Determination of the polarization discontinuity at the AlGaN∕GaN interface by electroreflectance spectroscopy

Abstract

The total polarization discontinuity ΔP at an Al0.31Ga0.69N∕GaN heterojunction has been determined by electroreflectance spectroscopy. This technique is based on the analysis of the Franz–Keldysh oscillations observed above the AlGaN band gap, yielding the barrier electric field strength as a function of the applied bias voltage. The threshold field strength, where the two-dimensional electron gas (2DEG) is depleted, corresponds to a ΔP of 1.1×1013e∕cm2 which is only 85% of the theoretical prediction. Applying the same optical method, the 2DEG density at the heterointerface can be accurately determined, as proven by comparison to Shubnikov–de Haas measurements.