Deep levels in a-plane, high Mg-content MgxZn1-xO epitaxial layers grown by molecular beam epitaxy

Deep level defects in n-type unintentionally doped a-plane MgxZn1-xO, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of MgxZn1-xO were examined with x=0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of E-c - 1.4 eV, 2.1 eV, 2.6V, and E-v +0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at E-c - 2.1 eV, E-v + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at E-v + 0.3 eV and E-c - 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the E-v +0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the E-c - 1.4 eV and E-c - 2.6 eV levels in Mg alloyed samples. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769874]