Electrical characteristics of In/ITO p-type ohmic contacts for high-performance GaN-based light-emitting diodes Joon-Ho Oh a , Kyoung-Kook Kim b , Hyun-Gi Hong c , Kyeong-Jae Byeon a , Heon Lee a , Sang-Won Yoon a,d , Jae-Pyoung Ahn d , Tae-Yeon Seong a,n a Department of Materials Science and Engineering, Korea University, Seoul 136-713, Republic of Korea b Department of Nano-Optical Engineering, Korea Polytechnic University, Gyeonggi 429-793, Republic of Korea c Material & Device Center, Samsung Advanced Institute of Technology, Yongin-si, Gyunggi-do 446-712, Republic of Korea d Advanced Analysis Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea article info Available online 5 January 2011 Keywords: Light-emitting diode ITO Ohmic contact Transparent electrode abstract We have investigated the annealing-induced improved electrical properties of In(10 nm)/ ITO(200 nm) contacts with p-type GaN. The contacts become ohmic with a specific contact resistance of 2.75  10 –3 O cm 2 upon annealing at 650 1C in air. X-ray photo- emission spectroscopy (XPS) Ga 2p core levels obtained from the interface regions before and after annealing indicate a large band-bending of p-GaN, resulting in an increase in the Schottky barrier height. STEM/energy dispersive X-ray (EDX) profiling results exhibit the formation of interfacial In-Ga-Sn-oxide. Based on the STEM and XPS results, the ohmic formation mechanisms are described and discussed. It is also shown that patterning by nano-imprint lithography improves the light output power of blue LEDs by 18–28% as compared to that of LEDs fabricated with unpatterned In/ITO contacts. & 2010 Elsevier Ltd. All rights reserved. GaN-based light-emitting diodes (LEDs) have attracted a lot of attention because of their potential use in solid-state lighting application and back light unit application in liquid crystal displays. For such application, LEDs must have high external quantum efficiency as well as high internal quantum effi- ciency. It is, however, well known that improvement in the external quantum efficiency of GaN-based LEDs is not easy because of the difficulty faced in the achievement of good p-type ohmic contacts and in the enhancement of light extraction. The former is due to the combined effects of the difficulty faced in obtaining high hole carrier concentrations and absence of contact schemes with a work function larger than that of p-type GaN [1]. This results in poor current injection efficiency. The latter is associated with a large difference in the refractive indices of p-type GaN and air [2] and the poor transparency of metallic electrodes [3,4]. In order to enhance the light extraction, transparent conducting oxides (TCOs) have been extensively investigated because of their high transmittance and reasonable electrical properties [5]. For example, Lin et al. [6] showed that ITO-based ohmic schemes produced a contact resistivity comparable to that of Ni/Au contacts, but a significantly higher transmittance— 95% at 400–460 nm upon annealing at  530 1C for 1 min in air. It was also shown that ITO contacts combined with a p-type NiO interlayer, with a large work function, resulted in low contact resistance [7]. Song et al. [8] introduced Cu-doped indium oxide thin films at the ITO/GaN interface and reported that the samples produced a contact resistivity comparable to that of the Ni/Au contact and a light transmittance of 95% at 400–460 nm, when annealed at 530 1C. Recently, Song et al. [9] introduced an indium interlayer at the interface between GaN and ITO, in order to enhance the electrical and optical proper- ties of LEDs. It was shown that the light output power of InGaN/ GaN multi-quantum well blue LEDs fabricated with the In/ITO p-contacts was improved by 91% as opposed to that of LEDs with conventional Ni/Au contacts. Furthermore, to enhance the light extraction efficiency, surface patterning and texturing have been widely studied [10]. In this work, we have Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/mssp Materials Science in Semiconductor Processing 1369-8001/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.mssp.2010.12.005 n Corresponding author. Tel.: +82 2 3290 3288; fax: +82 2 928 3584. E-mail address: tyseong@korea.ac.kr (T.-Y. Seong). Materials Science in Semiconductor Processing 13 (2010) 272–275