M. W. Akram

Hetero-gate-dielectric double gate junctionless transistor (HGJLT) with reduced band-to-band tunnelling effects in subthreshold regime

We propose a hetero-gate-dielectric double gate junctionless transistor (HGJLT), taking high-k gate insulator at source side and low-k gate insulator at drain side, which reduces the effects of band-to-band tunnelling (BTBT) in the sub-threshold region. A junctionless transistor (JLT) is turned off by the depletion of carriers in the highly doped thin channel (device layer) which results in a significant band overlap between the valence band of the channel region and the conduction band of the drain region, due to off-state drain bias, that triggers electrons to tunnel from the valence band of the channel region to the conduction band of the drain region leaving behind holes in the channel. These effects of band-to-band tunnelling increase the sub-threshold leakage current, and the accumulation of holes in the channel forms a parasitic bipolar junction transistor (n–p–n BJT for channel JLT) in the lateral direction by the source (emitter), channel (base) and drain (collector) regions in JLT structure in off-state. The proposed HGJLT reduces the subthreshold leakage current and suppresses the parasitic BJT action in off-state by reducing the band-to-band tunnelling probability.

Analog performance of double gate junctionless tunnel field effect transistor

For the first time, we investigate the analog performance of n-type double gate junctionless tunnel field effect transistor (DG-JLTFET) and the results are compared with the conventional n-type double gate tunnel field effect transistor (DG-TFET) counterpart. Using extensive device simulations, the two devices are compared with the following analog performance parameters, namely transconductance, output conductance, output resistance, intrinsic gain, total gate capacitance and unity gain frequency. From the device simulation results, DG-JLTFET is found to have significantly better analog performance as compared to DG-TFET.

P-type double gate junctionless tunnel field effect transistor

We have investigated the 20 nm p-type double gate junctionless tunnel field effect transistor (P-DGJLTFET) and the impact of variation of different device parameters on the performance parameters of the P-DGJLTFET is discussed. We achieved excellent results of different performance parameters by taking the optimized device parameters of the P-DGJLTFET. Together with a high-k dielectric material (TiO2) of 20 nm gate length, the simulation results of the P-DGJLTFET show excellent characteristics with a high ION of ~0.3 mA/μm, a low IOFF of ~30 fA/μm, a high ION/IOFF ratio of ~1 × 1010, a subthreshold slope (SS) point of ~23 mV/decade, and an average SS of ~49 mV/decade at a supply voltage of −1 V and at room temperature, which indicates that P-DGJLTFET is a promising candidate for sub-22 nm technology nodes in the implementation of integrated circuits.

A laterally graded junctionless transistor

This paper proposes a laterally graded junctionless transistor taking peak doping concentration near the source and drain region, and a gradual decrease in doping concentration towards the center of the channel to improve the IOFF and ION/IOFF ratio. The decrease of doping concentration in the lateral direction of the channel region depletes a greater number of charge carriers compared to the uniformly doped channel in the OFF-state, which in turn suppresses the OFF state current flowing through the device without greatly affecting the ON state current.

Spin Relaxation in Germanium Nanowires

We use semiclassical Monte Carlo approach along with spin density matrix calculations to model spin polarized electron transport. The model is applied to germanium nanowires and germanium two-dimensional channels to study and compare spin relaxation between them. Spin dephasing in germanium occurs because of Rashba Spin Orbit Interaction (structural inversion asymmetry) which gives rise to the D’yakonov-Perel (DP) relaxation. In germanium spin flip scattering due to the Elliot-Yafet (EY) mechanism also leads to spin relaxation. The spin relaxation tests for both 1D and 2D channels are carried out at different values of temperature and driving electric field, and the variation in spin relaxation length is recorded. Spin relaxation length in a nanowire is found to be much higher than that in a 2D channel due to suppression of DP relaxation in a nanowire. At lower temperatures the spin relaxation length increases. This suggests that spin relaxation in germanium occurs slowly in a 1D channel (nanowires) and at lower temperatures. The electric field dependence of spin relaxation length was found to be very weak.

Spin dephasing in silicon germanium (Si1−xGex) nanowires

In this work, we use semiclassical Monte Carlo simulation to study spin transport in silicon germanium nanowires. Spin relaxation in the channel is caused by Dyakonov-Perel (DP) relaxation and due to Elliott-Yafet (EY) relaxation. We investigate the dependence of spin relaxation on germanium mole fraction in silicon germanium nanowires. The spin relaxation length decreases with an increase in the germanium mole fraction. We also find that the temperature has a strong influence on the relaxation rate and spin relaxation lengths increase with decrease in temperature. The ensemble averaged spin components and the steady state distribution of spin components vary with initial polarization.

Semiclassical Monte Carlo simulation studies of spin dephasing in InP and InSb nanowires

We use semiclassical Monte Carlo approach to investigate spin polarized transport in InP and InSb nanowires. D’yakonov-Perel (DP) relaxation and Elliott-Yafet (EY) relaxation are the two main relaxation mechanisms for spin dephasing in III-V channels. The DP relaxation occurs because of bulk inversion asymmetry (Dresselhaus spin-orbit interaction) and structural inversion asymmetry (Rashba spin-orbit interaction). The injection polarization direction studied is that along the length of the channel. The dephasing rate is found to be very strong for InSb as compared to InP which has larger spin dephasing lengths. The ensemble averaged spin components vary differently for both InP and InSb nanowires. The steady state spin distribution also shows a difference between the two III-V nanowires.