The relation of dominant deep levels in MOCVD AlxGa1-xAs with growth conditions

Abstract

High quality undoped AlxGa1-xAs (0 x [les] 0.4) has been investigated by transient capacitance, deep level transient spectroscopy and photoluminescence measurement techniques. The crystals were intentionally grown under different ambient conditions. Five dominant electron traps with ionization energy ET ranging from 0.25 to 0.82 eV are present in crystals grown in the possible presence of moisture and oxygen. The density of four of these traps increase with increasing x suggesting the involvement of Al-O complexes in their formation. The density of the fifth, the well known EL2 electron trap, remains invariant. Only the EL2 center is identified in crystals grown in an oxygen- and moisture-free ambient. Two hole traps, with ET = 0.74 and 0.87 eV are present in crystals grown at 690[deg]C, but are absent in crystals grown at 750[deg]C. They introduce light-sensitivity and compensation in the crystals and are removed by a short-term post-growth heat-treatment in a H2 ambient. These centers are probably impurity-point defect complexes.