Deep level defects in Si-doped AI_xGa_(1-x)N films grown by molecular-beam epitaxy

摘要

The deep trap levels of Al_xGa_(1-x)N films with x in the range from 0 to 0.15 grown on c-plane sapphire substrates using rf-plasma-assisted molecular-beam epitaxy have been investigated by deep level transient spectroscopy measurements. Two distinct defect levels (denoted as E_i and D_i) were observed. The origins of the E_i and the D_i are associated with point defects such as the N vacancies and extended defects, such as the threading dislocations, respectively. According to Al content (x), the activation energy and capture cross section for the D_i defect ranged from 0.19 to 0.41 eV and 1.1-6.6 X 10~(-15) cm~2, respectively. The trap energy levels of D_i defects in Al_xGa_(1-x)N were calculated and the values were nonlinear with Al content. The bowing parameter of Al_xGa_(1-x)N films was determined to be b = 1.22.