Impact of wet-oxidized Al2O3/AlGaN interface on AlGaN/GaN 2-DEGs

We investigated the impact of wet-oxidation of AlGaN in an AlGaN/GaN heterostructure by selectively probing the metal/AlGaN interface. The two-dimensional electron gas (2-DEG) characteristics show improved mobility with increasing oxidation time and Al2O3 thickness. The change is attributed to an interplay of the interface trap density (Dit) and the oxide thickness. Dit is found to reduce progressively for thicker gate oxides as determined by selectively probing the Al2O3/AlGaN interface and employing frequency dependent capacitance and conductance spectroscopy on these devices. The energies of the interface traps are found to be in the range of 0.35-0.45 eV below the conduction band edge. The Dit is found to reduce from 2. x. 10(13) cm(-2) eV(-1) for 2.3 nm of Al2O3 to 5 x 10(12) cm(-2) eV(-1) for 16 nm of Al2O3. Contrary to the earlier reports of increased 2-DEG electron density, the primary advantage is found to be a reduction in Dit leading to an increased electron mobility from 1730 to 2800 cm(2)V(-1)s(-1)