Analysis of Schottky gate electron tunneling in polarization induced AlGaN/GaN high electron mobility transistors

(gate = nickel)/(barrier = GaN/Al(y)Ga(1 - y)N)/(buffer = GaN)/(substrate = SiC) polarizationinduced high electron mobility transistors (PI-HEMTs) show promise for ultrahigh power microwave amplification. The polarization fields in these Ga-face, wurtzite structures are used to engineer the conduction band profile in the absence of any doping. One important attribute of these PI-HEMTs is their ability to withstand electric fields up to 3 MV/cm without avalanche breakdown. The combination of high electric field under the gate necessary to pinch off the channel, and the high electric field fringing to the gate from the large drain-source bias voltage, makes it possible for electron tunneling from the gate into and through the GaN/Al(y)Ga(1 - y)N barrier into the GaN channel. A one-dimensional theoretical analysis of the tunneling current at pinchoff as a function of the aluminum fraction (0.05 < y < 0.45) in the barrier, the operating temperature of the gate metal at 300 and 573 K, and a uniform additional electric field of -1 and -2 MV/cm from drain bias reveals the potential for these GaN based devices to impose negligible current loading by the gate on a microwave driver. Unlike GaAs, avalanche breakdown induced by gate leakage is unimportant in these GaN based power devices. (C) 1999 American Institute of Physics. [S0021-8979(99)05617-0].