The Study On Defects In ZnO And GaN Wide Band Gap Semiconductors Using Positron Annihilation Techniques

In recent years,zinc oxide and gallium nitride have attracted extensive attention due to their excellent properties. The point defects in these materials have an important effect on their electrical and optical performance, so it's necessary to unambiguously distinguish and quantify these defects. Positron annihilation spectroscopy (PAS) is a powerful and sensitive technique to detect open-volume defects in metals, semiconductors and polymers. This thesis is aimed to investigate defect behaviors in ZnO bulk, Zno films and different polar GaN films with PAS in combination with photoluminescence(PL) spectroscopy et al. In addition, this section about slow positron beam updated is included. The main conclusions of this thesis are listed as following: Study on defects in ZnO bulk1. Theoretical calculation about defects in ZnO bulkThe positron lifetime around different defects are calculated by using Doppler software package, T_b = 178 ps,TV_Zn = 235.8 ps and TV_O = 180.7 ps for defect-free, zinc and oxygen vacancies, respectively. The information about electron momentum distribution also has been obtained. Positron annihilation occurs mainly with zinc 4s electrons in the region of electron longitudinal momentum P_L lessening 4×10^-3m₀c. Positrons dominantly annihilate with oxygen 2p electrons between 4×10^-3m₀c and 9×10^-3m₀c. The zinc 3d electrons prevail in higher momentum region.2. The defects in as-grown ZnO bulkThe defect type,concentration and its evolution with annealing temperature are investigated by positron lifetime spectra(PLS), coincidence Doppler broadening spec-tra(CDBS) and photoluminescence spectra. The experimental value of positron lifetime around defects is 237 ps, which is in coincidence with the calculation result of positron lifetime at zinc vacancies annihilation. Therefore zinc monovacanies appear in the as-grown ZnO bulk. The ZnO decomposition will not take place when the sample is annealed below 600℃, but this process will proceed in higher temperature range, the zinc vacancy concentration decreases and oxygen vacancy concentration grows up due to oxygen releasing and recombination between zinc interstitials and zinc vacancies.3. The defects in electron irradiated ZnO bulkThe electron irradiation damage and its annealing behavior could be observed by PLS, CDBS and PL. More zinc vacancies are introduced by electron irradiation, at the same time, these defects such as zinc intertitials, oxygen vacancies, oxygen in-tertitials are created. Zinc intertitials could recombine with zinc vacancies and oxygen intertitials assemble and release although the heat treatment temperature is below 600℃. So the zinc vacancy concentration is reduced and oxygen vacancy concentration rises. When the annealing temperature increases to 800℃, ZnO bulk seems to decompose, then the zinc vacancy concentration goes on abating, while oxygen vacancy concentration furthermore increases. Study on defects in ZnO films...