PIEZOELECTRIC EFFECTS IN HGCDTE DEVICES

Piezoelectric effect in long-wavelength infrared (LWIR) HgCdTe has bee n studied using metal-insulator-semiconductor (MIS) and p-n homojuncti on devices. A cantilever beam technique was used to measure the shift in flatband voltage in the MIS devices as a function of applied strain , from which piezoelectric constant was derived. This is the first tim e such a value has been reported in the literature. Subsequent calcula tion showed that the thermal stress from cryogenic cool (from 300 to 7 7K) of hybridized infrared devices fabricated on (111) HgCdTe surfaces induced a piezoelectric field of similar to 1840 V/cm. This field is present in the space charge regions in the semiconductor where there i s no free carrier. It reinforces the built-field in an n-on-p diode fa bricated on the (111)A HgCdTe surface. Thus, the diode is more prone t o the thermal stress than one fabricated on the (111)B surface. Electr ical measurement of reverse-bias dark currents in HgCdTe photodiodes u nder applied compressive and tensile stress confirmed the existence of a strain-induced field in the junction.