Improved transport properties of the two-dimensional electron gas in AlGaN∕GaN heterostructures by AlN surface passivation layer

Abstract

The transport properties of the two dimensional electron gas (2DEG) in AlGaN∕GaN heterostructures with AlN, Si3N4, and SiO2 passivation layers and without passivation layer were investigated using Hall effect measurements over a temperature range of 30–550°C. Compared to the Si3N4 and SiO2 passivation dielectrics, the AlN film led to an obvious increase not only in carrier concentration but also in mobility of the 2DEG. The variation of the carrier concentration with temperature in the AlN passivated sample is also smaller in comparison with the Si3N4 passivated sample. These indicate that the AlN film is a promising passivation dielectric. In addition, the results from Hall and high-resolution x-ray diffraction measurements show that the change of strain after passivation contributes only in a relatively small proportion to the variation of the carrier concentration in AlGaN∕GaN heterostructures.