Self-consistent calculations have been performed on a double barrier r
esonant tunneling diode (RTD) with asymmetric spacer layers under vari
ous biases. The quasi-static state charge distribution in the GaAs-Al0
.3Ga0.7As RTD was studied and the capacitance derived. The theoretical
capacitance-voltage (C-V) characteristic agrees qualitatively with ex
perimental results. In contrast to the general belief that charge accu
mulation in the quantum well results in the observed peak in capacitan
ce measurements, our results reveal that the peak is induced by the qu
antum well discharging process. Comparison between the theoretical and
experimental results also supports the suggestion that scattering and
localization effects are important in the device. Conditions for opti
mizing the C-V characteristic for high frequency operations are discus
sed.