Electrical properties and deep traps spectra in AlGaN films with nitrogen and gallium polarities prepared by molecular beam epitaxy

摘要

Electrical properties and deep traps spectra of Ga-face and N-face AlGaN films with Al mole fraction ranging from 0 to 0.6 were studied by means of current voltage, capacitance-voltage measurements, deep traps transient spectroscopy, admittance spectroscopy, photoluminescence spectroscopy. The films were grown by molecular beam epitaxy using a combined buffer consisting of a low temperature AlN nucleation layer and AlGaN/GaN superlattice. The polarity of the film is determined by whether the low temperature AlN is grown under the nitrogen-rich (promotes N-polarity) or Al-rich (promotes Ga-polarity) conditions. It shown that the Ga-face samples grown in this fashion have highly compensated p-type conductivity with the dominant acceptors being similar to standard acceptor species in GaN. For N-face films the conductivity is n-type and the dominant donors can be attributed to Si. The density of deep traps was found to be much higher for the N-face samples compared to the Ga-face samples.