Recombination Centers and Fast States on Unstable Germanium Surfaces

Abstract

Measurements of surface conductance, photoconductance, dark field effect, and field effect under illumination were made on single crystals of w-type and ^>-type germanium. The samples, freshly etched with CP-4, were exposed to the Brattain-Bardeen ambient cycles. During early cycles, the measurements were irreproducible. The irreproducibility was due to changes in the density of the dominant surface recombination centers. The density of these centers varied by an order of magnitude during the ambient cycle, whereas the energy levels and the capture probabilities remained constant. With these assumptions, quantitative agreement between theory and experiment was obtained. From the changes in the photoconductance and the dark-field effect during repeated ambient cycles, the density of the dominant recombination centers was found to change at the same rate as the density of the "fast" states near the center of the gap. In addition, the recombination centers and the "fast" states have the same energy levels. Therefore, the recombination centers and "fast" states are identical.

Influence of Adsorbed Water on Phonon and UV-Induced IR Absorptions of TiO2 Photocatalytic Particle Films

“…Weng et al., in a study of back-electron-transfer kinetics in dye-sensitized nanoparticulate TiO 2 , suggest a model of electron injection proposing that (1) injected electrons randomly populate a small region near the adsorbate molecule, (2) spatial diffusion between trap sites is negligible on the nanosecond time scale, and (3) injected electrons relax from shallow traps to deep trap states. It is well known that deep traps act as recombination centers in semiconductor materials. − ,,, Hoffmann and co-workers 7 have proposed that initially trapped electrons occupy an excited state trap and then relax into what is effectively a recombination center where electron−hole pairs recombine. They suggested that the process of relaxation is mediated by the presence of water.…”

“…In general, there is a lack of consensus about the dominant contributions to the broad IR absorptions induced by band gap irradiation of semiconductor particle systems. Some time ago, the behavior of free carriers in response to changes in surface hydration of germanium films was studied (Brattain-Bardeen ambient cycle). − The presence of water on the germanium surface resulted in a reduction in surface conductivity which was explained in terms of an increase in shallow trapping sites.…”

Chemical, Electronic, and Electrical Properties of Alkylated Ge(111) Surfaces

“…Prior work used an air gap between the semiconductor surface and the field plate, which allowed for the use of different gaseous atmospheres, but instability in such measurements has been reported to change the surface electronic properties. 5,6,48,49 The surface potential of the oxidized Ge(111) surfaces was observed to be on the opposite side of the intrinsic Ge Fermi level from the surface potential of the Grignard-derived alkylated Ge(111) surfaces. The surface potential position of the alkylated samples that displayed less band bending, such as ethyl-or decyl-terminated Ge(111) surfaces, could be produced by the presence of surface oxides at levels below the detection threshold of the XPS instrumentation.…”

“…This indicated that our system had either a lower surface state density or a higher field-plate capacitance. Prior work used an air gap between the semiconductor surface and the field plate, which allowed for the use of different gaseous atmospheres, but instability in such measurements has been reported to change the surface electronic properties. ,,, …”

MODIFICATION OF PbS NOISE SPECTRA BY RADIATION

“…Wang and Wallis (1957) have established that radiation can alter the surface potential of a semiconductor. Trapping effects in slow states, which are believed to give rise to l/f noise (Kingston 195G), would certainly be affected by any change in potential a t the surface.…”