JP2006128681A - Semiconductor light emitting device and exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To emit a blue or green light beam of small spot diameter and small incident angle. <P>SOLUTION: In the semiconductor light emitting device of surface light emission, a Bragg reflection mechanism comprising DBR multi-layer reflectors 64 and 69 on upper and lower layers sandwiching an active layer 66 is provided to restrict light emitting patterns by light quantum containment effect by the Bragg reflection mechanism. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a structure of a semiconductor light emitting device, and more particularly to a semiconductor light emitting device that outputs a green or blue light beam.

  In conventional silver halide photography digital printing devices, laser light is used as the light source, and since laser light is used as the light source, high-speed light beam scanning exposure using a polygon mirror or the like is possible, and high-speed printing is possible. In addition, it is not necessary to use high-speed paper feeding such as a drum for scanning, and simple paper feeding such as feeding with continuous paper is possible.

  Ideally, a laser light source that emits light in the three primary colors of RGB is used as the light source for the digital printing device. A gas laser has been mainly used as a conventional laser light source, but it requires a large size and special power source. However, it is difficult to adopt as a light source for a general-purpose device such as not having high reliability. Recently, the applicant has commercialized a digital printing apparatus “Frontier” equipped with a semiconductor laser as a red light source and a semiconductor laser pumped solid-state laser that generates a second harmonic as a blue and green light source. In the printing apparatus, by using a semiconductor laser-pumped solid-state laser as a blue and green light source, it becomes possible to provide a small-sized and high-quality laser light at a relatively low cost. Since the conversion is a semiconductor laser, the reliability is also improved. In addition, ordinary color paper that has the most stable characteristics and the least expensive three primary colors can be used.

  However, in order to further reduce the cost of these apparatuses, it is essential to reduce the cost of the laser light source that is a key device. There is no problem with red semiconductor lasers as light sources for high-density magneto-optical disks and DVDs (Digital Video Disks), but there are no prospects for practical semiconductor lasers for blue and green. In the case of a solid-state laser, parts and assembly costs are a barrier, and it is difficult to reduce the price as in the case of a semiconductor laser because of the configuration of the apparatus.

  On the other hand, a relatively inexpensive printing apparatus has been realized using a longer wavelength band semiconductor laser and a CMY (Cyan, Magenta, Yellow) color sensitive material (for example, Fujifilm Pictography). In such an apparatus, since a commercially available semiconductor laser (for example, 810 nm, 750 nm, 680 nm) can be used, the apparatus can be configured at a lower cost than when the solid laser is used.

  However, in order to use a commercially available semiconductor laser, it is necessary to prepare a special photosensitive material that matches the wavelength of the semiconductor laser, that is, a material whose sensitivity is shifted to a longer wavelength side than usual. There is a problem that the operating cost and the printing cost become high.

  On the other hand, in conventional light emitting diodes (LEDs), blue and green high-intensity LED light sources are realized using InGaN-based materials (“The Blue Diode”, S. Nakamura and G. Fasol, Springer, Berlin) 1997). These have a light emitting surface of about several hundred μm square like other red LEDs, and the light is divergent light. Therefore, when a spot with a diameter of several tens of μm is to be formed using these light sources in order to constitute a high-definition printer, the emitted light is condensed because it is collected by a lens of a finite size. The amount of light is extremely small, and since the image is formed by a reduction optical system of about 1/2 to 1/10, the distance between the lens and the light source is relatively increased, further reducing the coupling efficiency. There is a problem.

  In view of the above circumstances, the present invention emits blue and green light beams with a small spot diameter and a small radiation angle, and can be manufactured at low cost, which can be used in an exposure apparatus using a normal photosensitive material for visible light exposure. It is an object of the present invention to provide a semiconductor light emitting device that can be used and an exposure apparatus employing the semiconductor light emitting device.

The first semiconductor light emitting device of the present invention is a semiconductor light emitting device having a stripe structure having an optical waveguide mechanism and having a reflecting mirror formed on the light emitting end face,
A green light beam or a blue light beam having a wavelength of 450 nm or more is emitted by superradiance from the light emitting region limited by the optical waveguide mechanism.

The second semiconductor light emitting device of the present invention is a surface light emitting semiconductor light emitting device,
The upper and lower layers sandwiching the active layer are equipped with a Bragg reflection mechanism,
A green or blue light beam is emitted by superradiance with a light emission pattern limited by the quantum confinement effect of light by the Bragg reflection mechanism.

  Here, the phrase “light emission by superradiance” means light emission that is stimulated emission by the reflective structure of the element but is not laser oscillation.

The third semiconductor light emitting device of the present invention is a surface emitting semiconductor light emitting device,
A lens is formed on a part of the light emitting end face,
A portion other than the lens of the light emitting end face is covered with a light shielding member,
A green or blue light beam is emitted from the lens.

  Each of the semiconductor light emitting elements is preferably formed of an InGaN based semiconductor.

An exposure apparatus of the present invention comprises a light source comprising a red semiconductor light emitting element, a semiconductor light emitting element that emits the blue light beam of the present invention, and a semiconductor light emitting element that emits a green light beam,
And a scanning optical system.

  In the first semiconductor light emitting device of the present invention, since the light emitting region is limited by the optical waveguide mechanism and the stripe structure, a green or blue light beam having a small light emission diameter and a narrow emission angle can be output.

  Since the second semiconductor light emitting device of the present invention has a Bragg reflection (DBR) mechanism, the light emission pattern can be limited by the quantum confinement effect of light, and the green light emission angle is narrow and the light emission angle is narrow. Alternatively, a blue light beam can be output.

  The third semiconductor light emitting device of the present invention is a general surface light emitting diode (LED) in which a lens is formed on a part of a light emitting end face and the other part is covered with a light shielding member. The light emitting area is limited, and the lens can output a green or blue light beam having a small emission diameter and a narrow emission angle.

  The exposure apparatus of the present invention can be constructed at low cost by including a light source comprising the red semiconductor light emitting element and the above-described green semiconductor light emitting element and blue semiconductor light emitting element according to the present invention, and the semiconductor of the present invention. Since the green and blue light beams emitted from the light emitting elements have small emission diameters and narrow emission angles, they are as fast and high quality as conventional exposure equipment using laser light and second harmonics. Can be.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of an InGaN blue semiconductor light-emitting device according to the first embodiment of the present invention. As shown in FIG. 1, the semiconductor light emitting device according to the present embodiment has a double hetero structure in which an active layer 7 is sandwiched between clad layers 6 and 8, similar to the structure of a general stripe type semiconductor laser. Therefore, a stripe-shaped current injection window 12 is provided. Further, the cleavage surface of the element is a reflection surface, and a light reflection structure is formed. This device does not oscillate, but emits light with so-called super radiance due to the layer structure and the optical waveguide structure consisting of the ridge type refractive index waveguide structure and the light reflecting structure formed by reflection of both light emitting end faces. . Note that the semiconductor light emitting device of this embodiment emits a blue light beam in a 470 nm band.

  Hereinafter, the layer configuration of the semiconductor light emitting device will be briefly described together with the manufacturing method. Using MOCVD on the sapphire c-plane substrate 1, n-GaN low-temperature buffer layer 2, n-GaN buffer layer 3 (Si-doped, 5 μm), n-In0.05Ga0.95N buffer layer 4 (Si-doped, 0.1 μm) ), N-Al0.1Ga0.9N cladding layer 5 (Si-doped, 0.5 μm), n-GaN light guide layer 6 (Si-doped, 0.1 μm), undoped active layer 7, p-GaN light guide layer 8 (Mg-doped) 0.1 μm), p-Al0.1Ga0.9N cladding layer 9 (Mg-doped, 0.5 μm) and p-GaN cap layer 10 (Mg-doped, 0.3 μm) are successively grown. Thereafter, the p-type impurity is activated by heat treatment in a nitrogen gas atmosphere. The active layer 7 includes an undoped ln0.05Ga0.95N (10 nm), an undoped In0.28Ga0.72N quantum well layer (3 nm), an undoped In0.05Ga0.95N (5 nm), and an undoped In0.28Ga0.72N quantum well layer ( 3 nm), undoped ln0.05Ga0.95N (10 nm) undoped Al0.1Ga0.9N (10 nm).

  Next, in order to form a ridge stripe having a width of 6 μm by photolithography and etching, the epitaxial layer other than the ridge stripe portion is removed from the cap layer 10 to the middle of the clad layer 9 by RIBE (reactive ion beam etching) using chlorine ions. To do. Next, after the SiN film 14 is formed on the exposed surface including the upper portion of the ridge stripe portion by plasma CVD, light emission including the ridge stripe portion is performed to form an n-side electrode by RIBE using photolithography and chlorine. The epitaxial layer other than the region is removed by etching until the n-GaN buffer layer 3 is exposed. At this time, a resonator end face is formed. Thereafter, a stripe window 12 (width 10 μm) for current injection is formed in the SiN film 14 on the upper surface of the ridge, and Ti / Al / Ti / Au is used as the p-side electrode 13 so as to cover the stripe window 12. Ni / Au is vacuum-deposited as an n-side electrode 11 on the exposed portion of the n-GaN buffer layer 3 and then annealed in nitrogen to form an ohmic electrode.

  The semiconductor light-emitting device manufactured as described above can be obtained with a narrow emission spot diameter of about 6 μm × 1 μm and a radiation beam angle of about 40 degrees. The spot diameter and radiation beam angle are extremely small compared to ordinary light emitting diodes (LEDs), and the light coupling efficiency to the exposure optical system of the printer is 1 to 2 digits or more compared to the case where conventional LEDs are used as the light source. Improve. Conventional LEDs usually have a light emitting spot diameter of about 300 μm or more, so an optical system for reducing the size to about 50 μm or less is necessary to realize the high-definition characteristics required in a printer. However, the present semiconductor light emitting device having a small spot diameter does not require such an optical system, so that a bright lens having a large aperture can be used closer, and the coupling efficiency to the optical system can be further improved. . In the above embodiment, the light emitting end face is not coated with an optical coating, but Super Radiance is highly dependent on reflectance, so the purpose is to control this, and the purpose is to control the light emitting intensity of the front and rear end faces. Various optical coatings for controlling the end face reflectance can be applied. The composition and thickness of each layer can be appropriately selected as long as the optical waveguide condition is satisfied.

  In the above-described embodiment, the device emits a 470-nm blue light beam, but the emission wavelength can be controlled by changing the In composition of the InGaN quantum well layer. Green wavelength elements can also be realized.

  FIG. 2 shows a schematic cross-sectional view of the semiconductor light emitting device of the second embodiment according to the present invention.

  The layer configuration and manufacturing method of the semiconductor light emitting device of this embodiment are substantially the same as those of the semiconductor light emitting device of the first embodiment, and the same reference numerals are assigned to the same layers, and detailed description thereof is omitted. This semiconductor light emitting device has a configuration in which a conductive 6H—SiC substrate 21 is used as a substrate and an n-side electrode 11 is formed on the back surface of the substrate 21. Even in the light emitting element having such a stripe structure, it is possible to emit a light beam with a narrow emission angle at a minute light emission spot.

  FIG. 3 shows a schematic cross-sectional view of the InGaN blue semiconductor light emitting device of the third embodiment according to the present invention.

  The semiconductor light emitting device according to the present embodiment has a structure similar to a DBR laser (distributed Bragg-reflection laser) having DBR multilayer reflectors provided above and below an active layer, and the light emitted from the DBR multilayer reflector. The light emission pattern is controlled by quantizing light by the confinement effect. Similarly to the first embodiment, this element does not oscillate, but emits light with so-called superradiance by the light reflecting structure formed by the DBR multilayer reflecting mirror. Note that the semiconductor light emitting device of this embodiment emits a blue light beam in a 450 nm band.

  A method for manufacturing the semiconductor light emitting device will be briefly described. An n-GaN low-temperature buffer layer 62, an n-GaN buffer layer 63 (Si-doped, 5 μm), an n-type DBR multilayer reflector 64 (Si) are formed on the 6H-SiC substrate 61 having n-type conductivity by MOCVD. Doped), n-GaN layer 65 (Si doped, 0.09 μm), undoped In0.25Ga0.75N quantum well active layer 66 (2 nm), p-Al0.2Ga0.8N barrier layer 67 (Mg doped, 20 nm), p- A GaN layer 68 (Mg-doped, 0.09 μm), a p-type DBR multilayer reflector 69 (Mg-doped), and a p-GaN cap layer 70 (Mg-doped, 0.2 μm) are grown. Thereafter, the p-type impurities are activated by heat treatment in a nitrogen gas atmosphere. Thereafter, the p-side electrode 71 is formed on the cap layer 70, except for at least a circular portion having a diameter of 100 μm from which light is extracted. After the n-side electrode 72 is formed and heat-treated, an antireflection film 73 is coated on the light emitting portion. The n-type DBR multilayer reflector 64 is formed by laminating 40.5 periods of n-Al0.1Ga0.9N 64a (Si-doped, λ / 4 equivalent thickness, 45 nm) and n-GaN 64b (Si-doped, λ / 4 equivalent thickness, 46 nm). . Similarly, the p-type DBR multilayer reflector 69 includes p-Al0.1Ga0.9N69a (Mg-doped, λ / 4 equivalent thickness, 45 nm), n-GaN 69b (Mg-doped, λ / 4 equivalent thickness, 46 nm) in 20.5 periods. Laminate. The semiconductor light emitting device fabricated in this embodiment has an emission wavelength of 450 nm, and the light emission pattern is sharpened by the effect of the microresonator.

  FIG. 4 is a schematic cross-sectional view of an InGaN blue semiconductor light emitting device according to the fourth embodiment of the present invention. Although it is the structure which has a DBR multilayer reflective mirror similarly to the said 3rd embodiment, in this Embodiment, the light emission pattern is controlled by providing an upper DBR layer only in a light emission area | region.

  The layer structure of the semiconductor light emitting device will be briefly described together with the manufacturing method. An n-GaN low-temperature buffer layer 82, an n-GaN buffer layer 83 (Si-doped, 5 μm), an n-type DBR multilayer reflector 84 (Si) are formed on the 6H-SiC substrate 81 having n-type conductivity by MOCVD. Doped), n-GaN layer 85 (Si doped, 0.09 μm), undoped In0.25Ga0.75N quantum well active layer 86 (2 nm), p-Al0.2Ga0.8N barrier layer 87 (Mg doped, 20 nm), p- A GaN layer 88 (Mg doped, 0.09 μm) is grown. The n-type DBR multilayer reflector 84 is formed by laminating 40.5 periods of n-Al0.1Ga0.9N 84a (Si-doped, λ / 4 equivalent thickness, 45 nm) and n-GaN 84b (Si-doped, λ / 4 equivalent thickness, 46 nm). Is.

  Thereafter, the p-type impurity is activated by heat treatment in a nitrogen gas atmosphere. Thereafter, the p-side electrode 90 is formed by using a lift-off method except for a circular portion having a diameter of 100 μm for extracting light. Thereafter, the DBR layer 89 is formed by multilayer coating of ZnS 89a and SiO 289b (each λ / 4 equivalent thickness 30.5 cycles), and the DBR layer other than the light emitting region is removed by etching. Thereafter, an n-side electrode 91 is formed and heat-treated. As described above, in this embodiment, the upper DBR layer is formed of a dielectric film of ZnS and SiO2, and is formed by a process different from the crystal growth of the semiconductor layer.

  FIG. 5 is a schematic cross-sectional view of an InGaN-based green semiconductor light-emitting device according to the fifth embodiment of the present invention. As shown in FIG. 5, the semiconductor light emitting device according to the present embodiment includes a lens-shaped portion 48 on the light-emitting surface in the structure of a general surface-emitting diode, and a portion other than the lens-shaped portion 48 on the light-emitting surface. It is covered with a light shielding material 49 (see FIG. 6). In other words, this element focuses and outputs natural light emitted from a normal light emitting diode by the lens-like portion 48. Note that the semiconductor light emitting device of this embodiment emits a green light beam in the 530 nm band.

  The layer structure of the semiconductor light emitting device will be briefly described together with the manufacturing method. An n-GaN low-temperature buffer layer 42, an n-GaN buffer layer 43 (Si-doped, 5 μm), undoped In0.45Ga0.55N quantum well active layer on the 6H-SiC substrate 41 having n-type conductivity by MOCVD 44 (2 nm), p-Al0.1Ga0.9N cladding layer 45 (Mg-doped, 0.1 μm), and p-GaN cap layer 46 (Mg-doped, 1.2 μm) are grown. Thereafter, the p-type impurity is activated by heat treatment in a nitrogen gas atmosphere. Thereafter, a circular resist pattern with a diameter of 80 μm is formed, and by RIBE using chlorine ions, the substrate is rotated and a chlorine ion beam is incident obliquely so as to form a p-GaN cap layer 46 into a lens shape 48 with a diameter of about 80 μm. Etch. Thereafter, a SiN insulating film 47 is formed on the cap layer 46 in a region excluding the lens-shaped portion 48 and the contact portion between the electrode to be formed later and the cap layer 46. The insulating film 47 is for limiting the portion where the electrode is in ohmic contact with the cap layer 46 around the lens-shaped portion 48. Next, a p-side electrode is formed on the cap layer 46 exposed around the insulating film 47 and the lens-shaped portion 48. FIG. 6 is a top view of the element shown in FIG. 5. As shown in the figure, the p-side electrode is formed in a portion excluding the lens shape portion, and plays a role of shielding light emitted from other than the lens shape portion. The shape of the p-side electrode can be various shapes such as a ring shape surrounding the lens shape portion as shown in FIG. At this time, the portions other than the lens-shaped portion and the electrode portion on the upper surface of the element may be shielded from light by a light absorbing material 55 such as polyimide. In this way, it is possible to realize a minute light emission spot and a narrow radiation beam by combining the electrode structure and lens processing.

  As described above, the semiconductor light emitting device according to the embodiment of the present invention has been described. However, it is possible to configure a high-speed and simple exposure system using the semiconductor light emitting device having the above-described minute emission diameter and narrow emission angle. .

  As the light source, for example, a semiconductor light emitting device that outputs a blue light beam of 470 nm shown in the first embodiment, a semiconductor light emitting device that outputs a green light beam of 530 nm manufactured in the same manner, and the like A conventional red semiconductor laser is used.

  FIG. 8 is a schematic view showing the arrangement of an embodiment of the exposure apparatus of the present invention. For simplicity, only one semiconductor light emitting device is shown in the drawing. In the present exposure apparatus, the light beam emitted from the semiconductor light emitting device 100 is incident on a movable mirror 102 such as a galvanometer mirror via a first lens 101 for reducing the spread angle of the light beam. The light beam is polarized by a mirror 102, and the light beam is condensed on a medium such as a silver salt photosensitive material by a condenser lens 103. As described above, when a light emitting diode that emits conventional diffused light is used as a light source, a complicated optical system is required to reduce the light spot. However, the semiconductor light emitting element of the present invention described above is used. By doing so, an exposure system can be configured using a simple optical system similar to that used when a semiconductor laser is used as a light source.

  FIG. 9 is a schematic view showing the arrangement of an exposure apparatus according to another embodiment of the present invention. In this embodiment, the exposure apparatus uses only the minimum necessary condenser lens 113 as a lens, and a polygon mirror 112 as a polarizing device for optical scanning. In this exposure apparatus, the light beam emitted from the semiconductor light emitting device 110 is incident on the polygon mirror 112, is scanned and polarized by the polygon mirror 112, and is condensed on the medium via the condenser lens 113.

  As described above, high-speed and high-quality exposure is achieved by using the semiconductor light-emitting device of the present invention capable of outputting a light beam with a small emission diameter and a small emission angle in the blue and green wavelength regions where it is difficult to realize a semiconductor laser. A device can be constructed. Further, a simple optical system can be obtained as compared with the case where a light emitting diode is used as a light source.

1 is a schematic cross-sectional view of a semiconductor light emitting device according to a first embodiment of the present invention. Sectional schematic diagram of the semiconductor light emitting device according to the second embodiment of the present invention. Sectional schematic diagram of the semiconductor light emitting device according to the third embodiment of the present invention. Sectional schematic diagram of the semiconductor light emitting device according to the fourth embodiment of the present invention. Sectional schematic diagram of a semiconductor light emitting device according to a fifth embodiment of the present invention. Schematic top view of the semiconductor light emitting device according to the fifth embodiment Other upper surface schematic diagrams of the semiconductor light emitting device according to the fifth embodiment Configuration schematic diagram of exposure apparatus of the present invention Configuration schematic diagram of another exposure apparatus of the present invention

Explanation of symbols

61 6H-SiC substrate
62 n-GaN low temperature buffer layer
63 n-GaN buffer layer
64 n-type DBR multilayer reflector 64
65 n-GaN layer
66 In _0.25 Ga _0.75 N quantum well active layer
67 p-Al _0.2 Ga _0.8 N barrier layer
68 p-GaN layer
69 p-type DBR multilayer reflector 69
70 p-GaN cap layer
71 p-side electrode
72 n-side electrode
73 Anti-reflective coating

Claims (4)

A surface emitting semiconductor light emitting device,
The upper and lower layers sandwiching the active layer are equipped with a Bragg reflection mechanism,
A semiconductor light emitting device that emits a green or blue light beam by superradiance with a light emission pattern limited by a quantum confinement effect of light by the Bragg reflection mechanism. A surface emitting semiconductor light emitting device,
A lens is formed on a part of the light emitting end face,
A portion other than the lens of the light emitting end face is covered with a light shielding member,
A semiconductor light emitting element emitting a green or blue light beam from the lens. 3. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is formed of an InGaN based semiconductor. A light source comprising a semiconductor light emitting device that emits a blue light beam and a semiconductor light emitting device that emits a green light beam, and a semiconductor light emitting device that emits a red light beam according to any one of claims 1 to 3,
An exposure apparatus comprising a scanning optical system.

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