Monitoring HgCdTe layer uniformity by the differential absorption technique

Abstract

In this letter, we demonstrate how the differential absorption technique can be applied to study band gap uniformity in HgCdTe samples. The transmission of HgCdTe wafers is measured at room temperature and data filtering is used to remove both the interference fringes and high-frequency noise. This data treatment approach produces reliable transmission data for HgCdTe layers as thin as 8 μm. In addition, the spectrum of the interference fringes is used to estimate the HgCdTe layer thickness with an accuracy of ±0.1 μm. The absorption coefficient is differentiated twice with respect to the photon energy and an approximate value of the band gap is estimated from extrema of the derivatives. By applying this procedure to different points on the same HgCdTe wafer, we can determine both lateral and transverse fluctuations of the semiconductor band gap. The initial results indicate that the accuracy of the differential absorption technique is around ±0.5 meV for HgCdTe wafers. The differential absorption technique appears suitable for routine characterization of HgCdTe wafers because it is simple, nondestructive, and applicable at room temperature.