ELECTRICAL EFFECTS OF DISLOCATIONS AND OTHER CRYSTALLOGRAPHIC DEFECTSIN HG0.78CD0.22TE N-ON-P PHOTODIODES

An understanding of the effects of dislocations in HgCdTe diodes is co mplicated by several issues such as the diode architecture, diode form ation process, and the thermal history and location of the dislocation s. To help decouple the effects of these factors, high stress films we re used to lithographically introduce dislocations1 with different den sities and locations during the fabrication process of ion implanted, n-on-p diodes. Both array and diode test structures were studied. Afte r fabrication, the diodes were characterized with variable temperature I-V measurements and noise measurements. The diodes were then strippe d and defect etched to quantify the density and distribution of the di slocations. The effects of these process-induced dislocations were ana lyzed and compared to the effects of as grown dislocations, subgrain b oundaries and dislocations in other device architectures reported in t he literature.1,2 In general, high densities of either as grown or pro cess-induced dislocations in n-on-p, ion implanted diodes severely deg rade device performance by producing field dependent dark current. At 77K, dislocation densities greater than the mid 10(6) cm-2 can produce dark current densities in excess of the diode diffusion current. Disl ocations located near the outer periphery of the diode produce approxi mately ten times the dark current of interior dislocations. Grain boun daries, sub-grain boundaries, and twins also produce sufficient field dependent dark current to limit diode performance at 77K. The dark cur rent produced by dislocations is nearly temperature independent, sugge sting rather severe limitations on dislocation densities for low tempe rature diode operation.