Depletion region

About: Depletion region is a research topic. Over the lifetime, 9393 publications have been published within this topic receiving 145633 citations.

Hydrodynamic changes of the depletion layer of dilute polymer solutions near a wall

Abstract: The system studied in this work is a dilute solution of rod-like molecules under simple shear flow and near a hard wall. The time evolution of the probability density function is described by a diffusion equation; particle trajectories that correspond to this equation are generated by stochastic methods. Several algorithms are presented to handle the constraints imposed by the presence of the wall. In good agreement with recent experimental work on xanthan solutions, for high shear rates we observe an increase in the thickness of the depletion layer near the wall. For low to intermediate shear rates, however, we find a transient decrease of the depletion layer thickness that has not been observed experimentally. Based on the results of our simulations, we present a simple procedure to determine a few, well defined characteristic parameters from the experimental density profiles.

Effect of quantum well location on single quantum well p-i-n photodiode dark currents

Abstract: The photocurrent available from a p-i-n solar cell can be increased by the addition of quantum wells (QWs) to the undoped region. At the same time the QWs reduce the open-circuit voltage by introducing areas of lower band gap where recombination is enhanced. This increase in recombination should be as small as possible for the most favorable effect on the photovoltaic efficiency of the device. Theoretical considerations indicate that nonradiative recombination, which is the dominant loss mechanism in AlxGa1−xAs/GaAs QW structures, may be reduced by positioning the QWs away from the point where the electron-hole product is a maximum. For p-i-n diodes, where recombination is greatest at or near the center of the space charge region, this means locating the QWs closer to the doped regions. Spectral response should not be affected so long as the QWs are still located within the field bearing region. Thus, improved photovoltaic performance may be expected through strategic location of the QWs. We report on measurements on a series of Al0.36Ga0.64As p-i-n photodiodes, three of which contained a single 87 A GaAs QW within the i region, and one which was a control sample with no QW. The three QW samples were grown with the QW located nearer to the p-doped layer, centrally, and nearer to the n-doped layer, respectively. Spectral response measurements confirm that for good quality samples photocurrent is independent of QW location within the depleted region. Contrary to expectations, the dark current is highest for the sample with the QW located closer to the n region. We analyze these results in terms of structure and doping profile, and compare them with the predictions of a self-consistent model. The observed behavior is attributed to a relatively high unintentional background doping in the intrinsic region.

Subband Structures of N-Channel Inversion Layers on III–V Compounds –A Possibility of the Gate Controlled Gunn Effect–

Abstract: Multi-subband structures of n-channel inversion layers on the surface of p-type III–V compounds are calculated by a variational method. Nonparabolicity is taken into account in the bulk dispersion relation of the \(\varGamma\)-valley. When the surface electron density is low, electrons occupy only the subbands in the \(\varGamma\)-valley, while when it exceeds certain critical value, most electrons occupy the ground subband in the second minimum valleys. From this behavior, the working condition of the Gunn effect in the system can be changed by applying the gate voltage in the MOS structure. The critical surface electron density depends on the charge density in the depletion layer and the surface orientation, but in case of GaAs, it is about 7×10 12 cm -2 for typical operating conditions.

Switchable diode-effect mechanism in ferroelectric BiFeO3 thin film capacitors

Abstract: We investigate the mechanism of a switchable diode behavior observed in ferroelectric SrRuO3/BiFeO3 (BFO)/SrRuO3 capacitors. We experimentally demonstrate that the switchable diode effect observed in the capacitors is induced by the polarization reversal in the BFO film. The conductivity in an Ohmic region in different oxidation states provides direct evidence that electron hole acts as the majority carrier, delivering p-type conduction. Density functional theory (DFT) calculations show that the p-type conduction arises from an unoccupied gap state of Fe4+ in an FeO5 pyramid which is derived from Bi vacancy. Our experimental and DFT study leads to the conclusion that the switchable diode effect originates from an asymmetric band bending in the top and bottom depletion layers modulated by ferroelectric polarization and oxygen vacancies.

A study of lateral Schottky contacts in WSe2 and MoS2 field effect transistors using scanning photocurrent microscopy

Abstract: Schottky contacts, formed at metal/semiconductor interfaces, always have a large impact on the performance of field-effect transistors (FETs). Here, we report the experimental studies of Schottky contacts in two-dimensional (2D) transition metal dichalcogenide (TMDC) FET devices. We use scanning photocurrent microscopy (SPCM) to directly probe the spatial distribution of the in-plane lateral Schottky depletion regions at the metal/2D-TMDC interfaces. The laser incident position dependent and the gate voltage tunable polarity and magnitude of the short-circuit photocurrent reveal the existence of the in-plane Schottky depletion region laterally extending away from the metal contact edges along the channel. This lateral depletion region length is estimated to be around several microns and can be effectively tuned by the gate and drain–source biases. Our results solidify the importance of lateral Schottky depletion regions in the photoresponse of 2D TMDC optoelectronic devices.