JP3842539B2 - LED array - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device, and more particularly to an LED array used for an exposure light source of a photosensitive drum for a page printer.
[0002]
[Prior art]
A conventional LED array disclosed in Japanese Patent Laid-Open No. 10-242507 will be described with reference to FIG.
[0003]
According to this LED array, an n-type GaAs buffer layer 2, an n-type AlGaAs cladding layer 3, a P-type AlGaAs active layer 4, a P-type AlGaAs cladding layer 5 and a P-type are formed on an n-type GaAs substrate 1. The contact layer 6 is sequentially formed, the P-side electrode 7 is provided on the surface of the contact layer 6, and the n-side electrode 8 is provided on the back surface of the n-type GaAs substrate 1. ing.
[0004]
And about the LED array of the said structure, the gentle reverse mesa shape is formed by the wet etching at the time of element isolation, and, thereby, luminous efficiency is raised.
[0005]
That is, when elements are separated in an AlGaAs / GaAs LED array, wet etching using sulfuric acid / hydrogen peroxide / water is performed. At that time, anisotropic etching is performed, so that the light emitting element is oriented in a certain direction. Only the reverse mesa shape appears. When the film is formed on the (100) plane, an inverted mesa shape appears on the (011) plane, and a forward mesa shape appears on the (011) plane. Also, there is a difference in the etching rate between the AlGaAs layer and the GaAs layer, and the AlGaAs layer has a faster etching rate than the GaAs layer, and changes to an inverted mesa-shaped angle depending on this layer configuration.
[0006]
As described above, usually, it has a gentle inverted mesa shape, and the luminous efficiency is increased by using reflection at the interface.
[0007]
[Problems to be solved by the invention]
However, in the conventional AlGaAs-based LED array, as the light emitting elements are arranged at a high density, the size of each element is reduced, so that the area ratio that covers the element by the P-side electrode 7 is increased. Of the light emitted inside, the ratio of being blocked by the P-side electrode 7 tends to increase, and as a result, the emission intensity is significantly reduced. Accordingly, the present invention has been completed in view of the above, and an object thereof is to provide an LED array in which the light emission intensity of each element is increased.
[0008]
Another object of the present invention is to provide an LED array suitable for a high density page printer by arranging light emitting elements at a high density.
[0009]
[Means for Solving the Problems]
The LED array of the present invention is a light emitting device having a semiconductor substrate exhibiting one conductivity type and a plurality of islands arranged on the semiconductor substrate, the buffer layer exhibiting one conductivity type, and being refracted with respect to the emission wavelength. A light reflection layer in which layers having different rates are alternately stacked, a first cladding layer having one conductivity type, an active layer that emits light, and a second cladding layer of reverse conductivity type in which the emitted light is extracted from above. And the one electrode are sequentially formed, and the cross-sectional shape of the light emitting element forms an inverted mesa shape from the top toward the light reflecting layer, and the one electrode is near the end on the second cladding layer. And a light emitting element disposed outside the light reflecting layer, and the other electrode provided on the back surface of the semiconductor substrate.
[0010]
In contrast, LED array of the present invention, between the buffer layer and the first cladding layer as in the above-described configuration, is interposed a light reflecting layer formed by alternately stacking layers of different refractive index with respect to the emission wavelength , by cross-sectional shape of the light emitting element from the top to form a reverse mesa shape toward the light reflection layer, when separating the light-emitting element in an island shape, the light reflective cross-sectional shape of the light emitting device from the top Strong reverse mesa shape toward the layer .
[0011]
In addition, even if the one electrode is disposed outside the light reflecting layer in the vicinity of the end portion on the second cladding layer of the device, even if the current density directly below the one electrode increases, By forming a strong reverse mesa shape from the upper part toward the light reflecting layer from above , the current is concentrated at a location shifted from directly below the electrode, and therefore, the structure produces the strongest light emission other than immediately below the electrode, and as a result, The light emitted from the active layer can be extracted efficiently.
[0012]
The light emitted from the active layer spreads vertically and horizontally, but when the inverse mesa shape becomes strong at the interface where the light emitted in the lateral direction exits from the inside of the element where the refractive index is different, the angle of incidence on the interface is increased. It becomes wider and the reflectivity at the interface increases, thereby increasing the ratio of guiding the lateral light upward, and as a result, the luminous efficiency increases.
[0013]
Furthermore, in the present invention, since the light reflecting layer is interposed between the buffer layer and the first cladding layer, the light emitted downward is reflected upward by the effect of the reflecting mirror, thereby emitting light. Further improve efficiency.
[0014]
By the way, Dufour et al. Have reported that a reflecting mirror is formed by alternately laminating media having different refractive indexes as optical reflectors at an optical distance of ¼ wavelength (Rev. Opt. , vol.32 (1953) pp.321).
[0015]
According to this report, a structure in which films having different refractive indexes n with respect to an emission wavelength λ are alternately stacked with a thickness d = λ / 4n, and the difference in the refractive index of the alternately stacked media is larger. It is described that the reflection effect is large.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of semiconductor light emitting elements arranged in an island shape in the LED head of the present invention. In this example, a red AlGaAs LED array is illustrated.
[0017]
In FIG. 1, reference numeral 9 denotes a semiconductor substrate. On one main surface of the semiconductor substrate 9, a one-conductivity type buffer layer 10 and layers 11 a and 11 b constituting light reflecting layers having different refractive indexes with respect to the emission wavelength, The one-conductivity-type semiconductor clad layer 12 that is the first clad layer, the reverse-conductivity-type semiconductor active layer 13, and the reverse-conductivity-type semiconductor clad layer 14 that is the second clad layer are sequentially laminated, and further the reverse-conductivity-type semiconductor clad A reverse conductivity type contact layer 15 and one electrode 16 are sequentially stacked near the end on the layer 14.
[0018]
The other electrode 17 is formed on the other main surface of the semiconductor substrate 9.
[0019]
The semiconductor substrate 9 contains about 1 × 10 ¹⁷ to 10 ¹⁹ atoms / cm ³ of one conductivity type impurity, a single crystal semiconductor substrate such as silicon (Si), gallium arsenide (GaAs), indium phosphorus (InP), or sapphire (Al ₂ O ₃ ) or other single crystal insulating substrate.
[0020]
In the case of a single crystal semiconductor substrate, a substrate in which the (100) plane is turned off by 2 to 7 degrees in the <011> direction is preferably used. In the case of sapphire, a C-plane substrate is preferably used.
[0021]
The buffer layer 10 is made of gallium arsenide (GaAs) or the like and contains about 1 × 10 ¹⁷ to 10 ¹⁹ atoms / cm ^{3 of} one conductivity type impurity (Si or the like), and is a misfit consisting of lattice mismatch between the substrate 8 and the semiconductor layer. In order to prevent or reduce dislocation, it is formed to a thickness of about 2 to 4 μm.
[0022]
The light reflecting layer formed by alternately laminating layers having different refractive indexes with respect to the emission wavelength has a laminated structure of the layers 11a and 11b.
[0023]
The layer 11a is made of aluminum arsenide (AlAs) or aluminum gallium arsenide (AlGaAs) having an Al composition larger than that of the cladding layer 12 described later, and has a thickness of about 0.04 to 0.07 μm.
[0024]
The layer 11b is made of gallium arsenide (GaAs) and has a thickness of about 0.04 to 0.07 μm.
[0025]
And light reflectivity is obtained by laminating | stacking the layer 11a and the layer 11b alternately. It is preferable to provide at least five of these two layers.
[0026]
The layer 11a is formed of aluminum arsenic (AlAs) having a refractive index of 2.97 or aluminum gallium arsenide (Al _x Ga _1-x As) having a refractive index of 3.156 or less and an aluminum composition X = 0.7 or more as a first reflective film. The thickness is about 0.07 μm.
[0027]
The layer 11b uses gallium arsenide (GaAs) with a refractive index of 3.59 as the second reflective film, and has a thickness of about 0.04 to 0.07 μm. These are alternately repeated for 5 to 20 cycles, and finally aluminum arsenic (AlAs) or aluminum gallium arsenide (Al _x Ga _1-x As) is laminated. Thus, it can use as a reflecting mirror by making it the structure which laminated | stacked the medium from which a refractive index differs optically by the optical distance of 1/4 wavelength.
[0028]
The one-conductivity-type semiconductor clad layer 12 is configured as an electron injection layer. It is made of aluminum gallium arsenide (AlGaAs) and contains about 1 × 10 ¹⁶ to 10 ²¹ atoms / cm ³ of one conductivity type semiconductor impurity such as silicon and has a thickness of about 0.2 to 4 μm.
[0029]
The reverse conductivity type semiconductor active layer 13 is made of aluminum gallium arsenide (AlGaAs), contains about 1 × 10 ¹⁶ to 10 ²¹ atoms / cm ³ of reverse conductivity type semiconductor impurities such as zinc (Zn), and is about 0.1 to 4 μm. Of the thickness.
[0030]
The reverse conductivity type semiconductor clad layer 14 is made of aluminum gallium arsenide (AlGaAs) and contains reverse conductivity type semiconductor impurities such as zinc (Zn) at about 1 × 10 ¹⁶ to 10 ²¹ atoms / cm ^{3 and} about 0.2 to 4 μm. It is thickness.
[0031]
In consideration of the carrier confinement effect and light transmissivity, the mixed conductivity ratio of aluminum arsenic (AlAs) and gallium arsenide (GaAs) is different between the reverse conductive semiconductor active layer 13 and the reverse conductive semiconductor clad layer 14. Yes.
[0032]
The ohmic contact layer 15 is made of gallium arsenide (GaAs) and contains about 1 × 10 ¹⁹ to 10 ²⁰ atoms / cm ³ of a reverse conductivity type semiconductor impurity such as zinc (Zn) and has a thickness of about 0.01 to 1 μm.
[0033]
Next, a method for manufacturing such a semiconductor element will be described.
[0034]
First, the substrate 9 is heated to 700 ° C. to 1000 ° C. in an atmosphere of hydrogen (H ₂ ) and arsine gas (AsH ₃ ) by MOCVD to remove oxide on the surface of the substrate 9.
[0035]
Next, trimethyl gallium (hereinafter referred to as TMG), arsine gas (AsH ₃ ), and silane gas (SiH ₄ ) are supplied as dopant gases at a substrate temperature of 500 ° C. to 800 ° C. to form the buffer layer 10 having a thickness of 2 to 4 μm.
[0036]
A layer 11a is formed thereon using TMG, trimethylaluminum (hereinafter, TMA), arsine gas (AsH ₃ ), and silane gas (SiH ₄ ) as source gases as dopant gases. Next, the layer 11b is formed by using TMG, arsine gas (AsH ₃ ), and silane gas (SiH ₄ ) as raw material gases and a dopant gas.
[0037]
Thereafter, the one-conductivity-type semiconductor clad layer 12 is formed using silane gas (SiH ₄ ) as a dopant gas. A reverse conductive semiconductor active layer 13, a reverse conductive semiconductor clad layer 14, and an ohmic contact layer 15 are sequentially formed thereon using dimethyl zinc (hereinafter, DMZ) as a dopant gas.
[0038]
By sequentially laminating and etching each layer in this way, each element has a strong inverted mesa shape as shown in FIG.
[0039]
This etching process will be described with reference to FIGS. In the present invention, the etching rate of the layers 11a and 11b of the light reflecting layer is larger than the etching rate of both the one-conductivity type buffer layer 10 and the one-conductivity type semiconductor clad layer 12.
[0040]
According to such a configuration, a mesa structure is formed on the crystal layer after growth using a sulfuric acid / hydrogen peroxide etching solution. At this time, the etching solution etches the film from above, and the structure is shown in FIG. A gentle reverse mesa shape is formed. Reference numeral 18 denotes a resist mask used for etching.
[0041]
After that, the etching progresses, and when the light reflecting layer 11a and the layer 11b having a high Al composition appear, the etching rate becomes faster, and the etching in the lateral direction also proceeds greatly. As shown in FIG. Strong reverse mesa shape.
[0042]
Thereafter, as shown in FIG. 5, a buffer layer having a low etching rate appears, and has a forward mesa shape.
[0043]
Thereafter, the one electrode 16 and the other electrode 17 are formed by gold / germanium (AuGe) or the like by using a vapor deposition method or a sputtering method.
[0044]
Thus, according to the LED array of the present invention, the light reflecting layer composed of the layer 11a and the layer 11b having the above-described structure is interposed between the one-conductivity type buffer layer 10 and the one-conductivity type semiconductor clad layer 12, so that the light emitting element When the light emitting elements are separated into islands, the cross-sectional shape of the light emitting element becomes a strong inverted mesa shape, and the one electrode is disposed near the end of each element, so that the current density directly below the one electrode 16 is increased. However, the current is concentrated at a location deviated from directly below the electrode, and as a result, the strongest light emission occurs other than directly below the electrode 16, and as a result, the light emitted from the active layer can be extracted efficiently. .
[0045]
【The invention's effect】
As described above, according to the LED array of the present invention, a semiconductor substrate exhibiting one conductivity type, a light-emitting element arranged in a plurality of islands on the semiconductor substrate, the buffer layer exhibiting one conductivity type, A light reflection layer in which layers having different refractive indexes with respect to the emission wavelength are alternately laminated, a first cladding layer exhibiting one conductivity type, an active layer that emits light, and a reverse conductivity that extracts the emitted light from above. The second clad layer of the mold and one electrode are sequentially formed, and the cross-sectional shape of the light emitting element forms an inverted mesa shape from the top toward the light reflecting layer, and the one electrode is the second clad layer A light emitting element disposed outside the light reflecting layer in the vicinity of the upper end portion and a second electrode provided on the back surface of the semiconductor substrate are provided.
[0046]
In the conventional LED array, the electrode is provided at the substantially central portion of the element, so that the current density directly under the electrode becomes high, and thereby the light emission is the strongest directly under the electrode. However, the LED array according to the present invention has a buffer layer and a first layer as described above. A light reflecting layer formed by alternately laminating layers having different refractive indexes with respect to the emission wavelength is interposed between the cladding layer and the cross-sectional shape of the light emitting element has an inverted mesa shape from the top toward the light reflecting layer. in the the fact as to form, when separating the light-emitting element in an island shape, the sectional shape of the light emitting element has a strong inverse mesa, moreover, one electrode to a vicinity of the end on the second clad layer of the element Arranged outside the light reflecting layer Thus, even if the current density directly under one of the electrodes becomes high, the cross-sectional shape of the light-emitting element forms a strong reverse mesa shape as described above, so that the current is concentrated at a location shifted from directly under the electrode. The structure produced the strongest light emission except directly below, and as a result, the light emitted from the active layer could be extracted efficiently.
[0047]
Further, according to the present invention, the light emitted from the active layer spreads up and down, left and right, but when the reverse mesa shape becomes stronger at the interface where the light emitted in the lateral direction exits from the inside of the element where the refractive index is different, The angle incident on the interface is widened, and the reflectance at the interface is increased. As a result, the ratio of guiding the light in the lateral direction is increased, and the luminous efficiency is also remarkably increased.
[0048]
Furthermore, in the present invention, among the light emitted from the active layer, a light reflecting layer in which a medium having a different refractive index is alternately laminated at an optical distance of ¼ wavelength with respect to the remaining downward light, Reflected upward, the luminous efficiency was remarkably increased, and the luminous efficiency was remarkably improved in that respect.
[0049]
As described above, by adopting the configuration of the present invention, light in all directions of the upper, lower, left and right directions generated in the active layer can be efficiently extracted upward.
[0050]
Furthermore, in the present invention, an LED array suitable for a high-density page printer can be provided by increasing the light emission intensity of each element and arranging the light-emitting elements at a high density.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a light emitting element of an LED array of the present invention.
FIG. 2 is a cross-sectional view of a light emitting element of a conventional LED array.
FIG. 3 is a process diagram when the LED array of the present invention is manufactured.
FIG. 4 is a process diagram when the LED array of the present invention is manufactured.
FIG. 5 is a process diagram when the LED array of the present invention is manufactured.
[Explanation of symbols]
9 ... Semiconductor substrate
10 ... One conductivity type buffer layer
11a, 11b ... layers constituting the light reflection layer
12 ... One conductivity type semiconductor clad layer
13 ... Reverse conductivity type semiconductor active layer
14 ... Reverse conductivity type semiconductor clad layer
15 ... Reverse conductivity type contact layer
16 ... One electrode
17 ... Other electrode
18 ... Resist mask

Claims (1)

A semiconductor substrate exhibiting one conductivity type;
A plurality of island-like light emitting elements arranged on the semiconductor substrate, a buffer layer exhibiting one conductivity type, a light reflecting layer in which layers having different refractive indexes with respect to the emission wavelength are alternately stacked; A first clad layer exhibiting one conductivity type, an active layer that emits light, a second clad layer of opposite conductivity type that allows the emission to be extracted from above, and one electrode are sequentially formed . A light emitting device having a cross-sectional shape of an inverted mesa shape from the top toward the light reflecting layer, and the one electrode disposed outside the light reflecting layer in the vicinity of the end on the second cladding layer;
An LED array comprising: the other electrode provided on the back surface of the semiconductor substrate.

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