Temperature-dependent hall measurement of AlGaN/GaN heterostructures on Si substrates

For AlGaN/GaN high electron mobility transistor (HEMT) devices grown on Si substrates, we studied the influence of the surface defect density on the Hall mobility and the carrier concentration. We established a Hall measurement system over wide temperature range (8 ~ 800 K) by combining a closed-cycle refrigerator and a heating chamber. The two-dimensional electron gas (2DEG) in the epitaxially-grown AlGaN/GaN HEMT structures showed high mobilities, i.e., > 1500 cm²/Vs at 300 K and > 7000 cm²/Vs at 8 K. As the surface defect density increased, the mobility values at 8 K decreased due to scattering from charged impurities at low temperatures. However, at high temperatures where optical phonons are a major source of scattering, the mobilities do not show a significant dependence on the surface defect density. In addition, the carrier density showed an unexpected decrease at temperatures above 300 K, which is ascribed to a change in the misfit strain upon heating.