KR20050034686A - Iii-nitride photo disk emitters - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nitride semiconductor optical disk emitters, laser diodes, and modulators. In particular, in the growth of nitride semiconductors, a silicon (Si) substrate is used to provide an organic metal. Growing a nitride semiconductor epitaxy thin film by Chemical Vapor Deposition, etching circular disk by etching process, and lateral penetration etching method using silicon and silicon substrates by wet and dry etching The present invention relates to a method for fabricating a nitride semiconductor optical disk emitter (III-nitride Photo Disk Emitters), a laser diode and a modulator applied to an optical communication device and an optical module.

Optical disk laser light emitting device according to the present invention for achieving the above object is composed of a nitride semiconductor active layer and a clad layer on a silicon substrate, the light generated in the active layer in the optical disk Whispering Gallery Mode (WGM) It is characterized by having a structure for generating light efficiently.

Therefore, the nitride semiconductor optical disk laser light emitting device according to the present invention can be applied to fabricate an optical signal generating device and an optical modulation device in an optical communication field of a wavelength division method.

Description

Nitride Semiconductor Optical Disk Emitters {III-nitride Photo Disk Emitters}

Nitride semiconductors are direct-transition semiconductors with a wide energy bandgap, and are very useful materials for manufacturing light emitting devices capable of realizing light emission from visible light to ultraviolet light. The research on such nitride semiconductors has been progressing to a great extent in the 1990s with the successful development of high quality crystal growth technology using low temperature GaN buffer layer on sapphire substrate and the development of Mg-doped p-type GaN. In particular, the successful development of white light emitting diodes combining high brightness blue light emitting diodes and fluorescent organic materials has been rapidly applied in next-generation environment-friendly lighting, energy industries, and high-density optical recording media. In addition, the development of a nitride semiconductor growth method having high quality and low dislocation density has resulted in the development of a blue semiconductor laser diode and successfully succeeded in room temperature oscillation.

Since the nitride semiconductor epitaxy growth technology essentially lacks a nitride semiconductor and a lattice matching substrate, the conventional technology inserts GaN, AlN, or a compound thereof, AlGaN, InGaN buffer layer, grown at low temperature, on a sapphire substrate to provide high quality at a high temperature. GaN epitaxy thin film has been grown by the method. Based on this, the device was fabricated by the method of device fabrication by forming and etching layer structure of light emitting device and horizontal light emitting semiconductor laser device. Shiji Nakamura et al. Of Japan succeeded in oscillating nitride semiconductor blue laser diode. Shuji Nakamura et al., 'The Blue Laser Diode', ISBN 3-540-61590-3, Springer, 1997).

Regarding the remarkable achievements in the field of light emitting devices employing such nitride semiconductors, the present invention has produced an optical disk light emitting device that generates a constant resonance mode in the form of a circular disk as a form of an advanced semiconductor light emitting device.

An optical disk light emitting device is a laser device having a low oscillation voltage and a low driving voltage by using the characteristic that Whispering Gallery Mode (hereinafter referred to as WGM) is formed by total internal reflection in a disk having a circular thin film structure. Can be produced. The implementation of such a light emitting device has been a lot of research over the last few decades, many examples are implemented using a dielectric thin film and a semiconductor epitaxy thin film. Representative examples thereof are reported in the following references.

(1) S. L. Mccall et al., Applied Physics Letter, Vol. 60 (3), pp. 289-291, 1992.

(2) K.-S. Kim et al., Phys. Stat.sol. (B) vol. 228, no. 1, pages 169-172, 2001.

(3) Seung June Choi et al., IEEE Photonics Technology Letters, Vol. 15, No. 10, pages 1330-1332, 2003.

(4) T. J. Kippenberg et al., Applied Physics Letter, Vol. 83 (4), pp. 797-799, 2003.

The study of the optical disk light emitting device has a feature that can control the light emission wavelength and the resonant wavelength of the device differently according to the shape and size of each selected material and the fabricated device.

In addition, an optical disk light emitting device using a nitride semiconductor is also K.-S. As described by Kim et al. (Phys. Stat. Sol. (B) vol. 228, No. 1, pages 169-172, 2001.), the implementation of the characteristics of the light emission was confirmed. However, the sapphire substrate is a high-resistance insulator with no electrical conductivity, and it is difficult to form an electrode capable of injecting current on the sapphire substrate, and is chemically stable. Alternatively, dry etching is very difficult, so it is difficult to form an even spread of current when driving the nitride semiconductor light emitting device and the laser, and it is difficult to effectively discharge heat generated when driving the device, thereby increasing the driving voltage of the device, Increases the deterioration of

Therefore, the inventors of the present invention, in the fabrication of nitride semiconductor optical disk emitters (III-nitride Photo Disk Emitters), instead of the conventional sapphire substrate, a silicon (Si) surface orientation (111) substrate having good electrical conductivity and heat emission characteristics In this study, a method of fabricating an optical disk light emitting device by growing a high quality nitride semiconductor and forming a light emitting device layer was used. In addition, silicon semiconductor is a representative material of semiconductors for decades, and has a well-developed doping technique having n-type and p-type conductivity, and many semiconductor device manufacturing techniques have been developed, etching processes, doping techniques, and electrode forming techniques. This extremely developed and relatively good heat transfer property has a number of advantages as a substrate for manufacturing a nitride semiconductor light emitting device. In particular, in order to fabricate an optical disk light emitting device, the lower part of the optical disk must be etched. However, a method of effectively etching the lower part of the optical disk using only a sapphire substrate and leaving the optical disk is not possible due to the chemically stable sapphire substrate. . However, in the present invention, a method of fabricating an optical disk light emitting device is simpler and more effective by growing a nitride semiconductor using a silicon substrate and infiltrating etching to the lower end of the nitride semiconductor optical disk by using a chemically etched silicon substrate. Developed.

Therefore, in the present invention, the nitride semiconductor light emitting device structure is fabricated by epitaxial growth method on the silicon substrate, which is easier to chemically etch and form oxide film than the sapphire or silicon carbide (SiC) substrate, and the nitride semiconductor light emitting layer structure is circularly etched, The purpose of the present invention is to fabricate an optical disk by selectively growing on a patterned silicon substrate, and to fabricate a nitride semiconductor optical disk light emitting device and a laser diode by chemically penetrating etching the silicon substrate at the lower end of the optical disk.

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

1 is, according to an embodiment of the present invention, a structure growth layer of a light emitting device including a nitride semiconductor active layer and a clad layer on a silicon substrate is grown by an organometallic chemical vapor deposition method to form a nitride semiconductor in the form of an optical disc, A diagram showing a schematic form of a nitride semiconductor optical disk light emitting device fabricated by lateral penetration etching of a silicon substrate.

FIG. 2 is a top view (a) and a cross-sectional view (b) schematically showing the photonic crystal structure of a nitride semiconductor optical disk light emitting device structure formed on a silicon substrate as an embodiment according to the present invention.

 It is not easy to grow high quality nitride semiconductors because of very large lattice constant difference (~ 17%) and thermal expansion coefficient difference between silicon substrate and nitride semiconductor epitaxy thin film. This lattice mismatch is not epitaxially grown nitride semiconductor crystal structure, but is grown in grain shape, causing cracks in the thin film, and causing a lot of dislocations and defects in the crystals. It acts to lower the light efficiency.

Therefore, in order to grow the n-type contact layer 50, in the present invention, by using the AlN layer grown at high temperature as a buffer layer for growing a high quality GaN nitride semiconductor on a silicon substrate, two-dimensional epitaxy growth is performed. It acts as a growth nucleus to promote high quality two-dimensional semiconductor thin film growth. In addition, in order to prevent the growth of amorphous silicon nitride (SiN) by the combination of silicon atoms desorbed from the silicon substrate at the beginning of nitride semiconductor growth and nitrogen (N) atoms of ammonia (NH3) gas used as a nitride semiconductor growth source. By depositing trimethylaluminum (hereinafter referred to as TMAl) to a few atomic layers, the nitride semiconductor epitaxy thin film was grown on a two-dimensional plane. GaN thin films grown on such buffer layers still cause very high crack densities due to tensile stress occurring between the interface with the silicon substrate. Therefore, in the present invention, a GaN thin film having a thickness of about 0.3 μm is formed as a layer structure capable of compensating stress in order to suppress cracking caused by tensile stress, and then an AlN thin film having a thickness of about 250 nm is formed again at the interface with the substrate. By forming a structure to relieve stress, cracking of the GaN nitride semiconductor thin film could be suppressed. The Si doped n-type GaN layer was grown on the buffer layer and the stress relaxation structure layer. In addition, the silicon nitride (SiN) potential reducing layer stops the supply of ammonia gas, which is a nitrogen source, and supplies a larger amount of silane (SiH3), which is a source of Si doping, to partially form the SiN layer during the growth of the n-type GaN layer. Formed to block dislocations propagating from the underlying layer. As a result, the upper GaN layer was able to form a GaN thin film having very good quality with a sharp drop in dislocation density.

The semiconductor light emitting device has a large band gap composed of both an active layer 80 composed of a multiple quantum well structure for improving luminous efficiency and an active layer for increasing the bonding ratio of electrons and holes in the active layer. It is composed of layers. In the present invention, an active layer having an InGaN / GaN quantum well structure was grown, and the emission wavelength of the light emitting device can be controlled by controlling the In composition ratio of InGaN used as the quantum well layer. In addition, an Si-doped AlGaN layer was used as the n-type cladding layer 70. The luminous efficiency is different depending on the composition ratio and thickness of Al, but it is necessary to optimize the Al content and thickness in consideration of cracks and crystal defects. Preferably the Al content is on the order of 5 to 50% and the thickness is on the order of 10 to 300 nm. The p-type cladding layer 60 is an Mg-doped AlGaN layer and the Al content and thickness are similar to the n-type cladding layer 70.

As described above, after fabricating a wafer having a structure of a nitride semiconductor light emitting device formed on the silicon substrate by an organometallic chemical vapor deposition method, a process of forming an optical disk light emitting device thereon is as follows.

In order to form an optical disk, silicon oxide (SiO 2) is formed on a silicon substrate, and a nitride semiconductor structure layer 90 is selectively grown in a circular manner, and a nitride semiconductor structure layer 90 is formed on an entire silicon substrate. Afterwards, a circular optical disc may be manufactured by a dry etching method. In the method of forming by dry etching, a photoresist is applied on the grown wafer, exposed using a mask having a circular shape, and then removed by etching, leaving only the circular part of the optical disk by the dry etching process.

After fabrication of the optical disk shape, wet etching is performed with a chemical which etches only silicon out of the nitride semiconductor and silicon to etch the silicon substrate at the lower end of the remaining circular nitride semiconductor structure layer 90. As the etching liquid penetrates into the side surface of the nitride semiconductor lower portion as it deepens, a mushroom-shaped optical disk structure can be formed. At this time, as the type of etchant used, the etching rate can be controlled by mixing the chemicals of most acids and bases such as nitric acid, acetic acid, sulfuric acid, hydrochloric acid, ammonia and hydrogen peroxide. In general, since the nitride semiconductor is very stable in chemicals and its etching rate is extremely low, wet etching is very easy for fabrication of an optical disk light emitting device because it is not greatly damaged or deformed even by etching a general silicon wafer by wet etching. It can be called a method.

An n-type electrode 20 having a nitride semiconductor and ohmic characteristics and a p-type electrode 30 having ohmic characteristics are fabricated in the optical disk light emitting device structure manufactured as described above. The shape of the n-type electrode 20 is preferably formed in the form of a concentric circle, and has an advantage of controlling the resonance rate and the luminous efficiency of the emitted light according to the position at which the current is injected. In addition, in some cases, when manufacturing a polygonal shape, there is an advantage in that the polarization of the optical disk light emitting device can be controlled. It is possible to produce a preferable shape in accordance with the performance of the optical disk light emitting element.

The P-type electrode 30 is preferably formed around the pillar on the silicon substrate supporting the mushroom-shaped optical disk, but in order to fabricate a device having better electrical device characteristics, it is also preferable to deposit the side of the pillar. In addition, it is also possible to form an electrode on the lower surface of the nitride semiconductor by a plating method in order to prevent a rise in driving voltage due to an electrical potential barrier between the silicon substrate and the nitride semiconductor.

In addition, since the nitride semiconductor thin film is very fragile by several micrometers, the optical disk light emitting device structure may be passivated by filling the side etched portion using polyimide and dielectric deposition, and also introduced for the reliability of the device. to be.

Figure 3 shows an electron micrograph showing the shape of the optical disk light emitting device structure in the form of an array according to an embodiment of the present invention.

As described above, in the present invention, in fabricating a nitride semiconductor light emitting device, the semiconductor semiconductor light emitting device structure is epitaxially grown on a silicon (Si) substrate, and the optical disk structure is formed by the side penetration etching angle of the silicon substrate, thereby providing a whisper. It is characterized by having a structure for efficiently generating laser light in a ring gallery mode (hereinafter referred to as WGM).

1 is, according to an embodiment of the present invention, a light emitting device structure layer including a nitride semiconductor active layer and a clad layer on a silicon substrate is grown by an organometallic chemical vapor deposition method to form a nitride semiconductor in the form of an optical disc, and a silicon substrate Figure showing a schematic form of a nitride semiconductor optical disk light emitting device produced by the side penetration etching.

2 is a top view (a) and a cross-sectional view (b) schematically showing a photonic crystal structure of a nitride semiconductor optical disk light emitting device structure formed on a silicon substrate as an embodiment according to the present invention.

Figure 3 is an electron micrograph showing the shape of the optical disk light emitting device in the form of an array according to an embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

10 silicon substrate 20 n-type electrode

30 p-type electrode 40 p-type contact layer

50: n-type contact layer 60: p-type cladding layer

70: n-type cladding layer 80: active layer

90: nitride semiconductor structure layer

Claims (4)

A light emitting device structure including an n-type and p-type contact layer made of nitride semiconductor, an n-type and p-type cladding layer, and an active layer is formed on a silicon substrate, and the circular nitride semiconductor is etched by an etching process or a selective region growth method. After the formation, a circular optical disk is fabricated using side penetration etching by a selective wet etching process of a silicon substrate and a nitride semiconductor, and an ohmic n-type electrode and a p-type electrode which inject current therein are mounted and generated inside the active layer. It characterized in that it has a structure for generating the laser light by the whispering galley mode by the total reflection inside the optical disk, it is possible to add a non-reflective mirror layer structure on top of the optical disk to increase the internal total reflectance of the optical disk A nitride semiconductor optical disk light emitting device, characterized in that. The semiconductor light emitting device according to claim 1, wherein the shape of the n-type electrode is formed in a concentric circle structure, and the resonance wavelength is controlled according to the current injection position. The semiconductor light emitting device according to claim 1, wherein the shape of the n-type electrode is formed in a polygonal structure to control polarization characteristics. The semiconductor light emitting device of claim 1, wherein in manufacturing the optical disk light emitting device, polyimide or epoxy is filled to stably support the structure.