Suppression of Ge-based defects and auto-doping of p-type epitaxial GaAs by employing Al0.3Ga0.7As bi-layer buffer

Abstract

Development of high quality p-type epitaxial gallium–arsenide (epi-GaAs) film on germanium substrates with sub-nm surface roughness is much sought after for the next generation high speed transistors and optical device applications. In our work, zinc-doped p-type epitaxial GaAs with surface roughness of ∼0.3 nm is grown on germanium (Ge) substrate at 675 °C by employing bi-layer of Al0.3Ga0.7As buffer along with 300 nm thick un-doped GaAs. The structural quality and optical properties of p-type epi-GaAs layer with bi-layer Al0.3Ga0.7As on Ge substrate are examined through photoluminescence and Raman analysis. The presence of Al0.3Ga0.7As bi-layer suppresses Ge-based complex defects and background auto-doping (n-type) into epi-GaAs layer. The metal–oxide–semiconductor (MOS) capacitors are fabricated on p-type epi-GaAs layer by depositing Al2O3 (12 nm) as gate dielectric by using Atomic-layer-deposition (ALD) method. Capacitance-voltage and current-voltage characteristics show significant improvement of interface quality and bulk oxide quality with Al0.3Ga0.7As bi-layer buffer. The capacitance-voltage characteristics reveal that the epi-GaAs layer is p-type in nature with substrate doping of ∼1017 to 1018 cm−3. The frequency dispersion and interface defects are remarkably reduced for the device with bi-layer buffer and thus the introduction of bi-layer Al0.3Ga0.7As is crucial for the developing p-type epi-GaAs based electronic devices.