Spectroscopic, topological, and electronic characterization of ultrathin a-CdTe:O tunnel barriers

Abstract

Auger electron spectroscopy analysis of oxidation states of Te in amorphous CdTe oxide thin films Ultrathin oxygenated amorphous CdTe (a-CdTe:O) films are prepared by rf sputtering of CdTe in a background of argon or argon/nitrogen/oxygen mixtures. Atomic force microscopy ͑AFM͒ is used to characterize the films and shows that they have an island structure typical of most sputtered thin films. However, when sufficiently low powers and deposition rates are employed during sputtering, the resulting films are remarkably smooth and sufficiently thin for use as barrier layers in inelastic electron tunneling ͑IET͒ junctions. Four terminal current-voltage data are recorded for Al/a-CdTe:O/Pb tunnel junctions and conductance-voltage curves are derived numerically. WKB fits to the conductance-voltage curves are obtained using a two-component trapezoidal plus square ͑TRAPSQR͒ model barrier potential to determine values for the tunnel barrier parameters ͑height, shape, and width͒; these parameters are consistent with AFM topological measurements and values from similar devices reported in the literature. IET spectra are presented which confirm that electrons tunnel through ultrathin regions of the a-CdTe:O films, which contain aluminum oxide subregions in a manner consistent with the TRAPSQR barrier model. Because tunneling occurs predominantly through these ultrathin regions, IET spectroscopic data obtained are representative of states at, or within a few tenths of nanometers from, the surface and confirm that the a-CdTe:O surface stoichiometry is very sensitive to changes in the argon/oxygen/nitrogen concentration ratios during film growth. Full IET spectra, current-voltage, and conductance-voltage data are presented together with tunnel barrier parameters derived from ͑WKB͒ fits to the data. The results presented here indicate that inelastic electron tunneling spectroscopy is a useful tool for characterizing the surface states of a-CdTe:O and possibly other photovoltaic materials.

Characterization of vacuum evaporated CdTe thin films prepared at ambient temperature

“…The dark resistivity was found to be r dark ¼2. 10 reasons that we got smaller value of the resistivity are first nonstoichiometry of the films that they have excess Te and it is known that stoichiometry and resistivity are in opposite directions, and second the use of Cu contact. That is Cu will diffuse in the films and work as a dopant, even though we recorded the I-V measurements after about one hour from depositing contacts.…”

“…Physical techniques include close space sublimation (CSS) [4,8], molecular beam epitaxy (MBE) [9], r.f sputtering [10], electrodeposition [11][12][13], pulsed laser deposition (PLD) [14][15], and thermal evaporation [2,6,[16][17][18]. Chemical techniques include metal organic chemical vapor deposition (MOCVD) [19], chemical bath deposition (CBD) [20], successive ionic layer adsorption and reaction method (SILAR) [21][22], and spray pyrolysis [12,23,24].…”

The Effect of Annealing on the Structural, Electrical and Optical Properties of CdTe Thin Films

“…CdTe has direct band gap in the range (1.4 -1.5) eV, which is near the maximum solar energy conversion point [2,3]. CdTe has a high absorption coefficient (larger than 10 5 cm -1 at wavelengths around 700 nm), so that only thin film layers (a few microns) are needed for the absorption of the most of the solar spectra photons with energy higher than the band gap.…”

Influence of Water Condensation on Charge Transport and Electric Breakdown Between an Atomic Force Microscope Tip, Polymeric, and (Semiconductor) CdS Surfaces

“…Film thicknesses were determined in situ using a quartz crystal microbalance, and ranged from 100 -500 nm. Full details of our sputtering method and electrical and topological characterization the CdS films can be found elsewhere [14].…”