Dependence of carrier lifetime of InAlAs/InGaAs high-electron-mobility transistors on gate-to-source voltage

Recently, we have investigated the frequency dependence of the drain conductance G(d) of high-electron-mobility transistors (HEMTs) employing an InAlAs/InGaAs material system that is lattice-matched to an InP substrate in detail and showed that, on the basis of theoretical considerations, it is due to the accumulation of holes in the source region and their recombination with two-dimensional electron gas (2DEG) in the source region. To better understand this carrier recombination model, we have investigated in detail the dependence of the carrier lifetime tau on the gate-to-source voltage V-GS and on the effective drain-to-gate voltage V-DG,V-eff applied to the side of the gate-to-drain path. Experimental results for the V-GS dependence of the carrier lifetime T not only confirm that the recombination of holes accumulating in the source region with 2DEG is dominated by Auger recombination but also show that the gradients of T become less steep at a V-GS larger than 0.4 V. A theoretical study of this phenomenon revealed that excess electrons penetrate in the delta-doped layer with increasing V-GS and are captured by the ionized donors distributed delta-doped layer. As a result, the electrical field in the delta-doped layer decreases with increasing V-GS and then the surface potential drops.