JPS6355231B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for manufacturing a semiconductor light emitting device that oscillates in a fundamental transverse mode.

(Description of the Prior Art) First, before entering into the description of the present invention, we will first explain the first method of manufacturing a semiconductor laser that has a current confinement layer and oscillates in a fundamental transverse mode, which is an example of a conventional semiconductor light emitting device.
This will be explained with reference to Figures A and B.

Conventionally, as shown in FIG. 1A, an n-InP substrate 1 having a (100) surface is prepared,
This substrate 1 is placed in a liquid phase epitaxial growth furnace,
A p-InP layer 2 to become a current confinement layer is grown on the upper surface 1a of this substrate 1 by liquid phase epitaxial growth. Next, the substrate 1 is temporarily taken out of the growth furnace, and a layer 2 for an etching mask, such as SiO ₂ , is deposited and extended in the <011> direction by a normal photolithography method. A stripe window is opened, and a stripe-shaped groove 3 having a substantially V-shaped cross section is formed by etching from this layer 2 to the substrate 1. Next, this grooved substrate 1 having the current confinement layer 2 is placed in the growth furnace again, and as shown in FIG. A certain n-InP layer 4 is grown, then an active layer InGaAsP layer 5 is grown with the portion corresponding to the groove being curved downward in the direction of the groove, and then a second cladding layer 5 is grown.
Grow InP layer 6. Then, finally the substrate 1
Electrodes 7 and 8 are formed on the lower surface 1b and the second cladding layer 6, respectively.

However, according to this conventional manufacturing method,
Although the curved shape of the active layer is an important factor for fundamental transverse mode oscillation, it has been difficult to control the shape of the active layer.

Further, in this method, the substrate 1 is placed in a growth furnace to grow the current confinement layer 2, and then this substrate is temporarily taken out of the growth furnace to form grooves, and then the grooved substrate is placed in the growth furnace again. In order to carry out liquid phase epitaxial growth of the first cladding layer 4 and below, two independent epitaxial growth steps are required, and therefore the manufacturing process is complicated and time consuming, and there is a lot of loss of raw materials. Moreover, there was a drawback that the manufacturing yield was low.

Furthermore, since element members are taken in and out of the growth furnace, the surfaces of the substrates and the interfaces between the various layers are thermally damaged and cannot be maintained in a clean state.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate these conventional drawbacks by using a single continuous liquid phase epitaxial growth process with a low threshold current and in particular the need to curve the active layer. It is an object of the present invention to provide a method for manufacturing a semiconductor light emitting device, which can manufacture a semiconductor light emitting device capable of oscillating in a fundamental transverse mode without the use of a semiconductor light emitting device.

(Structure of the Invention) In order to achieve this object, according to the present invention,
The process of forming a groove from the (100) plane of the InP substrate with the (111) A plane as the side surface, and the process of forming a groove between the (100) plane and the (111)
A current confinement layer is grown on the surface of the substrate outside the trench by utilizing the plane orientation dependence of the crystal growth rate of InP with respect to the A-plane, and a light absorption layer of InGaAsP is grown on this current confinement layer. The first cladding layer is grown as a concave downwardly curved layer within the groove, and the first cladding layer is grown thicker on the light absorption layer in the groove portion and thinner on the light absorption layer outside the groove. Grow an active layer of InGaAsP on top,
Furthermore, it is characterized in that it includes a single liquid phase epitaxial growth step of growing a second cladding layer on this active layer.

(Description of Embodiments) An embodiment of the method for manufacturing a semiconductor light emitting device of the present invention will be described below with reference to FIGS. 2A to 3.

Figures 2A to 2J are manufacturing process diagrams showing the state of the semiconductor laser at the manufacturing stage, respectively, as a cross section taken at the cleavage plane of the laser element or a plane parallel to the cleavage plane, and the dimensions, shapes, etc. of each component are shown. The drawings are merely shown schematically to the extent that the structure of the present invention can be understood. In addition, hatching representing a cross section is omitted in the drawings.

First, as shown in FIG. 2A, an n-InP substrate 1 is
Prepare 1. The upper surface 11a of this substrate 11 is a (100) plane. Next, as shown in FIG. 2B, a layer 12 of, for example, SiO ₂ is formed on the substrate surface 11a to serve as an etching mask layer. Next, as shown in FIG. 2C, a stripe window 13 is formed on the etching mask layer 12 using a conventional photolithography method.
Open it so that it extends in the direction. The exposed surface 11a of the substrate 11 is etched through this window 13. By this etching, a concave groove 14 is formed, as shown in the perspective views of FIGS. 2D and 3. The width w of this groove is set to approximately 2 μm or less in consideration of oscillation in the fundamental transverse mode. The inclined side surface 14a of this groove becomes a (111)A surface, and this groove 14
The cross-sectional shape of the bottom surface 14b may be flat as shown in the figure, or may be slightly raised, or may have other shapes. In any case, the width of the bottom surface 14b must be kept to a width that will not allow InP to grow.

Next, the substrate 11 with the groove 14 formed thereon is placed in a liquid phase epitaxial growth furnace, and as shown in FIGS.
5 (FIG. 2E), an n-InGaAsP layer 16 (FIG. 2F) that is a light absorption layer, and an n-InGaAsP layer 16 that is a first cladding layer.
InP layer 17 (Figure 2G), InGaAsP active layer
layer 18 (FIG. 2H) and the second cladding layer p
- The InP layer 19 (FIG. 2I) is successively grown in one liquid phase epitaxial growth.

During this continuous epitaxial growth, the p-InP layer 15 grows on the substrate 1 due to the in-plane direction dependence of the crystal growth rate.
The growth rate on the (100) plane, which is the surface of 1, is fast;
Since the growth rate inside the groove 14, that is, on the side surface 14a of the (111) A plane, is extremely slow, by selecting the growth time, as shown in FIG. p-InP can be grown only on the flat surface 11a. The thickness d1 of this current confinement layer 15 is set to 1 μm or more. Subsequently, n- is grown on this p-InP layer 15 and groove 14.
The light absorption layer 16 of InGaAsP does not have strong surface orientation dependence like InP, but rather grows to eliminate unevenness, that is, to fill the grooves 14. Therefore, when grown for a long time, the growth surface becomes flat, but the growth is stopped to the extent that this does not occur, and the second layer is grown.
As shown in FIG.
This layer 16 is formed such that the surface of layer 16 curves downward into the groove to form a recess and is flat outside the groove.
grow. Thickness of this light absorption layer 16 outside the groove
It is sufficient for d2 to be about 0.3 μm. Here, this
The energy gap of InGaAsP should be smaller than that of the active layer.

The inclined plane of the light absorption layer 16 grown in this groove 14 is no longer a (111)A plane, so that the n-InGaAsP light absorption layer 16 is subsequently grown on the n-
When the InP first cladding layer 17 is grown, this cladding layer 17 also grows well inside the groove 14, as shown in FIG. 2G. In this case, the thickness d3 of the cladding layer 17 near the center of the groove is set to be 1 μm or more, and the thickness d4 of the flat portion outside the groove is made sufficiently thin, for example, 0.5 μm or less. Such growth can be easily controlled by adjusting the depth of the groove 14 dug in the substrate 11, the thickness of the current confinement layer 15, the thickness of the light absorption layer 16, etc.

Subsequently, as shown in FIG. 2H, an InGaAsP active layer 18 is grown. The thickness of this active layer 18 is
It should be 0.2μm or less. The geometry of this active layer 18 is such that when the first cladding layer 17 is grown,
If this layer 17 has a concave shape at the center of the groove 14, it will have a lens shape, and if this layer 17 has a flat shape, it will have a flat shape. In any case, the shape of the active layer does not matter as long as the thickness d5 of the portion of the active layer 18 corresponding to the central portion of the groove 14 is 0.2 μm or less. Note that it is preferable that the upper surface of the active layer 18 be flat.

Thereafter, as shown in FIG. 2I, a second cladding layer 19 of p-InP is grown on the active layer 18 to a thickness of 2 .mu.m or more, thereby completing the liquid phase epitaxial growth process.

After each liquid phase epitaxial growth layer is formed on the substrate 11 in this way, the substrate having these layers is taken out of the growth furnace, and the layers are deposited on the surface 19a of the second cladding layer 19 and on the lower surface 11b of the substrate 11. Electrodes 20 and 21 are deposited on the electrodes 20 and 21, respectively.

When an appropriate voltage is applied between both electrodes 20 and 21 of the semiconductor laser obtained in this way to cause an injection current to flow, the current flows through the layers 18→17→16→15→1.
In this case, the electrons and holes recombine in the active layer 18 to emit light, and the emitted light resonates at the cleavage plane to cause laser oscillation in the Fabry-Perot mode. At this time, since the current confinement layer 15 is reverse biased, no current flows outside the groove 14 and
A current path is formed only inside. Therefore, current injection efficiency increases even at low currents, and laser oscillation occurs.

In addition, the light obtained by recombination is confined near the center of the groove 14 due to the difference in refractive index between the active layer 18 and this layer 17 because the lower first cladding layer 17 is sufficiently thick; Since the first cladding layer 17 is thin in the portions located left and right away from the active layer 18 (including the flat portion outside the groove near the groove), the light that enters this layer 17 from the active layer 18 is absorbed by the light below. layer 16
reach up to. Since this light absorption layer 16 has a smaller energy gap than the active layer 18,
All light reaching this layer 16 is absorbed by this layer and does not contribute to laser oscillation. Due to this effect, only the region of the active layer 18 located at the upper part near the center of the groove oscillates in the fundamental transverse mode.

(Effects of the Invention) According to the method for manufacturing a semiconductor light emitting device of the present invention described above, each layer including the current confinement layer, light absorption layer, active layer, etc. is sequentially formed by one liquid phase epitaxial growth. can be formed continuously, and at that time,
This method has the advantage that a semiconductor light emitting device having a structure that oscillates in a fundamental transverse mode can be easily manufactured without requiring special control such as growing the active layer in a curved manner.

Furthermore, according to the method of the present invention, the substrate is not taken out of the growth furnace during liquid phase epitaxial growth, so no thermal damage is caused to the substrate surface, etc.
This manufacturing method has the advantages of being simple, time-consuming, saving raw materials, and having a high manufacturing yield.

Incidentally, in the above-mentioned embodiment, a semiconductor laser was explained, but if the end face of the manufactured light emitting element is not used as a cleavage plane, it becomes a semiconductor light emitting diode. In the above embodiment, an n-InP substrate was used as the substrate, but it goes without saying that a p-InP substrate may also be used, in which case the conductivity type of each epitaxial layer is reversed accordingly. It is necessary to do so.

Since the semiconductor light emitting device manufactured by the method of the present invention has a low threshold value and oscillates in the fundamental transverse mode,
This element is suitable for use as a light source for optical communications, information processing equipment, etc.

[Brief explanation of the drawing]

1A and 1B are manufacturing process diagrams for explaining a conventional method for manufacturing a semiconductor light emitting device having a structure having a current confinement layer, and FIGS. 2A to 2J are one implementation of the method for manufacturing a semiconductor light emitting device according to the present invention. FIG. 3 is a manufacturing process diagram for explaining an example, and is a perspective view showing the state of the substrate at one step of the process shown in FIG. 1, 11... Substrate, 1a, 11a... Upper surface of substrate, 1b, 11b... Lower surface of substrate, 2, 1
5... Current confinement layer, 3, 14... Groove, 4, 17...
...First clad layer, 5,18...Active layer, 6,1
9...Second cladding layer, 7, 8, 20, 21...
Electrode, 12... Etching mask layer, 13... Stripe window, 14a... Side surface of groove, 14b... Bottom surface of groove, 16... Light absorption layer, 19a... Upper surface of second cladding layer.

Claims (1)

[Claims] 1. When manufacturing an InGaAsP/InP semiconductor light emitting device using a liquid phase epitaxial growth method, a groove is formed whose side surfaces are inclined from the (100) plane to the (111)A plane of the InP substrate. A current confinement layer is grown on the substrate surface outside the groove by using the plane orientation dependence of the crystal growth rate of InP with respect to the (100) plane and the (111) A plane, and further,
A light-absorbing layer of InGaAsP is grown on the current confinement layer, and is also grown as a layer concavely curved downward in the trench, and the first cladding layer is formed to have a thick layer on the light-absorbing layer in the trench. InGaAsP is grown thinly on the light absorbing layer outside the grooves, and then an active layer of InGaAsP is grown on the first cladding layer, and then a second cladding layer is grown on the active layer in a single liquid phase process. 1. A method for manufacturing a semiconductor light emitting device, comprising: an epitaxial growth step.