CORRELATION OF THE CD-TO-TE RATIO ON CDTE SURFACES WITH THE SURFACE-STRUCTURE

We report here that reconstruction on (100), (111) A, and (111)B CdTe surfaces is either c (2 x 2), (2 x 2), and (1 x 1) or (2 x 1), (1 x 1), and (1 x 1) when they are Cd or Te stabilized, respectively. There is a mixed region between Cd and Te stabilization in which the reflected high-energy electron-diffraction (RHEED) patterns contain characteristics of both Cd- and Te-stabilized surfaces. We have also found that the Cd-to-Te ratio of the x-ray photoelectron intensities of their 3d3/2 core levels is about 20% larger for a Cd-stabilized (111) A, (111)B, or (100) CdTe surface than for a Te-stabilized one. According to a simple model calculation, which was normalized by means of the photoelectron intensity ratio of a Cd-stabilized (111) A and a Te-stabilized (111)B CdTe surface, the experimental data for CdTe surfaces can be explained by a linear dependence of the photoelectron-intensity ratio on the fraction of Cd in the uppermost monatomic layer. This surface composition can be correlated with the surface structure, i.e., the corresponding RHEED patterns. This correlation can in turn be employed to determine Te and Cd evaporation rates. The Te reevaporation rate is increasingly slower for the Te-stabilized (111) A and (111)B surfaces. In addition, Te is much more easily evaporated from all the investigated surfaces than is Cd, if the substrate is kept at normal molecular-beam-epitaxy growth temperatures ranging from 200-degrees-C to 300-degrees-C.