Neha Verma

Quantum Modeling of Nanoscale Symmetric Double- Gate InAlAs/InGaAs/InP HEMT

The aim of this work is to investigate and study the quantum effects in the modeling of nanosclae symmetric double-gate InAIAs/InGaAs/InP HEMT (High Electron Mobility Transistor). In order to do so, the carrier concentration in InGaAs channel at gate lengths (L g 100 ㎚ and 50㎚, are modelled by a density gradient model or quantum moments model. The simulated results obtained from the quantum moments model are compared with the available experimental results to show the accuracy and also with a semi-classical model to show the need for quantum modeling. Quantum modeling shows major variation in electron concentration profiles and affects the device characteristics. The tow triangular quantum wells predicted by the semi-classical model seem to vanish in the quantum model as bulk inversion takes place. The quantum effects thus become essential to incorporate in nanosclae heterostructure device modeling.

Modeling Quantum Effects In The Channel Of A Nanoscale Symmetric Double Gate InAlAs/InGaAs Double Heterostructure HEMT

This work models the quantization effects dominating a nano-dimensional symmetric InAlAs/InGaAs double heterostructure DG-HEMT (double-gate HEMT). This is done by solving the one-dimensional (1D) time- independent Schrodinger equation in the nanoscale channel comprising of symmetric double triangular quantum well (DTQW) separated by a barrier in the DG-HEMT. The electron confinement due to the finite potential profile of a DTQW is analyzed and eigenenergies and the wave functions are calculated. Effect of the external applied fields at the gates controlling the electron confinement in the channel has been studied. The electron concentration is calculated and its distribution between the two quantum wells in InGaAs channel under the influence of different gate bias has been studied. A shift in electron concentration profile is observed from one well to another by the tunneling phenomenon at different applied electric fields indicating coupling between the two quantum wells. The calculated electron concentration profile obtained at equilibrium has been compared with the simulated results obtained from Quantum moments model and also with a semi-classical model.

Impact of doping concentration and temperature variation on the noise performance of separate gate InAlAs/InGaAs DG-HEMT

Impact of donor-layer doping concentration and temperature variation on the various noise coefficients and minimum noise figure is investigated for separate gate InAlAs/InGaAs DG-HEMT, in this paper. The noise coefficients, which include the drain noise coefficient (P), gate noise coefficient (R), the correlation coefficient (C) and the minimum noise figure have been evaluated using Pucels charge control based approach. The behavior of P, R, C noise coefficients and the minimum noise figure with doping concentration and temperature variation predict their influence on the overall noise performance of the device.

Quantum modeling of electron confinement in double triangular quantum well formed in nanoscale symmetric double-gate InAlAs/InGaAs/InP HEMT

The electron confinement in double triangular quantum wells (DTQW) in nanoscale symmetric Double gate InAlAs/InGaAs/InP HEMT (DGHEMT) has been modeled and simulated including quantum effects at gate lengths (Lg) 100nm and 50nm. The trend towards thinner channel and shorter gate lengths is resulting in increased importance of quantum effects, as many of the semi-classical assumptions become invalid. At nanoscale-dimensions, there is a need to imagine the carriers as particle-waves rather than semi-classical particle and it becomes imperative to study the electron confinement in the channel quantum mechanically instead of semi-classically. The standard approach being followed earlier has been within semi-classical framework for a double gate InAlAs/InGaAs/InP HEMT. Most of the quantum simulations have been performed for single gate HEMT [1]. DGHEMT are very promising for high frequency [2] and low noise applications and hence quantum modeling of this device is required. This paper introduces a quantum model to investigate the DTQW consisting of two single triangular quantum wells formed in semiconductor InGaAs sandwiched between layers of InAlAs material with a wider bandgap. The quantum model used to simulate the channel confinement is Quantum Moments (Density Gradient) Model which accurately reproduces the carrier concentration in the channel. In order to facilitate our study at 50nm, the vertical dimensions are not scaled down when reducing Lg from 100nm to 50nm. Simulated structure of symmetric DGHEMT is shown in Fig.1, device dimensions are given in Table. I and electron concentration profiles in DTQW at (Lg) 100nm and 50nm are shown in Fig. 2 and Fig. 3 Comparison with the semi-classical model predicts that at nanodimensions, the effects of quantum confinement become so pronounced that the double triangular quantum well formed in the channel seems to behave as a single quantum well and shows the peak electron concentration at the centre of the channel. To conclude, the quantization of electron confinement in DTQW in nanoscale DGHEMT has been modeled by a quantum moments model and it can be seen that the peak electron concentration exists at the two channel interfaces with the spacer layers in semi-classical representation while quantum model shows the maximum electron concentration in the centre of the channel indicating double triangular quantum wells behaving as a single quantum well. Also Drain characteristics (Id-Vds) comparing semi-classical and quantum models with experimental results [3] have been shown in Fig. 4 for Lg=100nm, keeping Vgs constant at −0.1V and plotting Id as a function of Vds respectively. The proposed quantum model shows a good matching with the experimental results [3] in the linear region with only a slight reduction in the saturation current is observed in the quantum model. For DGHEMT having their gate lengths in the nanometric scale, our simulation emphasizes on the importance of quantum modeling of the channel so as to have a proper representation of the nanodimension device.

Quantum Simulation of a Double Gate Double Heterostructure in AlAs/InGaAs HEMT to Analyze Temperature Effects

This paper presents quantum simulation to analyze the effect of temperature on 100 nm symmetric tied gate double heterostructure In AlAs/InGaAs DGHEMT. In order to account the quantization effects manifesting in the nano-scale channel, a Density Gradient model or Quantum Moments model has been employed. DGHEMT is widely used for high frequency microwave applications and to investigate the device reliability at various temperatures, a wide temperature range is considered which is varied from 200 K (-73.15 °C) to 500 K (226.85 °C). The effects of temperature variation on significant device parameters like electron density, drain current and transconductance have been shown and discussed. A significant reduction in drain current is found with an increase in temperature, which is due to the decrease in mobility and electron saturation velocity.

A novel separate gate InAlAs/InGaAs/InAlAs DG-HEMT heterogeneous mixer

This paper presents an analytical model of a heterogeneous mixer using a InAlAs/InGaAs/InAlAs separate gate double heterostructure double gate HEMT (DG-HEMT). The local oscillator (LO) and radio frequency (RF) signals are applied at the same gate (gate 1) and a dc voltage is applied at the other gate (gate 2). The effects of dc gate bias are studied on mixer performance establishing a better control. The LO and RF frequencies chosen are 0.9 GHz and 1 GHz respectively, resulting in the desired down and up converted intermediate frequencies. The output frequency spectrum obtained for DG-HEMT based mixer using the analytical model is compared with the available DG-MOSFET mixer results.

Effect of variation in channel thickness on eigenenergies of double triangular quantum well in double gate InAlAs/InGaAs HEMT

The aim of this paper is to study the effect on eigenenergies due to variation in channel thickness where the channel comprises of a nanoscale symmetric double triangular quantum well (DTQW) separated by a barrier for double heterostructure double gate InAlAs/InGaAs HEMT. The eigenenergies are calculated analytically by solving one-dimensional (1D) time independent Schrodinger equation in the channel at equilibrium i.e. when no gate voltage is applied. The channel thickness variation implies an independent effect of different barrier width and well widths for the DTQW system. In particular, ground and first excited energy state for various barrier width and well widths are studied and presented in the paper.

Quantum Modeling of Enhanced Gate Control in a Nanoscale InAlAs/InGaAs DG-HEMT for millimeter-wave Applications

This paper presents quantum model for nanoscale InAlAs/InGaAs double heterostructure double gate HEMT (DG-HEMT) accounting enhanced gate control for millimeter-wave applications. The eigenenergies obtained for different gate voltages has been used to calculate the corresponding quantum electron density in the channel and is employed to calculate various device characteristics. The obtained results have been compared with the simulated results obtained from quantum moments model and are found to be in good agreement.

Quantum simulation for separate double gate InA1As/InGaAs HEMT

A quantum model is used for the simulation of the double-gate (DG) InAlAs/InGaAs HEMT for nanometer gate dimension with two separate gate controls. Classical approach fails from the nanoscale device modeling viewpoint. The Quantum Moments model includes the quantization effects and accordingly model the various vital characteristics of the device. The effect of quantization can be observed majorly in the electron concentration profile presented in the paper. Moreover, the separate gate provides an improved control on the channel and various device characteristics. ID-VDS, ID-VGS, transconductance, output conductance, capacitances and cut-off frequency of the device are shown and discussed in the paper.

Simulation of Enhanced Gate Control in a Double Gate Quantum Domain InAlAs/InGaAs/InP HEMT

Electron concentration profiles are simulated for the double-gate (DG) InAlAs/InGaAs/InP HEMT for nanometer gate dimension with two separate gate controls on either side of the double heterostructure. A Quantum Moments model has been used to account for the quantization effects in the device. The quantum simulation of the confinement of the charge carriers in the nano-dimensional channel formed between the two hetero structures reveals a single peak for electron concentration in the channel with enhanced gate control. Moreover, simulated quantum results obtained for ID-VDS are verified by comparing them with the experimental 100nm Double-gate InAlAs/InGaAs/InP HEMT and are in good agreement.