OXYGEN ON THE (100) CDTE SURFACE

We have investigated oxygen on CdTe substrates by means of x-ray photo electron spectroscopy (XPS) and reflection high-energy electron diffra ction (RHEED). A Te oxide layer that was at least 15 angstrom thick, w as found on the surface of as-delivered CdTe substrates that were mech anically polished. This oxide is not easily evaporated at temperatures lower than 350-degrees-C. Furthermore heating in air, which further o xidizes the CdTe layer, should be avoided. Etching with HCl acid (15% HCl) for at least 20 s and then rinsing with de-ionized water reduces the Te oxide layer on the surface down to 4% of a monoatomic layer. Ho wever, according to XPS measurements of the O 1s peak, 20%-30% of a mo noatomic layer of oxygen remains on the surface, which can be eliminat ed by heating at temperatures ranging between 300 and 340-degrees-C. T he RHEED patterns for a molecular beam epitaxially (MBE)-grown CdTe fi lm on a (100) CdTe substrate with approximately one monoatomic layer o f oxidized Te on the surface lose the characteristics of the normal RH EED patterns for a MBE-grown CdTe film on an oxygen-free CdTe substrat e.