MBE-growth of CdTe on GaSb substrates: A case study on the influence of substrate quality

Abstract

CdTe epitaxial layers were grown by MBE on GaSb (211)B substrates from two different suppliers in order to determine the influence of as-received substrate quality on the material quality of subsequently-grown CdTe epilayers. It is observed that GaSb substrates with smooth surface and lower degree of surface roughness can lead to CdTe epilayers with superior material quality, as evidenced by a lower dislocation density, lower etch pit density, lower degree of epilayer surface roughness, narrower XRD FWHM, and lower strain. It is concluded that in comparison to substrates with a relatively smooth surface (RMS surface roughness ∼ 0.62 nm), substrates with a high degree of surface roughness (RMS surface roughness ∼ 2.24 nm) lead to effects that generate misfit dislocations during the MBE growth process. This results in approximately an order of magnitude increase in measured etch pit density (from ∼9 × 105 to 7 × 106 cm−2) and the calculated dislocation density (from 6.51 × 105 to 6.87 × 106 cm−2, as determined from X-ray diffraction reciprocal space mapping), indicating that a smooth substrate surface is critical in achieving high quality CdTe epilayers on GaSb.