Surface impurity gradients in epitaxial GaAs

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Abstract
Zero‐bias Schottky barrier capacitance measurements indicate the presence of heavily‐doped surface impurity gradients in n‐type epitaxial layers of GaAs grown on n+ substrates. These impurity gradients are produced during epitaxial growth by the electric field due to 5×1011 cm−2 surface states in GaAs in 1000 K. For n‐type layers grown on Cr‐doped substrates, high‐resistance regions are observed at the surface. These regions are probably caused by the buildup of positively charged chromium atoms in the electric field at the surface. The redistribution of chromium atoms in ion‐implanted samples during annealing can also be explained by electric fields due to surface states and the implanted‐ion profiles.