KR940011275B1 - Laser diode and manufacturing method the same - Google Patents

Abstract

A laser diode includes a first conductive semiconductor substrate, insulating layers formed in stripe on a predetermined portion of the substrate, a first clad layer having reverse mesa shape, which is formed on a portion of the substrate in which the insulating layer is not formed, an active layer formed on the first clad layer, a second clad layer having flat surface, which is formed on the active layer, triangle-shape voids formed on the active layer, which is formed due to the reverse slope of the active layer, a cap layer formed on the second clad layer, a second conductive electrode formed between the voids placed on the cap layer, and a first conductive electrode formed on the back surface of the substrate.

Description

Laser diode and manufacturing method

1 is a cross-sectional view of a conventional VSIS type laser diode.

2 is a cross-sectional view of the laser diode according to the invention.

3 (a) to 3 (c) are manufacturing process diagrams of the laser diode according to the present invention.

The present invention relates to a laser diode and a method for manufacturing the same, and more particularly, to a laser diode and a method for manufacturing the same, which can be easily formed by crystal growth at a time without an etching process and are easily controlled.

In general, a laser diode (hereinafter referred to as LD) generates light by recombination of electrons and holes near a PN junction of a semiconductor, and is also called a semiconductor laser.

A light emitting diode (LED) used as a general display device emits light generated naturally, whereas LD emits light by induced emission, and thus has coherence and directionality. In addition, LD is smaller than general lasers such as solid state lasers and gas lasers, and has high efficiency, and is used for information processing devices such as optical communication and optical disk memory due to the characteristics of direct modulation of light. The field of use is expanding.

LD is classified into a gain guiding method and an index guiding method according to an operation mode. The gain guiding method limits a region having a high current density structurally from the outside to emit light only in the region. However, the LD of the gain guiding method emits light in a region having a high current density but is weak in a region having a low current density, but emits light, so it is difficult to obtain a recognized lateral mode. In the index guiding method, a stable horizontal mode may be obtained because light emitted as a current flows into a region having a high refractive index according to a difference in refractive index.

1 is a vertical cross-sectional view of a conventional VSIS (V-channel Substrate Inner Stripe) LD. The VSIS type LD is operated by an index guiding method.

In the VSIS type LD, an N-type GaAs current limiting layer 13 is formed on the surface of the P-type GaAa semiconductor substrate 11. The semiconductor substrate 11 and the current limiting layer 13 are mesa-etched to form a V-channel in a stripe shape. In addition, the first cladding layer 15 of P-type Al _y Ga _1-y As, the active layer 17 of P-type Al _X Ga _1-X As, and N-type Al on the current limiting layer 13. A second cladding layer 19 of _y Ga _1-y As and a cap layer 21 of N ⁺ type GaAsdml are sequentially formed. In this case, the first cladding layer 15 fills the V channel and is electrically connected to the semiconductor substrate 11. In addition, an insulating film 23 is formed on the cap layer 21 except for a portion corresponding to the V channel. An N-type electrode 25 is formed on the insulating layer 23 to contact an exposed portion of the cap layer 21, and the P-type electrode 26 is formed on the lower surface of the semiconductor substrate 11. have.

In the VSIS type LD having the above-described structure, when a voltage is applied between the P-type electrode 26 and the N-type electrode 25, holes are injected into the active layer 17 through the first cladding layer 15. Electrons are injected into the second cladding layer 19 through the fin layer 21 to recombine the electrons and holes in the active layer 17 to generate light. At this time, holes are injected only into the openings of the semiconductor substrate 11 in which holes are exposed to the V channel by the current limiting layer 13. The output mode of light and the threshold current are controlled by the size of the aperture width. Thus, the aperture width is reduced to keep the threshold current low while keeping the light output mode stable. In addition, the light generated in the above is limited to the active layer 17, and thus, in order to operate in an index guiding manner, an energy bandgap is formed in the active layer 17 than the first and second cladding layers 15 and 19. It has a compound composition ratio so that it is small and its light refractive index is large. The condition of the composition ratio is 1 y x 0 must be satisfied.

In addition, the above-described conventional VSIS type LD melt-back to remove the natural oxide film and impurities formed on the surface of the current blocking layer when forming the V channel to form a current path and then crystallized thereon. Method was used.

However, when melt back by liquid epitaxy, there is a problem in that the impurity is not completely removed but acts as an impurity or generates defects in the suited layers, thereby lowering reliability and yield.

Accordingly, an object of the present invention is to provide an LD in which the emitted light has a stable horizontal beam.

Another object of the present invention is to provide an LD which is formed by one-step crystal growth without an etching process for forming a region for limiting emitted light.

Another object of the present invention is to provide a method for producing the above-described LD.

In order to achieve the above objects, the present invention provides a laser diode in which a semiconductor substrate is doped with a high concentration of impurities of a first conductivity type on a predetermined crystal surface, and the surface of the semiconductor substrate is formed at a predetermined angle with a mitter frit at a predetermined portion. Insulating films formed in a stripe shape spaced apart from each other, a first cladding layer having an inverted mesa type doped with a first conductivity type impurity on a surface of a semiconductor substrate on which the insulating film is not formed, and a surface of the first cladding layer A second clad layer formed on the surface of the active layer, the second cladding layer formed on the surface of the active layer and doped with an impurity of a second conductivity type having a flat surface, and a triangular void formed by the reverse slope of the active layer on the insulating layer; And a cap layer formed on the surface of the second clad layer and doped with a high concentration of impurities of a second conductivity type, and a void on the cap layer. This formed the second conductivity type electrode, and is characterized in that it comprises a first conductive electrode formed on a lower surface of the semiconductor substrate.

In order to achieve the above object, the present invention provides a method of manufacturing a laser diode, wherein the insulating film has a predetermined crystal plane and a stripe-shaped insulating film formed at a predetermined angle with a major frit on the surface of a semiconductor substrate doped with a high concentration of impurities of a first conductivity type. A first step of forming a film, a second step of forming a first cladding layer doped with an impurity of a first conductivity type on a surface of the exposed semiconductor substrate in an inverted mesa shape, and an active layer on the surface of the first cladding layer And a fourth step of forming a second cladding layer doped with impurities of a second conductivity type having a flat surface where reverse inclined surfaces meet on the surface of the active layer, and on the surface of the second cladding layer. A fifth step of forming a cap layer doped with a high concentration of impurities of a second conductivity type, a sixth step of forming a second conductivity type electrode between the voids on the cap layer, and the semiconductor And a seventh process of forming the first conductivity type electrode on the lower surface of the substrate portion.

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

2 is a cross-sectional view of an LD according to an embodiment of the present invention.

Insulating films 33 made of any one of a dielectric such as SiO ₂ or Si ₃ N ₄ are formed in a stripe shape on a predetermined portion of the surface of the semiconductor substrate 31 of N ⁺ type GaAs (001) plane. Directions of the insulating layers 33 are deviated by about 20 to 30 degrees from a <110> direction indicating a major fret for displaying a crystal direction of the semiconductor substrate 31, and are formed parallel to each other by a predetermined distance. . An N-type Al _y Ga _1-y As first cladding layer 35 is formed on a surface of the semiconductor substrate 31 on which the insulating layers 33 are not formed. The first clad layer 31 is not formed on the surface of the insulating layer 33 and has a reverse mesa shape. In addition, an N-type, P-type, or I-type Al _x Ga _1-x As active layer 37 that is not doped with impurities is formed on the surface of the first cladding layer 35, and the surface of the active layer 37 is formed. A second cladding layer 39 of P-type Al _y Ga _1-y As is formed therein. The active layer 37 and the second cladding layer 39 are thinly formed on the reverse inclined surface of the first cladding layer 35. However, the active layer 37 and the second cladding layer 39 are formed on the upper surface of the first cladding layer 35 to the original thickness, and the reverse sloped surface of the second cladding layer 39 has a straight line. In a predetermined portion. Accordingly, triangular voids 41 surrounded by the second cladding layer 39 are formed on the insulating layer 33. A cap layer 43 of P ⁺ type GaAs is formed on the second clad layer 39. In addition, Au P-type electrode 45 is formed between the voids 41 on the cap layer 43, and N-type electrode 46 of AuGe / Ni / Au is formed on the lower surface of the semiconductor substrate 31, respectively. Ohmic contact is achieved.

The above-described LD is formed by any one of a molecular beam epitaxy (MBE), a metal organic chemical vapor deposition (MOCVD), and a liquid phase epitaxy (LPE). Therefore, the interlayer insulating film 33 is used as a mask, so that there is no passion growth in that portion. In addition, the side surfaces of the crystal-grown layers are determined according to the direction of the insulating film 33. When the insulating film 33 is shifted by about 20 to 30 ° in the <110> direction, the side surfaces of the crystal-grown layers form a reverse slope. do. When the reverse slopes are combined, a void 41 is formed therein, and layers are grown from the merged portion. The height of the void 41 is determined by the width of the insulating layer 33 and should be turned on rather than the thickness of the first clad layer 35.

When voltage is applied between the P-type and N-type electrodes 45 and 46 of the above-described LD, holes injected from the P-type electrode 45 are limited between the voids 41 before being diffused. It flows to the active layer 37 and recombines with electrons injected from the N-type electrode 46 to generate light. Therefore, the horizontal mode of light generated is precisely limited. In addition, the size of the horizontal mode of the light may be arbitrarily adjusted by adjusting the distance between the insulating layers 33. In order to limit the generated light to the active layer 37, the composition condition of 1≥y> x≥0 must be satisfied.

3 (a) to 3 (c) are manufacturing process diagrams of the LD according to the present invention.

Referring to FIG. 3 (a), an insulating film 33 of SiO ₂ or Si ₃ N ₄ is deposited to a thickness of about ₄₀₀ to 1000 GPa on an N ⁺ type GaAs semiconductor substrate 31 which is a (001) crystal plane. Then, the insulating film 33 is formed into two stripe shapes having a width of about 1.5 to 3 mu m by a conventional photolithography method. In this case, the insulating layers 33 are formed to be shifted by about 20 to 30 'from the <110> direction of the semiconductor substrate 31.

Referring to FIG. 3 (b), the first cladding layer 35 of N-type Al _y Ga _1-y As, N-type or P-type Al _x Ga _1-x As may be formed by any one of MOCVD, MBE, or LPE. The active layer 37, the second cladding layer 39 of P-type Al _y Ga _1-y As and the cap layer 43 of P ⁺ type GaAs are sequentially formed in one step. The first and second cladding layers 35 and 39 are each about 1 to 1.5 µm thick, the active layer 37 is about 400 to 1000 µm thick, and the cap layer 43 is about 5000 µm thick. It is formed to a thickness of. In this case, the first cladding layer 35 does not grow on the insulating layer 33 but grows only on the surface of the semiconductor substrate 31 with a reverse slope. In addition, the second cladding layer 39 formed on the surface of the active layer 37 hardly grows on the inclined plane and forms a straight line. Therefore, the second cladding layer 39 meets the reverse inclined surface at a predetermined thickness so that a triangular void 41 is formed on the insulating layer 33.

Referring to FIG. 3 (c), the surface of the cap layer 43 is formed of Au / Zn P-type electrode 45 between the voids 41 and N as AuGe / Ni / Au on the lower surface of the semiconductor substrate 31. The type electrode 46 is formed.

As described above, when the insulating film is formed on the surface of the semiconductor substrate and LD is formed by using the crystal growth characteristics according to the crystal direction, triangular voids are formed on the insulating film, and an electrode is formed between the voids, so that the current is voided. Limited between them.

Therefore, the present invention forms an area for limiting the horizontal mode of the emitted light without etching, thereby improving reliability by preventing defects in the grown layers. In addition, light emitted by the voids is improved. Has a stable landscape mode, there is an advantage that can be adjusted arbitrarily the size of the landscape mode.

In the above-described embodiment of the present invention, the semiconductor substrate was shown as GaAs having a (001) crystal plane, but without fail, the concepts (100), (110), (111), (010), (011), ( It may have a crystal plane, such as 101), and may be implemented with all Group VIII compounds such as InP and GaP.

Claims (8)

A laser diode comprising: a semiconductor substrate having a predetermined crystal name and doped with a high concentration of impurities of a first conductivity type, insulating films formed in a stripe form at a predetermined angle with a major frit at a predetermined portion of the surface of the semiconductor substrate, A first cladding layer having an inverse mesa type doped with a first conductivity type impurity on a surface of the semiconductor substrate on which the insulating film is not formed, an active layer formed on the surface of the first cladding layer, and a surface of the active layer And a second cladding layer doped with impurities of a second conductivity type having opposite inclined surfaces and having a flat surface, triangular voids formed by an inverted slope of the active layer on the insulating film, and a surface of the second cladding layer. A cap layer formed in the dopant and heavily doped with a second conductivity type impurity, a second conductivity type electrode formed between the voids above the cap layer, and the half A laser diode having a first conductivity type electrode formed on a lower surface of a conductor substrate. The laser diode of claim 1, wherein the semiconductor substrate is any one of GaAs, InP, and GaP. The laser diode of claim 1, wherein the semiconductor substrate is a (001) crystal plane. The laser diode of claim 1, wherein the stripes have an angle of about 20 to 30 degrees with a <110> direction. The laser diode of claim 1, wherein the insulating layers are any one of a dielectric such as SiO ₂ or Si ₃ N ₄ . A method of manufacturing a laser diode, comprising: a first step of forming stripe-shaped insulating films forming a predetermined angle with a major frit on a surface of a semiconductor substrate having a predetermined crystal plane and doped with a first conductivity type impurity; A second step of forming a first cladding layer doped with a first conductivity type impurity on the surface of the substrate in a reverse mesa shape, a third step of forming an active layer on the surface of the first cladding layer, and a surface of the active layer And a fourth step of forming a second cladding layer doped with impurity of the second conductivity type having opposite inclined planes on the surface thereof, and a cap layer doped with high concentration of impurity of the second conductivity type on the surface of the second cladding layer. A fifth process for forming a second conductive electrode, a sixth process for forming a second conductive electrode between the voids on the cap layer, and a first conductive electrode on the lower surface of the semiconductor substrate; A laser diode manufacturing method comprising the seventh step. The method of claim 6, wherein the second to fifth processes are made of any one of NOCVD, MBE, and LPE. The method of claim 6, wherein a triangular void is simultaneously formed when the reverse slopes meet in a fourth process.