Abstract:
We report on the space charge spectroscopy studies performed on thermally treated melt-grown
single crystal ZnO. The samples were annealed in different ambients at 700 C and also in oxygen
ambient at different temperatures. A shallow donor with a thermal activation enthalpy of 27meV
was observed in the as-received samples by capacitance-temperature, CT scans. After annealing the
samples, an increase in the shallow donor concentrations was observed. For the annealed samples,
E27 could not be detected and a new shallow donor with a thermal activation enthalpy of 35meV
was detected. For samples annealed above 650 C, an increase in acceptor concentration was
observed which affected the low temperature capacitance. Deep level transient spectroscopy
revealed the presence of five deep level defects, E1, E2, E3, E4, and E5 in the as-received samples.
Annealing of the samples at 650 C removes the E4 and E5 deep level defects, while E2 also
anneals-out at temperatures above 800 C. After annealing at 700 C, the T2 deep level defect was
observed in all other ambient conditions except in Ar. The emission properties of the E3 deep level
defect are observed to change with increase in annealing temperature beyond 800 C. For samples
annealed beyond 800 C, a decrease in activation enthalpy with increase in annealing temperature
has been observed which suggests an enhanced thermal ionization rate of E3 with annealing.
