Invited talk abstract

Key Words: Zinc oxide, defects, DLTS, proton irradiation

We have fabricated rectifying Au contacts to n-type vapour phase grown ZnO. From capacitance-voltage (C-V) measurements, the free carrier density of the ZnO was found to be 3.0±0.3x1016 cm-3. TSCAP measurements in the region 20 - 300 K showed that the diode capacitance, i.e. the number of ionised donors, reduces rapidly below 50 K, consistent with the presence of shallow donor(s) extracted from Hall measurements. We have used deep level transient spectroscopy (DLTS) to study the electrical properties of electron traps introduced in the ZnO during growth and subsequent high-energy proton iradiation. Four electron traps with DLTS peaks below 300 K could be detected in the as-grown ZnO. The most prominent of these, E1, is located at Ec - 0.12 eV and has an estimated concentration, Nt, of about 1016 cm-3. For the second most prominent level, E3, we have determined Ec - 0.29 eV and Nt = 1014 cm-3. Two less prominent defects, E2 and E4, with energy levels at 0.10 and 0.57 eV, respectively, were also characterised. After irradiation with 1.8 MeV protons at room temperature, the two most prominent defects detected were Ep1 and Ep2. Ep1 has approximately the same DLTS signature as E4 and for Ep2 we found Ec - 0.29 eV. A comparison of the introduction rates of electron traps introduced in GaAs, GaN and ZnO by proton irradiation revealed that ZnO is remarkably radiation hard compared to the other two semiconductors.