Carrier-removal rate and mobility degradation in heterojunction field-effect transistor structures

In this paper, we report experimental results and theoretical investigations of neutron irradiation-induced carrier-removal rate and mobility degradation in AlGaAs/GaAs heterojunction field-effect transistor structures. The measured two-dimensional (2-D) carrier removal rate of ∼6.0 × 10^-3 is found to be consistent with a net (volume) introduction rate of ∼20 cm^-1 acceptor-like defects in the GaAs layer. Radiation-induced acceptors in the GaAs layer have the most significant effect on the 2-D electron concentration, whereas the acceptors in AlGaAs layer have negligible effect for neutron fluence up to 5 × 10¹⁴ cm^-2. The measured 77-K mobility degradation, which is very sensitive to ionized impurity scattering, however, suggests that the introduction rate of the combined donor-like and acceptor-like defects is almost an order of magnitude higher (200 cm^-1). The 300-K mobility, which is dominated by polar-optic phonon scattering, shows only marginal degradation.