Investigations on the Cosputtered ITO-ZnO Transparent Electrode Ohmic Contacts to n-GaN

Wei-Hua Hsiao,Hong-Jyun Lin,Day-Shan Liu,Li-Wen Lai,Nan-Jay Wu,Jyun-Yong Li,Tai-Hong Chen,Ching-Ting Lee

doi:10.3390/app6020060

Abstract

Transparent indium tin oxide (ITO) and cosputtered ITO-zinc oxide (ZnO) films’ contacts to an n-GaN epilayer were investigated. Both of these electrodes’ contact to the n-GaN epilayer showed Schottky behavior, although the contact resistance of the ITO-ZnO/n-GaN system was lower than that of the ITO/n-GaN system. By placing a thin Ti interlayer between the ITO-ZnO/n-GaN interface, nonalloyed ohmic contact was achieved. The inset Ti interlayer was both beneficial both for enhancing the outdiffusion of the nitrogen atoms at the surface of the n-GaN and suppressing the indiffusion of oxygen atoms from the surface of the ITO-ZnO to n-GaN. The figure-of-merit (FOM), evaluated from the specific contact resistance and optical property of the Ti/ITO-ZnO system’s contact to the n-GaN epilayer, was optimized further at an adequate thickness of the Ti interlayer.

Highlights

Group III-nitride semiconductors are crucial materials for the fabrication of optoelectronic devices [1,2]
indium tin oxide (ITO)/n-gallium nitride (GaN) and ITO-zinc oxide (ZnO)/n-GaN contact systems were rapidly annealed at 100, 200, and 300 ̋ C, respectively, for 1 min under vacuum ambient. Another set of the n-GaN epilayer surface was deposited by a Ti interlayer with the thickness ranging from 2 nm to 10 nm using the electron beam evaporation system prior to the cosputtered ITO-ZnO film deposition
This ohmic contact behavior achieved from the nonalloyed ITO‐ZnO/Ti/n‐GaN contact system was achieved by this mechanism: the inset Ti interlayer functioned to effectively induce the outdiffusion of the N atoms at the n‐GaN surface and to suppress the indiffusion of the O atoms from the cosputtered ITO‐ZnO film to the n‐GaN epilayer

Summary

Introduction

Group III-nitride semiconductors are crucial materials for the fabrication of optoelectronic devices [1,2]. Tang et al demonstrated an ITO/ZnO/n-GaN ohmic contact system with a specific contact resistance of 3.0 ˆ 10 ́4 Ωcm after annealing at 500 ̋ C in H2 ambient for 5 min [7]. Kang et al used a thin In interlayer inset between the ITO/N-face n-GaN interface to realize a specific contact resistance of 1.8 ˆ 10 ́5 Ωcm after annealing at 300 ̋ C in N2 ambient for 60 s [10]. Guo et al used a thin Ti interlayer to optimize the ITO/n -GaN ohmic contact behavior with a specific contact resistance of 4.2 ˆ 10 ́6 Ωcm after annealing at 600 ̋ C in N2 ambient for 5 min [11]. An optimal ITO-ZnO/Ti/n-GaN contact structure was obtained by considering both the behavior of the ohmic contact and the optical transmittance

Experimental

Results and Discussions

Conclusions