KR100287207B1 - Semiconductor laser device and its manufacturing method - Google Patents

Abstract

PURPOSE: A semiconductor laser device and a manufacturing method thereof are provided to enhance the focusing efficiency of current by shielding the flow of current through a schottky barrier on the active layer and by shielding the flow of current through a reverse junction under the active layer. CONSTITUTION: A channel stripe of recessed shape having a flat bottom and inclined portions is formed on a first conductive type substrate(11). A buffer layer(12) is formed on the substrate while maintaining the recessed shape. A lower clad layer(13) is formed on the buffer layer while maintaining the recessed shape, and has first conductivity in the bottom and outside of the inclined portions and second conductivity on the inclined portions. An activation layer(14) is formed on the lower clad layer while maintaining the recessed shape. A second conductive type upper clad layer(15) is formed on the activation layer while maintaining the recessed shape. A cap layer(17) is filled in the recess of the upper clad layer for ohmic contact. A second conductive type metal electrode layer(18) is formed on the cap layer and the exposed upper clad layer, and forms a schottky barrier at a contact surface with the upper clad layer.

Description

Semiconductor laser device and manufacturing method thereof

1 is a cross-sectional view showing a conventional refractive index waveguide laser diode.

2 is a cross-sectional view showing an example of a refractive index waveguide semiconductor laser diode according to the present invention.

(A)-(c) is sectional drawing which shows an example of the manufacturing method of the semiconductor laser diode by this invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device and a method for manufacturing the same, and more particularly, to a refractive index waveguide semiconductor laser device widely used as a light source for recording and reproducing a high density optical recording device, and a method for manufacturing the same.

In general, in the thermal equilibrium state of the material, the absorption of photons in a state where the energy level is higher than that of induction emission occurs, but it can be brought to a negative temperature state in which natural emission exceeds absorption by a certain method.

The laser generates light and oscillates using this negative temperature state, and is characterized by coherence, unipolarity, directivity, and high intensity. Helium (He-Ne) There are various types ranging from lasers, gas lasers such as argon (Ar) lasers, and solid state lasers such as YAG lasers and ruby lasers, to semiconductor lasers which can be easily modulated by deflecting bias current at a small size and high frequency.

In particular, the semiconductor laser diode is a semiconductor device that includes the concept of quantum electrons based on PN junctions, and artificially induces electron-hole recombination by injecting a current into a thin film made of a semiconductor material, that is, an active layer. By doing so, the principle is to emit light corresponding to the reduced energy of recombination. Due to the above characteristics, it is expanding the application range by replacing conventional gas lasers such as helium-neon as information processing equipment such as compact disc player (CDP), optical memory, high speed laser printer, and optical communication equipment. .

In particular, in order for the semiconductor laser device to be used as a light source of the above-described optical recording device, the oscillation and astigmatism distance of the stable basic mode must be small, which is made possible by the device of the refractive index waveguide structure.

1 is a cross-sectional view showing a refractive index waveguide semiconductor laser diode of a conventional SBR (Selectively Buriedl Ridge) structure using AlGaInPrP-based semiconductor materials.

Referring to FIG. 1, an N-type AlGaInP lower cladding layer 2 is formed on an n ⁺ GaAs substrate 1 via an n GaAs buffer layer 2, and on the lower cladding layer 3, a GaInP active layer ( 4) is thinly formed. On the active layer 4, a p-type AlGaInP upper clad layer 5 is formed in which a stripe ridge is formed at the center thereof. An n ⁺ GaAs current blocking layer 7 is formed on the upper cladding layer 5 while contacting the sidewall of the ridge structure. A p-type GaInP conducting layer 6 is formed on an upper surface of the ridge, and a p ⁺ GaAs cap layer 8 is formed on the conducting layer 6 and the current blocking layer 7 of the ridge structure. have. In addition, the cap layer 8 is connected to the p-type metal electrode 9, the n-type substrate 1 is connected to the n-type metal electrode 10 to complete the diode structure.

Looking at the process of manufacturing the laser diode of the SBR structure as follows.

First, an n-type buffer layer 2, a lower cladding layer 3, an active layer 4, an upper cladding layer 5, and a conductive transfer layer 6 are first grown on the n-type substrate 1. To form sequentially.

Subsequently, after forming a silicon oxide (SiO ₂ ) layer on the entire surface of the current transfer layer 6, a silicon oxide pattern for forming a ridge stripe is formed by a conventional photolithography technique. Subsequently, using the silicon oxide pattern as an etch mask, a part of the current transfer layer 6 and the upper cladding layer 5 is etched to form a ridge stripe at the center of the upper cladding layer 5.

Subsequently, the current blocking layer 7 is formed by selective regrowth on the upper clad layer 5 of the ridge periphery. Subsequently, after removing the silicon oxide pattern, the cap layer 8 is formed by crystal growth.

Subsequently, a p-type metal electrode 9 is deposited on the cap layer 8 by a common method, and an n-type metal electrode 10 is deposited and connected to the n-type substrate 1.

In the laser diode of the SBR structure, optical waveguides having a low-wavelength waveguide are realized by an effective refractive index difference in the lateral direction of the active layer.

However, in the prior art, since the substrate exposed to air is oxidized during regrowth for forming the current blocking layer 7, the crystallinity of the regrown layer is lowered.

In addition, in the conventional structure, a step caused by the ridge stripe occurs on the surface of the substrate, so that die bonding becomes difficult.

In addition, in the structure of the conventional semiconductor laser device, when openings are formed in an insulating film such as a silicon oxide pattern or an aluminum oxide film used as an etching mask for forming the ridges to deposit ohmic metal on the ridges, the openings are formed. It is very difficult to align correctly, the opening area is too small, the contact resistance is large, and the electrical characteristics are degraded. The resulting heat also reduces the efficiency and reliability of the device. SUMMARY OF THE INVENTION In order to solve the problems of the prior art described above, the present invention is advantageous for basic mode oscillation having an optical waveguide structure of a bent wave guide type to provide a refractive index waveguide semiconductor laser device having a small astigmatism distance. The purpose is.

In addition, the present invention provides a semiconductor laser device in which current flow is blocked by a Schottky Barrier on the active layer, and current flow is blocked by reverse junctions under the active layer, thereby improving current focusing efficiency. The purpose is to provide.

It is a further object of the present invention to provide a suitable method for manufacturing the semiconductor laser device of the present invention by primary epitaxy process.

In order to achieve the above object of the present invention, the semiconductor laser device of the present invention,

A first conductive type substrate having a concave channel stripe having a flat bottom portion and an inclined portion in a central upper portion thereof;

A buffer layer formed on the substrate while maintaining the shape of the recess;

A lower clad layer formed on the buffer layer while being formed in a first conductivity type on the bottom portion and an inclined portion outer portion while maintaining the shape of the concave portion;

An active layer formed on the lower clad layer while maintaining the shape of the recess;

An upper cladding layer of a second conductivity type formed on the active layer while maintaining the shape of the recess;

A cap layer for ohmic contact filled in the recess of the upper clad layer; And

And a second conductive metal electrode layer formed on the cap layer and the exposed upper clad layer and forming a Schottky barrier at the contact surface with the upper clad layer.

As a specific type of the present invention, the current transfer layer is formed in the recess of the upper cladding layer while maintaining the shape of the recess, and the cap layer is formed in the recess of the current transfer layer. desirable.

In addition, in order to achieve the above another object of the present invention, the manufacturing method of the semiconductor laser device of the present invention,

Forming a concave channel stripe having a flat bottom portion and an inclined portion on the center of the first conductive substrate;

Forming a buffer layer on the substrate to maintain the recess shape;

Forming a lower clad layer on the buffer layer so as to be of a first conductivity type on the bottom surface and an inclined portion outer side and to be of a second conductive type on the inclined portion;

Sequentially forming an active layer, an upper cladding layer of a second conductive type, and a cap layer for ohmic contact while maintaining the concave portion shape on the lower cladding layer;

Etching a portion of the cap layer to expose only an upper clad layer other than the recessed portion so as to be filled only in the recessed portion of the upper clad layer; And

And forming a second conductive metal electrode layer on the cap layer and the exposed upper clad layer to form a Schottky barrier at the contact surface with the upper clad layer.

As a specific type of the present invention, the formation of the subsequent buffer layer, lower clad layer, active layer, upper clad layer and cap layer while maintaining the shape of the concave portion of the substrate may be carried out by organometallic vapor phase deposition (MOCVD) or molecular beam epitaxy ( It is preferable to set it as the primary epitaxy process by the vapor phase growth method, such as MBE method. In particular, the step of forming the lower cladding layer on the buffer layer to be of the first conductivity type on the bottom surface and the inclined portion outer side while maintaining the shape of the concave portion, and to form a second conductive type on the inclined portion is MOCVD method. In this paper, a technique of simultaneously doping n-type and p-type impurities is used. In the MBE method, a technique using a characteristic of the amphoteric behavior of doped silicon is used.

In addition, in the step of etching the cap layer, it is preferable that the cap layer filled in the concave portion of the upper clad layer and the upper cladding layer forms a flat surface with each other.

In addition, as another specific type of the present invention, in the step of forming the upper cladding layer by the first epitaxy process, after forming the upper cladding layer, further comprising the step of forming a current passivation layer is preferable in view of the characteristics of the current flow In this case, in the step of etching the cap layer is characterized in that the conductive layer is also etched together so as to remain only in the recess.

In the structure of the present invention, an electric current flows through ohmic contact between the second conductive metal electrode layer and the cap layer, while a Schottky barrier is formed between the second conductive metal electrode layer and the upper clad layer so that the current flows. The current flows only to the channel portion, and under the active layer, reverse bias is applied to the inclined portion by the pn junction formed in the transverse direction of the lower clad layer, thereby blocking the flow of the current. Therefore, the current flow is restricted both above and below the active layer, and thus the device efficiency is excellent and high output operation is possible.

In addition, since the energy band gap of the active layer formed on the inclined portion is larger than that of the active layer formed on the flat bottom portion under the influence of the inclined portion of the concave portion, the confinement of the current is improved, thereby improving the efficiency of the device. In addition, the structure is advantageous for basic mode oscillation because it performs the vent waveguide type optical waveguide, and the astigmatism distance is very small.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is a cross-sectional view showing an example of a semiconductor laser diode according to the present invention, which will be described in more detail on the basis of an example applied to a semiconductor compound of InGaP / InGalP system.

That is, a concave channel stripe having a flat bottom portion and an inclined portion is formed in the center upper portion of the n-type GaAs substrate 11, and the n-type GaAs is sequentially maintained while maintaining the concave portion shape on the substrate 11. The laser oscillation structure of the double hetero structure which consists of the buffer layer 12, the InGaAlP lower cladding layer 13, the InGaP active layer 14, and the p-type InGaAlP upper cladding layer 15 is formed.

On the other hand, the lower clad layer 13 maintains the concave portion shape on the buffer layer 12, and n-type impurities are injected onto the bottom surface portion and the inclined portion outer portion, and p is formed on the inclined portion 20. It is formed in a mold.

In the concave portion of the upper cladding layer 15, a p-type InGaP conducting layer 16 and a p-type GaAs cap layer 17 are flat with the exposed upper cladding layer 15 other than the concave-shaped channel stripe. And a Schottky barrier at the contact surface with the upper clad layer 15 on the recessed portions filled with the conductive layer 16 and the cap layer 17 and the exposed upper clad layer 15. The p-type metal electrode layer 18 is formed. In addition, an n-type metal electrode layer 19 is formed on the n-type substrate 11 to complete the device structure.

In the laser diode of the present invention, a so-called Schottky barrier is used as the current blocking means on the top of the active layer 14. The junction formed by the metal and the exogenous semiconductor is either rectifying or non-rectifying, the former being at the contact surface of the p-type metal electrode layer 18 and the upper cladding layer 15 which is used as a barrier for current blocking in the present invention. The latter is a Schottky junction formed, the latter being an ohmic contact formed at the contact surface of the metal electrode layer 18 and the cap layer 17.

In general, when a metal and an n-type semiconductor make a Schottky junction, the barrier to electrons flowing from the metal layer to the semiconductor side through the junction is determined by the difference between the work function of the metal and the electron affinity of the semiconductor.

On the other hand, when the junction is made of metal and p-type semiconductor, the hole flow is the center, so the Schottky barrier is made by the difference between the Fermi level of the metal, the vacuum level on the semiconductor side, and the energy on the top of the valence band. According to the Mead's Rule, in the case of a p-type semiconductor, the height of the Schottky barrier corresponds to 1 / 3Eg, so that the semiconductor having a large energy band gap increases the height of the Schottky barrier.

Therefore, in the present invention, InGaP having a larger energy band gap than the InGaAlP upper cladding layer 15 is used to sufficiently increase the height of the Schottky barrier between the p-type metal electrode layer 18 and the upper cladding layer 15. Semiconductor materials, such as these, can also be used.

On the other hand, the active layer 14 may be formed as a single layer, but the difference in energy bandgap between the active layer and the cladding layer is not large, so that carriers injected into the active layer easily flow into the cladding layer, thereby driving the device current. Due to the high value and the difficulty of oscillation at high temperature, techniques for introducing a multi-quantum well (MQW) structure or a multi-quantum barrier (MQB) structure in the active layer have been known. In the structure, the height of the hetero-barrier is increased, so that the above problems are improved, and thus, these structures may be formed.

Hereinafter, an example of a method of manufacturing a refractive index waveguide semiconductor laser diode according to the present invention will be described with reference to FIGS. 3A to 3C. Like reference numerals in FIG. 2 denote like elements.

FIG. 3A illustrates a step of forming a concave channel stripe having a flat bottom portion and an inclined portion in the center upper portion of the substrate 11.

3B illustrates a buffer layer 12, a lower cladding layer 13, an active layer 14, an upper cladding layer 15, an electricity transfer layer 16 and an ohmic contact on the substrate 11. A step of sequentially forming the cap layer 17 to maintain the shape of the recess is shown. That is, the concave shape is continuously maintained by a first epitaxy process such as a vapor phase growth method, for example, an organometallic vapor phase growth method (MOCVD method) or a molecular beam epitaxy method (MBE method).

At this time, while maintaining the shape of the recessed portion on the buffer layer 12, the bottom cladding layer is formed to be n-type on the bottom surface and the inclined portion, the p-type on the inclined portion 20. In the MOCVD method, a technique of simultaneously doping n-type impurities and a p-type impurity is used, and in the MBE method, a technique using a characteristic of the amphoteric behavior of doped silicon is performed.

FIG. 3C illustrates a portion of the transfer layer 16 and the cap layer 17 that are etched so as to be filled only in the recesses of the upper cladding layer 15, and thus the upper cladding layer 15 other than the recesses. Exposing step. In this case, it is not only excellent in step characteristics that the exposed upper clad layer 15, the filled conductive layer 16, and the cap layer 17 are kept flat with each other through a normal photolithography process and a wet etching process. Subsequent diebonding can be done as well. This also works advantageously for quickly releasing heat generated in the active layer.

Subsequently, a Schottky barrier can be formed at the contact surface with the upper clad layer 15 on the recess filled with the conductive layer 16 and the cap layer 17 and the exposed upper clad layer 15. When the metal electrode layer 18 into which the p-type impurity is implanted is deposited, and the n-type metal electrode layer 19 is deposited on the n-type substrate 11, the vent waveguide structure as shown in FIG. 2 is formed. The refractive index of the waveguide semiconductor laser diode structure is completed.

As described in the above embodiments, in the structure of the laser device of the present invention, the current flows through ohmic contact between the spiral p-type metal electrode layer 18 and the cap layer 17, while the p-type metal electrode layer 18 ) And a schottky barrier is formed between the upper cladding layer 15 to block the flow of current so that the current flows only to the channel portion, and under the active layer 14, the flat bottom portion and the inclined portion of the lower cladding layer 13 are different from each other. The pn junction, which is electrically conductive and is formed in the transverse direction, receives a reverse bias on the inclined portion to block the flow of current. Therefore, the flow of current is limited both above and below the active layer, so that the efficiency of the device is excellent and high output operation is possible.

In addition, since the energy band gap of the active layer formed on the inclined portion is larger than that of the active layer formed on the flat bottom portion under the influence of the inclined portion of the concave portion, the confinement of the storage becomes good and the efficiency of the device is improved.

In addition, the structure is advantageous to the basic mode oscillation because it performs the bent waveguide type optical waveguide, and the astigmatism distance is very small, it is suitable to be used as a light source of the application.

In addition, according to the present invention, since the fabrication of the device is completed only by the primary epitaxy, the problem that the crystallinity is lowered by regrowth does not occur, thereby improving the efficiency and reliability of the device and improving productivity.

The invention is not limited to the above embodiment, for example, in addition to the InGaP / InGaAlP-based, the technical gist of the claims hereinafter claimed as the active layer can be applied as long as its characteristics allow, such as InGaAs, clad layer InGaP or InGaAlP It will be readily apparent to those skilled in the art that many variations of the material can be made within the scope of the invention.

Claims (10)

A first conductive type substrate having a concave channel stripe having a flat bottom portion and an inclined portion in a central upper portion thereof; A buffer layer formed on the substrate while maintaining the shape of the recess; A lower clad layer formed on the buffer layer while being formed in a first conductivity type on the bottom portion and an inclined portion outer portion while maintaining the shape of the concave portion; An active layer formed on the lower clad layer while maintaining the shape of the recess; An upper cladding layer of a second conductivity type formed on the active layer while maintaining the shape of the recess; A cap layer filled in a recess of the upper clad layer; And And a second conductive metal electrode layer formed on the cap layer and the exposed upper clad layer and forming a Schottky barrier at the contact surface with the upper clad layer and in ohmic contact with the cap layer. device. The electricity transfer layer is further formed inside the recess of the upper clad layer while maintaining the shape of the recess, and the cap layer is formed in the recess of the electricity transfer insect. Semiconductor laser device. The semiconductor laser device according to claim 1, wherein the material of the active layer / clad layer is one selected from the group consisting of InGaAs / InGaAlP, InGaP / InGaAlP, and InGaAs / InGaP. Forming a concave channel stripe having a flat bottom portion and an inclined portion on the center of the first conductive substrate; Forming a buffer layer on the substrate to maintain the recess shape; Forming a lower clad layer on the buffer layer so as to be of a first conductivity type on the bottom surface and an inclined portion outer side and to be of a second conductive type on the inclined portion; Sequentially forming an active layer, an upper cladding layer of a second conductive type, and a cap layer for ohmic contact while maintaining the concave portion shape on the lower cladding layer; Etching a portion of the cap layer to expose only an upper clad layer other than the recessed portion so as to be filled only in the recessed portion of the upper clad layer; And And forming a second conductive metal electrode layer on the cap layer and the exposed upper clad layer to form a schottky barrier at the contact surface with the upper clad layer. The method of claim 4, wherein the forming of the buffer layer, the lower clad layer, the active layer, the upper clad layer, and the cap layer while maintaining the shape of the concave portion of the substrate is performed by primary epitaxy by organometallic vapor phase deposition (MOCVD). Method for manufacturing a semiconductor laser device, characterized in that carried out by the step. 6. The lower clad layer according to claim 5, wherein the lower clad layer is formed on the buffer layer so as to have a first conductivity type on the bottom surface and an inclined portion outer side, and on the inclined portion, a lower clad layer. The method of manufacturing a semiconductor laser device, characterized in that performed by the simultaneous doping (simultaneous doping) n-type impurities and p-type impurities. The method of claim 4, wherein forming the buffer layer, the lower clad layer, the active layer, the upper clad layer, and the cap layer while maintaining the shape of the concave portion of the substrate is performed by a primary epitaxy process by a molecular beam epitaxy method (MBE method). Method of manufacturing a semiconductor laser device, characterized in that performed by. The method of claim 7, wherein the lower cladding layer is formed on the bottom of the bottom portion and the inclined portion while the shape of the recess is formed on the buffer layer, and the lower cladding layer is formed on the inclined portion to form a first conductive type. Is performed using a technique utilizing the characteristics of the amphoteric behavior of doped silicon. The method of manufacturing a semiconductor laser device according to claim 4, further comprising forming a passivation layer while maintaining the shape of the recess after forming the upper clad layer. The method of claim 9, wherein the passivation layer is etched together such that the passivation layer also remains in the recess in the etching of the cap layer.