Capacitance transient analysis of (Hg,Cd)Te MIS structures

New theoretical and experimental results are presented on the utility of the capacitance transient response Hg1-xCdxTe Metal Insulator Semiconductor structures for the measurement of So. Two types of MIS structures are investigated: single and dual gate. For the single gate case, we have performed a complete numerical analysis of the capacitance transient response to a depleting voltage step which shows that the surface current component decays in 10^-7s for silicon at 300K and in 10^-10s for HgCdTe at 77K for reasonable values of so. Capacitance transients cannot be resolved by standard ac measurement techniques at these time scales. This limitation has not been fully recognized previously. To circumvent the limitations of the pulsed single gate MIS technique a dual gate MIS structure consisting of two concentric electrically isolated metal gate electrodes was developed for (Hg1-xCdx)Te. A subtraction technique using different bias conditions allows the surface current component to be accurately measured. Dual gate measurements on n-type Hg.63Cd.37Te resulted in a determination of sobetween 30 and 300 cm/s for an anodic oxide -(Hg,Cd)Te interface.