Anju Agrawal

Threshold voltage model for small geometry AlGaN/GaN HEMTs based on analytical solution of 3-D Poisson's equation

A simple and accurate analytical model for the threshold voltage of AlGaN/GaN high electron mobility transistor (HEMT) is developed by solving three-dimensional (3-D) Poisson equation to investigate the short channel effects (SCEs) and the narrow width effects present simultaneously in a small geometry device. It has been demonstrated that the proposed model correctly predicts the potential and electric field distribution along the channel. In the proposed model, the effect of important parameters such as the thickness of the barrier layer and its doping on the threshold voltage has also been included. The model is, further, extended to find an expression for the threshold voltage in the sub-micrometer regime. The accuracy of the proposed analytical model is verified by comparing the model results with 3-D device simulations for different gate lengths and widths.

Device linearity and intermodulation distortion comparison of dual material gate and conventional AlGaN/GaN high electron mobility transistor

Abstract In the work proposed, linearity performance of dual material gate (DMG) AlGaN/GaN HEMT has been analyzed and compared with the corresponding performance of Single Material Gate (SMG) AlGaN/GaN HEMT using ATLAS device simulation. Specifically, we investigate the linearity of DMG and conventional AlGaN/GaN HEMT based on the linearity metrics such as gm, g m 2 , g m 3 , VIP2, VIP3, IIP3, IMD3 and 1-dB compression point. The impact of various device parameters on the device linearity such as the channel length, doping and thickness of the barrier and spacer layer, Al mole fraction and the work function difference of the two gate metals has also been investigated. It is observed that a suitably designed DMG AlGaN/GaN HEMT can considerably improve the linearity performance and minimize intermodulation distortion due to reduced drain induced barrier lowering and high-field effect; and a more uniform electric field for applications in 3-G mobile communication and low noise amplifiers.

SUBSTRATE-EFFECT-DEPENDENT SCATTERING PARAMETER EXTRACTION OF SHORT-GATE-LENGTH IGFET FOR MICROWAVE FREQUENCY APPLICATIONS

A model is deeloped considering the substrate effect, fringing field effect, and gate and drain contact pad effect to ealuate the scattering parameters for a short-gate-length insulated gate field-effect transistor by extracting the admittance parameters for its microwae frequency applications. The parasitic elements are also incorporated in the analysis, and the merits of different deice dimensions are shown in termsarious gains at microwae frequencies. Q 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 341)348, 2000.

Investigation of temperature dependent microwave performance of AlGaN/GaN MISHFETs for high power wireless applications

The objective of this paper is to investigate and explore the potential of AlGaN/GaN based metal insulator semiconductor heterostructure field effect transistor (MISHFET) device for high temperature applications. A temperature dependent analytical model is proposed taking into account the effect of various temperature dependent material properties. The electrical characteristics like drain current, transconductance, cut-off frequency and saturation output power are evaluated for temperature range up to 573 K and a relative comparison is done with conventional HFET structures.

Total cross sections for electron scattering by oxides of iron

Abstract Total (elastic + inelastic) cross sections for electron impact on FeO, Fe2O3 and Fe3O4 have been calculated in the energy range 20–5000 eV by employing the additivity rule which expresses the total cross section of a molecule as an incoherent sum over the total cross sections of the constituent atoms of the molecule. The electron-atom cross sections have been obtained by a complex optical potential method through partial-wave analysis. The total cross sections for all the oxides of iron exhibit a maximum around 30 eV. The inelastic cross sections are upper bounds to the corresponding ionisation cross sections. Bethe parameters for inelastic cross sections are given.

Performance assessment and sub-threshold analysis of gate material engineered AlGaN/GaN HEMT for enhanced carrier transport efficiency

The present work explores the features of gate material engineered (GME) AlGaN/GaN high electron mobility transistor (HEMT) for enhanced carrier transport efficiency (CTE) and suppressed short channel effects (SCEs) using 2-D sub-threshold analysis and device simulation. The model accurately predicts the channel potential, electric field and sub-threshold current for the conventional and GME HEMT, taking into account the effect of work function difference of the two metal gates. This is verified by comparing the model results with the ATLAS simulation results. Further, simulation study has been extended to reflect the wide range of benefits exhibited by GME HEMT for its on-state and analog performance. The simulation results demonstrate that the GME HEMT exhibits much higher on current, lower conductance and higher transconductance as compared to the conventional HEMT due to improved CTE and reduced SCEs. This in turn has a direct bearing on the device figure of merits (FOMs) such as intrinsic gain, device efficiency and early voltage. Tuning of GME HEMT in terms of the relative lengths of the two metal gates, their work function difference and barrier layer thickness has further been carried out to enhance the drive current, transconductance and the device FOMs illustrating the superior performance of GME HEMT for future high-performance high-speed switching, digital and analog applications.

3-dimensional analytical modeling and simulation of fully depleted AlGaN/GaN modulation doped field effect transistor

We propose a simple and accurate three- dimensional (3-D) analytical model for the threshold voltage of AlGaN/GaN modulation doped field effect transistor (MODFET) taking into account the short channel effects (SCEs) and the narrow width effects (NWEs) present simultaneously in a small geometry device. The model includes the effect of vital parameters such as doping and thickness of the barrier layer on the threshold voltage. The accuracy of the proposed analytical model is verified by comparing the model results with 3-D device simulations. It has been demonstrated that the proposed model correctly predicts the potential, the electric field distribution along the channel and the threshold voltage.

Two-dimensional analytical sub-threshold modeling and simulation of Gate Material Engineered HEMT for enhanced carrier transport Efficiency

A 2- dimensional analytical sub-threshold model for exploring the novel features of AlGaN/GaN gate material engineered (GME) high electron mobility transistor (HEMT) for reduced short channel effects (SCE) and enhanced carrier transport efficiency (CTE) is proposed. The model accurately predicts the channel potential and electric field (EF) of the conventional and GME HEMT structures. In GME HEMT, the gate is made up of two materials and the work function (WF) difference between the two gate materials results in (1) improved CTE (due to a more uniform electric field along the channel) leading to rapid acceleration of charge carriers and (2) diminished SCEs due to a step in the channel potential. The analytical results have been validated by the device simulator ATLAS.

Analytical Modeling and Simulation of Potential and Electric Field Distribution in Dual Material Gate HEMT For Suppressed Short Channel Effects

In this paper, we present a simple 2- dimensional analytical model for exploring the novel features of the dual material gate (DMG) high electron mobility transistor (HEMT) for reduced short channel effects (SCE). The model accurately predicts the channel potential and electric field for single material gate (SMG) and DMG structures. It is seen that the work function difference of the two metal gates leads to a screening effect of the drain potential variation, by the gate near the drain resulting in suppressed drain induced barrier lowering (DIBL) and hot carrier effect. Moreover, carrier transport efficiency improves due to a more uniform electric field along the channel. The model takes into account the effects of the lengths of the two metal gates and their work function difference. The results predicted by the model are compared with those obtained using ATLAS device simulator to verify the accuracy of the proposed model.

M1 transition probabilities between fine structure components2L J (L ≥ 1)

Spontaneous emission transition probabilities of the magnetic dipole transitions between states of ground state configurations consisting of onenl electron (or a hole) outside a closed shell have been calculated by using relativistic terms of order α2Z2 and using hydrogenic orbitals to calculate the required overlap integrals. The line strengths calculated for the Boron and Fluorine isoelectronic sequences are in excellent agreement with the calculations involving Dirac wavefunctions for all ions uptoZ=60. The maximum difference at the highest value ofZ=92 is about 6%. Our calculated lifetimes for the state 2p52P1/2 for Fluorine-like Mg IV and Fe XVIII are 5.03 s and 51.7 µs respectively which are in excellent accord with corresponding values 5.00 s and 51.0 µs calculated by using sophisticated configuration interaction wavefunctions within the Breit-Pauli approximation. Our calculated value of lifetime for Thalium-like Pb II is 40.0 ms which is in good accord with the experimental value of 41.2 ms. New results are presented for the highly ionized ions in the Al-like and Cl-like isoelectronic sequences. The present analysis can be exploited for all the ions in the isoelectronic sequences of elements of groups III A, III B VII A of the periodic table.