Effect of Nitrogen implantation on the optical characteristics of Zn 0.85 Mg 0.15 O thin film at low temperature
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Effect of Nitrogen implantation on the optical characteristics of Zn0.85Mg0.15O thin film at low temperature S. Saha, S. Nagar and S. Chakrabarti1 1
Department of Electrical Engineering Indian Institute of Technology Bombay Powai, Mumbai 400076, India ABSTRACT The importance of ZnxMg1-xO is increasing day by day because of its wider bandgap than ZnO. This ternary semiconductor finds its application in the fields of optoelectronics, spintronics, superlattices due to its unique blueshifted UV-luminescent property. n- to p-type conduction which is the motive of the project can be achieved with increasing Mg content in ZnMgO. The optical characteristics of the nitrogen doped ZnxMg1-xO (x=0.85) grown on 2 inch Si wafer by RF sputtering are studied and analyzed thoroughly using low temperature (15K) photoluminescence measurements. Nitrogen implantation was carried out by Plasma immersion Ion Implantation technique on the sample. Rapid Thermal Process was employed to remove defects resulting from implantation. The samples were annealed at 700°C, 800°C, 900°C, and 1000o C for 10 seconds in an oxygen ambient. Photoluminescence (PL) measurements were performed at low temperature (15K) which exhibited acceptor-boundexciton peak (A˚X) and donor-bound-acceptor pair (DAP) at 3.336 eV and 3.236 eV respectively. At 3.364 eV, S peak was found for the sample annealed at 800˚C after implantation. This peak was attributed to the existence of ZnO-like composition. Localized and de-localized exciton peaks were found around 3.42 and 3.45 eV respectively. This result is very important because though dominant acceptor peak was not found but proper optimization of the parameters can lead to p-type ZnMgO which is the main motive of this project.
INTRODUCTION ZnO, with a wide band-gap of 3.37 eV and large exciton binding energy of 60 meV at room temperature, has been one of the most important semiconductors in recent years in the area of optoelectronic devices, [1]. Due to its high exciton binding energy it has excellent excitonic effects from room temperatures to 550K as reported by Ohtomo et al.[2]. So, ZnO is regarded as the most promising choice for the next generation ultraviolet light emitting devices. Several growth methods like MBE [3], MOCVD [4], PLD [5], sputtering [6] processes are employed for the growth of ZnO. It can be used in solar cells [7, 8], light-emitting devices [9], gas sensors [10], thin film transistors [11]. However, bandgap engineering is necessary to increase the bandgap of ZnO in order to achieve material like ZnMgO which can be used as barrier material for quantum well, HEMT devices. It has already been proved by several researchers that incorporation of MgO in ZnO can increase the band gap by shifting the conduction band edge upward, thus increasing the distance from the intrinsic shallow donor states, which essentially increases the activation energy of the defect donors of ZnO. The ionic radius of Mg2+ (0.57 Å) and Zn2+ (0.60 Å) also are very close to each other. However, during growth , keeping the lattice
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