The surface differential reflectivity (SDR) and photoemission methods were used to study surface electronic structure of CdTe and ZnTe (110) surface. The changes of the reflectivity coefficient were caused by the changes of electric field (band bending) induced at the surface region by high power laser illumination of the sample. The obtained results are interpreted as corresponding to the Franz-Keldish effect . The CdTe and ZnTe samples were grown by modified Bridgeman method in the Institute of Physics PAS in Warsaw . The SDR spectra were measured for the (110) surface illuminated by the Argon laser (radiation in range between 457 and 514.5 nm, power 500 mW). The SDR spectra were obtained as a function of laser power illumination and the linear increase of the measured amplitude of SDR spectra was observed. The shift of the surface potential was estimated on photoemission spectra as a shift of the Cd 4d level position caused by the laser illumination of the surface. The exponential time decay of the amplitude of SDR spectra were measured after turning of the laser illumination. The decay time constant was estimated on 1300 sec for clean surface of CdTe. The attempts were done to discuss obtained results in the frame of the Franz-Keldish effect description.
This work was supported within: Eur. Comm.IHP-Cont.HPRICT199900040/2001-00140; and KBN SPUB-M/DESY/P-03/DZ-213/2000; and European Community Prog. G1MA-CT-2002-4017(Center of Excellence, CEPHEUS).
2.A.Mycielski at all. J. Cryst. Growth, 197, 423 (1999)