The characterization of aluminum gallium arsenide resonant tunneling diodes at microwave frequencies

Abstract

Double-barrier, single-quantum-well, resonant tunneling diodes employing variable thickness Al$\sb{0.25}$Ga$\sb{0.75}$As barriers and 5 nm GaAs wells have been studied. Low doped GaAs buffer regions ($N\sb D$ $\approx$ 5 $\times$ 10$\sp{16}$ cm$\sp{-3}$) were placed next to the barriers to reduce the device capacitance and to prevent dopant migration into the barriers.

The diodes were mounted in a coplanar waveguide test circuit that was placed in a microwave test fixture employing Wiltron K Connector spark plug launchers to transition from the coplanar waveguide to coax. Small-signal reflection coefficient measurements were made on these diodes. The measurements were de-embedded using a two-tiered error correction scheme composed of the line-reflect-match and thru-reflect-line techniques.

A small-signal equivalent circuit model consisting of a resistor, $R\sb S$, in series with the parallel combination of a nonlinear conductance, G, and a capacitance, C, was used. The series resistance and shunt capacitance were found to be independent of bias voltage while the conductance was found to be related to the dc current-voltage characteristic $\lbrack I(V)\rbrack$ of the diode by$$G = {{dI\over dV}\over{1-{dI\over dV}R\sb S}}.$$

The large-signal behavior of the diode was investigated. The small-signal equivalent circuit model for the diode was used for the large-signal analysis by replacing the nonlinear conductance with an ac conductance, $G\sb{\rm ac}$ = $I\sb1$/$V\sb1$, where $v(t)$ = $V\sb B$ + $V\sb1$ cos $\omega t$ is the instantaneous voltage across the conductance with $V\sb B$ being the bias voltage and where $i(t)$ = $I\sb0$ + $I\sb1$ cos $\omega t$ + $I\sb2$ cos 2$\omega t$ + $\cdots$ is the Fourier series representation of the instantaneous current through the conductance as calculated from the current-voltage curve that has been corrected for the series resistance, $R\sb S$. The effects of higher harmonic voltage terms was found to be negligible.

The diode was studied as a microwave detector. When biased at the peak in the current-voltage curve, the diode provides a novel, full-wave rectification of a superimposed ac signal. The diode's performance as a detector is comparable to Schottky point contact detectors at low frequencies, while the resonant tunneling diode's performance degrades at higher frequencies because of its intrinsic parasitics.