Mobility Enhancement in AlGaN/GaN Metal-Oxide-Semiconductor Heterostructure Field Effect Transistors
It has been demonstrated experimentally that the electron drift mobility of a two-dimensional electron gas in the channel of AlGaN/GaN metal-oxide-semiconductor heterostructure field effect transistors (MOSHFETs) may be appreciably higher than that in the conventional AlGaN/GaN HFETs for structures with a thin (10 nm) AlGaN barrier layer. For the conventional AlGaN/GaN heterostructures with barrier thickness of 10 nm, the maximum electron drift mobility in the 2D channel, μd, is equal to ~600 cm2 Vs−1, which is much lower than the Hall mobility measured with the same wafer (μH ≈ 1400 cm2 Vs−1). Introduction of a 7 nm thick SiO2 layer between the gate and the AlGaN layer to fabricate MOSHFETs leads to an increase in the electron drift mobility to μd ≈ 1400 cm2 Vs−1. Introduction of a SiO2 layer with the same thickness into the AlGaN/GaN heterostructures with relatively thick (25 nm) AlGaN barrier does not affect the maximum electron drift mobility in the channel of the heterostructures. The results obtained correlate well with published data on the influence of the barrier thickness on the high-power performance of AlGaN/GaN HFETs.