Aynur Eray | Hacettepe University (original) (raw)

Papers by Aynur Eray

AIP Conference Proceedings, 2017

Journal of Materials Science Materials in Electronics

In this study, we discuss measurements of the J–V characteristics of an a-Si : H n+-i-n+ structur... more In this study, we discuss measurements of the J–V characteristics of an a-Si : H n+-i-n+ structure, and the results of numerical simulation using the AMPS-1D simulation program. Application of the AMPS simulation model to the sample structures considered allows us to determine the structural properties of the a-Si : H n+-i-n+ structure. The one-dimensional simulation program was examined in n+-i-n+ structures with different qualities and thicknesses of the i-layer. We find that the n+/i interface is more abrupt for a device with a high density of states (DOS), resulting in high values of the activation energy (E act). In contrast, thin samples of good quality (low DOS) give low values of E act. Analysis by numerical modeling confirms the experimental results.

$Research paper thumbnail of AMPS-1D Modeling of a-Si: H n^{+}-in^{+} Structure: the Validity of Space Charge Limited Current Analysis$

Physical Concepts of Materials for Novel Optoelectronic Device Applications I: Materials Growth and Characterization, 1991

ABSTRACT For a-Si1 C :H samples prepared with /([CH4J + [SiH4J) ratios of 0. 1 0. 2 dxO. 25 the d... more ABSTRACT For a-Si1 C :H samples prepared with /([CH4J + [SiH4J) ratios of 0. 1 0. 2 dxO. 25 the density of deep states has been investigated by means of post-transit-time photocurrent analysis and thermally stimulated conductivity. Both techniques yield results which are in good agreement and show a localized states density which rises towards midgap.

MRS Proceedings, 1995

ABSTRACTIn this paper we present a study of ac the Constant Photocurrent Measurement (CPM) with t... more ABSTRACTIn this paper we present a study of ac the Constant Photocurrent Measurement (CPM) with the aim to assess the precision of this method compared to the de CPM. In particular, we introduce a small signal theory of the ac photoconductivity, we relate the sub-bandgap absorption to the density of defects, and we assume a combination of a constant plus a sinusoidal generation rate. The method allows to calculate the variation occurring in defect occupation as a function of the wavelength and intensity of the light, and of the ac test frequency. We show that, in ac condition, carriers lifetime is a complicated function of the chosen parameter, and it is affected by the delay due to charge accumulation of free and trapped carrier densities. Large influence on the lifetime is played not only by recombination, which takes place all along the gap defects included between the two quasi-Fermi levels, but also by the process of carrier trapping and emission by defects located close to the...

Solar Energy Materials and Solar Cells, 2003

The states in the mobility gap of amorphous hydrogenated silicon play an important role in determ... more The states in the mobility gap of amorphous hydrogenated silicon play an important role in determining its optical and electrical properties, and it is essential to know their density and distribution in the gap. Space Charge Limited Current (SCLC) is a classic and a well-known method for determining this density of states [1–4]. In SCLC measurements, the superlinear I–V dark characteristics due to injected charges from the ohmic contacts are measured. When the injection is large enough to displace significantly the quasi Fermi level from its equilibrium position, the current start to rise super-linearly. The magnitude of the current and the shape of the curve depend on the density of states just above the equilibrium Fermi level, so this portion of the curve can be used to determine this quantity.

Solar Energy Materials and Solar Cells, 2001

Creation and annealing of light-induced defects and their effect on photocarrier lifetime have be... more Creation and annealing of light-induced defects and their effect on photocarrier lifetime have been studied at 120 and 300K using constant photocurrent method (CPM) and steady-state photoconductivity measurements. A hysteresis-like relation is observed between photoconductivity and light-induced defect density. This relation depends on both degradation temperature and light intensity used for the degradation. A broad, resembling a two-component distribution of

Materials Science and Engineering: B, 2003

Materials Science and Engineering: B, 1992

ABSTRACT Thin film samples of hydrogenated amorphous silicon carbide with varying carbon content ... more ABSTRACT Thin film samples of hydrogenated amorphous silicon carbide with varying carbon content were prepared by conventional plasma deposition from an SiH4CH4 gas mixture. Optical transmission and reflection spectroscopy together with constant-photoconductivity measurements show that the widening of the optical gap with increasing carbon content is accompanied by an increased optical absorption at lower energies.

Journal of Non-Crystalline Solids, 1999

Applied Physics Letters, 2013

This work describes the preparation of a doped layer-free hydrogenated amorphous silicon (a-Si:H)... more This work describes the preparation of a doped layer-free hydrogenated amorphous silicon (a-Si:H) thin film solar cell consisting of a vanadium pentoxide (V2O5-x) window layer, an intrinsic a-Si:H absorber layer, and a lithium fluoride (LiF)/aluminum (Al) back electrode. The large difference between the work functions of the V2O5-x layer and the LiF/Al electrode permitted photogenerated carriers in the i-a-Si:H absorber layer to be effectively separated and collected. The effects of the V2O5-x layer thickness and the oxidation states on the photovoltaic performance were investigated in detail. X-ray photoelectron spectroscopy analysis confirmed that the major species of the sputtered V2O5-x thin films were V5+ and V4+. Optimization of the V2O5-x window layer yielded a power conversion efficiency of 7.04%, which was comparable to the power conversion efficiency of a typical a-Si:H solar cell (7.09%).

Journal of Non-Crystalline Solids, Jan 1, 1990

The dc conductivity of amorphous germanium films, prepared by thermal evaporation in high vacuum,... more The dc conductivity of amorphous germanium films, prepared by thermal evaporation in high vacuum, was investigated between 77 and 300 K as a function of applied electric field. The dc conductivity of these films obeys Mott&amp;#x27;s variable range hopping conductivity law below ...

Turk J Phys, Jan 1, 2002

Constant Photocurrent Method (CPM) and steady state photoconductivity measurements are used to in... more Constant Photocurrent Method (CPM) and steady state photoconductivity measurements are used to investigate the creation of light-induced metastable defects in a-Si:H at room temperature and their annealing. Light-induced metastable defect concentration Nd varies with exposure time te as t r e with r=0.34±0.02, as expected from the recombination induced weak bond breaking model . The validity of a stretched exponential model is also studied . From the annealing experiments, the distribution of thermal annealing activation energies is calculated following the method proposed by Hata and Wagner . Defects created at room temperature show a narrow distribution of annealing activation energies peaking at 0.97eV. The relation between photoconductivity and Nd is strongly nonlinear. Defects created at earlier times of illumination degrade photoconductivity more strongly, and these defects anneal out more easily than those created at later times of illumination.