Study Of Two-dimensional Electron Gas Research Articles

Simulation study of two-dimensional electron gas in N-polar GaN/AlGaN heterostructure

By the self-consistent solution of the Schrödinger and poisson equations, the effects of GaN channel layer, AlGaN back barrier layer with and without Si doping and AlN interlayer on two-dimensional electron gas in N-polar GaN/AlGaN heterostructure are systematically studied. The results indicate that the increases of the thickness values of GaN channel layer and AlGaN back barrier layer and Al content value can improve the density of 2DEG to a certain degree, and the influences of different Si doping forms on 2DEG sheet density are not the same, also the confinement of 2DEG could be strengthened by increasing Al content value and thickness value of the AlGaN barrier layer. The AlN interlayer is a comparatively outstanding one in improving the performance of the 2DEG such as the 2DEG sheet density and confinement. When GaN channel layer thickness is less than 5 nm, there is no 2DEG in the simulation, when it exceeds 20 nm the 2DEG sheet density tends to be saturated. 2DEG has a tendency to be saturated when the thickness value of AlGaN back barrier is more than 40 nm. 2DEG sheet densities with uniform doping and delta doping in AlGaN back barrier are saturated when the doping concentration is more than 5×1019 cm-3. The 2DEG sheet density could be increased from 0.93×1013 cm-2 without AlN interlayer to 1.17×1013 cm-2 with 2 nm AlN interlayer.

Quaternionic vector coherent states for spin-orbit interactions

This work addresses the study of two-dimensional electron gas in a perpendicular magnetic field in the presence of both Rashba and Dresselhaus spin-orbit (SO) interactions, with effective Zeeman coupling. Exact analytical expressions are found for the eigenvalue problem giving the Landau levels and the associated eigenstates, thanks to an appropriate method of parametrization used to quantize the physical system. Such a system exhibits interesting properties of quaternions for which vector coherent states are built. Similarity with the Weyl-Heisenberg group and some relevant properties of these vectors are discussed.

Two-dimensional electron gas formed on the indium-adsorbedSi(111)3×3-Ausurface

Electronic structure of the In-adsorbed $\text{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{-Au}$ surface was investigated by core-level and angle-resolved photoelectron spectroscopy. On the $\text{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{-Au}$ surface, In adsorbates were reported to remove the characteristic domain-wall network and produce a very well-ordered $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ surface phase. Detailed band dispersions and Fermi surfaces were mapped for the pristine and In-dosed $\text{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{-Au}$ surfaces. After the In adsorption, the surface bands shift toward a higher binding energy, increasing substantially the electron filling of the metallic band along with a significant sharpening of the spectral features. The resulting Fermi surface indicates the formation of a perfect isotropic two-dimensional electron-gas system filled with 0.3 electrons. This band structure agrees well with that expected, in a recent density-functional theory calculation, for the conjugate-honeycomb trimer model of the pristine $\text{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{-Au}$ surface. Core-level spectra indicate that In adsorbates interact mostly with Si surface atoms. The possible origins of the electronic structure modification by In adsorbates are discussed. The importance of the domain wall and the indirect role of In adsorbates are emphasized. This system provides an interesting playground for the study of two-dimensional electron gas on solid surfaces.

Optical studies of two-dimensional electron gas in an InGaAs/AlGaAs pseudomorphic high electron mobility transistor structure

We present the studies of two-dimensional electron gas (2DEG) in an InGaAs/AlGaAs pseudomorphic high electron mobility transistor (pHEMT) structure using photoluminescence (PL), photoreflectance (PR), photoconductivity (PC) and Hall measurements in the temperature range 10–300 K. The energies of intersubband transitions (11H, 21H and 22H) can be determined through the experimental results and theoretical fitting data of PC, PL and PR. The Fermi level is extracted from the curve-fitting data of PL and PR with the subband filling effect taken into account. It is shown that the Fermi level reaches the 2nd electron subband E 2 and thus the 1st electron subband E 1 is nearly fully occupied so that the 11H PR absorption feature becomes almost invisible due to the severely suppressed probability of transition to E 1. The curve-fitting data of PL and PR also give the carrier concentration of 2DEG, and the value is found to be in great consistency with the Hall data. Our work as a whole exhibits consistent results in the 2DEG properties through various methods and clearly shows that optical technologies (PL and PR) provide useful alternatives for contactless, non-destructive characterization of the 2DEG carrier concentration.

Correlations in Hexagonal Lattice Systems - Application to Carbon Nanotubes

We present exact diagonalization studies of two-dimensional electron gas on hexagonal lattice. Using Lanczos method we analyze the influence of the Coulomb correlations on the density of states and spectral functions. Choosing appropriate boundary conditions we simulate the geometry of a single wall carbon nanotube. In particular, integration over the boundary condition in one direction and summation in the other one allows us to perform cluster calculations for a tube-like system with a finite diameter and infinite length.

Two‐Dimensional Electron Dynamics in GaN/AlGaN Heterostructures

(a) Institut fu¨r Schichten und Grenzfla¨chen, Forschungszentrum Ju¨lich, 52425 Ju¨lich,Germany(b) Institute of Semiconductor Physics, NASU, Kiev 03028, Ukraine(c) School of Electrical Engineering, Cornell University, Ithaca, New York 14853, USA(Received July 22, 2002; accepted October 1, 2002)PACS: 72.80.Ey; 72.90.+y; 73.40.KpThis report addresses the study of two-dimensional electron gas (2DEG) transport at low andmoderate electric fields. The devices under study are group-III nitride-based (AlGaN/GaN)gateless heterostructures grown on sapphire for HEMT applications. The transmission line model(TLM) patterns of different channel lengths L and the same channel width are used. We havedeveloped a simple theoretical model to adequately describe the observed peculiarities in the I–Vcharacteristics measured in steady-state and pulsed (10

Growth and optical studies of two-dimensional electron gas of Al-rich AlGaN/GaN heterostructures

Al 0.5 Ga 0.5 N/GaN heterostructures were grown by metalorganic chemical vapor deposition on sapphire substrates. Time-resolved photoluminescence (PL) emission spectroscopy was employed to study the optical properties of these samples. A very strong and broad emission band was observed under high excitation intensity (Io=104 W/cm2) and its spectral peak position varies from 3.382 and 3.444 eV (at 10 K) depending on the top AlGaN layer thickness (d). This emission line is related to the recombination between the two-dimensional electron gas (2DEG) and photoexcited holes in Al0.5Ga0.5N/GaN heterostructures. In a sharp contrast to the AlGaAs/GaAs heterostructure system in which the PL emission line associated with the 2DEG is observable only at low temperatures (T<20 K), the 2DEG emission line in Al0.5Ga0.5N/GaN heterostructures is observable at temperature as high as 220 K. This is due to the strong piezoelectric polarization and deep triangular potential resulting from the large band offset in high Al content AlGaN/GaN heterostructures. For AlxGa1−xN/GaN (x=0.5) heterostructures with d=110 Å, five emission lines were resolved at 10 K at emission energies 70, 97, 126, 157, and 216 meV below the GaN bound exciton peak under a low excitation intensity (10 W/cm2), due to the recombination between the 2DEG electrons in different subbands and photoexcited holes.

High magnetic field studies of two-dimensional electron gas in a GaN/GaAlN heterostructure: Mechanisms of parallel conduction

We report on quantum Hall effect (QHE) and Shubnikov–de-Haas (SdH) measurements for a GaN/GaAlN heterostructure in high magnetic fields (up to 35 T). The observed well defined SdH oscillations, correlated with QHE plateaus, confirm the existence of a two-dimensional electron gas at the GaN/GaAlN interface. The Shubnikov–de-Haas oscillations are superimposed on a strong positive magnetoresistance. We show that this positive magnetoresistance can be linked to a parallel conduction channel. The analysis of the high magnetic field data yields information about the carrier concentration and mobility in this channel. The concentration and mobility of two-dimensional gas and the parallel conduction layer are analyzed in a wide temperature range (1.9–77 K). A physical model (based on the band diagram and mobility calculations) explaining the origin of parallel conduction is presented.