Electrical properties of grain boundaries in polycrystalline materials under intrinsic or low doping

Abstract

An analytical model is developed to study the electrical properties (electric field and potential distributions, potential energy barrier height and polarization phenomenon) of polycrystalline materials at intrinsic or low doping for detector and solar cell applications by considering an arbitrary amount of grain boundary charge and a finite width of grain boundary region. The general grain boundary model is also applicable to highly doped polycrystalline materials. The electric field and potential distributions are obtained by solving Poisson's equation in both depleted grains and grain boundary regions. The electric field and potential distributions across the detector are analysed under various doping, trapping and applied biases. The electric field collapses, i.e. a nearly zero-average electric field region exists in some part of the biased detector at high trapped charge densities at the grain boundaries. The model explains the conditions of existence of a zero-average field region, i.e. the polarization mechanisms in polycrystalline materials. The potential energy barrier at the grain boundary exists if the electric field changes its sign at the opposite side of the grain boundary. The energy barrier does not exist in all grain boundaries in the low-doped polycrystalline detector and it never exists in intrinsic polycrystalline detectors under applied bias condition provided that there is no charge trapping in the grain.

Amorphous and Polycrystalline Photoconductors for Direct Conversion Flat Panel X-Ray Image Sensors

“…In some x-ray photoconductors one species of carriers has a very limited range and becomes deeply trapped very quickly. The trapped carriers effectively polarize the sample, and modify the field and can reduce the charge collection efficiency [ 71 , 83 ].…”

Anionic segregation of chloride and fluoride doped-nano ZnO: microstructure evolution, electrical conductivity and photocatalysis.

“…The GBs usually present several crystallographic defects such as dislocations, vacancies, interstitial, dangling bonds, and distorted bond angles. These irregularities lead to the formation of electronic states, which may have energies in the band gap, acting as trap centers for charge carriers [46]. The GBs can exhibit an electron depletion layer that induces an electric potential across the barrier that controls the charge carrier mobility.…”

“…The GBs can exhibit an electron depletion layer that induces an electric potential across the barrier that controls the charge carrier mobility. Thus, the GB region's properties play a crucial role in controlling the charge transport properties of polycrystalline materials [46].…”

“…This electric potential barrier at the GBs prevents the intergranular transport of electrons (e − ) and holes (h + ), reduces the band gap, and increases the electron-phonon non-adiabatic couplings [14], leading to an increased charge recombination [13][14][15]. Therefore, the composition of the GB plays a crucial role in controlling the charge transport properties of polycrystalline materials [45,46,48], even when in the challenging form of unsintered pressed powder. Surfacesegregated dopant and adsorbed molecules also affect both the DSB at the GB by injecting or extracting electrons in the depletion layer, thus altering the barrier height [49] and the surface conductivity due to high mobile ions.…”

Relação dos defeitos cristalinos e da composição química das interfaces com a eficiência fotocatalítica do TiO2 durante a dopagem com iodeto ou óxido de nióbio.

“…A Figura 2 exibe os mecanismos de excitação eletrônica nas bandas de energia de semicondutores do tipo n e do tipo p. No estudo do comportamento do par elétron-buraco em semicondutores policristalinos, os contornos de grão desempenham um papel particularmente importante no controle da mobilidade dos portadores de carga. Como essas regiões apresentam diversos defeitos cristalográficos como vacâncias, interstícios ou ângulos de ligação distorcidos, estados eletrônicos com níveis de energia dentro do band gap podem se formar e atuar como centros de aprisionamento de portadores de carga 26 . Um modelo usado em varistores é aplicado para descrever esta barreira nos contornos de grão 27 .…”