Measurement of drift mobility in AlGaN GaN heterostructure field-effect transistor

Low-field mobilities for electrons in the channel of an Al0.15Ga0.85N/GaN h eterostructure field-effect transistor are derived from direct current tran sistor characteristics. The dependencies of mobility on gate bias, sheet ca rrier concentration, and temperature are obtained. For negative gate bias v oltages, mobility is found to increase monotonically with increasing sheet carrier concentration, which we interpret as a consequence of increased scr eening of carrier scattering. For positive gate bias voltages, mobility is found to decrease with increasing gate bias due to the onset of parallel co nduction in the AlGaN barrier layer. The mobility varies approximately as T -alpha with alpha approximate to 1.6-1.8 for temperature ranging from 200 t o 400 K, indicating that phonon scattering is dominant in the two-dimension al electron gas in this temperature range. (C) 1999 American Institute of P hysics. [S0003-6951(99)01225-5].