Electron reflection and interference in the GaAs/AlAs-Al Schottky collector resonant-tunneling diode

Abstract

Schottky collector resonant-tunneling diodes (SCRTD's) have potential for increased oscillator bandwidth, but may be prone to electron reflection at the semiconductor-metal interface of the Schottky collector. This reflection has been observed previously using collectors deposited in situ by molecular beam epitaxy: the reflection was manifested as interference oscillations on the rising slope of the resonant current. This paper extends the room temperature results of that work to cover the 1.5 K--300 K range, revealing valuable information on the semiconductor-metal interface, scattering rates, scattering mechanisms, peak-to-valley ratios, electron distribution, and electron transport. The SCRTD oscillation strength was found to depend on the above-barrier reflection coefficient of the collector metal, and the effect of scattering on virtual states confined by this reflection. Increased scattering degrades the oscillation strength as temperature is increased. The primary scattering mechanism was determined to be LO phonon emission, which had a related role in degrading the main peak-to-valley ratio through scattering in the well of the resonant-tunneling diode (RTD). The number of oscillations was dependent on the emitter electron distribution, with thermally activated oscillations appearing at high temperature. Increasing temperature caused a voltage shift of the oscillations that followed the GaAs band-gap temperature dependence, implying pinning relative to the GaAs valence band and interface states with valence-band wave functions. Postresonant oscillations were thought to arise from transport through the transverse $X$ valley of the second AlAs RTD barrier. An Airy function model of device transmission and current is presented.