GaAs field-effect transistor with an atomically precise ultrashort gate

Abstract

We present a new type of depletion-mode field-effect transistor (FET) with an inherently ultrashort gate length. The device is fabricated exclusively via molecular beam epitaxy (MBE) in GaAs/AlGaAs by cleaved-edge overgrowth of a suitably prepared MBE-grown substrate. The channel, as well as the gate, of this T-FET consists of a high-mobility, two-dimensional electron gas (2DEG) generated by modulation doping of GaAs quantum wells. The planes of the 2D systems are orthogonal to one another forming a ‘‘T’’ whose legs approach each other at the intercept to within 200 Å. In this way, the thickness of one of the quantum wells (200 Å) established the gate length of the device. All elements of the T-FET are completely immersed into the semiconductor material and all relevant length scales are established to atomic precision by MBE. Schottky barriers do not enter the device characteristics. Our first T-FET reaches transconductances of 196 and 410 mS/mm at 77 and 4.2 K, respectively.