reduce the leakage current to the layer as much as possible, and also to suppress the decrease in the breakover voltage of the SiRisk structure, and it is possible to cope with high output without impairing the advantages of the conventional BH structure.

EXAMPLE The present invention will be described in more detail using an example in which the present invention is actually applied. FIGS. 1A to 1D are cross-sectional views in order of steps of an embodiment of the present invention. The first liquid phase epitaxial growth resulted in a flat (100)N type, as shown in Figure 1a! On the nP substrate 6, an N-type 1nP cladding layer 5°In, Ga, -xAs, P
,-,active layer 4. P-type 1nP cladding layer 3. P-type InG
The aAsP ohmic contact layer 2 has a film thickness of 3
μ ring, 0.1 μm, 2.5 μ■.

After growing in a lattice-matched manner as a 0.5μ film, a 5i02 film 1 of approximately 3000A is buried on the surface, and <0
11> Form a striped pattern with a width of approximately 6μ in the crystal direction, and then etching it with a 1% bromine methanol solution for 50 seconds to form a striped pattern at the minimum width position of the inverted mesa, as shown in Figure 1. The active layer 4 having a width of about 2 μm is positioned. After this, when etching is performed for 30 seconds with a solution containing 1=2 of hydrochloric acid and phosphoric acid, N
The type InP layer 5 was etched vertically by about 2.5 μm, and the remaining width was about 2 μm, which is almost the same as the active layer. Following this, in the second liquid phase epitaxial growth,
As shown in FIG. 1d, the buried first
Grow P-type 1nP8, then embed the second layer of N
Type InP7 was grown. Furthermore, after removing the pattern of the 5i02 film 1 and forming an electrode part, a semiconductor laser was actually fabricated and the current-light output characteristics were measured.
The results shown in characteristic curve 9 in the figure were obtained. In the conventional method, the optical output suddenly decreased and reached saturation at a current value of about 30 On+A, whereas in the BH structure semiconductor laser according to the present invention, the optical output increased up to a high current value of 500 mA or more, and reached 60 On+A. We were able to achieve higher output than cW, #acet. Moreover, the threshold current remained the same as before, and the fundamental transverse mode was obtained.

In the embodiment of the present invention, the case where an N-type 1nP substrate is used has been described, but it goes without saying that the same effect can be obtained when a P-type 1nP substrate is used.

Effects of the Invention The present invention is a method for manufacturing a BH structure semiconductor laser, in which etching with a solution containing hydrochloric acid is added to the mesa etching process of the cladding layer, thereby achieving excellent high output, fundamental transverse mode, and low threshold current. characteristics can be achieved, and its technical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an example process showing an outline of the method for manufacturing a semiconductor laser according to the present invention, and FIG. 2 is a comparison of the current-light output characteristics of semiconductor lasers obtained by the conventional method and the method of the present invention. 3 are cross-sectional views showing the structure of a conventional InGaAsP buried semiconductor laser. 1...<011> Striped pattern 5i in crystal direction
02 film, 2... InGaAsP ohmic contact layer, 3... InP cladding layer, 4...
...InGaAsP active layer, 5...InP cladding layer, 6...InP substrate, 7...I
nP buried first layer, 8... buried second layer. Name of agent Patent attorney Toshio Nakao and one other person Figure 2 o too zoo 300
46) θ 9° Den Ryo, Fig. 3

Claims (1)

[Claims] (100) InP
For multilayer epitaxial layers grown on the substrate surface,
<011> Etching of a striped mask in the crystal direction As a first step, etching is performed with a bromine methanol solution until the position of the minimum width of the inverted mesa exceeds the active layer, and then as a second step, etching is performed with hydrochloric acid. A method for manufacturing a semiconductor laser, comprising the step of etching a predetermined depth region below the minimum width of the inverted mesa to a width approximately equal to the minimum width of the inverted mesa, using a solution containing the inverted mesa.