JPH04207089A - High-output semiconductor laser diode and its manufacture - Google Patents

Abstract

PURPOSE:To enable a withstand voltage level of a current-prevention layer to be increased and linearity of an application current versus optical output characteristic to be improved by providing a semiconductor layer with a band- gap energy difference at a PNPN junction part of the current-prevention layer. CONSTITUTION:A double-striped grooves 20, 20 and a mesa-type projecting part which is sandwiched by these stripe grooves 20 are formed on a semiconductor substrate 10 and then an activation layer 13, a first clad layer 12, a current- preventing layer 11, and a cap layer 19 are formed on this semiconductor substrate 10 in sequence by epitaxial growth process. Current is narrowed by the current-prevention layer 11 at the grooves 20 at both sides of the projecting part and current flows to a part of a top 21 of a mesa projecting part only. Also, since the activation layer thickness is thick at both sides and is curved gradually, light is leaked to both sides of the projecting part and a high-order horizontal mode does not exist since a change in an effective refractive index is small. Also, since a quaternary layers is provided also at a channel part, laser beam output increases linearly and a high-output operation can be achieved.

Description

Detailed Description of the Invention This invention relates to the structure of a semiconductor laser diode that can control the oscillation mode in a single manner and has a current confinement layer inside. The present invention relates to a mesa stripe type semiconductor laser diode for optical communication and a method for manufacturing the same.

Shinpo 4 companies 1 Conventionally, this type of laser diode has adopted the following structure in order to achieve low current operation and unify the oscillation mode, as shown in FIG. That is, an active layer 13 with a high refractive index is sandwiched between cladding layers 10.12 with a low refractive index to form an optical waveguide, and the active layer 13 in the parallel direction, which forms a double heterojunction, is sandwiched between two deeper layers. parallel grooves 20
A mesa-shaped stripe is left in between to form a light emitting region 22. Thereafter, a current blocking layer 11 is buried and grown in a region other than this light emitting region to form a current blocking region, thereby realizing a reduction in drive current due to current confinement and a single laser oscillation mode. (For example, “ElectronLe
tter″18 (1982) 953 pages)
": In the conventional laser diode having the structure shown in FIG. 5, the cladding layer 10.1
A current I ct passes through the PN junction of the channel portion stacked with 2 and the active layer 13 .

IC2 accounts for 30% or more of the oscillation threshold current Ith and is a leakage current component. Furthermore, when the applied voltage increases, the PNPN junction formed by the current blocking layer 11 in the current blocking section turns on the thyristor and becomes conductive.
, In2 increases and the optical output becomes saturated.

Decrease. As a result, the linearity of the current-optical output characteristic in a single mode is lost, making high-output operation impossible.

As described later, this is the PNPN of the channel section above.
A semiconductor layer with an energy gap difference, for example, a quaternary compound semiconductor layer does not exist in the A junction. In other words, the extent to which the electron flow is blocked by the potential barrier due to the energy cap difference is greater than the PN in the area other than the channel area.
The fact that it is smaller than the PN1 thyristor is thought to be a factor in increasing the carrier transport efficiency, resulting in a decrease in the withstand voltage of the thyristor, and preventing high output driving.

Furthermore, by continuing to conduct electricity, the PN junction interface 20 of the channel part
It is known that when the laser diode deteriorates, the leakage currents C1 and IC2 that do not contribute to laser oscillation increase, the driving current further increases, and the current deterioration is accelerated. This is because the PN junction in the channel part is etched after the first growth process and then formed in the second growth process, which is a discontinuous process. This is also said to be due to the large number of interface states.

A detailed analysis of the problems of the prior art is as follows.

In a transistor, if the current gain coefficient is α and the injection efficiency is γ, then the transport efficiency of the minority carriers injected into the E to reach the collector can be expressed as α = γα.

C7 of the binary compound is α−r = [:cosh (WB
/LD)]-”C7 of the quaternary compound is βL2/Ll 6 = sinhr, 5Inhr2+L2/Ll βcosh
r, coshr2, βαeXP (−ΔEg
/RT) Conduction band effective density of states and E in binary and quaternary layers
From the difference in g, from the definitional formula, 4-element layer → β (ΔEg is large) is small β is small → C1 is small Even when γ = 1, α is small The laser diode of this invention has several times the output level of conventional laser light This occurs during high output operation. In order to prevent the current blocking region (PNPN junction) from being turned on as the flowing current component increases, it has a structure in which semiconductor layers with different energy gaps are arranged in the channel portion.

That is, the present invention comprises a semiconductor substrate having a mesa-shaped striped protrusion sandwiched between double striped grooves on the surface of the first conductivity type semiconductor substrate, and a material having a smaller band gap than this substrate. A light emitting layer in which a semiconductor layer is disposed over the entire surface and an active region is formed flat on the upper surface of the convex portion, a second conductivity type semiconductor layer as a cladding layer, and a first conductivity type semiconductor layer as a current blocking layer. A semiconductor laser diode having a double channel buried structure is provided in a region other than the convex portion, and further includes a second conductivity type semiconductor buried layer laminated over the entire surface.

Furthermore, the present invention includes the steps of sequentially forming a reflective conductivity type first cladding layer and a cap layer on the entire surface including the active layer, forming the active layer, forming the second cladding layer,
Either the steps of forming the current blocking layers of opposite conductivity type and one conductivity type are performed in one successive growth step by liquid phase epitaxial growth method, or the step of forming the active layer and second cladding layer is performed by organometallic vapor phase epitaxy. The present invention provides a method for manufacturing a semiconductor laser diode, in which a current blocking layer, a second cladding layer, and a cap layer are formed by a liquid phase epitaxial growth method.

According to the above configuration, the injection current contributing to laser oscillation is injected into the active layer, which is the light emitting region, and the slope of the convex portion. Regarding the oscillation mode, which will be explained in detail in the embodiment section, single mode oscillation is guaranteed.

As mentioned above, the high-power operation of the laser beam, which is a feature of this invention, is achieved by using a material with a band gap energy difference in the PNPN junction as the current blocking layer, which blocks current and transports minority carriers. As efficiency decreases, the current gain factor decreases. Therefore, the breakdown voltage of the PN junction increases. In other words, even if leakage current increases due to high output operation, the turn-on withstand voltage of the thyristor can be maintained.

Furthermore, unlike conventional manufacturing methods, the channel portion of the present invention allows the channel to be formed in advance on the substrate and crystal growth is performed.
N-junctions are formed through successive crystal growth steps. Therefore, as described in the problem section, the deterioration of the PN junction due to current conduction caused by the discontinuous process is reduced, and the increase in leakage current can be suppressed.

Five Kyotane Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a main sectional view of an element perpendicular to a laser beam according to an embodiment of the present invention, and FIG. 2 is a perspective view showing the manufacturing process of a current confinement portion. In this embodiment, a semiconductor substrate 10 as shown in FIG.
Double stripe groove on top (double channel) 20.2
0 and a mesa-shaped convex portion sandwiched between these striped grooves 20 are formed, and an active layer 13, a first cladding layer 12, a current blocking layer 11, and a mesa-shaped convex portion are formed on this semiconductor substrate 10.
A cap layer 19 is sequentially formed in an epitaxial growth process.

In the embodiment, the current is constricted by the current blocking layer 11 in the grooves 20 on both sides of the convex portion, and the current flows only at the top 21 of the mesa convex portion.

Regarding the controllability of the transverse mode, the effective refractive index Neff of the active layer generally becomes smaller as the layer thickness becomes thinner, and leakage becomes more likely. Also, as the rate of change of Neff of the active layer increases in the direction parallel to the junction, the light confinement effect increases,
When the emission spot size is 2 to 3 μm or more, a high-order transverse mode easily occurs. However, as shown in FIG. 3, the width of the top 21 of the convex portion in this embodiment is about 1 to 2 μm, and the active layer is thicker on both sides of the groove and curved gently. Therefore, since light leaks to both sides of the convex portion and the change in the effective refractive index is small, no higher-order transverse modes exist. Therefore, stable single mode control is possible with only the basic mode.

The semiconductor laser diode of the present invention further has a forward current of about 100 to 300 for high output operation of laser light.
As mentioned in the operation section, even when a current of about mA is applied, the quaternary layer is also provided in the channel section, so the drop in breakdown voltage of the current blocking layer due to an increase in leakage current is suppressed, and the laser light output is reduced to 1.
It increased linearly from 00 to 200 mW level, making high-power operation possible.

Actual temperature [ FIG. 4 is a longitudinal sectional view of a laser diode showing a second embodiment of the present invention. In this embodiment, a growth layer is added to the first embodiment so that the first layer of buried growth has the same conductivity type, and the same parts are given the same reference numerals. , the explanation thereof will be omitted.

In this example, when forming the current blocking layer 11 in the second stage, a layer 15 of the same conductivity type as the underlying layer is formed, and then a PN junction is continuously formed to solve the problem of high resistance. It is characterized by a structure that suppresses the deterioration of the PN junction, which is the drawback mentioned above.

Next, a method for manufacturing a semiconductor laser diode according to the present invention will be explained.

FIG. 2 is a cross-sectional view for explaining the method of manufacturing a laser diode of the present invention.

First, as shown in FIG. 2, a photoresist is applied to the top surface of the n-type 1nP substrate IO with the (100) plane as the top surface.
This is then selectively etched in a stripe shape with a width of several μm and an interval of 200 to 300 μm, and the width of the top 21 of the mesa convex portion is 0.5 to 2 μm, and the grooves f& are 2 to 5 μm each on both sides of the convex portion. A heavy channel 20 is formed.

After the substrate IO is cleaned, ordinary boat slide liquid phase epitaxial growth is performed. That is,
After arranging the n-type 1nP substrate IO and each layer growth material in a high-purity graphite boat, it was held at approximately 630-670°C for 2-4 hours in a high-purity hydrogen gas atmosphere, and then the cooling rate was 0.3. The n-type 1nGaAsP quaternary mixed crystal is gradually aged at ~0.8°C/mjn, and when the temperature is lowered by several°C, the active layer wavelength composition is controlled to the desired active layer wavelength composition, and the active layer thickness is increased to 120 layers at the top 21 of the convex portion. It is grown so that it becomes 0.05 to 0.15 μm.

The growth conditions are to suppress the degree of supercooling of the solution to an extremely low level and to control it to a quasi-equilibrium state. That is, an important growth condition is to increase the dependence of the growth rate on the plane orientation, so that the solute diffuses to the inclined surface of the convex portion and does not exist near the top 21 of the convex portion.

Furthermore, zinc is added to increase the carrier concentration from 5 to 20X1.
A P-type 1nP layer of 0 [cj] is grown to a thickness of 1 to 3 μm, and a P-type cap layer I5 for electrode formation is grown to a thickness of 0.5 μm.
It is formed by a liquid phase epitaxial growth process of ~3 μm 1-degree. Next, in the wafer manufacturing process, electrodes are formed and
Through the device manufacturing process, by passing a forward current through the semiconductor laser diode, it is possible to obtain a single mode optical output of several mW or more with an oscillation threshold of about several mA, and as the applied current increases, the laser light increases. Increases linearly, several tens of mW-100
A light output of mW can be obtained.

In addition, as shown in Table 1, the manufacturing method in the case where the steps of forming the active layer 13 and the cladding layer 18 are formed by metallurgical vapor phase epitaxy is shown below.

After forming the substrate 10, the substrate 10 placed on a susceptor was introduced into a generally used horizontal or vertical quartz reactor through a cleaning process, and the growth temperature was increased to 600°C.
~650°C1 pressure 10 torr, Java gas flow rate 1~10! The elemental ratio (
Under a carrier and sonis flow rate of (V/I ratio), about 0.05 to 0.15 μm of InGaAsP is deposited on the substrate 10.
A quaternary compound semiconductor layer is grown, and the first cladding layer 12 is successively grown to a thickness of about 0.5 to 1.5 μm.

After the subsequent step of forming the current blocking layer 11, the device is manufactured using the liquid phase epitaxial growth method.

Main sail q effect As explained above, firstly, this invention provides a semiconductor layer with a band gear knob energy difference at the PNPN junction of the current blocking layer, thereby increasing the withstand voltage level of the current blocking layer. The linearity of the applied current vs. output characteristic is approximately 200
It has the effect of being able to maintain up to mW. Second, since the PN junction surface can be formed in a continuous process, it is possible to suppress an increase in leakage current due to deterioration of the junction surface and to provide a highly reliable semiconductor laser diode.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of a semiconductor laser diode according to an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view showing the active layer and cladding layer formed in the first growth step, and FIG. FIG. 2 is a perspective view showing how double stripe grooves are formed on an InP substrate with the 100 plane as the top surface to form a light emitting region and a current path, and FIG. 4 is a perspective view showing a second embodiment of the present invention. FIG. 5 is a vertical cross-sectional view showing the main parts of a conventional semiconductor laser diode. 10... Semiconductor 1nP substrate, ■1... Current blocking layer (n''lnP layer) 12...
...First cladding layer, 13... Active layer (InGaAsP layer), 15.
...First buried layer serving as a current path, 18...
...Clad layer by embedding, 19...
Cap layer, 20... double stripe grooves (channels),
21... Current path, 22... Light emitting region (current injection part). 13 Shizo 1, (p・shizosai T7 paaa・7toko゛′
-44nA to 4L) Figure 2 Figure 21 Figure 3 Figure 1114 (σ) Figure 5 Procedural Amendment (Method) April 11, 1991 1, Indication of Case 1990 Patent Application No. 339893 2, Title of the invention: High power semiconductor laser diode and method for manufacturing the same 3;
Relationship with the case of the person making the amendment Patent applicant: 5 Kansai NEC Corporation, 2-9-1 Seiran, Otsu City, Shiga Prefecture, 520 Subject of amendment (1) The "Detailed Description of the Invention" column of the application specification. (2) “Drawing” 76 attached to the application specification, contents of amendment/(1) Line 1θ of page 13 of the specification is corrected as shown in the attached sheet. (2) Figure 1 on the same drawing as Figure 5 of the drawings attached to the specification
The table is as shown in Table 1 below.
Made by

Claims (2)

[Claims] (1) A single-conductivity type semiconductor substrate that has double striped grooves on both sides and mesa-shaped striped protrusions sandwiched between the double grooves, and has a smaller band gap energy than this substrate. A semiconductor layer of one conductivity type is provided on the entire surface, an active layer as a light emitting region formed flat on the top surface of the convex portion, a reflective conductivity type semiconductor layer as a cladding layer, and adjacent to the active layer, a first current blocking layer of an opposite conductivity type provided to fill the area other than the flat part at the top of the convex portion; a second current blocking layer of one conductivity type; and an opposite conductivity type provided on the active layer. A semiconductor laser diode comprising: a second cladding layer; and a cap layer provided on the second cladding layer. (2) (a) A step of forming mesa-shaped striped convex portions on a semiconductor substrate of one conductivity type; (b) A step of forming an active layer of one conductivity type on the entire surface including the convex portions; c) forming a second cladding layer of opposite conductivity type on the entire surface including the convex portion; (d) forming a current blocking layer of opposite conductivity type and one conductivity type on the portion other than the flat portion at the top of the convex portion; and (e) sequentially forming a second cladding layer of an opposite conductivity type and a cap layer on the entire surface including the active layer, and each of the steps (b) to (e) above. It can be done in one continuous growth step by liquid phase epitaxial growth method, or
Manufacturing a semiconductor laser diode, characterized in that the steps (b) and (c) are formed by metal organic vapor phase epitaxy, and then the steps (d) and (e) are performed by liquid phase epitaxial growth. Method.