Piezoelectric effects in HgCdTe devices
Piezoelectric effect in long-wavelength infrared (LWIR) HgCdTe has been studied using metal-insulator-semiconductor (MIS) and p-n homojunction 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 time such a value has been reported in the literature. Subsequent calculation showed that the thermal stress from cryogenic cool (from 300 to 77K) of hybridized infrared devices fabricated on (111) HgCdTe surfaces induced a piezoelectric field of∼1840 V/cm. This field is present in the space charge regions in the semiconductor where there is no free carrier. It reinforces the built-field in an n-on-p diode fabricated on the (111)A HgCdTe surface. Thus, the diode is more prone to the thermal stress than one fabricated on the (lll)B surface. Electrical measurement of reverse-bias dark currents in HgCdTe photodiodes under applied compressive and tensile stress confirmed the existence of a strain-induced field in the junction.