Paper EM-WeA3
High Level of Mg Alloying Effects on the Deep Level Defects in Mg_xZn_1-xO

Wednesday, November 2, 2011, 2:40 pm, Room 210

The Mg_xZn_1-xO material system is very promising for ultraviolet emission and detection applications because of its direct band-gap, band-gap tunability, low lattice mismatch, and low polarization field. Using molecular beam epitaxy, a-plane 1.5 micron thick n-type Mg_xZn_1-xO films (x=0, 0.26, 0.36, 0.43, 0.52) were grown on r-plane sapphire. Semi-transparent 100 Å thick Au Schottky contacts were used for deep level optical spectroscopy measurements (DLOS). The Schottky diodes (SD) exhibited rectification with low leakage currents and barrier heights between 1.00-1.19 eV from Mg_0.52Zn_0.48O to ZnO. The frequency dependence of the capacitance caused by the high series resistance of the SDs required low frequency lock-in based capacitance measurements for accurate determination of capacitance. Lock-in 1kHz DLOS measurements revealed six deep levels in Mg_xZn_1-xO samples while only three deep levels were observed in ZnO. In all samples, the energy of the deep levels relative to the conduction or valence band was independent of Mg content. The ~Ec-1.4 eV, ~Ec-1.85 eV, and ~Ec-2.50 eV levels follow the conduction band while ~Ev+1.20 eV, ~Ev+0.60eV, and ~Ev+0.28 eV follow the valence band. Because of high concentration of two dominant deep levels, lighted capacitance-voltage measurements was applied on all the samples in order to obtain true values of the concentration of the traps. The concentration of the two dominant compensating centers at ~E_v+0.28 eV and ~E_v+0.60 eV are ~3x10¹⁶ cm^-3 and ~1x10¹⁶ cm^-3, respectively.