A simplified fabrication process for HgCdTe photoconductive detectors using CH4/H-2 reactive-ion-etching-induced blocking contacts

A fabrication procedure using dry plasma process technology has been develo ped for HgCdTe photoconductive detectors. Dry plasma, in the form of CH4/H- 2 reactive ion etching, was used in a multi-functional process capacity aft er the mesa delineation of individual detector elements and prior to metal contact deposition to (i) etch the passivation layer to open contact areas for metal deposition and (ii) take advantage of the increase in effective d oping in HgCdTe material when it is exposed to the CH4/H-2 plasma and incre ase the n-type doping in the opened contact areas. The limited undercut tha t results from etching the passivation layer with dry plasma, as opposed to traditional wet-chemical etching techniques, eliminates the need for a pho tolithographic masking step to align the metal contacts over the contact ar eas after they have been opened in the passivation layer. Increasing the n- type doping in the contact areas has the purpose of providing both low-resi stance ohmic contacts and a potential barrier to minimize photogenerated ca rrier recombination at the semiconductor/metal interface and thereby improv e detector responsivity performance. The process improvements outlined in t his paper make it possible to fabricate high-performance infrared photocond uctive devices using two photolithographic masking steps. Mid-wavelength in frared HgCdTe photoconductive detectors fabricated using this procedure dem onstrate a background-limited D-lambda* of 2.0 x 10(11) cm Hz(1/2) W-1 at a n operating temperature of 80 K, illustrating the application of dry plasma technology to HgCdTe infrared detector fabrication for both process and pe rformance optimization.