The feasibility of a new transistor structure was demonstrated through an experimental observation of current gain and voltage gain. The proposed transistor structure is a hot electron transistor without a base layer to minimize scattering. Electron emission from the emitter is controlled using positively biased Schottky gate electrodes located on both sides of the emitter mesa. Monte Carlo simulation shows an estimated delay time of 0.17 ps and low gate leakage current with open-circuit voltage gain over unity. To confirm the basic operation, the device with a 25 nm wide emitter was fabricated. To obtain saturated current-voltage characteristics, the emitter was surrounded by gates and parasitic regions were eliminated by electron beam lithography. The observed open-circuit voltage gain was 25. To obtain a low leakage current, an electron energy smaller than the Γ-L separation was necessary to maintain the ballistic nature of the electron. When the gate-emitter voltage was 0.8 V, the gate leakage current was only 4% of the collector current. Thus voltage amplication and current amplification were confirmed simultaneously.

GaSb/InAs hot electron transistors (HETs) composed of a type-II misaligned quantum well operate at room temperature. The collector current is well described by the thermionic emission from the emitter. In order to get insight of the electron transport in the HET, the base width was varied or the collector barrier was modulated. The emitter's barrier height for the thermionic emission decreases with decreasing base width. This is caused by the increase of the quantum confinement energy in the InAs base with decreasing base width. Among HETs with a GaSb collector, a GaInSb abrupt layer, or a GaInSb graded layer at the collector edge, the latter type has the largest collector current. This indicates that collector grading reduces not only the collector barrier height, but also the quantum mechanical reflection of electrons. Collector-graded HETs with a 5 nm-thick base show a current gain of 8. The sheet resistance of InAs base is one order of magnitude less than bulk InAs without doping. This reduction is partly due to the accumulation of electrons transferred from the GaSb valence band to the InAs conduction band.