Characterization of mercury cadmium telluride surface and interface using surface acoustic wave technique

Abstract

Hg 1− x Cd x Te is extensively used today as a versatile infrared detector material with increasing importance in the fabrication of focal plane arrays. In this work electronic properties of passivated and unpassivated Hg 1− x Cd x Te surfaces and SiO 2 interfaces are investigated using nondestructive SAW technique. The transverse acoustoelectric voltage (TAV) is monitored across the Hg 1− x Cd x Te sample which is placed in proximity of a LiNbO 3 delay line. The TAV is developed due to the nonlinear interaction between the electric field accompanying SAW, and the free carriers near the Hg 1− x Cd x Te surface. One- and two-beam contactless TAV and surface photovoltage spectroscopy have been carried out to determine the bandgap and thus the alloy composition, x, of Hg 1− x Cd x Te. The subbandgap spectral responses due to interface states energy levels within the bandgap have also been analyzed. The TAV versus voltage measurements are also performed for further investigation of Hg 1− x Cd x Te surface properties such as flatband potential, interface charge and surface state density as a function of location in the energy bandgap. This technique has also been applied to other semiconductors such as Si and GaAs. The above-mentioned parameters and others such as conductivity, generation lifetime and surface generation velocity have been measured for these semiconducting materials. Nondestructive depth profiling of the free carrier concentration and some of the above electrical properties have also been measured. Details of these results with emphasis on the HgCdTe samples are presented.