Influence of polarization coulomb field scattering on the subthreshold swing in depletion-mode AlGaN/AlN/GaN heterostructure field-effect transistors

Abstract

Using the measured capacitance–voltage (C–V) curves and current–voltage (I–V) curves for the prepared AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs), the relationship between polarization Coulomb field scattering (PCF scattering) and the subthreshold swing for depletion mode (D-mode) AlGaN/AlN/GaN HFETs has been investigated. It was found that the S value (S=(∂lg(IDS)/∂VGS)−1) of subthreshold swing is smaller for the device with the stronger PCF scattering, and the S value decreases by more than 26% for the D-mode AlGaN/AlN/GaN HFET samples. The reason is attributed to the big gradient of the mobility and the gate-source bias curve which is generated by the PCF scattering.