Application and device modeling of diamond FET using surface semiconductive layers

Hydrogen-terminated diamond surfaces exhibit p-type conduction without doping impurities. The surface conductive layers possess a suitable thickness of ∼10 nm for FET channels. The present work describes the fabrication of high-performance MESFETs and MOSFETs using the surface conductive layers on hydrogen-terminated homoepitaxial CVD diamond films. In the case of MESFETs, both enhancement-mode (normally off) and depletion-mode (normally on) operations are realized by selecting the gate metals. In the case of MOSFETs, depletion-mode operation is realized at present. The best transconductances in diamond are obtained in both MESFETs and MOSFETs. In addition, the dc operation of the diamond surface-channel FETs has been evaluated with device simulations using several models for the surface conductive layer. Consequently, a model with acceptors distributed two-dimensionally on the surface reproduces the actual I-V characteristics. Moreover, based on the model, the dc performance of self-aligned 1-μm-gate MESFETs not realized in diamond has been simulated. As a result, their transconductances exceed 100 mS-mm^-1.