Two-dimensional Electron Gas Sheet Density Research Articles

Atomic-column resolution quantitative composition analysis of AlN interlayer in MOCVD-grown AlGaN/AlN/GaN heterostructure using HAADF-STEM

Quantitative compositional analysis using high-angle annular dark-field scanning transmission electron microscopy was performed for a metal-organic chemical vapor deposition-grown AlGaN/AlN/GaN heterostructure at atomic-column resolution. In addition, the effects that different concentrations of Al in the AlN interlayer had on the electronic properties were evaluated. The maximum Al concentration in the AlN interlayer was 0.41, and the compositional grading at the upper and lower AlN interfaces resulted in an asymmetric broadening of the interface. Calculations show that increasing the Al concentration in the AlN interlayer leads to an approximately linear increase in the two-dimensional electron gas sheet density. The alloy scattering is also effectively suppressed when the Al concentration is greater than 0.4.

Characterization of trap states in AlN/GaN superlattice channel high electron mobility transistors under total-ionizing-dose with 60Co γ-irradiation

In this Letter, the effects of trap states in AlN/GaN superlattice channel HEMTs (high electron mobility transistors) under total ionizing dose with γ-irradiation have been systematically investigated. After 1 Mrad γ-irradiation with a dose rate of 50 rad/s, negative drifts in threshold voltage and C–V characteristics are observed. Simultaneously, the two-dimensional electron gas sheet density of the upper channel increases from 5.09 × 1012 to 5.47 × 1012 cm−2, while that of the lower channel decreases from 4.41 × 1012 to 3.86 × 1012 cm−2, respectively. Furthermore, frequency-dependent capacitance and conductance measurements are adopted to investigate the evolution of trap states in an electron channel. The trap state density (DT = 0.21–0.88 × 1013 cm−2 eV−1) is over the ET range from 0.314 to 0.329 eV after irradiation for the upper channel, while the trap state in the lower channel decreases from 4.54 × 1011 cm−2 eV−1 at ET = 0.230 eV to 2.38 × 1011 cm−2 eV−1 at ET = 0.278 eV. The density (1.39–1.54 × 1011 cm−2 eV−1) of trap states with faster τT (0.033–0.037 μs) generated in a lower channel is located at shallower ET between 0.227 and 0.230 eV. The results reveal the mechanism of trap states in the channel, affecting the performance of HEMTs, which can provide a valuable understanding for hardening in space radiation.

Performance Analysis of AC and DC Characteristics of AlGaN/GaN HEMT at Various Temperatures

This paper verifies the simulated transfer characteristics and ID–VD characteristics with the experimental data of an AlGaN/GaN high electron mobility transistor of gate length 0.7 µm. Various parameters are analyzed based on the effect of temperature. 2D device simulation is performed using the TCAD Atlas numerical simulation tool. Simulation of various important DC parameters such as the transfer characteristics, ID–VD characteristics, transconductance and threshold voltage is carried out at different temperatures. We have also performed radio frequency analysis to analyze figure of merits such as the current gain cut-off frequency at various temperatures. The simulation analysis is performed in the temperature range of 300–500 K. From the simulation results, we found that the saturation current and I–V characteristics in the linear region decreased because of mobility degradation. However, both the threshold voltage and two-dimensional electron gas sheet density increased with temperature. Hence, the selection of operating temperature is critical as it influences the device performance.

Conduction band fluctuation scattering due to alloy clustering in barrier layers in InAlN/GaN heterostructures

In InAlN/GaN heterostructures, alloy clustering-induced InAlN conduction band fluctuations interact with electrons penetrating into the barrier layers and thus affect the electron transport. Based on the statistical description of InAlN compositional distribution, a theoretical model of the conduction band fluctuation scattering (CBFS) is presented. The model calculations show that the CBFS-limited mobility decreases with increasing two-dimensional electron gas sheet density and is inversely proportional to the squared standard deviation of In distribution. The AlN interfacial layer can effectively suppress the CBFS via decreasing the penetration probability. This model is directed towards understanding the transport properties in heterostructure materials with columnar clusters.

Modelling temperature dependence on AlGaN/GaN power HEMT device characteristics

This paper reports extensive modelling and analysis of the temperature dependence on the device characteristics of the AlGaN/GaN high electron mobility transistors (HEMTs). A physics-based model is proposed in this study in order to correctly predict the gate flat-band Schottky barrier height, energy band Fermi-level (EC–EF) at the AlGaN/GaN interface, two-dimensional electron gas sheet density, gate threshold and (ID–VG) at sub-threshold voltages, and drain current–voltage (ID–VD) characteristics under various high-temperature conditions. The analytical results are then verified by comparing with the laboratory measurement as well as the numerical results obtained from the Sentaurus TCAD simulation. The proposed model is found to be useful for power electronic device designers on the prediction of the AlGaN/GaN HEMT device performance under high-temperature operation.

The behavior of two-dimensional electron gas in GaN/Al xGa 1− xN/GaN heterostructures with very thin Al xGa 1− xN barriers

The behavior of two-dimensional electron gas density, induced by spontaneous and piezoelectric polarization, in non-intentionally doped GaN/Al x Ga 1− x N/GaN heterostructures with very thin barriers has been studied. The sheet carrier concentration, N s, induced by polarization charges was determined self-consistently from the coupled Schrödinger and Poisson equations, by taking into account the image and exchange-correlation potential and by considering five energy levels. As a result, the physical values such as potential distribution, subband energies, wave function, Fermi level, total sheet density and occupation of different subbands have been obtained and discussed for different capping and barrier layer thickness and temperatures. The numerical results show: (a) the formation of the quantum well in GaN, when x (the Al composition in barrier) =1, is possible for every AlN thin barrier thickness, but when x<1, the minimum barrier thickness necessary for the formation of the well is depended on x. Also when x=1, depending upon two-dimensional electron gas sheet density, N s, the number of occupied levels of the well, can be one, two or even three, (b) the above-mentioned values are almost highly sensitive to capping layer thickness. The temperature evolution of the sub-band occupation number shows that there is still an efficient confinement even at very high temperature (900 K) for a thinner capping layer system.