Electrical Characterization of N + -implanted n -type ZnO Single Crystals: p-n Homojunction and Deep Level Defects
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1035-L10-08
Electrical Characterization of N+-implanted n-type ZnO Single Crystals: p-n Homojunction and Deep Level Defects Qilin Gu1, Xuemin Dai1, Chi-Chung Ling1, Shijie Xu1, Liwu Lu1, Gerhard Brauer2, Wolfgang Anwand2, and Wolfgang Skorupa2 1 Department of Physics, The University of Hong Kong, Hong Kong, Hong Kong 2 Institut f¨¹r Ionenstrahlphysik und Materialforschung, Forschungszentrum Dresden-Rossendorf, Dresden, 01314, Germany ABSTRACT Unintentionally doped n-type ZnO single crystals were implanted by nitrogen ions with different fluences of 1013, 1014 and 1015 cm-2 respectively. ZnO p-n homojunction was successfully fabricated due to the formation of p-type layer after 650oC post-implantation annealing in air for 30 minutes. Further thermal evolution of deep level defects was studied through thermal annealing up to 1200oC. Electrical characterization techniques including current-voltage (I-V), capacitance-voltage (C-V), Deep Level Transient Spectroscopy (DLTS) and double-correlation DLTS (DDLTS) were used for investigating the control sample, all the as-implanted and annealed samples through Au/n-ZnO Schottky diodes and ZnO p-n junctions. Detailed electrical properties of fabricated devices and characteristics of implantation induced defects were analyzed based on plentiful spectra. Moreover, low-temperature photoluminescence (LTPL) experiments of all the as-implanted and annealed samples were performed and the correlation between results from electrical and optical characterizations was discussed. INTRODUCTION The absence of reproductive and reliable p-type ZnO has become a major challenge for device fabrication. Ion implantation, with advantages of accurate control of implantation dose and depth distribution, is an effective technique for doping of semiconductors. Nitrogen has been considered as the most promising p-type dopant for ZnO.1, 2 There have been several reports on the studies of nitrogen implantation into ZnO,3-5 to our knowledge, however, very few electrical characterizations have been performed on ion-implanted ZnO. In the present work, current transport properties and capacitance-voltage behaviors were investigated by I-V and C-V measurements. Through thermally stable rectifying Au/n-ZnO diodes and ZnO p-n homojunctions, deep levels in N+-implanted zinc oxide samples were detected through Deep Level Transient Spectroscopy (DLTS). Low-temperature photoluminescence experiments (LTPL) (at 4K) were also carried out to study optical properties of N+-implanted ZnO samples. DLTS is a very sensitive method of measuring the characteristics of electrically active defects in semiconductor materials. It requires a depletion region that can be changed with applied bias, such as a Schottky diode, p-n junction diode, or MOS structure. The defects in the semiconductor can trap a charge carrier. After filling the traps, the bias is changed to bring the Fermi level below the defect energy level. The emission rate is measured as a change in capacitance, as the defects release their charges. By using a double b
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