Transient electron transport in wurtzite GaN, InN, and AlN

Transient electron transport and velocity overshoot in wurtzite GaN, InN, and AlN are examined and compared with that which occurs in GaAs. For all materials, we find that electron velocity overshoot only occurs when the electric field is increased to a value above a certain critical field, unique to each material. This critical field is strongly dependent on the material, about 4 kV/cm for the case of GaAs but much higher for the III–nitride semiconductors: 140 kV/cm for GaN, 65 kV/cm for InN, and 450 kV/cm for AlN. We find that InN exhibits the highest peak overshoot velocity and that this velocity overshoot lasts over the longest distances when compared with GaN and AlN. Finally, using a one-dimensional energy–momentum balance approach, a simple model is used to estimate the cutoff frequency performance of nitride based heterojunction field effect transistors (HFETs) and a comparison is made to recently fabricated AlGaN/GaN HFETs.