Quantum and transport lifetimes in a tunable low-density AlGaN/GaN two-dimensional electron gas

We experimentally determine the density dependence of the transport lifetime (tau(t)) obtained from low-field Hall measurements and the quantum lifetime (tau(q)) derived from analysis of the amplitude of Shubnikov-de Haas oscillations in a tunable high mobility two-dimensional electron gas (2DEG) in a Al0.06Ga0.94N/GaN heterostructure. Using an insulated gate structure, we are able to tune the 2DEG density from 2x10(11) to 2x10(12) cm(-2), and thus, monitor the evolution of the scattering times in a single sample at T=0.3 K in a previously unexplored density regime. The transport lifetime tau(t) is a strong function of electron density, increasing from similar to2.7 ps at n(e)=2x10(11) cm(-2) to similar to11 ps at n(e)=1.75x10(12)cm(-2). Conversely, we find that the quantum scattering time tau(q) is relatively insensitive to changes in electron density over this range. The data suggest that dislocation scattering accounts for the density dependence of tau(q) as well as tau(t) in our low-density sample. (C) 2004 American Institute of Physics.