A. Matulionis

Monte Carlo simulation of hot-phonon and degeneracy effects in the AlGaN/GaN two-dimensional electron gas channel

Ensemble Monte Carlo simulation of two-dimensional electron transport is carried out for an AlGaN/GaN heterostructure channel subjected to an electric field applied in the plane of electron confinement. The envelope wavefunctions for the confined electrons are calculated using a self-consistent Poisson–Schrodinger solver. The effects of electron-gas degeneracy and hot phonons on electron energy relaxation and drift velocity are investigated. The best fit between Monte Carlo simulation and experimental results is received with optical-phonon relaxation time τph = 1 ps. The results of simulation show that the degeneracy reduces the electron drift velocity while the hot phonons reduce the electron drift velocity and increase the electron energy relaxation time. Electron energy relaxation time approaches 0.3 ps at 10 kV cm−1 at room temperature.

Ultrafast Removal of LO-Mode Heat From a GaN-Based Two-Dimensional Channel

Dissipation of the Joule heat, accumulated in non-equilibrium longitudinal optical (LO) phonon modes, is considered in terms of LO-phonon lifetime. The dependence of the lifetime on electron density, hot-electron temperature, and supplied electric power are presented for a voltage-biased GaN-based channel with a two-dimensional electron gas (2DEG). An improved understanding of conversion of LO phonons into acoustic and other phonons is reached. A nonmonotonous dependence of the lifetime on the electron density is observed. The optimal 2DEG density for ultrafast decay of the LO-mode heat is estimated and explained in terms of LO-phonon-plasmon resonance. A new limitation of the frequency performance is predicted for heterostructure field effect transistors under the off-resonance conditions of operation. The shortest hot-phonon lifetime of ~60± 20 fs is found, at a high level of supplied power, in nearly lattice matched InAlN/AlN/GaN.

Impact of pad and gate parasitics on small-signal and noise modeling of 0.35 /spl mu/m gate length MOS transistors

Microwave noise performance of p and n-type MOSFETs fabricated on the. same wafer was investigated in order to study the effect of the pad and gate parasitic circuit elements on noise performance. At low drain currents, the gate parasitic circuit was involved in the modeling to explain the observed kinks and loops in the s-parameters. Simulation of the noise parameters for p and n-type devices, measured in the 2-26 GHz frequency range, was performed by using extracted small-signal models of the transistor in connection with parasitic pad and gate circuits. Under the bias far from the optimal one, the additional parasitic inductance in the gate circuit was found responsible for the degradation of the noise performance by exhibiting peaks in the noise parameters.

Experiments on hot electron noise in semiconductor materials for high-speed devices

Experimental results on noise temperature and spectral density of current fluctuations (electron diffusion) at high electric fields in silicon, gallium arsenide, and indium phosphide are presented. The dominant noise sources are discussed in their relation to electron scattering mechanisms. Physical backgrounds of high speed-low noise performance (noise-speed tradeoff) are considered. Suppression in short samples of the fluctuations having long correlation time constant and (or) high threshold energy is discussed. >

Hot-phonon lifetime in a modulation-doped AlInAs/GaInAs/AlInAs/InP

The experimental dependence of microwave noise temperature on supplied electric power is used to study hot phonons in an InP-based modulation-doped In0.52Al0.48As/In0.53Ga0.47As/In0.7Ga0.3As/In0.52Al0.48As heterostructure with a two-dimensional electron gas channel (n2D = 2.3 × 1012 cm−2). The effective hot-phonon temperature is extracted for two-subband and six-subband models treated in the electron-temperature approximation. The estimated value for the hot-phonon lifetime with respect to the longitudinal optical phonon conversion into other vibration modes is (0.9 ± 0.3) ps at room temperature.

Hot-electron energy relaxation, noise, and lattice strain in InGaAs quantum well channels

Energy loss by hot electrons in lattice-matched and strained InGaAs layers is estimated from experimental data on microwave noise obtained for InP-based quantum well channels containing two-dimensional electron gas. A strong correlation of the energy relaxation time and the lattice strain is observed.

Hot-electron transport in 4H–SiC

Nanosecond-pulsed technique is used to study hot-electron transport in donor-doped 4H–SiC (n=2×1017cm−3) biased parallel to the basal plane. The measurements of current with 1ns voltage pulses are carried out at average electric fields up to 570kV∕cm. A region with a negative differential conductance is observed for the range of fields exceeding 280kV∕cm, followed by a sharp increase in the current at fields over 345kV∕cm. The dependence of drift velocity on electric field is deduced for the field range below the onset of the negative differential conductance to appear: the value of the saturation velocity is estimated as 1.4×107cm∕s at room temperature.

Hot phonons in InAlN/AlN/GaN heterostructure 2DEG channels

Non-equilibrium (hot) occupancy of longitudinal-optical (LO) phonon modes is considered for InAlN/AlN/GaN and related structures with two-dimensional electron gas (2DEG) channels located in GaN and subjected to high electric fields. The channel operation is found to depend critically on the LO-mode occupancy controlled by hot-phonon lifetime. The lifetime dependences on the occupancy and the 2DEG density are presented and discussed in terms of plasmon-assisted decay of hot-phonons. The optimal 2DEG density for the fastest removal of the LO-mode heat is estimated.

Comparative analysis of microwave noise in GaAs and AlGaAs/GaAs channels

Abstract Hot electron noise at 10 GHz microwave frequency is investigated in an AlGaAs/GaAs heterostructure channel with two-dimensional electron gas (2DEG), and the results are compared to those for 3DEG channels of GaAs. An experimental evidence of noise due to 2DEG⇆3DEG transfer at 80 K is presented. The related longitudinal diffusion of hot electrons in long 2DEG channels is found to dominate at the intermediate fields which are well below the threshold field for intervalley diffusion in GaAs. A tendency to suppress the intervalley noise and diffusionby the 2DEG⇆DEG transfer is observed at the high fields. Possible suppression of the dominant sources of microwave noise in modulation-doped field-effect transistor channels is discussed.

Microwave Noise In Biased AlGaN/GaN And AlGaN/AlN/GaN Channels

Noise temperature is measured at 10 GHz at room temperature for biased AlGaN/GaN and AlGaN/AlN/GaN two‐dimensional channels. Interpretation of the experimental results, through Monte Carlo simulation, takes into account interaction of hot electrons with phonons. The calculated longitudinal noise temperature exceeds the transverse one, but the resultant anisotropy of noise becomes substantially weaker when accumulation of nonequilibrium (hot) optical phonons is taken into account. The considered intense interaction of hot electrons with hot phonons and weak coupling with the thermal bath shifts the hot‐electron‐hot‐phonon subsystem closer to the equilibrium at the elevated temperature as compared with the hot‐electron subsystem interacting with the equilibrium phonons.