In this letter, we demonstrate how the differential absorption techniq
ue 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-fr
equency noise. This data treatment approach produces reliable transmis
sion data for HgCdTFe layers as thin as 8 mu m. in. addition, the spec
trum of the interference fringes is used to estimate the HgCdTe layer
thickness with an accuracy of +/-0.1 mu m. The absorption coefficient
is differentiated twice with respect to the photon energy and an appro
ximate value of the band gap is estimated from extrema of the derivati
ves. By applying this procedure to different points on the same HgCdTe
wafer, we can determine both lateral and transverse fluctuations of t
he semiconductor band gap. The initial results indicate that the accur
acy 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, no
ndestructive, and applicable at room temperature. (C) 1996 American In
stitute of Physics.