The Origin of Dark Region in LPE GaP Associating with Macrostep Riser

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Abstract
The origin of the dark region in LPE grown GaP crystals associated with macrostep is investigated by observation of photoluminescence (PL) image and spatially resolved photolumenescence (SRPL) spectroscopy. PL image from the cleaved surface of undoped, N, S, and Zn doped layers showed that the dark region appeared only when nitrogen was doped irrespective of simultaneous doping of S or Zn. The result of SRPL measurement showed that the concentration of N was lower in the dark region compared with the bright region. This could be explained by the difference of the step velocity on the riser and the tread of the macrostep.