Synthesis of oxygen-free nanosized InN by pulse discharge
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Synthesis of oxygen-free nanosized InN by pulse discharge a.
Wei-Dong Yang a, b, K.W. Cheah b, Pei-Nan Wang a and Fu-Ming Li a State Key Joint Laboratory for Materials Modification by Triple Beams, Department of Optical Science and Engineering, Fudan University, Shanghai 200433 b. Department of Physics, Center for Surface Analysis and Research, Hong Kong Baptist University Kowloon Tong, Hong Kong
Abstract Oxygen-free nanosized InN was synthesized by pulse discharge. NH3/N2 mixture and bulk indium were used as nitrogen source and discharge cathode, respectively. Optical emission spectra show that N2 and NH3 were highly dissociated in the discharge and oxygen could be eliminated effectively. A comparison was made among samples produced in the discharge of N2, NH3 and N2/NH3, respectively. The XPS was used to determine the composition of the synthesized materials. Only In-N was produced when N2/NH3 was used as the discharge gas, whereas indium oxide was found in the case using N2 or NH3 as the discharge gas. The size of the produced InN was between 5 and 200 nm. A broad band with a blue shift of 150 nm from that of bulk InN was detected in the photoluminescence of the produced nanosized InN. Index codes: PACS: 52.80.-s, 73.22.-f, 78.55.-m, 78.67.-n, 81.07.-b 1. Introduction The III-V nitrides have long been viewed as promising compound materials for optoelectronic application in the visible and near-ultraviolet wavelength range [1-3]. The recent achievement of extremely bright blue and green light-emitting diodes and blue laser in InGaN/GaN/AlGaN-based hereostructure encouraged further research. [4] However, it was noticed that the intrinsic defects and the unintentional introduced impurities affected greatly the performance of group III nitride-based devices. The introduction of oxygen impurity was unavoidable in nearly all the growth of AlN, GaN, InN and their alloys [5-9]. Oxygen was suspected to be at least partially responsible for the unintentionally doped n-type behavior of the nitride [10] and was also thought to serve as nonradiative recombination centers. [11]. It was generally believed that there are two possible sources of oxygen impurity: (i) oxygen originates from the sapphire substrate and is incorporated into the first ~ 1 µm of the growing GaN film [12-13]; (ii) oxygen impurity in the nitrogen source, such as nitrogen gas or ammonia [14]. As to the former case, oxygenic substrate can be avoided or to grow a thick buffer layer on it to prevent the incorporation of oxygen. However, the latter is difficult to resolve because there is no absolutely 100% purity of nitrogen gas or ammonia. In fact, the efficiency of generating reactive nitrogen species in their nitrogen plasma source is only 2%-5% as reported by C. R. Elsass et al [14]. Atomic nitrogen plays an important role in the synthesis of nitrides due to its high chemical reactivity. The deficiency of atomic nitrogen in the nitrogen source increases the relative amount of oxygen in the synthesized film. The same problem appeared in the I3.50.1
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