Antimony segregation in the oxidation of AlAsSb interlayers

Abstract

The lateral wet oxidation of strained AlAsSb was studied. AlAs0.80Sb0.20 interlayers were grown on a GaAs substrate and capped with a lattice-matched In0.25Ga0.75As layer. The AlAsSb was oxidized between 350 and 450 °C. Oxidation temperatures >400 °C resulted in poor surface morphology and delamination. Oxidation of thicker AlAsSb interlayers (h≈2000 Å) resulted in metallic Sb layers forming between the AlOx and the semiconductor interfaces. The remaining Sb metal at the oxide–semiconductor interface was ∼15% oxidized. Lateral wet oxidation of thinner AlAsSb interlayers (h⩽500 Å) resulted in Sb inclusions at the oxide–semiconductor interface. The Sb inclusions were 1.5–2.0 μm in diameter and the inclusion thickness was approximately equal to the AlAsSb layer thickness. Methanol (CH3OH) was added to the water mixture with the intent to stabilize the otherwise unstable stibine (SbH3) such that Sb could be removed from the oxidizing structure. However, methanol addition resulted in a decreased oxidation rate and a change in the Sb precipitate morphology. The Sb inclusions observed in pure water oxidation changed to a Sb finger-like morphology with increasing methanol concentration. The Sb fingers were 1.0–2.0 μm wide and as long as the oxidation depth. Oxidation of AlAsSb interlayers h⩽200 Å were limited by the incorporation of Ga from the substrate and capping layer into the oxidation layer. Doping the oxidation AlAsSb interlayer 1×1018 cm−3 n type (Si or Te) did not result in any improvement in Sb segregation.