Theoretical and experimental results for the inversion channel heterostructure field effect transistor

Abstract

New theoretical and experimental findings for the inversion channel HFET are presented to address the modelling needs of inversion channel opto-electronic integrated circuit (OEICs). This FET is well suited to OEICs since the gate is an ohmic contact (in contrast to a Schottky contact) controlling the channel conductivity from a substantial distance. Consequently, the region around the channel is formed as a graded index structure with a single or multiple quantum well active region which allows the FET to operate as a laser, a detector and an absorption modulator forming a complete component base for integration. It is shown that the threshold voltage of this FET demonstrates unique dependencies on charge sheet, barrier, and collector dopings, which allows wide design flexibility and a substantially higher operating voltage than other III–V FETS. The effect of device length on threshold is examined experimentally and it is found that the gradient dVTH/dL may be positive or negative which raises the prospect that the condition dVTH/dL ≃ 0 may be found to allow scaling to very small dimensions. The device threshold and the bipolar injection from the gate contact are controlled by a p contact to the collector region which serves as an additional gate for the FET.