XPS and SIMS studies of MBE-grown CdTe/InSb(001) heterostructures

A series of MBE-grown CdTe/InSb(001) heterostructures with different substrate growth temperatures is studied using X-ray photoelectron spectroscopy (XPS) and secondary-ion mass spectrometry (SIMS). XPS shows that Te exists mainly as TeO₂ at the sample surface, while In exists as In ₂O and In₂O₃. The Cd/Te ratio is greater than one indicating that the surface is Cd rich. Both XPS and SIMS reveal In interdiffusion directly. The SIMS depth profiles and the XPS In 3D and 4D spectra indicate that the In concentration in the CdTe film grown at high substrate growth temperature, T_s, is significantly higher than at low T_s. This is attributed to the diffusion of indium across the CdTe/InSb interface from the InSb substrate. Dislocations also enhance the diffusion of In from the InSb substrate. It is deduced that CdTe and InSb have an exact lattice match at growth temperatures of about 180 degrees C since the surface In concentration is a minimum for samples grown at T_s approximately 180 degrees C. The SIMS depth profiles for Te⁺ also give evidence of some diffusion of tellurium across the interface into the substrate for samples grown at high T_s. Furthermore, the SIMS data suggest that some In_xTe_y compound, probably In ₂Te₃, forms at the interface, but further studies using other analytical techniques are required to confirm this.