Monte Carlo study of the quasi two-dimensional electron gas in the high electron mobility transistor (original) (raw)
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A two-dimensional self-consistent numerical model for high electron mobility transistor
IEEE Transactions on Electron Devices, 1991
A new two-dimensional self-consistent numerical model for High Electron Mobility Transistor (HEMT) is presented. In previous two-dimensional models, the quantization of electrons in the quantum well has been treated by using a triangular well approximation in which the width of the quantum well is assumed to be zero and the quantized electrons are assumed to reside right at the heterojunction. In this paper, we do not make the above assumptions. Instead, the spatial spreading of the electron concentration in the quantum well normal to the heterojunction is taken into account by solving Schrodinger's and Poisson's equations self-consistently. The Boltzmann transport equation in the form of a current continuity equation and an energy balance equation are solved to obtain the transient and steady-state transport behavior. The id-vd characteristics, transconductance, gate capacitance, and unity-gain frequency of a single quantum-well HEMT is discussed. Also discussed are the dependencies of the device performance on the gate length and the doping concentration of the AlGaAs layer.
TWO-DIMENSIONAL NUMERICAL MODELS FOR THE HIGH ELECTRON MOBILITY TRANSISTOR
A two-dimensional drift-diffusion model for the high electron mobility transistor (HEMT) is described. Special attention is paid to the modeling of the AlGaAs/GaAs heterojunction. Also, an energy transport model for the HEMT is proposed. The internal distributions of electron density, voltage and current density are discussed. The influence of hot electron effects in HEMT's is demonstrated. The results obtained using these models are found to agree with those obtained from experimental devices.
High Electron Mobility Transistor: A Review on Analytical Models
In recent years, high electron mobility transistors (HEMTs) have attracted much attention in high-speed and high-power applications. One of the most interesting properties of these devices is the formation of the two-dimensional electron gas (2-DEG) with a very high electron mobility at the hetero interface. AlGaAs/GaAs HEMTs have been and are promising candidates for high speed and mm-wave applications. GaN-based HEMTs have attracted much attention for application in high-frequency and high-power devices due to the large bandgap, high saturated electron velocity, and high breakdown electric field. Significant improvements in the fabrication and performance of high electron mobility transistors (HEMT) have stimulated a considerable interest in the modeling of such structures. In this paper, we review working principle and various structures of HEMT, also different analytical models available for HEMT.
Journal of Applied Physics, 2014
It is commonly accepted that interface states at the passivation surface of AlGaN/GaN heterostructures play an important role in the formation of the 2DEG density. Several interface state models are cited throughout literature, some with discrete levels, others with different kinds of distributions, or a combination of both. The purpose of this article is to compare the existing interface state models with both direct and indirect measurements of these interface states from literature (e.g., through the hysteresis of transfer characteristics of Metal-Insulator-Semiconductor High Electron Mobility Transistors (MISHEMTs) employing such an interface in the gate region) and Technology Computer Aided Design (TCAD) simulations of 2DEG densities as a function of the AlGaN thickness. The discrepancies between those measurements and TCAD simulations (also those commonly found in literature) are discussed. Then, an alternative model inspired by the Disorder Induced Gap State model for compound semiconductors is proposed. It is shown that defining a deep border trap inside the insulator can solve these discrepancies and that this alternative model can explain the origin of the two dimensional electron gas in combination with a high-quality interface that, by definition, has a low interface state density.
Open Journal of Applied Sciences, 2014
In this letter we propose analytical evaluation method for the electron density and the energy density in multi-layered high electron mobility transistors (HEMTs). The algorithm is used to simulate the variation of the electron density and the energy density against temperature of heterojunction AlGaN/GaN. The proposed procedure guaranties the reliable application of the contribution of multi-layered HEMTs structure. In conclusion, the obtained results are estimated and discussed.
Charge control of the heterojunction two-dimensional electron gas for MESFET application
IEEE Transactions on Electron Devices, 1981
Previous works have shown that a two-dimensional electron gas (2 DEG) is accumulated at the interface of GaAs (n)/Al,Gal-,As (n) isotype heterojunctions. In this paper, a MESFET structure working with this 2 DEG is presented. Theoretical treatments are given, considering that the charge control results from the interpenetration of the Schottky space-charge region and the accumulation layer. A semi-analytical calculation is then developed: conductance, capacitance, source-to-drain current at saturation, and transconductance are predicted for a large-gate FET. Source-todrain saturation current in short-gate FET is also given. Experimental results obtained in our laboratory and those recently published are compared to calculated data. The good agreement observed in all cases, including low-temperature measurements, clearly shows that the 2 DEG MESFET behavior is actually valid. The high mobility of electrons one can expect from the 2 DEG, particularly at 77 K, suggests that the 2 DEG MESFET is a promising device for microwave and high-speed devices. NOTATIONS Indices 1 and 2 are, respectively, related to the small-gap and large-gap semiconductor. C Capacitance. d Layer width. & Electric field. &S Threshold field for intervalley transfer. Ee Energy difference (in volts) between the G Conductance. gtn 0 Transconductance of a FET at VG = 0. I Channel current of a FET. K Boltzmann's constant. L Gate length. N Donor density (per unit volume). N c Effective density of states in conduction 4 Electron charge. QI Free electron surface density. Qacc Part of Ql relative to the accumulation layer. Qgcc Qacc in quasi-equilibrium conditions. T Temperature. conduction band edge and the Fermi level. IDSS Saturation current of a FET for VG = 0. n Free electron density (per unit volume).
physica status solidi (a), 2018
The role of surface donors at the oxide/semiconductor interface of III-N metal-oxide-semiconductor (MOS) high-electron mobility transistors (HEMTs), by creating a two-dimensional electron gas (2DEG) and the device performance, are investigated. Al 2 O 3 /GaN/AlGaN/GaN MOS HEMTs show the surface donor density (N d,surf) of 2.2 Â 10 13 cm À2 , which is increased up to 3.4 Â 10 13 cm À2 after post-deposition annealing. In the latter, surface donors fully compensate the surface polarization charge and the HEMT threshold voltage decreases substantially with the oxide thickness. On the other hand, an open-channel drain current is found to be independent of N d, surf , while marginal trapping is completely removed when N d,surf increases with annealing. Consequently, ionized surface donors behave like a fixed charge and are clearly distinguishable from trapping states. Open-channel 2DEG densities of %1.1 Â 10 13 cm À2 are extracted from capacitance-voltage measurements. Similarly, recent data on enhancement-mode HfO 2 /InAlN/ AlN/GaN MOS HEMTs are analyzed where N d,surf is reduced down to 1 Â 10 13 cm À2 while 2DEG densities reach %2.7 Â 10 13 cm À2. It is suggested that under the open-channel condition, 2DEG is supplied also by an injecting source contact if N d,surf is lower than the QW polarization charge. Our charge quantifications are supported by calculating energy-band diagrams.
Electron mobility limits in a two-dimensional electron gas: GaAs-GaAlAs heterostructures
Physical Review B
A theoretical model was formulated for electron scattering in a two-dimensional electron gas confined in a triangular potential well. For the first time, the effects of intersubband scattering were included. An inherent mobility limit is imposed by phonon, alloy, and remote impurity scattering. Intersubband scattering was found to play a significant role in determining this mobility limit. The model accounted very satisfactorily for the reported electron mobility characteristics in GaAs-GaA1As heterostructures. The two-dimensional electron gas confined at a GaA1As-GaAs interface has received a great deal of attention' 6 because its unique transport characteristics play a key role in a new generation of ultra-high-speed semiconductor devices. Thus, in "selectively doped" GaAlAs-GaAs heterostructures, electrons confined at the GaAs side of the interface and separated from their parent donors, which are in GaAlAs, have exhibited mobilities as high as 2& 10 cm'/Vs;~this value is about one order of magnitude greater