Spectrally resolved thermoluminescence in electron irradiated AlN submicrocrystals

Aluminum nitride crystals of regular geometric shape and with 0.1-2.0 mu m size have been synthesized by original gas-phase technique. Using chemical composition analysis, the presence of main impurities of oxygen and silicon have been testified. The spectral features of cathodoluminescence (CL) and thermoluminescence (TL) under electron irradiation have been studied in grown AIN. It has been found that the measured CL and TL spectra have an almost identical form of single wide peak at 420 nm (2.95 eV), which can be approximated by superposition of three Gaussian components - weak 2.04 and 2.46 eV, predominant 2.87 eV. The possible origin of observed emissions has been discussed taking independent data into account. It has been found that 2.87 and 2.46 eV recombination processes occurred through electron transitions with participating of impurity O-N and oxygen-vacancy centers (V-Al-O-N). 2.04 eV emission was caused by radiative transition between hole (V-Al-O-N)-levels and valence band. Analyzing measured three-dimensional TL dependence in AlN microcrystals after 14.6 kGy irradiation, it has been established that the maximum of the TL emission is observed at 420 nm and at a temperature of 345 K. Experimental TL curves have been described numerically in the frame of the general-order kinetic formalism with high accuracy to determine the activation energy E-A = 0.58 eV of V-N-trap which is responsible supposedly for the thermally stimulated emission observed. Taking calculated values of the kinetic parameters into account, it has been concluded that the recapturing of charge carriers to the indicated vacancy levels is characterized by a high probability in mechanisms of the radiation-stimulated response of AIN microcrystals irradiated with electrons.