JPH0666526B2 - Semiconductor laser diode and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser diode having a current confinement layer capable of operating at a low current and controlling a single oscillation mode, and a method for manufacturing the same. The present invention relates to a semiconductor laser diode capable of realizing the formation of a constriction layer and the formation of a light emitting region layer and the like in a single epitaxial growth step, and capable of high-speed and high-power operation, and a manufacturing method thereof.

2. Description of the Related Art Various structures for realizing low current operation and single mode operation of laser diodes have been proposed and implemented in various places.

For example, 1812 in the magazine “Applied Optics” 1.June (1979).
CPS laser is shown on page (1st literature), TS laser is shown on page pp. 3P-Z-484 (2nd literature), Proceedings of Autumn Society of Applied Physics, 1978, Regarding the internal stripe type laser with a current constriction layer inside the crystal, Spring 1980, Proceedings of the Japan Society of Applied Physics, Paper No. 2a
-G-8 page 158 (3rd document) SML laser is shown,
Furthermore, Proceedings of IEICE Electronic Devices Research Group ED79-5
0,49 (1979) (4th reference) shows a VSIS laser. As a semiconductor laser diode for optical communication, a DC-PBH laser disclosed in "Elcxtron Letter" 18 (1982), page 953 (fifth document) has been put into practical use.

In order to achieve low current and low threshold operation, these laser diodes limit the injection region, and for single-mode control, an active layer with a high refractive index is sandwiched by a clad layer with a low refractive index. In the active layer in the direction parallel to the heterojunction, various stripe structures are formed to adopt the "gradient distribution waveguide type" for confining light by the refractive index difference.

However, in the above-mentioned first and second reference lasers, it is necessary to diffuse stripes of zinc or the like in order to limit the implantation region, and for that purpose, the laser oscillation part and the current passage are required. It is necessary to precisely align the diffusion mask so that and coincide with each other. Further, in the third and fourth reference lasers, in order to form the current confinement layer inside, the path of the confinement layer must be formed in the etching step after the layer growth, and the light emitting region must be formed again in the epitaxial growth step. I have to. This is because the layer grown in the first epitaxial step is oxidized or contaminated in the processing step, a good quality growth layer cannot be formed in the second epitaxial step, and the materials that can be used in the first epitaxial step are limited. It becomes a big design constraint.

Further, in the laser diode of the fifth document which has been put into practical use as a laser diode for optical communication, the Inp system, which is a material in which the layer is relatively oxidized in the first epitaxial step, is used, and a double diode is used as a light emitting region. In order to form a heterojunction structure, and then to form a current injection region inside the double channel, an internal stripe is formed by a photoresist etching process, and then a current confinement layer is buried and grown in a second epitaxial process. is doing. Furthermore, in recent years, an example in which a semi-insulating layer is used as a current confinement layer of the DC, PBH laser of the fifth document has been published in a magazine “Applied Physics Le”.
tters "48 (23) 9.June 1986, page 1572 (6th document), but like the 5th document, it must undergo two growth steps.

As described above, in the conventional technique, the light emitting region and the current injection region are formed in separate steps. That is, the method of the first, second, fifth, and sixth literatures in which the light emitting region is formed first and the current injection region is formed later, and the constriction region for current injection is formed first, and the light emission is performed later. There are 3rd and 4th methods to form areas,
Since both are formed by a two-step epitaxial growth process, high process capability is required in order to prevent a decrease in yield. Further, since the manufacturing process is complicated and the time is long, the manufacturing cost is significantly increased and the productivity is poor.

As a problem in device characteristics, the conventional current constriction blocks the current (hole) by blocking the reverse bias barrier of the PN junction and blocks conduction. Therefore, when the applied current increases, the leakage current component also increases. , The internal efficiency decreases. In the case of the DC, PBH laser diode of the fifth document, the thyristor of the PNPN junction in the constriction turns on and becomes conductive, and the optical output is saturated / decreased. Therefore, the current in single mode −
There is a drawback that the linearity of the light output characteristic is lost and high output operation cannot be performed.

Means for Solving the Problems In order to solve the above-mentioned conventional technique, the present invention adopts a semi-insulating layer as a current confinement layer for forming a current injection region, and the semi-insulating layer is used in a single liquid phase epitaxial process. It has a structure and a manufacturing method that enable formation of a current confinement region and a light emitting region.

The semiconductor laser diode of the present invention is provided on the surface of a semiconductor substrate having a mesa-type stripe-shaped convex portion sandwiched in a double-stripe-shaped groove on the surface of the substrate and a portion of the substrate excluding the flat top portion of the convex portion. A first semi-insulating layer, an active region made of a material having the same conductivity type as that of the substrate and having a bandgap smaller than that of the substrate, and the first semi-insulating layer provided on the first semi-insulating layer; A second semi-insulating layer having the same bandgap as the adjacent substrate, a clad layer having a different conductivity type and the same bandgap from the substrate adjacent to the convex active region, and a second semi-insulating layer provided on the convex active region. And a cap layer.

The method for manufacturing a semiconductor laser diode of the present invention comprises forming a mesa-shaped stripe-shaped convex portion sandwiched between double stripe-shaped grooves on a semiconductor substrate of one conductivity type, and using a boat slide type liquid phase epitaxial growth method to form the mesa-shaped stripe-shaped convex portion. A step of forming a semi-insulating layer to which iron (Fe) or cobalt (Co) is added as a current confinement layer except the flat portion on the top of the convex portion, and one conductivity type active layer on the entire surface including the convex portion. In the step of forming a layer and on the portion except the flat portion on the top of the convex portion (c)
Similar to the step, it includes a step of forming a second current narrowing layer and a step of sequentially forming a clad layer and a cap layer of opposite conductivity types.

By the manufacturing method of the above means, the semi-insulating layer is formed on the portion excluding the stripe-shaped convex portion, and the active layer and the clad layer are formed on the flat surface on the top of the convex portion to form the injection current confinement layer. Is eliminated, the injection current density is increased, the oscillation threshold of the semiconductor laser diode is lowered, and low current operation becomes possible. Further, even if the applied current is increased, it does not turn on, so that a high output operation up to about 150 to 200 mw level, which is the optical output up to the optical damage to the reflecting surface of the laser diode, becomes possible.

EXAMPLES 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 a manufacturing process of a current constriction portion. In this embodiment, as shown in FIG. 2, a double stripe groove (double channel) 20 and a mesa-shaped convex portion sandwiched by these stripe grooves 20 are formed on a semiconductor substrate 10. The first semi-insulating layer 11, the active layer 12, the second semi-insulating layer 13, the second cladding layer 14, and the cap layer 15, which are current confinement layers, are continuously formed on the substrate 10 in one epitaxial growth step. Are sequentially formed.

In the present embodiment, in the grooves 20 on both sides of the convex portion, the current is confined by the first and second semi-insulating layers 11 and 13, and the current flows only in the top portion 21 of the mesa convex portion.

Regarding the controllability of the transverse mode, generally, the effective refractive index Neff of the active layer becomes smaller as the layer thickness becomes thinner, and the active layer easily leaks. Further, when the rate of change of Neff of the active layer increases in the direction parallel to the junction, the effect of confining light increases, and when the emission spot size becomes 2 to 3 μm or more, a higher-order transverse mode easily occurs. However, as shown in FIG.
The width of the apex 21 of the convex portion of this embodiment is about 1 to 2 μm, and the thickness of the active layer is thicker on both sides of the groove and is gently curved. Therefore, light leaks to both sides of the convex portion and the change in the effective refractive index is small, so that the higher-order transverse modes do not exist. Therefore, only the basic mode is available and stable single mode control is possible.

From this, a transverse mode controlled high power laser is proposed as a second embodiment. That is, even if the width of the apex 21 of the convex portion is expanded to 2 to 4 μm, if the active layer is gently curved as in the present embodiment, the higher order mode does not occur, so that the injection level is further increased and the efficiency is high. It enables high power semiconductor laser diodes.

As for the low current operation, as described in the above [Operation], the implementation of the present invention makes it possible to reduce the leakage current to the utmost limit, and enables the high output operation with a low oscillation threshold. .

Next, a method of manufacturing the semiconductor laser diode of the present invention will be described.

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

First, as shown in FIG.
Photoresist is applied to the upper surface of the InP substrate 10, and is selectively etched in a stripe shape with a width of several μm and an interval of 200 to 300 μm. The width of the top 21 of the mesa protrusion is 0.5 to 2 μm.
Then, double channels 20 having a groove width of 2 to 5 μm are formed on both sides of the convex portion.

Then, after the substrate 10 is washed, the ordinary boat slide method liquid phase epitaxial growth is performed. That is, the n-type InP substrate 10 and the high-purity graphite boat,
After arranging the materials for growing each layer, after keeping them in a high-purity hydrogen gas atmosphere at about 630 to 670 ° C. for 2 to 4 hours, gradually cooling at a cooling rate of 0.3 to 0.8 ° C./min, and lowering the temperature by several ° C. , The first semi-insulating layer 11. Iron or cobalt 0.3 to
The growth solution added with 0.1 [atom%] is brought into contact with the substrate 10 to grow the first Inp semi-insulating layer 11 having a specific resistance of 10 Ω ⁵ cm or more on a portion other than the top 21 of the convex portion. This growth condition is to control the supercooling degree of the solution to be extremely small and to control it in a quasi-equal state. That is, it is an important growth condition that the growth rate dependence of the plane orientation is strengthened so that the solute is not diffused to the inclined surface of the convex portion and allowed to exist near the peak 21 of the convex portion.

Next, as shown in FIG. 3, by controlling the n-type InGaAsP quaternary mixed crystal to a desired active layer wavelength composition, the active layer 12 at the peak 21 of the convex portion is controlled.
Is grown to a layer thickness of 0.05 to 0.15 μm.

Further, under the same growth conditions as the first semi-insulating layer 11, the second semi-insulating layer 13 is grown to a portion other than the convex portion, and then zinc is added to form the second cladding layer 14. A P-type Inp layer having a concentration of 5 to 20 × 10 ¹⁷ [cm ⁻³ ] is grown to 1 to 3 μm, and a P-type cap layer 15 for forming an electrode is formed to a thickness of 0.1 μm.
5 to 3 μm, formed in a single liquid phase epitaxial growth step. Then, through the wafer manufacturing process, electrodes are formed, and further, through the device manufacturing process, a forward current is applied to the resulting semiconductor laser diode, and the oscillation threshold is several mA at several mA.
The above single-mode light output can be obtained, and when the applied current is increased, the laser light linearly increases, and the light output of several tens mW to 100 mW can be obtained.

Effects of the Invention The effects of the present invention are as follows.

(A) Since the current confinement stripe is provided on the convex portion of the substrate, it is not necessary to precisely align the mask position for forming the stripe for limiting the current injection area with the light emitting area. Therefore, the instability of the oscillation mode due to the asymmetry of the injected carrier density distribution caused by the shift between the injection region and the light emitting region is eliminated, and the single mode control can be easily realized.

(B) Since the semi-insulating layer is adopted as the current confinement layer, the leakage current component can be suppressed to the utmost limit, and both reduction of the oscillation threshold and high output operation can be realized at the same time.

(C) The so-called “twice epi” in which the current constriction region forming step is interposed between the epitaxial growth steps is eliminated, and the intended purpose can be achieved by one epitaxial growth step.

(D) Since the semi-insulating layer controls the capacitance of the device, high speed operation is possible.

Therefore, the yield can be greatly improved in the manufacturing process, and the growth apparatus and the growth man-hours can be reduced by half, resulting in extremely high mass productivity.

As is apparent from the above description, according to the present invention, a single mode semiconductor laser diode which operates at a high output with a low threshold value can be obtained with high productivity.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a semiconductor laser diode according to an embodiment of the present invention, and FIG. 2 is a plan view of the InP substrate with the (100) plane of FIG. In the area,
FIG. 3 is a perspective view in which a semi-insulating layer for current confinement is formed by liquid phase epitaxial growth, and FIG. 3 is an enlarged sectional view of a main part of the diode in FIG. 10 ... Semiconductor (InP) substrate, 11 ... First semi-insulator (InP or InGaAsp quaternary mixed crystal) layer, 12 ... Active layer, 13 ... Second semi-insulator (InP or InGaAsp quaternary) (Mixed crystal) layer, 14 ... second cladding layer, 15 ... cap layer, 16 ... current confinement and emission region, 20 ... double stripe groove (channel), 21 ... top of mesa protrusion.

Claims (2)

[Claims] 1. A one-conductivity-type semiconductor substrate having a mesa-type stripe-shaped convex portion sandwiched between double stripe-shaped grooves, and a portion of the convex portion excluding a flat top portion of the convex portion so as to fill the groove. A first current confinement layer of a semi-insulating material, an active layer of one conductivity type having a bandgap smaller than that of the substrate, which is provided on the first current confinement layer, and adjacent to the active layer, except for the flat top portion of the convex portion. A second current confinement layer of a semi-insulating material that is provided so as to fill the groove in a portion, a clad layer of opposite conductivity type provided on the active layer, and a cap layer provided on the clad layer A semiconductor laser diode comprising: 2. A step of: (a) forming a mesa-shaped stripe-shaped convex portion sandwiched between double-stripe-shaped grooves on a semiconductor substrate of one conductivity type; and (b) excluding a flat portion on the top of the convex portion. A step of forming a current confinement layer of a semi-insulating compound semiconductor layer of Inp using a solution containing iron or iron or cobalt, and (c) forming an active layer of one conductivity type on the entire surface including the convex portion. A step of forming the second current confinement layer on the active layer except the flat portion on the top of the convex portion (d) in the same manner as the step (c); And a step of sequentially forming a clad layer and a cap layer of opposite conductivity type, wherein each of the steps (b) to (e) is performed in one continuous growth step by a liquid phase epitaxial growth method. Manufacturing method of laser diode.