The evaluation of curved extended electrodes for off-area bonding of HgCdTe photoconductive detectors

The formation process of devices' electrodes is one of the key techniques in the fabrication of HgCdTe infrared photoconductive detectors. A new structure of extended electrode has been developed and improved for low temperature stability. The parts of HgCdTe wafers exposed by photolithography are first dry etched until the sapphire substrate by ion beam milling (IBM). Then the contact metal films are deposited on HgCdTe and sapphire respectively. The main innovation of this paper is the optimization of the thickness of contact metal films. The traditional method of evaluation the stability of electrodes is to measure the changes of resistance when the devices are taken from normal temperature into low temperatures. Nevertheless, the changes of resistance are not sensitive to microdefects. So as to the effective evaluation of the contact metal films, another means (SEM) is utilized to get details about the microstructure of the contact metal films on the sidewall. In this paper, the topography of the improved sidewall contact metal was investigated by SEM. The outcome shows that a continuous columnar structure is gained by that optimization. No voids could be seen in the contact metals on the sidewall of etched HgCdTe, which reveals that the improved process is valid. It also indicated that SEM is a reasonable and efficient means to evaluate the quality of deposited metal film on the sidewall of a mesa structure in the fabrication of HgCdTe photoconductive detectors.