X-ray photoelectron and Auger electron spectroscopic study of the CdTe surface resulting from various surface pretreatments: Correlation of photoelectrochemical and capacitance-potential behavior with surface chemical composition

Abstract

The surface chemistry and stoichiometry of p- and n-type CdTe photoelectrodes treated with oxidizing and reducing etches have been characterized by x-ray photoelectron and Auger electron spectroscopies. The results of surface analysis have been correlated with the photoelectrochemical and capacitance–potential behavior of the photoelectrodes. ‘‘Oxidized’’ surfaces are covered by a thin Te0/TeO2 layer (or a thicker Te0 layer, if the etching procedure is slightly altered), resulting in Fermi level pinning: a constant photovoltage is found for a wide range of redox potentials and potential-independent space charge layer capacitance obtains. ‘‘Reduced’’ surfaces closely resemble ion sputtered CdTe in chemical state and stoichiometry, resulting in more nearly ‘‘ideal’’ behavior: the semiconductor/electrolyte interface is rectifying in the dark; capacitance–potential behavior follows the Mott–Schottky equation near flat band conditions; and photovoltage varies with redox potential, from 0 to ∼0.7 V for p-CdTe.

Chemical Interaction of CdTe and CdZnTe with Aqueous Solutions of H2O2-HI-Tartaric Acid

“…There have been several reports on the investigation of CdTe surface layers that result from various surface treatments. [1][2][3] The study of the surface composition of etched samples by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy confirms cadmium ''washing out'' and enriching a surface by tellurium as a result of chemical treatment. For example, nitric acid, ethylenediaminetetraacetic acid (EDTA), and K 2 Cr 2 O 7 /Ag + solution leave the surface depleted of Cd over at least several nanometers and should be avoided in device fabrication.…”

“…1 Bromine dissolved in methanol and mineral acids also leaves the surface depleted of Cd. 2 A nearly stoichiometric surface results from soaking of CdTe in an aqueous solution of KOH. 3 The best of all obtained surfaces, however, is a vacuum-heated and air-cleaved face, which seems to be stoichiometric and clean.…”

Investigation of HgCdTe surface films and their removal

“…The compositions of native, anodic, chemical and photochemical oxides, as well as their generation techniques, have all been the subjects of investigation. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] A variety of sample preparations were also examined. Treatments with Br-based etches [2][3][4][5][6]8,10,11,[14][15][16] acids 3,9,16 and ion bombardment 1,3,15 are but a few of the simpler examples of the techniques used.…”

Surface stoichiometry of pulsed ultraviolet laser treated polycrystalline CdTe

“…30 stoichiometry changes induced by a particular surface treatment or processing condition where relative changes are compared to a reference sample. 30,[41][42][43][44] However, in most cases, even the reference samples give Cd:Te ratios that deviate from the expected stoichiometric value 1:1, which typically goes unexplained. This work shows that the segregation at the surface of even sub-monolayers of Cd and Te leads to large enough deviations from stoichiometry to account for the variations seen in literature (typically about 610% from stoichiometry).…”