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Title: Two high-field thermodynamically stable conductivity states in photoconductive CdS, one n-type and one p-type

Photoconductive CdS is known to be n-type and develops high-field domains in the range of negative differential conductivities. These domains have been extensively discussed, and when remaining attached to the electrodes have been renamed Böer domains (a broader definition suggested earlier is misleading) [K. Thiessen, Phys. Status Solidi B 248, 2775 (2011)]. They are occurring at high applied voltage in a range at which the current becomes highly non-ohmic that is conventionally described as N-shaped when the conductance decreases with increasing bias or as S-shaped when the current starts to increase again. In this paper only such cases will be discussed in which the current stays below significant Joule heating (no current channel formation), and only for stationary electrode-attached high-field domains. These are the cathode-attached domains that are maintained by field-quenching and are thermodynamically stable. Their finding is summarized in the first segment of this paper. When the applied voltage is increased, an anode-attached hyper-high-field domain develops that is stabilized by a hole blocking anode and will be analyzed in more detail below. It will be shown that they are a thermodynamically stable p-type photoconductive state of CdS. These two new states can be used to determine the carrier densitiesmore » and mobilities as function of the field and the effective work function in dependence of the spectral distribution of the optical excitation. In a thin slab adjacent to a blocking cathode, the quasi-Fermi levels are spread to a precise amount and are kept there in the entire high-field region. This opens the opportunity to analyze with small modulation of the excitation the trap transition coefficients near these quasi-Fermi levels separately, without broadening interference from other signals. This has already resulted in the discovery of an unusually sharp electron quenching level when the CdS was in a p-type state with an anode adjacent domain. It is also shown that the domains are responsible for the high efficiency of CdTe solar cells when covered with a thin layer of CdS by eliminating junction leakage and increase hole suction into the CdS.« less
Authors:
 [1]
  1. Department of Physics and Astronomy, 217 Sharp Lab, University of Delaware, Newark, Delaware 19716 (United States)
Publication Date:
OSTI Identifier:
22494812
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANODES; CADMIUM SULFIDES; CADMIUM TELLURIDES; CARRIER DENSITY; CARRIER MOBILITY; CATHODES; ELECTRIC CONTACTS; ELECTRIC POTENTIAL; ELECTRONS; EXCITATION; FERMI LEVEL; HOLES; JOULE HEATING; N-TYPE CONDUCTORS; P-TYPE CONDUCTORS; QUENCHING; SOLAR CELLS; THERMODYNAMICS; THIN FILMS; WORK FUNCTIONS