Density of states determination from steady-state photocarrier grating measurements

We present a method to obtain the density of states (DOS) of photoconductive insulators based on steady-state photocarrier grating (SSPG) measurements. A simple expression—relating the DOS at the electron quasi-Fermi level to measurable quantities—is deduced by performing suitable approximations from the analytical solution of the generalized equations that describe the SSPG experiment. The validity of the approximations and the applicability of the final expression are verified from numerical simulations of the process. The usefulness of the method is demonstrated by performing measurements on a standard hydrogenated amorphous silicon sample.Fil: Schmidt, Javier Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Longeaud, C.. Université Paris VI et XI; Franci

Photoinduced Schottky Barrier in Photorefractive Materials

We report on the first experimental evidence of a Schottky barrier effect produced by the action of light in an otherwise purely Ohmic contact between a nominally undoped photorefractive titanosillenite Bi(12)TiO(20) crystal and a transparent conductive SnO(2) electrode. The photorefractive crystal is sandwiched between two transparent electrodes and a Schottky barrier is built up in the illuminated crystal-electrode interface under the action of light with photonic energy large enough to excite charge carriers from the Fermi level into the conduction band. The contact remains purely Ohmic under illumination with photonic energy below that of the Fermi gap and the photoinduced barrier almost disappears if the photonic energy is large enough to produce electron-hole pairs.1041

Ultrahigh drive current and large selectivity in GeS selector

Funder: National Key Research and Development Program of China (2017YFB0206101); Strategic Priority Research Program of the Chinese Academy of Sciences (XDB44010200); Hundred Talents Program (Chinese Academy of Sciences); Shanghai Pujiang Talent Program (18PJ1411100)Abstract: Selector devices are indispensable components of large-scale nonvolatile memory and neuromorphic array systems. Besides the conventional silicon transistor, two-terminal ovonic threshold switching device with much higher scalability is currently the most industrially favored selector technology. However, current ovonic threshold switching devices rely heavily on intricate control of material stoichiometry and generally suffer from toxic and complex dopants. Here, we report on a selector with a large drive current density of 34 MA cm−2 and a ~106 high nonlinearity, realized in an environment-friendly and earth-abundant sulfide binary semiconductor, GeS. Both experiments and first-principles calculations reveal Ge pyramid-dominated network and high density of near-valence band trap states in amorphous GeS. The high-drive current capacity is associated with the strong Ge-S covalency and the high nonlinearity could arise from the synergy of the mid-gap traps assisted electronic transition and local Ge-Ge chain growth as well as locally enhanced bond alignment under high electric field

Some results on the germanium telluride density of states

International audienc

Deconvolution of the transient photocurrent signals : application to the study of the density of states of a BTO crystal

International audienc

Analysis of the steady-state photocarrier grating method for the determination of the density of states in semiconductors

IIn this paper we present a complete theoretical analysis of the steady-state photocarrier grating (SSPG) method, starting from the generalized equations that describe charge transport and recombination under grating conditions. The analytical solution of these equations and the application of simplifying assumptions leads to a very simple formula relating the density of states sDOSd at the quasi-Fermi level for trapped electrons to the SSPG signal at large grating periods. By means of numerical calculations reproducing the experimental SSPG curves we test our method for DOS determination. We examine previous theoretical descriptions of the SSPG experiment, illustrating the case when measurements are performed at different illumination intensities. We propose a procedure to estimate the minority-carriers mobility-lifetime product from SSPG curves, introducing a correction to the commonly applied formula. We illustrate the usefulness of our technique for determining the DOS in the gap of intrinsic semiconductors, and we underline its limitations when applied to hydrogenated amorphous silicon. We propose an experimental procedure that improves the accuracy of the SSPG-DOS reconstruction. Finally, we test experimentally this new method by comparing the DOS obtained from SSPG and modulated photocurrent measurements performed on the same samples. The experimental DOS obtained from both methods are in very good agreement.Fil: Schmidt, Javier Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Longeaud, C.. Universités Paris VI et XI; Franci

Density of states in Bi12TiO20 from time of flight measurements

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