Tl incorporation in InSb and lattice contraction of In_1-x Tl_xSb

Ternary In_1-xTl_xSb thin films are grown by low pressure metalorganic chemical vapor deposition in the high In composition region. Infrared photoresponse spectra of the In_1-xTl_xSb epilayers show a clear shift toward a longer wavelength compared to that of InSb. Tl incorporation is confirmed by Auger electron spectroscopy. In contrast to the theoretical expectation, high resolution x-ray diffraction study reveals that the lattice of the In_1-xTl_xSb epilayers is contracted by the incorporation of Tl. As more Tl is incorporated, the lattice contraction is observed to increase gradually in the experimental range. A possible origin of this phenomenon is discussed. Our experimental results suggest that the Tl incorporation behavior in In_1-xTI_xSb differs from that of other group III impurities in III antimonides.