JP3559463B2 - Semiconductor light emitting device and method of manufacturing the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device used as an exposure light source of a photosensitive drum for a page printer.
[0002]
Problems to be solved by the prior art and the invention
FIGS. 4 to 6 show a conventional semiconductor light emitting device. 4 and 5 are sectional views, and FIG. 6 is a plan view. 4 to 6, 21 is a semiconductor substrate, 22 is a semiconductor layer of one conductivity type, 23 is a semiconductor layer of opposite conductivity type, 24 is an individual electrode, and 25 is a common electrode.
[0003]
On the semiconductor substrate 21, a semiconductor layer 22 of one conductivity type and a semiconductor layer 23 of opposite conductivity type are provided, and a common electrode 25 (25a, 25b) is connected to an exposed portion R of the semiconductor layer 22 of one conductivity type. An individual electrode 24 is connected to the conductive semiconductor layer 23. 4 and 5, reference numeral 26 denotes a protective film made of a silicon nitride film or the like. As shown in FIG. 4, the common electrodes 25 (25a, 25b) are divided into two groups so as to belong to different groups for the adjacent island-shaped semiconductor layers 22 and 23, and are connected to each other. , 23 are connected to the same individual electrode 24.
[0004]
In such a light emitting diode array, each light emitting diode can selectively emit light by selecting a combination of the individual electrode 24 and the common electrode 25 (25a, 25b) and flowing an electric current.
[0005]
However, in this conventional semiconductor light emitting device, when the semiconductor layer is separated into a plurality of light emitting elements, mesa etching is performed to form an island shape. In this case, the electrode take-out portion was formed in a forward mesa shape in order to prevent disconnection, but the side wall portion in the lateral direction was in an inverted mesa shape.
[0006]
In this case, the light emitted in the lateral direction is reflected by the sidewalls of the inverted mesa and emitted to the upper side of the island-shaped semiconductor layer, and as shown in FIG. The light emission intensity distribution is prominent, which is a cause of deteriorating printing quality.
[0007]
Further, as shown in FIG. 8, light emitted from the side wall portion is reflected on a wire bonding ball for connecting to an external circuit, and this also causes deterioration of printing quality.
[0008]
In order to prevent such a prominent emission intensity distribution at the end face, there is also a method of coating the end face with an electrode material, but the portion where the electrode material is applied cannot be limited to only a part of the side wall, It is necessary to cover with more electrode material, and there is a problem that the emission intensity is reduced. In addition, since it is difficult to completely cover the side wall portion, light leakage from the side wall portion occurs as a result, and there is a problem that printing quality is not completely improved.
[0009]
The present invention has been made in view of such a problem of the conventional device, and has been made to improve the emission intensity distribution generated due to the fact that the side wall portion of the adjacent island-shaped semiconductor layer has an inverted mesa structure, and It is an object of the present invention to provide a semiconductor light emitting device in which degradation of printing quality due to light emission from a section and stray light is eliminated.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, in the semiconductor light emitting device according to claim 1, a plurality of island-shaped semiconductor layers in which a semiconductor layer of one conductivity type and a semiconductor layer of opposite conductivity type are stacked on a substrate are provided, and an electrode is provided on each semiconductor layer. In the semiconductor light emitting device connected to the above, an oxidized region is provided on the side wall of the inverted mesa structure of the island-shaped semiconductor layer.
[0011]
In the above semiconductor light emitting device, it is desirable that the semiconductor layer provided with the oxidized region is made of AlGaAs.
[0012]
In the above-mentioned semiconductor light emitting device, it is preferable that the island-shaped semiconductor layer on which the oxidized region is formed is covered with an insulating film.
[0013]
Further, in the method for manufacturing a semiconductor light emitting device according to claim 4, an island-like semiconductor layer in which AlGaAs and GaAs are stacked on a substrate is provided, and a side wall portion of the AlGaAs reverse mesa structure is oxidized in water vapor, and thereafter, An electrode is connected to GaAs.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a sectional view showing one embodiment of a semiconductor light emitting device according to the present invention, and FIG. 2 is a plan view.
[0015]
1 and 2, 1 is a substrate, 2 is a semiconductor layer of one conductivity type, 3 is a semiconductor layer of opposite conductivity type, 4 is an individual electrode, 5 is a common electrode, 6 is an insulating film, and 7 is an oxidized region.
[0016]
The substrate 1 is composed of a single crystal semiconductor substrate such as silicon (Si) or gallium arsenide (GaAs) or a single crystal insulating substrate such as sapphire (Al2O3). In the case of a single crystal semiconductor substrate, a substrate whose (100) plane is turned off by 2 to 7 ° in the <011> direction is preferably used. In the case of sapphire, a C-plane substrate is preferably used.
[0017]
The one conductivity type semiconductor layer 2 includes a buffer layer 2a, an ohmic contact layer 2b, and an electron injection layer 2c. The buffer layer 2a is formed to a thickness of about 2 to 4 μm, the ohmic contact layer 2b is formed to a thickness of about 0.1 to 1.0 μm, and the electron injection layer 2c is formed to a thickness of about 0.2 to 0.4 μm. Is done. The buffer layer 2a and the ohmic contact layer 2b are formed of gallium arsenide or the like, and the electron injection layer 2c is formed of aluminum gallium arsenide (AlGaAs) or the like. The ohmic contact layer 2b contains one conductivity type semiconductor impurity such as silicon at about 1 × 10 ¹⁶ to 10 ¹⁷ atoms / cm ³ , and the electron injection layer 2c contains one conductivity type semiconductor impurity such as silicon at 1 × 10 ¹⁶ to 10 ^19. It contains about atoms / cm ³ . At this time, the Al composition of the electron injection layer 2c is formed so that x = 0.24 to 0.5. The buffer layer 2a is provided to prevent misfit dislocation due to mismatch of the lattice constant between the substrate 1 and the semiconductor layer, and does not need to contain semiconductor impurities.
[0018]
The opposite conductivity type semiconductor layer 3 includes a light emitting layer 3a, a cladding layer 3b, and a second ohmic contact layer 3c. The light emitting layer 3a and the cladding layer 3b are formed to a thickness of about 0.2 to 0.4 μm, and the ohmic contact layer 3c is formed to a thickness of about 0.01 to 0.1 μm. The light emitting layer 3a and the cladding layer 3b are made of AlGaAs or the like. The second ohmic contact layer 3c is made of gallium arsenide or the like.
[0019]
The light emitting layer 3a and the cladding layer 3b have different mixed crystal ratios of aluminum arsenide (AlAs) and gallium arsenide (GaAs) in consideration of the electron confinement effect and the light extraction effect. The light emitting layer 3a and the cladding layer 3b contain opposite conductivity type semiconductor impurities such as zinc (Zn) at about 1 × 10 ¹⁶ to 10 ¹⁸ atoms / cm ³ , and the second ohmic contact layer 3c has a reverse conductivity type semiconductor such as zinc. Impurities are contained at about 1 × 10 ¹⁹ to 10 ²⁰ atoms / cm ³ .
[0020]
The insulating films 6a and 6b are made of silicon nitride or the like and have a thickness of about 3000 to 5000 degrees. The individual electrode 4 and the common electrode 5 are made of Au / AuGe / Cr or the like and have a thickness of about 1 μm.
[0021]
In the semiconductor light emitting device of the present invention, as shown in FIG. 2, the island-shaped semiconductor layers 2 and 3 composed of the one-conductivity-type semiconductor layer 2 and the opposite-conductivity-type semiconductor layer 3 are arranged in a row on the substrate 1 so that adjacent islands are formed. Each of the semiconductor layers 2 and 3 is connected to the same individual electrode 4, and the lower one conductivity type semiconductor layer 2 connected to the same individual electrode 4 is divided into two groups so as to be connected to different common electrodes 5. You. By selecting the individual electrode 4 and passing an electric current, it is used as an exposure light source for a photosensitive drum for a page printer.
[0022]
One of the island-shaped semiconductor layers 2 and 3 has a forward mesa structure and the other opposed wall has an inverted mesa structure due to the relationship between the crystal orientation and the etching.
[0023]
In the present invention, the one conductivity type semiconductor layer 2c made of AlGaAs and the opposite conductivity type semiconductor layers 3a and 3b made of AlGaAs are oxidized from the side to form the oxidized region 7. In addition, as shown in FIG. 2, the opposite conductivity type semiconductor layer 3b was exposed by etching in the peripheral portion of the upper surface of the light emitting surface to form an oxide region 7 similarly. The oxidized region 7 is formed of Al ₂ O _x having a thickness of about 10 to 1200 °.
[0024]
By oxidizing the one-conductivity-type semiconductor layer 2c made of AlGaAs and the opposite-conductivity-type semiconductor layers 3a and 3b made of AlGaAs from the side surfaces to form the oxidized region 7, the oxidized region 7 has an electrical resistance of 2 ×. It increases to about 10 ¹³ Ω · cm. Therefore, recombination of light emission in the peripheral portion of the island-shaped semiconductor layer hardly occurs, and light emission in the peripheral portion of the island-shaped semiconductor layer is reduced, so that the angular emission intensity distribution is reduced. Further, when the refractive index of the oxidized region 7 is n = 1.66, light can be reflected and absorbed. The light transmittance of the light from the light emitting layer 3a becomes maximum when the refractive index n = 1.87. The insulating film 6 is also formed close to the insulating film 6, but by providing an oxidized region 7 having a different light refractive index from the insulating film 6, light transmission from the side wall can be prevented. For example, when the wavelength is 740 nm, light absorption is more effective as the film thickness is smaller, and light absorption is small at 1114 °. Thereby, as shown in FIG. 3, the light emission distribution can also improve the light emission intensity distribution at the end of the island-shaped semiconductor layer. Further, light leakage from the side surface can be completely suppressed.
[0025]
Next, a method for manufacturing the above-described semiconductor light emitting device will be described. First, a semiconductor layer 2 of one conductivity type and a semiconductor layer 3 of opposite conductivity type are sequentially formed on a single crystal substrate 1 by MOCVD or the like.
[0026]
When these semiconductor layers 2 and 3 are formed, the substrate temperature is first set to 400 to 500 ° C., an amorphous gallium arsenide film is formed to a thickness of 200 to 2000 °, and then the substrate temperature is increased to 700 to 900 ° C. Thus, semiconductor layers 2 and 3 having a desired thickness are formed.
[0027]
In this case, TMG ((CH ₃ ) ₃ Ga), TEG ((C ₃ H ₅ ) ₃ Ga), arsine (AsH ₃ ), TMA ((CH ₃ ) ₃ Al), TEA ((C ₂ H ₅ ) ₃ Al) or the like is used, and silane (SiH ₄ ), hydrogen selenide (H ₂ Se), TMZ ((CH ₃ ) ₃ Zn), or the like is used as a gas for controlling the conductivity type. As the carrier gas, H ₂ or the like is used.
[0028]
Next, the semiconductor layers 2 and 3 are patterned in an island shape so that adjacent elements are electrically separated. This etching is performed by wet etching using a sulfuric acid-hydrogen peroxide-based etchant, dry etching using CCl ₂ F ₂ gas, or the like.
[0029]
Next, etching is performed to expose a part of the one conductivity type semiconductor layer 2 on one end side. Further, a part of the surface of the semiconductor layer 3c on the surface is etched. Each etching is also performed by wet etching using a sulfuric acid hydrogen peroxide type etching solution, dry etching using CCl ₂ F ₂ gas, or the like.
[0030]
Next, the AlGaAs layers 2c, 3a, and 3b exposed on the side and upper surfaces are oxidized using the semiconductor layer 3c on the surface as a mask. This oxidation is performed at a temperature of about 350 to 500 degrees by steam oxidation. The fact that the surface is oxidized when the composition of Al is x = 0.15 or more is described in J. Am. APPL. Phys. 71 (4), 15 February 1992 Reported by Mesarwi et al. In this case, since GaAs or Si hardly grows as an oxide layer, the AlGaAs layers 2c, 3a, 3b can be selectively oxidized.
[0031]
Next, an insulating film made of silicon nitride is formed and patterned by a plasma CVD method using silane gas (SiH ₄ ) and ammonia gas (NH ₃ ). Next, chromium and gold are formed by a vapor deposition method or a sputtering method and patterned, and an insulating film made of silicon nitride is formed again by a plasma CVD method using silane gas (SiH ₄ ) and ammonia gas (NH ₃ ). And completed by patterning.
[0032]
Thus, a portion of the GaAs layer serving as the cap layer selectively oxidizes the exposed portion etch, by a structure forming an insulating film such as SiN _x after the oxidation region formed adjacent island-shaped semiconductor A semiconductor light emitting device is provided in which the emission intensity distribution generated due to the side wall portion of the layer having an inverted mesa structure is improved, and stray light due to light emission from the side surface is prevented to prevent deterioration in printing quality.
[0033]
【The invention's effect】
As described above, in the semiconductor light emitting device according to the first aspect, since the side wall portion of the inverted mesa structure of the island-shaped semiconductor layer and the peripheral portion of the upper surface are forcibly oxidized, the side wall of the adjacent island-shaped semiconductor layer is formed. It is possible to provide a semiconductor light emitting device in which the emission intensity distribution generated due to the portion having the inverted mesa structure is improved, and stray light due to light emission from the side is prevented to improve the printing quality.
[0034]
In the method of manufacturing a semiconductor light emitting device according to claim 4, AlGaAs and GaAs are stacked on the substrate, and the sidewalls of the AlGaAs inverted mesa structure are oxidized in a water vapor atmosphere, and then the surface of the GaAs is formed. Since an electrode is connected to the portion, an oxidized region can be easily and reliably formed on the side wall portion of AlGaAs, and the light emission intensity distribution generated due to the side wall portion of the adjacent island-shaped semiconductor layer having an inverted mesa structure It is possible to provide a semiconductor light emitting device with improved print quality and improved printing quality by preventing stray light due to light emission from the side.
[Brief description of the drawings]
FIG. 1 is a sectional view showing one embodiment of a semiconductor light emitting device according to the present invention.
FIG. 2 is a plan view showing one embodiment of a semiconductor light emitting device according to the present invention.
FIG. 3 is a diagram showing a light emission intensity distribution of the semiconductor light emitting device according to the present invention.
FIG. 4 is a sectional view showing a conventional semiconductor light emitting device.
FIG. 5 is a sectional view of another portion showing the conventional semiconductor light emitting device.
FIG. 6 is a plan view showing a conventional semiconductor light emitting device.
FIG. 7 is a diagram showing a light emission intensity distribution of a conventional semiconductor light emitting device.
FIG. 8 is a diagram showing a state of light emission from a side surface of a conventional semiconductor light emitting device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... one conductivity type semiconductor layer, 3 ... reverse conductivity type semiconductor layer, 4 ... individual electrode, 5 ... common electrode, 6 ... insulating film, 7 ... ... oxidized area

Claims (4)

In a semiconductor light emitting device in which a plurality of island-like semiconductor layers in which a semiconductor layer of one conductivity type and a semiconductor layer of the opposite conductivity type are stacked on a substrate are provided, and an electrode is connected to each semiconductor layer, an inverted mesa structure of the island-like semiconductor layer is provided. A semiconductor light emitting device, wherein an oxidized region is provided on a side wall portion. 2. The semiconductor light emitting device according to claim 1, wherein the semiconductor layer provided with the oxidized region is made of AlGaAs. 2. The semiconductor light emitting device according to claim 1, wherein the island-shaped semiconductor layer having the oxidized region is covered with an insulating film. A method of manufacturing a semiconductor light emitting device in which an island-like semiconductor layer in which AlGaAs and GaAs are stacked on a substrate is provided, and a sidewall portion of the AlGaAs reverse mesa structure is oxidized in a water vapor atmosphere, and then an electrode is connected to the GaAs.

Images