An InAlAs/n+-InGaAs MISFET with a modulation-doped channel

A recently demonstrated device that consists of a thin high-doped n⁺-InGaAs active channel and an undoped InAlAs insulator layer has shown microwave performance superior to that of state-of-the-art MODFETs reported in the same ternary system. The main drawback of this highly doped channel device is the reduced mobility and peak velocity of the conducting electrons, which can result in inferior overshoot properties in future scaled FETs. A modulation-doped channel MISFET has been proposed and demonstrated to alleviate this problem. In this device the active InGaAs channel consists of a thin, highly doped subchannel buried below a very thin undoped subchannel adjacent to the InAlAs interface. In the depletion mode this device operates with a similarity to the doped-channel MISFET. In the accumulation mode, however, electrons are accumulated at the thin undoped InGaAs layer, and consequently the electron mobility is much higher than in the doped-channel MISFET. Improved transconductance and current-gain cutoff frequency are obtained