Decrease In Doping Concentration Research Articles

A Theoretical Study on Adjustment of Negative Differential Resistance Effect in Monolayer GeS via Substitutional Doping

Density functional theory and nonequilibrium Green's function theory are used to systematically explore the electronic structures and transport characteristics of doped monolayer GeS with group V (N, P, As) atoms. The calculated band structures demonstrate that the doping of N, P, and As atoms results in the transformation of monolayer GeS from semiconducting to metallic properties. Further, an obvious negative differential resistance (NDR) behavior is obtained by altering the dopant atom and the doping concentration. In particular, for N‐doped monolayer GeS, the NDR behavior appears in the millivolt region as the doping concentration decreases, and the current peak‐to‐valley ratio (PVR) is up to 107 (order of magnitude 7). These findings have significant implications for future design of low‐power novel nanoelectronic devices based on monolayer GeS.

Metal-free phthalocyanine single crystal: Solvothermal synthesis and near-infrared electroluminescence

Abstract A metal-free purple H2Pc single crystal was synthesized by a facile solvothermal method, and its solubility and near-infrared (NIR) optical properties were also investigated due to its potential applications as a light-emitting layer for OLEDs. The H2Pc single crystal is insoluble in 1-chlorine naphthalene and other organic solvents. It gives a wide absorption in the range from 620 nm to 679 nm and a wide emission in near 922 nm. As an active light-emitting layer, H2Pc was employed to fabricate electroluminescent (EL) devices with a structure of ITO/NPB (30 nm)/Alq3:H2Pc (30 nm)/BCP (20 nm)/Alq3 (20 nm)/Al. The emission center is at 936 nm when the H2Pc doping concentration is 20 wt%. The doping concentration strongly governs the emission intensity. When doping concentration decreases from 10 wt% to 1 wt%, the emission intensity remarkably fades, and simultaneously the emission center undergoes a blue shift.

Optimization of InGaN/GaN superlattice structures for high-efficiency vertical blue light-emitting diodes

We investigate carrier distribution and efficiency characteristics of GaN-based vertical blue light-emitting diodes (LEDs) having InGaN/GaN short-period superlattice (SL) structures by using numerical simulations. The SL structures exist between multiple-quantum-well active layers and an n-GaN layer. The In composition and doping concentration of SL layers are found to have strong influence on the electron concentration distribution in the plane of QWs, internal quantum efficiency, and forward voltage of vertical LEDs. The electron distribution becomes homogenous as the In composition increases or doping concentration decreases, which results in the reduction of efficiency droop and the increase of forward voltage. Based on the simulation results, optimum SL structures for obtaining the maximum wall-plug efficiency are found.

First Principle Study on Mn-Doped Ceria with Different Doping Concentration

First-principle software bundle based on the density functional theory (DFT) is used to investigate pure CeOB2B and Mn-doped CeOB2B with different doping concentration. The structural model of CeOB2B crystal is constructed and geometrically optimized, the electron density of states and band structure calculated. The results are as follows: the valence band top of CeOB2B is made up with O2p and Ce5d states, and the existence of 4f unoccupied molecular orbital of CeOB2B facilitates the electronic storage. The theoretical calculation models of Mn-doped CeOB2B with different concentration are constructed and calculated, including 2*1*1, 2*2*1 and 2*2*2 supercell models. After CeOB2B is doped, hybridization happens between 4s orbitals of Mn atoms and 2p orbital of O atoms, resulting in 4s orbitals of Mn atoms lose electrons.Moreover, Mn atom is electron donor and O atoms is the electron acceptor. As the doping concentration decreases, the formation energy also decreases.And a smaller formation energy leads to a more stable structure.

First-Principles Study of Silicon Nanowire Approaching the Bulk Limit

First-principles density functional theory calculations on hydrogenated silicon nanowires (SiNWs) with diameters up to 7.3 nm are carried out for comparing to experimentally relevant SiNWs and evaluating its radial doping profiles. We show that the direct band gap nature of both the small diameter (110) and (100) SiNWs fades when the diameter reaches beyond about 4 nm, where the difference of direct and indirect band gaps are close, within the experimental measurement uncertainty of ±0.1 eV, suggesting the diameter size where the gap nature transition starts. In addition, we reveal that core-surface boron (B) codoped SiNW forms more preferably at large diameter than that of the surface-surface codoped one, attributing to the lower energy configuration raised by the core B dopant at large diameter SiNW. More importantly, the diameter for such a preferential transition increases as the doping concentration decreases. Our results rationalize photoluminescent measurements and radial doping distributions of SiNWs.

Well-Aligned Zn-Doped InN Nanorods Grown by Metal-Organic Chemical Vapor Deposition and the Dopant Distribution

We report the synthesis and characterization of Zn-doped InN nanorods by metal-organic chemical vapor deposition. Electron microscopy images show that the InN nanorods are single-crystalline structures and vertically well-aligned. Energy-dispersive X-ray spectroscopy analyses suggest that Zn ions are distributed nonhomogenously in InN nanorods. Simulations based on diffusion model show that the doping concentration along the radial direction of InN nanorod is bowl-like from the exterior to the interior, the doping concentration decreases, and Such dopant distribution result in a bimodal EDXS spectrum of Zn across the nanorod. The study of the mechanism of doping effect is useful for the design of InN-based nanometer devices. Also, high-quality Zn-doped InN nanorods will be very attractive as building blocks for nano-optoelectronic devices.'

Degradation and Recovery of Si Diodes by 20-Mev Protons And 220-Mev Carbon Particles

AbstractResults are presented of a study on the degradation of the electrical performance of Fe contaminated n+p Si diodes, subjected to a 220-MeV carbon irradiation. The reverse current of the diodes increases after irradiation, while the capacitance and hence the doping concentration decreases. The areal and peripheral components of the leakage current are extracted from diodes with different area to perimeter ratios. Both the generation and the recombination lifetime calculated from I/V and C/V characteristics also decrease. The deep levels in the Si substrate induced by the irradiation are mainly responsible for the degradation of the diode performance. The radiation damage is also studied for 1 -MeV electrons and 1 -MeV fast neutrons. The performance degradation for carbon irradiation is three orders of magnitude larger than that for electron irradiation. The differences in the radiation damage are explained by the differences in the number of knock-on atoms and the nonionizing energy loss (NIEL), which is attributed to the difference of mass and the possibility of nuclear collision with target Si atoms

Effect of grain size on the resistivity of polycrystalline material

In this paper the effects of grain size and doping concentration on the resistivity of polycrystalline silicon are investigated. A new relation is presented for the resistivity of large-grain polycrystalline material. Assuming localized states at the grain boundaries, the predicted variations in resistivity with grain size and doping concentration show reasonable agreement with the experimentally observed variations. Computations show that, as the grain size increases, the sensitivity of the resistivity of the polycrystalline material to the doping concentration decreases. For grain sizes less than 10 μm, the resistivity is predominantly controlled by the average carrier concentration, while for grain sizes greater than 10 μm the resistivity is mainly controlled by the effective mobility.