Effects of CdCl2 treatment on the local electronic properties of polycrystalline CdTe measured with photoemission electron microscopy

Abstract

To investigate the effects of CdCl 2 treatment on the local electronic properties of polycrystalline CdTe films, we conducted a photoemission electron microscopy (PEEM) study of polished surfaces of CdTe films in superstrate configuration, with and without CdCl 2 treatment. From photoemission intensity images, we observed the tendency for individual exposed grain interiors to vary in photoemission intensity, regardless of whether or not films received CdCl 2 treatment. Additionally, grain boundaries develop contrast in photoemission intensity images different from grain interiors after an air exposure step, similar to observations of activated grain boundaries using scanning Kelvin probe force microscopy studies. These results suggest that work function varies locally, from one grain interior to another, as well as between grain boundaries and grain interiors.

Local Electronic Structure Changes in Polycrystalline CdTe with CdCl2 Treatment and Air Exposure

“…X-ray photoelectron spectroscopy showed less than 1 atom % oxygen and 17 atom % carbon after sputtering . After sputter-cleaning, the samples were transferred in N 2 (<0.1 ppm O 2 , <0.1 ppm H 2 O) to the UHV PEEM measurement chamber, without additional exposure to air.…”

“…17 X-ray photoelectron spectroscopy showed less than 1 at% oxygen and 17 at% carbon after sputtering. 18 After sputter-cleaning, samples were transferred in N2 (<0.1 ppm O2, <0.1 ppm H2O) to the UHV PEEM measurement chamber, without additional exposure to air. After initial PEEM measurement, samples were exposed to air for 30 minutes, reintroduced into UHV, and examined to investigate the impact of air exposure.…”

“…40 An inert environment sample transfer system was used to transfer samples between a dry N2 (<0.1 ppm O2, <0.1 ppm H2O) glovebox and vacuum systems to avoid unintentional exposure of samples to air.The surface compositions of the films were verified after each step using x-ray photoelectron spectroscopy. 18 After all PEEM measurements, cross-sections of samples were examined with scanning electron microscopy to verify the polished CdTe layer thicknesses (3.2 µm and 2.5 µm for CdCl2-treated and untreated films). PEEM measurements were conducted in an Elmitec LEEM-III system with an electron energy analyzer and a tunable deep-ultraviolet (DUV) light source.…”

Impact of CdCl2 Treatment in CdTe Thin Film Grown on Ultra-Thin Glass Substrate via Close Spaced Sublimation

“…Presumably, fewer grain boundaries lead to reduced scattering and recombination of photogenerated carriers and the prevailing description is that Cl from the CdCl 2 treatment segregates to grain boundaries, depleting or even inverting them with respect to grain interiors. Junctions between grain interiors and grain boundaries are expected to repel holes and conduct electrons to the back contact more efficiently [43]. Overall morphology results in this work imply that the films are uniform, smooth, homogeneous, and nearly dense-packed as well as free from voids, cracks, or pinholes.…”