JP3205049B2 - Light source for optical printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source for a high-density optical printer using a light emitting diode array as a means for writing on a photosensitive member or the like.

[0002]

2. Description of the Related Art A light emitting diode array has been studied for the purpose of application to a light source or the like of an optical printer or the like employing a printing method using electrophotography. Here, the light-emitting diode array of the light source for the optical printer is composed of a self-luminous array element, and the light-emitting diode array emits light in accordance with an image signal, and forms an electrostatic latent image on the surface of the photoreceptor with the same-magnification imaging element. And printing and printing by an electrophotographic method. Since the light emitting diode array has no moving parts and few components, when used in such a head of an optical printer, the size of the print head can be reduced. In addition, self-emission type, high extinction ratio, good contrast can be obtained, furthermore, it is possible to cope with longer length by connecting the chip, and it is possible to cope with higher speed by increasing the output of the light emitting diode. Can benefit. In this case, the light emitting diode array used may be a surface emitting type light emitting diode array in which a large number of light emitting units such as squares are arranged in a predetermined direction in a plane parallel to the substrate surface, or a predetermined direction from an end surface perpendicular to the substrate surface. There is an edge-emitting light-emitting diode array that can provide a large number of light outputs.

First, as a basic structure of a surface emitting type light emitting diode array, for example, a structure as shown in FIG. 7 has been reported (Preliminary Proceedings of the Communication Division of the Institute of Electronics and Communication Engineers, 1980, 1-1-1. See section 211). In such a surface-emitting type light-emitting diode array, in many cases, electrodes 6 are formed at both ends or around the light-emitting portion in order to make the intensity of the light output obtained from the light-emitting portion 5 uniform within the light-emitting surface. I have. As described above, in the surface emitting type light emitting diode array, since the light emitting portion 5 from which light output is taken out and the electrode 6 are on the same surface, the width required per unit element is determined by the width of the light emitting portion 5 and the electrode 6. It is the sum of the width and the width of the element isolation region, and it is extremely difficult to form a light emitting portion with a high density of, for example, 600 dpi (dotsper inch) or more.

Next, as an edge emitting type light emitting diode array, for example, there is one as shown in FIG. 8 (see Japanese Patent Application Laid-Open No. Sho 60-32373). In this example, a plurality of light emitting units 7 are formed in a laminated structure on a substrate, and these light emitting units are formed in a direction parallel to the substrate surface and in a direction perpendicular to the end surface. The separation groove 3 electrically and spatially separates each other. In such an edge emitting type light emitting diode array, the light emitting unit 7 from which light output is taken out
And the electrodes 21 and 25 do not exist on the same surface, and the width required per unit element is the sum of the width of the light emitting section and the width of the element isolation region. Can also be formed in principle. For this reason,
It can be said that an edge emitting type light emitting diode array is suitable as a light emitting diode array for a high density optical printer head.

[0005]

When the edge emitting light emitting diode array having the above-mentioned features is changed from a wafer state to a chip state, chips must be cut out by a method such as dicing. In order to cut out a chip such as dicing, a terrace having a length of about 5 to 10 μm is necessarily formed on the substrate from the light emitting end face of each light emitting diode element as shown in FIG. This terrace reflects light emitted from each element of the light-emitting diode, and causes a subpeak in a far field pattern (FFP) in a direction perpendicular to the substrate, as shown in FIG. In addition, non-uniform chipping of the substrate called chipping may occur at the tip of the terrace due to dicing. For this reason, the positions of the sub-peaks are shifted, the number of the sub-peaks is different, the sub-peaks are eliminated, and the like, so that the uniformity of the far-field image is impaired. Due to this non-uniformity, when light emitted from the light-emitting diode array is incident on the unit-magnification imaging element, non-uniformity of the incident light amount occurs. There is a possibility that high quality and high resolution printing with high density uniformity may not be possible.

The present invention has been made in view of the above circumstances, and in order to realize high-density, high-quality, high-gradation printing, a light-emitting portion can be formed at a high density of, for example, 600 dpi or more. A light source for an optical printer using an edge-emitting light-emitting diode array that eliminates the above-mentioned drawbacks and has high uniformity of print dots and print density, and enables high-quality, high-resolution print printing. The purpose is to provide.

[0007]

In order to achieve the above object, the present invention provides a laminated structure including at least a light emitting layer of a light emitting diode and an electrode for causing the light emitting layer to emit light, formed on a semiconductor substrate. In the light source for an optical printer constituted by a light emitting diode array formed by separating each layer by a plurality of electric and spatial separation grooves provided at equal intervals, an edge emitting light emitting diode capable of obtaining light output from the laminated end face, Each light emitting diode of the above light emitting diode array
Peak of far-field image perpendicular to the iodine substrate
Light emitting end face of each light emitting diode
Inverted taper shape, specified from the normal direction of the semiconductor substrate
It is characterized by tilting at an angle .

That is, according to the present invention, a plurality of light emitting diodes are provided, and a plurality of light emitting diode arrays are arranged at least in a row at a predetermined pitch. In an optical printer light source for forming an image divided into dots, while using an edge emitting light emitting diode array made of a compound semiconductor for the light emitting diode array,
Reverse the light emitting end face in the above edge emitting light emitting diode
By tapering and tilting at a specific angle from the normal direction of the semiconductor substrate, it becomes possible to shift the peak of the far-field image perpendicular to the substrate of each light emitting diode to the upper surface side, so that the same far-field image Can be suppressed, and the far-field pattern of each edge-emitting light emitting diode becomes uniform in the chip and in the wafer. As a result, when the light emitted from the light-emitting diode array is incident on the unit-magnification imaging element, the amount of incident light is uniform, and the dot size and print density are highly uniform at high densities such as 600 dpi or more. This enables high-resolution printing and printing.

Hereinafter, the configuration and operation of the light source for an optical printer according to the present invention will be described in detail. The light source for an optical printer according to the present invention has a structure in which an edge-emitting light-emitting diode array made of a compound semiconductor is formed on a GaAs substrate 11 by epitaxial growth as shown in FIG. In order to easily obtain an edge emitting light emitting diode array having a high dot density simply by providing a separation groove, the light emitting portion has a three-layer slab DH (Double Heterro) structure (cladding layer 13, active layer 14, cladding layer). 15). A GaAs cap layer 16 and a GaAs contact layer 17 are formed on the three layers, and electrodes are formed thereon. Separation grooves 19 for electrical and spatial isolation between adjacent elements are formed over each layer. The present invention is characterized in that the light emitting end face 30 of each light emitting diode element 27 is inclined at a specific angle from the normal direction of the substrate 11 at the same time as the above step. Also, substrate 1
An electrode 25 is formed on the back surface side of 1.

Here, the refractive index of the active layer 14 of the light emitting portion made of the compound semiconductor having the three-layer slab structure is defined as n = N (≧
1). Since the light source for the optical printer according to the present invention is an edge-emitting light emitting diode array, the emitted light is emitted through the active layer 14 into the air (n = 1). Here, when light is incident from the medium having the refractive index n _{1 to} the medium having the refractive index n ₂ , the angle between the incident angle θ ₁ and the emission angle θ ₂ is:
It is known that there is a relationship such as the following equation (1). sin θ ₁ : sin θ ₂ = n ₂ : n ₁ (1) From equation (1), when light is emitted from the medium having the refractive index N (active layer) to the medium having the refractive index 1 (air). , Incident angle θ ₁ <
It can be seen that the emission angle θ ₂ holds. Based on this principle,
As shown in FIG. 1, the light emitting end face 3 of each light emitting diode element 27
By inclining 0 at a specific angle from the normal direction of the substrate 11 and providing an angle of a reverse taper, the peak of the emitted light can be shifted to the upper surface side. For example, when Al _0.2 Ga _0.8 As (N = 3.45) is selected as the active layer 14, there is a relationship between the incident angle θ ₁ and the output angle θ ₂ as shown in FIG.

That is, as shown in FIG.
Is the refractive index of n, the emission angle of emitted light by the DH structure is φ, the length of the terrace of the substrate 11 formed by dicing is x, and the height to the active layer 14 due to the etching depth for element isolation. Is d, and the angle of the reverse taper angle of the light emitting end face is θ, by setting the above parameters so as to satisfy the following equation (2), a uniform far-field image without a subpeak can be obtained (however, 1 ≧ nsin (90 °-
θ); from total reflection condition). sin ~ ¹ (nsin (90 ° −θ)) + φ / 2 + tan ~ ¹ ((x−d / tanθ) / d) + 90 ° −θ ≦ 180 ° (2) Thus, the above condition is satisfied. By setting each parameter in this way, it becomes possible to shift the peak of the far-field image in the direction perpendicular to the substrate of each light-emitting diode to the upper surface side, thereby making it possible to suppress the sub-peaks of the same far-field image. In addition, the far-field image of each edge emitting light emitting diode becomes uniform in the chip and the wafer. As a result, when the light emitted from the light-emitting diode array is incident on the unit-magnification imaging element, the amount of incident light is uniform, and the dot size and print density are highly uniform at high densities such as 600 dpi or more. This enables high-resolution printing and printing.

[0012]

In the light source for an optical printer according to the present invention,
By using an edge emitting light emitting diode array made of a compound semiconductor for the light emitting diode array, a simple electrode stripe type DH (Double Heterro) structure can be obtained, and the adjacent elements can be formed to have a desired high dot density. It is possible to freely form an electrical and spatial separation groove by selecting the pitch of (1). Thereby, a light source for a high dot density light emitting diode printer can be realized. In addition, an edge-emitting light-emitting diode array is adopted, and the light-emitting end face of each light-emitting diode element of the light-emitting diode array is inverted.
By tapering and tilting at a specific angle from the normal direction of the semiconductor substrate, it becomes possible to shift the peak of the far-field image perpendicular to the substrate of each light emitting diode to the upper surface side, so that the same far-field image , And the far-field images of the edge emitting light emitting diodes become uniform in the chip and in the wafer. As a result, when the light emitted from the light-emitting diode array is incident on the unit-magnification imaging element, the amount of incident light is uniform, and the dot size and print density are highly uniform at high densities such as 600 dpi or more. This enables high-resolution printing and printing.

[0013]

Embodiments of the present invention will be described below in detail. FIG. 1 is a perspective view of a main part of a light source for an optical printer according to an embodiment of the present invention.
Is a buffer layer, 13 is a cladding layer, 14 is an active layer (light emitting layer), 15 is a cladding layer, 16 is a cap layer, 17 is a contact layer, 19 is a separation groove, 24 is a wiring electrode, and 25 is an electrode on the back side of the substrate. , 27 are end emitting light emitting diode elements, 30 is a light emitting end face of each end emitting light emitting diode, and the light emitting portion is a three-layer slab DH composed of three layers of a cladding layer 13, an active layer 14, and a cladding layer 15. (Double Heter
ro) structure. In FIG. 1, the dimensions of each element of the edge-emitting light emitting diode array are 600 dp.
In order to realize i, the width is 32.3 μm and the element length is 5
The height was set to 0 μm, the height was set to 5 μm, and the width of the separation groove 19 between the elements was set to 10 μm. Then, in order to suppress the sub-peak of the far-field image, the light emitting end face 30 is set at a distance of 10 from the normal direction of the substrate 11.
° It is manufactured by tilting. Chips are cut out by dicing, and the terrace length is 7 μm.

The most important feature of the present invention is that the light emitting end face 30 of the edge emitting light emitting diode 27 is inclined at a specific angle from the normal direction of the semiconductor substrate 11.
It is possible to shift the peak of the far-field image in the direction perpendicular to the substrate of each light emitting diode 27 to the upper surface side. For this reason, it becomes possible to suppress the subpeak of the far-field image, and the far-field image of each edge-emitting light emitting diode 27 becomes uniform in the chip and the wafer. As a result, when the light emitted from the light-emitting diode array is incident on the unit-magnification imaging element, the amount of incident light becomes uniform, and 600 dp
At a high density such as i, high-quality, high-resolution print printing with high uniformity of dot size and print density becomes possible.

Next, an example of a manufacturing process of the light source for the optical printer according to the present invention will be described with reference to FIGS. First, as shown in FIG.
MBE (Molecular Beam Epitaxy) method or LPE (L
iquid Phase Epitaxy) method or MOCVD (Metal
For example, using a crystal growth method such as an Organic Chemical Vapor Deposition method, for example, the n-GaAs buffer layer 12,
n-Al _0.4 Ga _0.6 As clad layer 13, Al _0.2 Ga _0.8 As active layer 14 as a light emitting layer, p-Al _0.4 Ga _0.6 A
An s cladding layer 15, a p-GaAs cap layer 16, and a p @ + -type GaAs contact layer 17 doped with zinc at a high concentration are sequentially formed. Next, as shown in FIG. 4B, after a photoresist coating and a photolithography process, Cr evaporation is performed, and a Cr mask 18 is formed by a lift-off method. Next, as shown in FIG.
CR-RIBE equipment (Electoron Cyclotron Resonance-
By dry etching using Reactiv Ion Beam Etching, a separation groove 19 having a depth of about 3.5 μm and at least reaching the n-cladding layer 12 is formed. next,
As shown in FIG. 4D, a Cr mask 18 is formed using HCl or the like.
After the application of a photoresist and a photolithography process, Au-Zn / Au deposition is performed, and the upper electrode 21 is formed by a lift-off method.

Next, as shown in FIG. 5A, an insulating film 22 of SiO ₂ or the like is formed by EB evaporation or CVD.
Next, as shown in FIG. 5B, a contact hole 23 is formed in the insulating film 22 by a photolithography process and a wet etching process using hydrofluoric acid. Next, as shown in FIG. 5 (c), after a photoresist coating and a photolithography process, Cr / Au deposition is performed to form an upper wiring 24 using a lift-off method, and further, EB is formed.
A protective film 20 such as SiO ₂ is formed by vapor deposition or CVD. Finally, as shown in FIG. 5D, a back electrode 25 made of AuGe / Ni / Au or the like is provided on the back surface of the substrate 11.
Is formed, and a light source for an optical printer is formed on the n-type GaAs substrate 11 by forming an edge-emitting light emitting diode array made of a compound semiconductor by epitaxial growth.

In order to realize the light source for an optical printer according to the present invention, it is necessary to etch the light emitting end face so as to have an inversely tapered shape during dry etching at the time of element isolation. For this reason, in the embodiment according to the present invention, the ECR-RIB
The sample holder 41 of the E apparatus is tilted by 10 ° as shown in FIG. 6, and the light emitting end face is tilted by 10 ° by performing dry etching so that the ion beam enters the sample at an angle of 10 °. I have. Further, in the embodiment, Cr is shown as a mask for dry etching. However, the present invention can be implemented by using a mask such as SiO ₂ , TiO ₂ , or resist. Further, as the insulating film, it is possible to use SiN in addition to SiO ₂ . Although several examples using an n-type GaAs substrate as the substrate 11 have been described, a p-type GaAs substrate may be used. In this case, p-GaAs, The cladding layer 13 is p-Al _0.4 Ga _0.6 As, the active layer 14 is Al _0.2 Ga _0.8 As, and the cladding layer 15 is n-Al _0.4
Ga _0.6 As, n-GaAs is used for the cap layer 16, and n + GaAs is used for the contact layer 17, and an injection current for driving the element flows from the substrate 11 to the contact layer 17. It goes without saying that the composition of the compound semiconductor layer can sufficiently function even with a composition other than the above. In addition, other than AlGaAs-based materials, for example, In
The present invention can be implemented using other compound semiconductors and mixed crystal semiconductors such as GaP, InGaAs, and InAlAsP.

Further, a feature of the semiconductor light emitting device according to the present invention is that the light emitting diode array device portion has a simple electrode stripe type DH structure.
It is possible to form electrical and spatial separation grooves by selecting a pitch between adjacent elements so as to obtain a desired high dot density, thereby realizing a light source for a high dot density light emitting diode array printer. This means that at least one junction which emits light by forward bias current injection, such as an SH (Single Hetero) structure or a homojunction structure, has at least one junction parallel to the element end face and perpendicular to the light emission end face. Any light-emitting element having a light-emitting structure can be used.

[0019]

As described above, in the light source for an optical printer according to the present invention, an edge emitting type light emitting diode array is adopted for the light emitting element portion, and the light emitting end face is inverted.
By making it par-shaped and tilting at a specific angle from the normal direction of the semiconductor substrate, it is possible to suppress the sub-peak of the far-field image in the direction perpendicular to the substrate of each light-emitting diode, and to the light-emitting diode array Can be made uniform when the light emitted from the
At high densities such as pi or higher, high-quality, high-resolution print printing with high dot size and uniform print density can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of a light source for an optical printer according to an embodiment of the present invention.

FIG. 2 shows an active layer of the light source for the optical printer shown in FIG.
₅ is a graph showing a relationship between an incident angle θ ₁ and an outgoing angle θ ₂ in Expression (1) when _0.2 Ga _0.8 As is used.

3 is an explanatory diagram of Expression (2), and is a cross-sectional view of a main part of an edge-emitting light emitting diode of the light source for the optical printer shown in FIG.

4 (a) to 4 (d) are explanatory views showing steps for manufacturing a light source for an optical printer according to the present invention.

5 (a) to 5 (d) are explanatory views showing manufacturing steps after FIG. 4 (d).

FIG. 6 is an explanatory view of a method of forming an inverted tapered light emitting end face of a light source for an optical printer according to the present invention.

FIG. 7 is a view showing an example of the prior art, and is a plan view of a surface-emitting type light-emitting diode array.

FIG. 8 is a diagram showing another example of the prior art, and is a perspective view of an edge emitting light emitting diode array.

FIG. 9 is a perspective view of a main part of a light source for an optical printer using a conventional edge emitting light emitting diode array.

FIG. 10 is a graph showing a far-field image in a direction perpendicular to the substrate when having a subpeak.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Semiconductor substrate 12 ... Buffer layer 13, 15 ... Cladding layer 14 ... Active layer (light emitting layer) 16 ... Cap layer 17 ... Contact layer 18 ... Cr mask 19 ..Element isolation groove 20 ... Protective film 21, 25 ... Electrode 22 ... Insulating film 23 ... Contact hole 24 ... Wiring 27 ... Each light emitting diode element

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-233268 (JP, A) JP-A-60-32372 (JP, A) JP-A-5-69592 (JP, A) 88954 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/44 B41J 2/45 B41J 2/455 H01L 33/00 H04N 1/036

Claims (1)

(57) [Claims] An edge emitting light emitting diode having a laminated structure formed on a semiconductor substrate and including at least a light emitting layer of a light emitting diode and an electrode for causing the light emitting layer to emit light, wherein a light output is obtained from a laminated end face. In a light source for an optical printer constituted by a light emitting diode array formed by separating each layer by a plurality of electrical and spatial separation grooves provided at equal intervals, the light emitting diode substrate of the light emitting diode array and
Shift the far-field image peak in the vertical direction to the upper side.
The light emitting end face of each light emitting diode has a reverse tapered shape.
And a light source for an optical printer, wherein the light source is tilted at a specific angle from the normal direction of the semiconductor substrate .