Effects of etching with a mixture of HCl gas and H2 on the GaAs surface cleaning in molecular-beam epitaxy

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Abstract
In situ cleaning of GaAs substrates with a HCl gas and hydrogen mixture prior to molecular‐beam epitaxy has been investigated. The chemical reaction during etching was monitored using a quadrupole mass spectrometer. After etching, reflection high‐energy electron diffraction patterns revealed (2×4) arsenic‐stabilized surfaces and (4×2) gallium‐stabilized surfaces as reconstructed structures in the gas‐etched substrate surface. These structures suggest that the gas‐etched substrate surface is atomically flat, resembling an epitaxial layer surface. To study the effect of gas etching, the carrier depletion layer and the residual carbon impurity around the substrate epitaxial interface were measured by capacitance‐voltage carrier profiling and secondary‐ion mass spectroscopy. After gas etching, the carrier depletion was greatly reduced, from 1.2×1012 to 1×1010 cm−2. The carbon impurity around the interface also decreased by one order of magnitude. We discussed the surface‐cleaning mechanism using the atomic hydrogen terminating model of the GaAs surface during etching. We then applied this etching technique to in situ cleaning of semi‐insulating GaAs substrates prior to the growth of selectively doped GaAs/N‐AlGaAs heterostructures with very thin GaAs buffer layers.