Doping Dependent Mobility Research Articles

The impact of valley profile on the mobility and Kerr rotation of transition metal dichalcogenides

The transport and optical properties of semiconducting transition metal dichalcogenides around room temperature are dictated by electron–phonon scattering mechanisms within a complex, spin-textured and multi-valley electronic landscape. The relative positions of the valleys are critical, yet they are sensitive to external parameters and very difficult to determine directly. We propose a first-principles model as a function of valley positions to calculate carrier mobility and Kerr rotation angles, and apply it to MoS2, WS2, MoSe2, and WSe2. The model brings valuable insights, as well as quantitative predictions of macroscopic properties for a wide range of carrier density. The doping-dependent mobility displays a characteristic peak, the height depending on the position of the valleys. In parallel, the Kerr rotation signal is enhanced when same spin-valleys are aligned, and quenched when opposite spin-valleys are populated. We provide guidelines to optimize and correlate these quantities with respect to experimental parameters, as well as the theoretical support for in situ characterization of the valley positions.

Impact of Device Parameter Variation on the Electrical Characteristic of N-type Junctionless Nanowire Transistor with High-k Dielectrics

Metallurgical junction and thermal budget are serious constraints in scaling and performance of conventional metal-oxide-semiconductor field-effect transistor (MOSFET). To overcome this problem, junctionless nanowire field-effect transistor (JLNWFET) was introduced. In this paper, we investigate the impact of device parameter variation on the performance of n-type JLNWFET with high-k dielectrics. The electrical characteristic of JLNWFET and the inversion-mode transistor of different gate length (L G ) and nanowire diameter (d NW ) was compared and analyzed. Different high-k dielectrics were used to get an optimum device structure of JLNWFET. The device was simulated using SDE Tool of Sentaurus TCAD and the I-V characteristics were simulated using Sdevice Tools. Lombardi mobility model and Philips unified mobility model were applied to define its electric field and doping dependent mobility degradation. A thin-film heavily doped silicon nanowire with a gate electrode that controls the flow of current between the source and drain was used. The proposed JLNWFET exhibits high ON-state current (I ON ) due to the high doping concentration (N D ) of 1 x 10 19 cm -3 which leads to the improved ON-state to OFF-state current ratio (I ON /I OFF ) of about 10% than the inversion-mode device for a L G of 7 nm and the silicon d NW of 6 nm. Electrical characteristics such are drain induced barrier lowering (DIBL) and subthreshold slope (SS) were extracted which leads to low leakage current as well as a high I ON /I OFF ratio. The performance was improved by introducing silicon dioxide (SiO 2 ) with high-k dielectric materials, hafnium oxide (HfO 2 ) and silicon nitrate (Si 3 N 4 ). It was found that JLNWFET with HfO 2 exhibits better electrical characteristics and performance.

Impact of Device Parameter Variation on the Electrical Characteristic of N-type Junctionless Nanowire Transistor with High-k Dielectrics

Metallurgical junction and thermal budget are serious constraints in scaling and performance of conventional metal-oxide-semiconductor field-effect transistor (MOSFET). To overcome this problem, junctionless nanowire field-effect transistor (JLNWFET) was introduced. In this paper, we investigate the impact of device parameter variation on the performance of n-type JLNWFET with high-k dielectrics. The electrical characteristic of JLNWFET and the inversion-mode transistor of different gate length (L G ) and nanowire diameter (d NW ) was compared and analyzed. Different high-k dielectrics were used to get an optimum device structure of JLNWFET. The device was simulated using SDE Tool of Sentaurus TCAD and the I-V characteristics were simulated using Sdevice Tools. Lombardi mobility model and Philips unified mobility model were applied to define its electric field and doping dependent mobility degradation. A thin-film heavily doped silicon nanowire with a gate electrode that controls the flow of current between the source and drain was used. The proposed JLNWFET exhibits high ON-state current (I ON ) due to the high doping concentration (N D ) of 1 x 10 19 cm -3 which leads to the improved ON-state to OFF-state current ratio (I ON /I OFF ) of about 10% than the inversion-mode device for a L G of 7 nm and the silicon d NW of 6 nm. Electrical characteristics such are drain induced barrier lowering (DIBL) and subthreshold slope (SS) were extracted which leads to low leakage current as well as a high I ON /I OFF ratio. The performance was improved by introducing silicon dioxide (SiO 2 ) with high-k dielectric materials, hafnium oxide (HfO 2 ) and silicon nitrate (Si 3 N 4 ). It was found that JLNWFET with HfO 2 exhibits better electrical characteristics and performance.

Effect of Channel Width Variation on Electrical Characteristics of Double Lateral Gate Junctionless Transistors; A Numerical Study

In this paper, the effect of channel width variation on performance of double lateral gate junctionless transistors in the depletion and accumulation regimes is investigated. The characteristics of the device with various channel widths is comprehensively examined through analysis of on and off state current, threshold voltage (V th), transconductance (g m) and drain conductance (g D) variation in each operating regime. The carriers’ density distribution, electric field components and mobility are investigated through 3-D numerical simulations of the device to illustrate the variation of output characteristics. The results show that as the width decreases, the off-current (I OFF) decreases significantly as a result of better electrostatic control of the lateral gates over the channel. The on-current (I ON) is also decreased mainly due to the doping-dependent mobility degradation.It is also indicated that between the flat-band and fully depleted (pinch off) variation of the majority carriers is the main parameter that modifies the characteristics of the device, while the mobility variation is recognized as the basic factor in the accumulation regime.

The effects of channel doping concentration for n-type junction-less double-gate poly-Si nanostrip transistors

In this study, novel n-type double-gate (DG) junction-less (J-less) polycrystalline silicon (poly-Si) nanostrip transistors with different channel doping concentrations (NC) have been fabricated and investigated. The effects of channel doping concentration on device characteristics were examined comprehensively in this work. The experimental data show that as the channel doping concentration of the J-less device increases, the threshold voltage (VTH) becomes more negative. Besides, the drain-induced barrier lowering and the subthreshold swing of the J-less transistors become larger as the channel doping increases. We also found that as the channel doping increases, the off-current (IOFF) increases and the on-current (ION) actually decreases due to the doping-dependent mobility degradation. The conduction mechanisms under different channel doping concentrations were also investigated by TCAD simulation. The experimental results suggest that the n-type DG nanostrip J-less transistor with lower channel doping will have superior device characteristics.

Dependence of Photoresponse Characteristics on I-Layer Doping for GaN Based P-I-N Ultraviolet Photodetectors

We report on two-dimensional (2D) numerical simulations of photoresponse characteristics for GaN based p-i-n ultraviolet (UV) photodetectors. Effects of doping density of absorption layer (n i ) on the photoresponse have been investigated. The Poisson and continuity equations are solved along each grid point in the 2D structure with three generation-recombination processes as Auger, Shockley-Read-Hall and optical generation-recombination. In order to accurately simulate the device performance, the theoretical calculation includes doping-dependent mobility degradation by Arora model and high field saturation model. Optimal doping concentration of absorption layers at different wavelength are extracted numerically. Theoretical modeling shows that the doping density of the absorption layer can significantly affect the photoresponse of GaN based p-i-n UV photodetectors.

Local Doping Profiles for Height-Selective Emitters Determined by Scanning Spreading Resistance Microscopy (SSRM)

In order to confirm the existence of a height-selective emitter, we compared local doping profiles of such emitters with profiles of a standard homogeneous emitter. The concept of a height-selective emitter is based on the classical selective emitter but in a smaller scale. The pyramid tips are highly doped. The sides and valleys are lowly doped. The comparison of the doping profiles was addressed by using a high-spatial-resolution analysis method: scanning spreading resistance microscopy. The measurement was performed on fully produced cells with a height-selective emitter and a standard homogeneous emitter, both with random pyramid textured surfaces. We prepared samples from these cells and investigated the cross sections. A representative pyramid of each type of emitter was selected. We found that for height-selective emitters the surface concentration can strongly vary depending on the measured position of the selected pyramid. The tip of the pyramid is heavily doped, while the bottom is lowly doped. For standard cells with a homogeneous emitter, the doping profiles do not differ dramatically as for the sample with a height-selective emitter. We calculated the local sheet resistance by using the measured local emitter profiles and a doping-dependent mobility model for phosphorus-doped silicon.

Physical modeling based on hydrodynamic simulation for the design of InGaAs/InP double heterojunction bipolar transistors

A physical model for scaling and optimizing InGaAs/InP double heterojunction bipolar transistors (DHBTs) based on hydrodynamic simulation is developed. The model is based on the hydrodynamic equation, which can accurately describe non-equilibrium conditions such as quasi-ballistic transport in the thin base and the velocity overshoot effect in the depleted collector. In addition, the model accounts for several physical effects such as bandgap narrowing, variable effective mass, and doping-dependent mobility at high fields. Good agreement between the measured and simulated values of cutoff frequency, ft, and maximum oscillation frequency, fmax, are achieved for lateral and vertical device scalings. It is shown that the model in this paper is appropriate for downscaling and designing InGaAs/InP DHBTs.

Effect of Band-Edge Interface Traps and Transition Region Mobility on Transport in 4H-SiC MOSFETs

We present physics based models for the occupation of interface traps and the mobility of the transition layer found in 4H-SiC MOSFETs and extract values for the same using combined numerical simulation and experimental characterization. The Si-C-O transition layer found in 4H-SiC MOS devices is electrically modeled as having a doping dependent mobility that is different from the regular bulk 4H-SiC bulk mobility. Compared to the high intrinsic bulk mobility of 4H-SiC, the transition layer intrinsic mobility was extracted to be approximately 165cm2/Vs. The occurrence of the excessive high density of interface traps near the conduction band edge led us to develop a new model for the occupation of traps lying inside the conduction band itself. Due to the conduction band trap densities being comparable to the conduction band electron states, a non-zero probability exists for their occupation, which causes the occupied trap densities to be very high in strong inversion. Detailed numerical simulations and corroboration with experiment have been performed to calibrate the models and extract physical parameter values.

Modeling and simulation of electronic and excitonic emission properties in organic host–guest systems

We propose electronic and excitonic emission models for the quantitative simulation of organic light emitting diodes comprising host–guest system in emission layer. The electronic model contains the thermionic injection at the electrodes, the charge transport with the field- or doping-dependent mobility, and Langevin’s recombination. The excitonic emission model includes radiative (or nonradiative) decay, exciton diffusion, singlet–triplet intersystem-crossing, exciton annihilation, and polaron quenching. Förster and Dexter energy transfers as well as exciton blocking are also added to the excitonic emission model for the simulation of phosphorescent host–guest system. When these models are applied to a series of tris(2-phenylpyridine) iridium (Ir(ppy) 3)-doped 4,4′-bis( N-carbazolyl)-1,1′-biphenyl (CBP) devices with various doping concentration, the simulated electronic and excitonic emission properties are in good agreement with experimental results. The real devices show gentle efficiency roll-off at high Ir(ppy) 3 concentration and current efficiency reversion between 10% and 15% doping concentrations at over 20 mA cm −2, which are successfully realized by the proposed models in which triplet–triplet annihilation in host sites is considered. It is also numerically demonstrated that exciton confinement in emitting layer by controlling the energy, lifetime, and diffusion of exciton results in improvement of luminance efficiency of the devices.

Two-Dimensional Quantum-Mechanical Modeling and Simulation of Strained-Si Fin Field Effect Transistor (FinFET) on SiGe-On-Insulator

A strained-Si fin field effect transistor (SSFinFET) on SiGe-on-insulator is modeled and using two-dimensional Schrödinger and Poisson equations quantum-mechanically simulated in a self-consistent manner. The quantum electron concentration in an SS fin is then obtained using a two-dimensional Schrödinger equation. The field-dependent mobility in SS fin is calculated using the doping-dependent mobility which considered strain and velocity overshoot effects. These effects give rise to an enhancement in the drain current of SSFinFET by up to 25% compared with the conventional FinFET using relaxed Si-on-insulator (RSFinFET). For the gate length 1.5 times longer than fin width, the drain induced barrier lowering (DIBL) and subthreshold swing are below 0.1 V/V and 60 mV/dec, respectively, regardless of whether Si-fin experiences a strain. These results indicate that the ratio of gate length to fin width should be above approximately 1.5 to suppress short channel effects and DIBL in both SSFinFET and RSFinFET.

Steady state analysis of integrated injection logic

The current components occurring in the bulk of the conventional l2L device have been found solving the continuity equation incorporating the effects of heavy doping on the bandgap lowering, doping dependent mobility and time constants. The current gains of the forward and inverse operated pnp transistor and the upward operated npn transistor are found and compared with the available experimental results. The effect of various process parameters on the current gains has been studied. The current gains for the Substrate Fed Logic are also found. The theoretical results of the present analysis are found to be in close agreement with the experimental results.

The effect of doping-dependent mobility on base transit time in transistors

The effect of doping-dependent mobility on base transit time in transistors

Doping-dependent mobility analysis of junction field-effect transistors

An analysis of a junction field-effect transistor, taking into account the doping-dependent mobility, is presented for an assumed arbitrary impurity distribution in the channel. The values of transconductance and drain current obtained from the new relationships are found to deviate considerably from the theoretical values of these parameters estimated from the existing relationships.