Frequency Dependence of Drain Conductance due to Hole Accumulation in InAlAs/InGaAs High Electron Mobility Transistors

Abstract

The frequency dependencies of the drain conductance (Gd) and the responsivity of InAlAs/InGaAs high electron mobility transistors were investigated using a network analyzer. The Gd exhibited the same frequency dependence as responsivity under 1.3-µm-wavelength laser illumination, indicating that the frequency dependence of Gd arises from the recombination of holes that have accumulated in the source region with the two-dimensional electron gas (2DEG). The holes were generated in the drain region by impact ionization under the strong electric field and drifted toward the source region. The drain conductance due to impact ionization can be expressed as Lorentz frequency dependence with f3dB being the 3-dB-down frequency. The minority carrier (hole) lifetime, τ, was estimated using the relation 1/2 πf3dB. The frequency dependence of Gd at several drain-to-source and gate-to-source voltages was investigated. The recombination lifetime for a system in which both electrons and holes co-exist was theoretically estimated, taking account of self-consistent solutions of both the Schrödinger and Poisson equations and the nonradiative Auger recombination mechanism. The experimental and theoretically estimated results clearly show that the frequency dependence of Gd is caused by the accumulation of holes in the source region and their recombination with the 2DEG. Based on the experimental and theoretical results, the distribution of holes in the channel and the multiplication factor due to the impact ionization are discussed in details.