TWI230979B - Method of making transparent conductive oxide ohmic contact electrode on GaN - Google Patents

Abstract

A method of making transparent conductive oxide ohmic contact electrode on GaN is provided, which includes forming a transparent conductive film on a GaN film; using an ion diffusion method to form a transparent conductive hetero-junction with opposite electric characteristic on the surface of the GaN film; and then building a metallic thick layer on the transparent conductive hetero-junction for the subsequent wire bonding process, so as to form an ohmic contact electrode to improve the Fermi energy level of hetero-junction by using the tunnel effect of electron and hole from the aforementioned ion diffusion method.

Description

1230979

V. Description of the invention (1) [Technical field to which the invention belongs] The present invention relates to a method for manufacturing an ohmic electrode of a conductive oxide film, and more particularly to a method of forming an ohmic electrode of a conductive oxide film on a gallium nitride film layer by ion diffusion. '' [Previous technology] Gallium nitride (GaN) series materials have direct bandgap (Eg) in the ultraviolet and blue-green light bands, so they can be used as high-efficiency white and visible light sources. Currently commercialized products include blue, green, white, white and light emitting diodes (White Light-Emitting Diode).

) 'And Laser Diode (LD) in Lanwu and light bands. Because the values of the energy level and electron affinity of the gallium nitride series materials are quite south ’, taking gasification records as examples, Eg = 3.4 eV,% = 2 · 9 eV. Therefore, when forming a metal contact electrode, especially when forming p-type gallium nitride (p_GaN) as an ohmic contact electrode, it is necessary to use a metal having a high work 'function (work function Φπι), such as nickel Ni (φιη = 5 · 15 eV), Au Au (Φιη = 5.1 eV), Palladium Pd (Φπι = 5.12 eV), Platinum Pt ((Dm =: 5 · 6 5 e V), Na Ru, Ag I r, The hole is made from a metal electrode through a hole injection to p-type gallium nitride. Conventionally, as disclosed in US Patent No. 5,562,422 (10/8/1996) of Nichia Chemical Industries, Ltd., Ni / Au / p-GaN is used as the contact electrode of p-GaN, and undergoes an annealing treatment process higher than 400 ° C to form a transparent conductive film. Another disclosed technology, such as Japan's Toyota Synthetic

Toyoda Gosei Co., Ltd.'s US patent 6620 643 (9/6/20 03) discloses that Au / Co / p-GaN is used as the contact electrode of p-GaN.

Page 6 1230979 V. Description of the invention (2) As for the mechanism of the high work function metal that can form p-GaN ohmic contact after the annealing process, according to H. W. Jang et al., Mechanism for ohmic contact formation of oxidized

According to Ni / Au on p-type GaN, Journal of Applied Physics vol. 94, No. 3, pp. 1748-1752 (August 1, 2003), the current understanding is that in the high temperature oxidation process, Au / Ni The / GaN interface is taken as an example. A high temperature causes Ni to diffuse outside and forms a p-type transparent conductive film NiO / Au / GaN on the GaN surface. At the interface, not only does the phenomenon of gallium ((ja) melting into ^ occur (for example, at 49 ° C, the melting point of Ga atom of low melting point in Au is 13%), but also the interface The remaining Ga atoms will still react with 0 to form gallium oxide (GhO3). Further understanding is the change of the interface state caused by the melting and oxidation of Ga atoms at the interface. According to JL Lee et al., Applied Physics Letters vol. 74, 2289 (1 999) and others, not only (1) the formation of Ga vacancy at the interface 'specific formation of acceptor (acceptor) at the p_GaN interface Therefore, it can provide additional hole concentration on the surface of p-GaN. At the same time according to α ·

Motayed et al. '' High-transparency Ni / Au bilayer contacts to n-type GaN, '丨 Journal of applied physics vol. 92, no. 9, pp. 5218-5227 (November i, 2000) The 'can also know (2) the purpose of reducing the surface work function (work functión Φπι). Moreover, "the above-mentioned effect obtained by changing the surface state of GaN" can improve the position of the Fermi level of the GaN surface, which is advantageous for forming an ohmic contact electrode with Ni 0. However ’via H. W. Jang et al. &Quot; Transparent ohmic

1230979 V. Description of the invention (3) contacts of oxidized Ru and Ir on p-type GaN, 丨 丨 Applied Physics Letters vol · 93, no · 9, pp. 5416-5418 (May 1, 2003). Au / GaN formed electrodes have poor thermal stability. For example, after annealing at 500 ° C for 24 hours, the resistance of Ni / Au will increase up to 840 times. In addition, because Au has strong absorption in the visible light band, for the production of light-emitting diodes (Light-E mi 11 ing Diode, LED) with blue and green light, an ultra-thin gold (Au) film (thickness 5 ~ 1 Onm) as a transparent conductive layer. Therefore, the current development of p-GaN ohmic contact electrode technology will be directed towards the use of non-Au electrodes. Recently published technologies are (1) n: ITO / Au / Ni / p-GaN (S. Υ · Kim et al ·, 丨 Effect of an indium-tin-oxide over 1 ayer on transparent Ni / Au ohmic contact on p-type GaN, " Applied Physics Letters, vol. 82, No. 1, pp · 6 and 63, (Jan. 6, 2003). (2) A1: ZnO / Ni / p-GaN (J. 0 · Song et al., &Quot; Highly low resistance and transparent Ni / ZnO ohmic contacts to p-type GaN ,, f Applied Physics Letters vol. 83, No. 3, pp. 479-481 (July 21, 2003) 〇The above technology The following transparent oxide film stacks are mainly used to form ohmic contact electrodes with p-GaN: ITO (60nm) / Au (3nm) / Ni (2nm) / p-GaN (annealed at 500 ° C); and AZO (450nm ) / Ni (5nm) / p-GaN (annealed at 550 ° C). The common feature of these two technologies is the use of a high work function (φ m

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> 4 eV) n-type transparent conductive oxide film, such as Sn: In2〇3 (IT〇) '' I · ZnO (AZO), and a mouth-shaped transparent conductive oxide with a similar work function · ΝίΟ (Φπι = 5 eV) are stacked back and forth to form an ohmic contact with a semiconductor (such as GaN) having a high electron affinity. This kind of work function engineering concept uses a η / p-type transparent oxide film with two work functions close to each other to form an ohm with a wide bandgap material such as GaN.

The two limitations of using the above-mentioned indium tin oxide (ιτο), aluminum-doped zinc oxide (AZ〇) and nickel oxide (Ni〇) to form a p-GaN ohmic electrode are (1) ITO, AZO, and The difference in work function of NiO is 0.3 ~ 05 eV. (2) The absorption energy gap of ITO, AZ0, NiO is about 3.6 eV, which is not far from GaN. (1) will cause the forward operating voltage of the GaN light-emitting diode element to increase by 5V; and (2) will cause the two kinds of oxide films to be stacked, resulting in a reduction in the transmittance of the light wavelength outside the beam and thus a decrease External efficiency at this short wavelength. For example: the transmittance of a: IT0 (250nm) / Ni (10nm) / p-GaN and b: Au (5nm) / Ni (10nm) at 350nm drops to ~ 55%. Its a proof is detailed .. R.-H. Horng et al., &Quot; Low-resistance and high- transparency Ni / ITO ohmic contacts to p-type GaN, n

Applied Physics Letters, vol. 79, no. 18, pp. 2925-2927 (Oct 29, 20 01). 1) Detailed proof: J.K. Ho et al ·, " Low resistance ohmic contact to p-type GaN, 1 丨 Applied Physics Letters vol · 74, no. 9, pp · 1275-1277 (

March 1, 1999).

Page 9 1230979 V. Description of the invention (5) [Summary of the invention] The beauty is that the main purpose of the present invention is to solve the above-mentioned problems, the main purpose of which is to solve the problem; ‚Lost number (ΙΤ〇, AZ0) The gap with NiO / GaN is too large, which is disadvantageous. The other purpose is to solve the problem of the absorption of the oxide film in the ultraviolet light band (the pressure is known; the anti-reflection) is to achieve the above purpose, which is based on gallium nitride. On the film layer, an ion diffusion method is used for the conductive transparent film. The transparent film is transparent and transparent. Ί: layer surface layer, and in this process, a thick metal film is laid on the surface to serve as a subsequent hole making method. The ion diffusion method uses electrons and ions to make the heterogeneous interface form an ohmic contact electrode. ^ Details and technical descriptions of the present invention are shown in the following table. Please refer to the following table for the schematic diagram. This is the work function of the transparent conductive oxide film: Gap2 〇3 S n: I n2 03 A 1: Zn η 0 ni 0

Month b gap value Eg (eV) 4. 9 3 · 6 1N1U work function Φιη (eV) 5 · 〇4? · 4 _ 4 · '4 · 5 5 · 0 * r 5 The η-type conductive oxidation with high work function and the same gap value sprayed by the method, = the number of blades and N i 〇) Lightning guide 4 servants, dragons and commonly used P-type nickel oxide (

"Comparison of conductive oxide films. We noticed that oxygen C has the same work function as NiO (pore red (Ga203), except for ^ m_beV), and its energy gap value Eg =

Page 10 1230979 V. Description of the invention (6) 4. 9: V ′ is also a light-emitting diode with a wavelength as short as about 250 nm in the above conductive oxide film. By applying this to wavelengths, we have disclosed an ohmic formation technique in the present invention. For the convenience of explanation, please refer to [the first] ^-和 之 ^^^ 11t® 〇E, b2 film 20, the main steps and technical features of the present invention are as follows: face 1) and first prepare: nitrogen, gallium film layer 10 'Then the gallium nitride film layer u = a conductive transparent film 20 with a work function. The high-power, transparent conductive film 20 is selected from the group consisting of oxide (μ), indium oxide (μ), aluminum oxide (Alz 0 3), or a combination thereof. ^ (b) Ion diffusion is applied to the conductive transparent film 20 to form a transparent conductive heterogeneous interface with opposite electrical characteristics 2 on the gallium nitride film layer 丨 the surface layer, n + / p transparent conductive with the same work function The transparent film 20 forms a hetero interface 21 on the surface of the gallium nitride film layer 10. 'The ion diffusion method ^ can choose ion implantation or high temperature impurity diffusion; and the Li ion system of the ion diffusion method can be p-type doped zinc (Zn), nickel (Ni), cobalt (c) , Beryllium (Be), magnesium (Mg), calcium (Ca), gills (Sr), barium (Ba), silver (Ag

Page 11 1230979 V. Description of the invention (Ό Although the concept of tunneling n + / p or p + / n to form a junction (junCfi〇n), it was used in the manufacture of silicon Si, germanium Ge, etc. as early as the 1960s. 2. Gallium arsenide GaAs ohmic contact electrode (Details: L N. Holonyak Jr. etal. Gallium Arsenide tunnel diodes " proceedings of the IRE νο 1.48, pp 1405-1409 (1960) (Details: 1

Easaki, New phenomenan in narrow Germanium pn junctions.nphys. Rev. voll〇9, pp 603-604 (1958)), and applied to the gallium arsenide laser diode (GaAs LD) technology (foreign · JJ Wierer etal · `` Buried twine contact junction AlGaAs-GaAs-InAs quantum well heterostructure lasers with oxide-defined lateral currents 丨 丨, Appl.phys · Let · vo 171 · pp2286-2288, (1997)), and at 200 1 Applied to GaN LED technology (Details · T · Takeuchi etal · 1'GaN-based light emitting diodes with tunnel junctions ", Jpn J. Appl phys vol 40, PP.L861-L863 (2001 )). However, for GaN LED technology, the tunneling electrode is limited to the n + / p semiconductor homo-junction, and the 'hetero-junct ion' technology using a transparent conductive oxide film, After a long period of research by the inventors, it was first disclosed in the patent of the present invention. The effect of the present invention is shown by the following examples: Example '—: In a GaN structure with n-type, photoelectronization is first used Anodic oxidation, partial oxidation of n-GaN surface to form silicon-doped oxide

Page 12 1230979 V. Description of the invention (8) Gallium (Ga2 03). After annealing at an appropriate phase transition temperature, different phases of Ga 2 03 can be obtained, and its X-ray diffraction photography (X-raydiffracti ο η, XRD) can be known to generate crystalline Ga2 03 on the sample surface (see " (See Figure 2). Through tomographic analysis of x-ray photoelectron emission spectroscopy (XPS), it was found that in addition to the formation of Ga2 03 on the surface, a graded layer GaON with a thickness of about 20 nm was formed at the GaN interface, ( (See "Figure 3").俾 The gradient layer can use ion implantation or impurity diffusion (d if fusion) technology, which can change the electrical characteristics and surface work function of this interface. (The formation of this graded layer is an important technique for forming a tunnelable interface, and the detailed application is as follows in Example 2 and Example 3.) Example 2 In a η-type InGaN / GaN structure, a photoelectrochemical anode is used Oxidizing to partially oxidize the n-type I nGaN surface to form an n-type Ga ^ 3 with indium I n and Si Si doping, and forming a GaON graded layer at the GaN interface. The relationship between the growth rate of the GagO3 anodization and the pH of the electrolyte is shown in [Figure 4]. When the above is used to fabricate a diode with a metal oxide semiconductor (MOS) structure, please refer to "Figure 5". When the thickness of the surface Ga2 03 is 40, 20, 10 nm, With the decrease of GaO3 thickness, the electrical conductivity of the polar body will change from a Schottky barrier contact to an ohmic contact.

1230979 V. Description of the invention (9) Example 3: In a structure with η-type I n G a N / G a N structure, the surface of η-type InGaN is partially oxidized by photoelectrochemical anode emulsification to form a η-type (InGa) 2 03 (IG0) and the GaON graded layer are at the GaN interface. And p-type doping such as nickel Ni, zinc Zn is used to change the resistivity of the ^ -type transparent conductive film. When a circular transmission line pattern on IG 0 is used, the transmission line width ((japw 丨 dth)) is different. The voltage obtained (-) is as shown in "Figure 6", and The resistivity measurement results are shown in [Figure 7]. From the comparison of [Figure 7], it is known that when IG0, which is essentially type 0, is doped with Ni and Zn, its sheet resistivity (heart) is changed from the original value 486 Ω-cm2 increased to 0.28 Ω-cm2 and 3.331 Q-cm2. However, the above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the invention. All changes and modifications are covered by the patent scope of the present invention.

Page 14 1230979 Brief description of the drawings [Simplified description of the drawings] Figure 1 is a schematic view of the gallium nitride conductive electrode of the present invention. FIG. 2 is a schematic diagram of an X-ray diffraction photograph of Embodiment 1. FIG. FIG. 3 is a schematic diagram of a GaN interface according to the first embodiment. Fig. 4 is a graph showing the relationship between the growth rate and pΗ value in the second embodiment. FIG. 5 is a relationship diagram of diode conduction tunneling current-voltage in the second embodiment. Fig. 6 is a relation diagram of the conducting current-voltage (I-V) of the I G0 transmission line with different widths (Gap) in the third embodiment. Fig. 7 is a graph showing the relationship between I G0 resistivity and transmission line width (Gap) in the third embodiment. [Explanation of reference numerals] GaN film layer 1 0 conductive transparent film 2 0 heterogeneous interface 21 metal thick film 30

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Claims (1)

1230979 6. The scope of patent application can be P-doped zinc (Zn), nickel (Ni), cobalt (Co), beryllium (Be), town (Mg), office (Ca), crane (Sr), Barium (Ba), silver (Ag) 〇6, "The manufacturing method of GaN transparent conductive oxide film ohmic electrode" as described in item 1 of the scope of patent application, wherein the thick metal film is selected from titanium (Ti) Formed of an oxide film of aluminum, aluminum (A1), nickel (Ni), and gold (Au). 7. The method for manufacturing a gallium nitride transparent conductive oxide film ohmic electrode as described in item 1 of the scope of the patent application, wherein the thick metal film is titanium (Ti), aluminum (A1), nickel (Ni), Gold (Au) combination. Page 17