Dislocation scattering in n-GaN

The scattering of carriers due to dislocations is studied. Unlike semiconductors such as Si or GaAs, the major scattering mechanism for undoped or lightly doped samples is dislocation scattering instead of ionized impurity scattering. It was found that for GaN samples in the dislocation scattering region, the mobility is a function of the dislocation density and free carrier concentration, via a relationship. Temperature-variation mobility plots also indicate that a T^3/2 dependence component is present, which is also attributed to dislocation scattering.     

AlGaN/GaN异质结辐射感生界面态电荷对二维电子气输运的影响

根据荷电中心与自由载流子间的库仑散射作用,给出了异质结辐射感生界面态电荷对二维电子气(2DEG)迁移率的散射模型.计算了在不同沟道电子面密度下,界面态电荷密度与其所限制的迁移率之间的关系.运用马德森定则分析了辐射感生界面态电荷散射对总迁移率的影响.分析表明,辐射感生界面态电荷在累积到一定量后,会显著影响迁移率,一定程度上提高2DEG密度能抑制界面态电荷散射的作用     

Critical discussion on unified 1/f noise models for MOSFETs

Recently, unified noise models, like BSIM3, have been proposed in literature to describe the 1/f noise of n- and p-type MOSFETs in all operating regimes. These models combine carrier number fluctuations and correlated mobility fluctuations. The latter are induced by the Coulomb scattering of free carriers at trapped interface charge. The unified 1/f noise models assume implicitly that the mobility, limited by Coulomb scattering, does not depend on the inversion carrier density. However, this assumption is not correct in view of theoretical calculations and recent experimental results. In this paper, we show that the correlated mobility fluctuations are negligible, if the correct dependence on inversion carrier density is taken into account for the Coulomb scattering limited mobility. Consequently, the unified 1/f noise models cannot predict the 1/f noise observed experimentally in p-type MOSFETs, except if nonphysical fitting parameters are used. This paper serves as a critical discussion on the unified 1/f noise models for MOSFETs. Here it is not our intention to propose a new 1/f noise model     

Mobility of holes in p-type silicon determined by the self-consistent method

The mobility of majority carriers is calculated in p-type silicon in the impurity concentration range from 10¹⁶ to 10²⁰ cm^?3. Taking into account the complexity of the band structure of holes and using the self-consistent model development earlier for electrons, the value of the Fermi energy and the screening length is determined. The following scattering types are considered: scattering by acoustical phonons, scattering by non-polar optical phonon and scattering by ionized impurities. The influence of interband transition of heavy and light holes on the total relaxation time is analysed. It is shown that it does not lead to essential changes in mobility. The obtained results are compared with experimental results and satisfactory agreement is found.     

Mobility of majority carriers in doped noncompensated silicon

A unique theoretical model of mobility calculation of majority carriers in n-type doped noncompensated silicon at T = 300 K is given. Starting with the Fermi statistics and spherical but non-parabolic equienergetic surfaces, a procedure to calculate mobility is proposed which allows to take complex dependence between the density of states and energy in heavily doped semiconductors under consideration. The following types of scattering are observed; scattering by ionized impurities, acoustic-mode scattering and intervalley scattering. Besides, electron-electron scattering influence is also taken under consideration. Based on the suggested model the calculation of mobility in a phosphorous doped silicon in the impurity concentration range from 10¹⁵ to 10²⁰ cm^?3, and the comparison with the experiment were done.     

Model for 1/f; noise in MOS transistors biased in the linear region

1/f; Noise calculations and experiments are presented for conductance fluctuations in inversion layers. The layers are biased in the ohmic region at very low drain-source voltages. The model makes use of an experimental fact that competing scattering mechanisms other than lattice scattering lead to a reduction of 1/f; noise, but does not consider trapping of charge carriers in surface states as the source of 1/f; noise. The free charge carrier distribution and a mobility profile play an important part in the model. The model describes the measured results well. A reduction of the effective mobility with increasing gate voltage is accompanied by a strong reduction of the noise.     

Scattering of charge carriers at the boundaries of crystallites in films of polycrystalline silicon

Scattering of charge carriers by the potential barriers at grain boundaries in films of polycrystalline silicon is considered. The influence of this scattering mechanism on charge-carrier mobility is analyzed. Satisfactory agreement between the calculated and experimental values of mobility is observed. The model developed in this study can be used to gain insight into other kinetic phenomena.     

Scattering of screened excitons by free carriers in semiconductingquantum well structures

The theoretical treatment of the scattering of excitons by free electrons and holes in a two-dimensional semiconducting quantum-well system is extended to take into account screening by the free carriers. The scattering cross sections are calculated using the Born approximation for elastic scattering of the excitons by the free carriers. For the heavy-hole exciton, the screening by the free carriers reduces the cross section for free-carrier exciton scattering for all values of the energy of relative motion of the free carriers and the excitors. For the light-hole exciton, however, screening can actually lead to an enhancement of the scattering cross section for low values of the energy of relative motion when the density of free carriers is high. This is because screening not only reduces the interaction between the free carriers and the exciton, but also decreases the binding of the exciton, leading to a larger effective radius of the exciton. The results for the scattering cross sections are then applied to calculate the contribution of the exciton linewidth due to elastic scattering of the excitons by free carriers. It is found that this contribution to the exciton linewidth is decreased below its value in the absence of screening for both the heavy- and light-hole excitons     

SiO_2/SiC界面对4H-SiC n-MOSFET反型沟道电子迁移率的影响

提出了一种基于器件物理的4 H- Si C n- MOSFET反型沟道电子迁移率模型.该模型包括了界面态、晶格、杂质以及表面粗糙等散射机制的影响,其中界面态散射机制考虑了载流子的屏蔽效应.利用此模型,研究了界面态、表面粗糙度等因素对迁移率的影响,模拟结果表明界面态和表面粗糙度是影响沟道电子迁移率的主要因素.其中,界面态密度决定了沟道电子迁移率的最大值,而表面粗糙散射则制约着高场下的电子迁移率.该模型能较好地应用于器件模拟.     

Screened impurity scattering in heavily doped covalent semiconductors

A method is presented for determining the relative strengths of acoustic lattice scattering and screened impurity scattering in heavily doped semiconductors from measurements of their Hall mobility and thermoelectric power. Screening of the impurity centres by the free carriers results in an appreciable reduction in the impurity-scattering contribution, and this effect is estimated for heavily doped n type germanium.     

Minority-charge-carrier mobility at low injection level in semiconductors

From the kinetic equations, the distribution functions for majority and minority charge carriers are obtained at a low injection level. For describing the electron-hole collisions, the Landau collision integral is used. The carrier scattering at ionized or neutral impurity and at acoustic phonons is taken into account. The majority-carrier distribution function is presented in the analytical form. The minority-carrier mobility is calculated and analyzed, and the features of its behavior at low temperatures are revealed. It follows from the developed theory that the hole mobility in an n-type material increases with doping and neutral-impurity concentration. This effect is attributed to mutual charge-carrier collisions and different effective masses of different-sign carriers.     

Improving strained-Si on Si1-xGex deepsubmicron MOSFETs performance by means of a stepped doping profile

We have made use of a stepped doping profile to improve the performance of strained-Si ultra-short MOSFETs. Electron mobility curves are calculated by a Monte Carlo simulator including electron quantization and Coulomb scattering, in addition to phonon and surface roughness scattering. In the first part of the paper, the effect of Coulomb scattering due to both interface charges and bulk impurities is carefully analyzed. We show that the strain enhances the Coulomb-limited mobility due to the interface-trapped charges as a consequence of a better screening of these charges by mobile carriers. However, we also show that this improvement in the Coulomb-limited mobility does not occur if the Coulomb scattering is due to bulk doping impurities, since they share the same physical spare with the carriers, and therefore the screening is the same for the same inversion charge concentration. Nevertheless, we have shown that the use of a stepped doping profile bypasses this inconvenience. The introduction of a low doped layer below the oxide reduces the scattering produced by the bulk ionized impurities, enhancing Coulomb-limited mobility in deep-submicron devices. On the other hand, we have seen (by using MINIMOS-NT) that the use of the low doped silicon layer significantly improves the drain current while degrade the turn-off behavior of very short-channel devices only moderately. This design provides the possibility of taking full advantage of the great reduction in phonon scattering produced by the strain in the Si layer in these MOSFETs     

GeOI pMOSFETs空穴迁移率的物理模型

A physical model of hole mobility for germanium-on-insulator p MOSFETs is built by analyzing all kinds of scattering mechanisms, and a good agreement of the simulated results with the experimental data is achieved, confirming the validity of this model. The scattering mechanisms involved in this model include acoustic phonon scattering, ionized impurity scattering, surface roughness scattering, coulomb scattering and the scattering caused by Ge film thickness fluctuation. The simulated results show that the coulomb scattering from the interface charges is responsible for the hole mobility degradation in the low-field regime and the surface roughness scattering limits the hole mobility in the high-field regime. In addition, the effects of some factors, e.g. temperature, doping concentration of the channel and the thickness of Ge film, on degradation of the mobility are also discussed using the model, thus obtaining a reasonable range of the relevant parameters.     

An improved technique and experimental results for the extractionof electron and hole mobilities in MOS accumulation layers

For the first time, experimental results are presented for electron and hole mobilities in the electron and hole accumulation layers of a MOSFET for a wide range of doping concentrations. Also presented is an improved methodology that has been developed in order to enable more accurate extraction of the accumulation layer mobility. The measured accumulation layer mobility for both electrons and holes is observed to follow a universal behavior at high transverse electric fields, similar to that observed for minority carriers in MOS inversion layers. At low to moderate transverse fields, the effective carrier mobility values are greater than the bulk mobility values for the highest doping levels. This is due to screening by accumulated carriers of the ionized impurity scattering by accumulated carriers, which dominates at higher doping concentrations. For lower doping levels, surface phonon scattering is dominant at low to moderate transverse fields so that the carrier mobility is below the bulk mobility value     

Effects of electric field on the exciton linewidth broadening dueto scattering by free carriers in semiconducting quantum-well structures

The effects of an applied electric field perpendicular to the well layers on the broadening of the exciton linewidth due to scattering by free carriers in semiconducting quantum well (QW) structures is theoretically investigated based on a finite confining potential model. The dependence of the free carrier-exciton linewidth broadening on carrier concentration, temperature, and well width are calculated and discussed for various electric field strengths. It is found that the influence of the electric field on the linewidth broadening is appreciable in wide wells, while in narrow wells little change is shown even in the presence of a strong electric field     

Die abhängigkeit der trägerbeweglichkeit in silizium von der konzentration der freien ladungsträger—I

As long as the concentration of the free charge carriers in a semi-conductor are not too high, the carriers are scattered essentially only by the phonons of the lattice vibrations and possibly by the impurities in the lattice. Starting at concentrations of approximately 10¹⁶ cm⁻³ a third scattering mechanism becomes noticeable, namely the mutual scattering of the free carriers. In a rectifier or thyristor structure injected that strongly, the sum of the mobilities μ_n + μ_p therefore starts to decrease. The quantitative degree of this effect was determined experimentally by measurement of the voltage step when a psn structure was switched from the forward into the reverse direction. The measured results obtained on silicon diodes are compared with the theories of Fletcher and Davies. Good agreement is obtained particularly with Fletcher's theory.     

An accurate Coulomb mobility model for MOS inversion layer and itsapplication to NO-oxynitride devices

In this paper, a new mobility model for device simulation is presented that incorporates Coulomb scattering due to ionized impurities in the MOS inversion layer. It is well known that the Coulomb scattering strongly depends on carrier concentration because of the screening effect. A crucial technique is used in the modeling procedure, with which a local dependency of the mobility on carrier concentration is derived from the experimental data of the effective mobility. Consequently, the present model has the ability to reproduce the experimental effective mobility over a wide range of impurity concentration with a single parameter set. Comparisons of the simulated and measured I_DS-V_GS curves show good agreement for 0.15 μm CMOS devices having pure SiO₂ and NO-based oxynitride gate oxides     

A comprehensive model for inversion layer hole mobility forsimulation of submicrometer MOSFET's

A comprehensive model of effective (average) mobility and local-field mobility for holes in MOSFET inversion layers is presented. The semiempirical equation for effective mobility, coupled with the new local-field mobility model, permits accurate two-dimensional simulation of source-to-drain current in MOSFETs. The model accounts for the dependence of mobility on transverse and longitudinal electric fields, channel doping concentration, fixed interface charge density, and temperature. It accounts not only for the scattering by fixed interface charges, and bulk and surface acoustic phonons, but it also correctly describes screened Coulomb scattering at low effective transverse fields (near threshold) and surface roughness scattering at high effective transverse fields. The model is therefore applicable over a much wider range of conditions compared to earlier reported inversion layer hole mobility models while maintaining a physically based character     

One-carrier space-charge-limited-currents in non-homogeneous solids under planar,spherical and cylindrical flow

The general expressions of the one carrier space-charge-limited-current (SCLC) are derived for a solid in which the permittivity, mobility and trap concentration are position dependent. The treatment is based on a model which neglects the diffusion current and the space-charge of free carriers. The traps are considered to be distributed in energy, and the analytical expressions are obtained considering the planar, spherical and cylindrical geometry of contacts. The rectification due to the non-homogeneity of the material is also discussed.     

A carrier-mobility model for high-k gate-dielectric Ge MOSFETs with metal gate electrode

A mobility model for high-k gate-dielectric Ge pMOSFET with metal gate electrode is proposed by considering the scattering of channel carriers by surface-optical phonons in the high-k gate dielectric. The effects of structural and physical parameters (e.g. gate dielectric thickness, electron density, effective electron mass and permittivity of gate electrode) on the carrier mobility are investigated. The carrier mobility of Ge pMOSFET with metal gate electrode is compared to that with poly-Si gate electrode. It is theoretically shown that the carrier mobility can be largely enhanced when poly-Si gate electrode is replaced by metal gate electrode. This is because metal gate electrode plays a significant role in screening the coupling between the optical phonons in the high-k gate dielectric and the charge carriers in the conduction channel.