X-ray diffraction characterization of LPE HgCdTe heterojunction photodiode material

Abstract

High-resolution x-ray diffraction has been used to measure the composition difference between P and N layers in HgCdTe heterojunction photodiode material grown by liquid phase epitaxy. The composition (band gap) difference is a critical parameter in long wavelength photodiodes because it affects dark current and the formation of photocurrent collection barriers. We find that symmetric 333 reflections cannot resolve the small composition differences of interest. However, by making use of the asymmetric 246 reflection, small composition differences (0.03) can be resolved. There is good agreement between rocking curves and secondary ion mass spectroscopy composition depth profiles, both in the value of the composition difference and in the extent of compositional grading in the top layer. High-resolution x-ray diffraction shows promise as a nondestructive, relatively rapid technique for screening as-grown heterojunction material for carrier collection barriers.