Unintentional incorporation of B, As, and O impurities in GaN grown by molecular beam epitaxy

Abstract

We have investigated systematically the effects of growth parameters upon the unintentional incorporation of B, As, and O impurities in GaN grown by molecular beam epitaxy with an RF-plasma activated nitrogen source. The prepared samples were analyzed using secondary ion mass spectrometry to determine the absolute concentration of the impurities. The boron background concentration in the unintentionally doped GaN was found to strongly correlate with the nitrogen plasma power used during the growth, indicating a decomposition of the pBN crucible in the plasma source. Due to previous GaAs growth in the same chamber, a considerably large amount of As contamination (≈3×1018 at/cm3) was also observed in the grown layer. The presence of Al in GaN is found to facilitate the incorporation of oxygen impurities in the layer. We determined an empirical formula, Cot/Cob 3.8×(CAl/CAl)0.27, representing the correlation between O concentration and Al mole fraction (%) in the small range of Al content, 0.03≈1%, in the layer. The residual oxygen level was substantially reduced from 3.4×1019 to mid-1018 at/cm3 in the GaN layer when the buffer layer structure was changed from low temperature grown GaN single buffer to GaN/AlN double buffer layer. We ascribe this significantly lowered oxygen impurity level to improved crystalline quality of the layer due to the double buffer layer structure.