Two-dimensional Electron Gas Density Research Articles

Impact of InGaN back barrier layer on performance of AIInN/AlN/GaN MOS-HEMTs

In the present work, we have discussed the effect of InGaN back barrier on device performances of 100 nm gate length AlInN/AlN/GaN metal oxide semiconductor high electron mobility transistor (MOS-HEMT) device and a wide comparison is made with respect to without considering the back barrier layer. The InGaN layer is introduced in the intension to raise the conduction band of GaN buffer with respect to GaN channel so that there is an improvement in the carrier confinement and at the same time witnessed excellent high frequency performance. The simulations are carried out using 2D Sentaurus TCAD simulator using Hydrodynamic mobility model by taking interface traps into consideration. Due to high value of two-dimensional electron gas (2DEG) density and mobility in AlInN/AlN/GaN MOS-HEMT device, higher drain current density is achieved. Simulation are carried out for different device parameters such as transfer characteristic (Id-Vg), transconductance factor (gm), drain induced barrier lowering (DIBL), Subthreshold slope (SS), conduction band energy, transconductance generation factor (gm/Id) and electric field. We have also examined the RF performance such as, total gate capacitance (Cgg), current gain cutoff frequency (fT) and power gain cutoff frequency (fmax) of the proposed devices. Use of InGaN back barrier tends to increase threshold voltage towards more positive value, reduced DIBL, and improves SS and significant growth in (gm/Id) by 5.5%. It also helps to achieve better frequency response like substantial increase in fT up to 91 GHz with current gain 60 dB as compare to 67 GHz with 56 dB for the device without considering back barrier and increase in fmax up to 112 GHz with respect 94 GHz. These results evident that use of InGaN back barrier in such devices can be better solution for future analog and RF applications.

Ultra-strong light–matter coupling and superradiance using dense electron gases

Abstract The physics of the interaction between a dense two-dimensional electron gas and a microcavity photonic mode is reviewed. For high electronic densities, this system enters the ultra-strong coupling regime in which the Rabi energy, which measures the strength of the light–matter coupling, is of the same order of magnitude as the matter excitation. The ultra-strong coupling has been experimentally demonstrated by inserting a highly doped semiconductor layer between two metal plates that produce a microcavity, with extreme sub-wavelength confinement of the electromagnetic field. A record value at room temperature (73%) of the ratio between the Rabi and the matter excitation energies (the relative Rabi energy) has been measured together with a very large photonic gap induced by the polariton splitting. The ultra-strong coupling is a manifestation of a huge cooperative dipole, which is proportional to the number of electrons participating in the interaction. Such a phenomenal interaction with light appears also in the absence of a microcavity and, for a dipole coupled with free space, it gives rise to superradiance.

Electrical properties of GaN-based heterostructures adopting InAlN/AlGaN bilayer barriers

Electrical properties of GaN-based heterostructures adopting InAlN/AlGaN bilayer barriers are investigated by Hall-effect and current–voltage measurements. It is found that this structure possesses both merits of high two-dimensional electron gas (2DEG) density and low gate leakage current density, while maintaining high 2DEG mobility. Furthermore, temperature dependence of the 2DEG density in this structure is verified to follow a combined tendency of InAlN/GaN (increase) and AlGaN/GaN (decrease) heterostructures with increasing temperature from 90K to 400K, which is mainly caused by superposition of the effects from carrier thermal activation induced by extrinsic factors in InAlN layer and the reduced conduction-band discontinuity.

Kinetic magnetism at the interface between Mott and band insulators

We show that the interplay of a high density two-dimensional electron gas and localized electrons in a neighboring Mott insulator leads to kinetic magnetism unique to the Mott/band insulator interface. Our study is based upon a bilayer Hubbard model at $U=\infty$ with a potential difference between the two layers. We combine analytic results with DMRG simulations to show that magnetism, and especially ferromagnetism, is greatly enhanced relative by the proximity of the two subsystems. The results are potentially relevant to recent experiments suggesting magnetism in $R$TiO$_3$/SrTiO$_3$ heterostructures.

Enhancement of performance of AlGaN/GaN high-electron-mobility transistors by transfer from sapphire to a copper plate

We transferred AlGaN/GaN high-electron-mobility transistors (HEMTs) from a sapphire substrate to a copper plate using the hexagonal boron nitride epitaxial lift-off technique. After transfer, the negative slope in the drain current Id decreased owing to the suppression of the self-heating effect. The significant increase in Id and the negative shift of threshold voltage indicate an increase in two-dimensional electron gas (2DEG) density. The increase in 2DEG density is at least partially caused by the reduction in compressive stress in the GaN layer after the transfer, which is revealed from the E2 peak shifts of −1.3 cm−1 in Raman spectroscopy measurements. We also estimated the temperature in the active region of HEMTs by micro-Raman spectroscopy. For the transferred HEMT, the temperature at the gate edge on the drain side was 100 °C at a power dissipation of 0.9 W. In contrast, the temperature reached 240 °C at a power dissipation of only 0.7 W for the HEMT on the sapphire substrate. This indicates that the transfer technique can enhance the performance of AlGaN/GaN HEMTs.

The role of polarization coulomb field scattering in the electron mobility of AlGaN/AlN/GaN heterostructure field-effect transistors

The electron mobility for the prepared AlGaN/AlN/GaN heterostructure field-effect transistor (HFET) with the ratio of the gate length to the drain-to-source distance being less than 1/2 has been studied by comparing the measured electron mobility with the theoretical value. The measured electron mobility is derived from the measured capacitance-voltage (C-V) and current-voltage (I-V) characteristics, and the theoretical mobility is determined by using Matthiessen’s law, involving six kinds of important scattering mechanisms. For the prepared device at room temperature, longitudinal optical phonon scattering (LO scattering) was found to have a remarkable effect on the value of the electron mobility, and polarization Coulomb field scattering (PCF scattering ) was found to be important to the changing trend of the electron mobility versus the two-dimensional electron gas (2DEG) density.

New Al0.25Ga0.75N/GaN high electron mobility transistor with partial etched AlGaN layer

In this letter, a new Al0.25Ga0.75N/GaN high electron mobility transistor (HEMT) with the AlGaN layer is partial etched is reported for the first time. The two-dimensional electron gas (2DEG) density in the HEMTs is changed by partially etching the AlGaN layer. A new electric field peak is introduced along the interface between the AlGaN layer and the GaN buffer by the electric field modulation effect. The high electric field near the gate in the proposed Al0.25Ga0.75N/GaN HEMT is effectively decreased, which makes the surface electric field more uniform. Compared with the conventional structure, the breakdown voltage can be improved by 58% for the proposed Al0.25Ga0.75N/GaN HEMT and the current collapse can be reduced resulting from the more uniform surface electric field.

A new expression of Ns versus Ef to an accurate control charge model for AlGaAs/GaAs

Semi-conductor components become the privileged support of information and communication, particularly appreciation to the development of the internet. Today, MOS transistors on silicon dominate largely the semi-conductors market, however the diminution of transistors grid length is not enough to enhance the performances and respect Moore law. Particularly, for broadband telecommunications systems, where faster components are required. For this reason, alternative structures proposed like hetero structures IV-IV or III-V [1] have been.The most effective components in this area (High Electron Mobility Transistor: HEMT) on IIIV substrate. This work investigates an approach for contributing to the development of a numerical model based on physical and numerical modelling of the potential at heterostructure in AlGaAs/GaAs interface. We have developed calculation using projective methods allowed the Hamiltonian integration using Green functions in Schrodinger equation, for a rigorous resolution “self coherent” with Poisson equation. A simple analytical approach for charge-control in quantum well region of an AlGaAs/GaAs HEMT structure was presented. A charge-control equation, accounting for a variable average distance of the 2-DEG from the interface was introduced. Our approach which have aim to obtain ns-Vg characteristics is mainly based on: A new linear expression of Fermi-level variation with two-dimensional electron gas density in high electron mobility and also is mainly based on the notion of effective doping and a new expression of AEc

Enhancement mode AlGaN/GaN double heterostructure high electron mobility transistor with F plasma treatment

Effects of double heterostructure materials (AlGaN/GaN/AlGaN/GaN) with different GaN channel thickness values (14 nm, 28 nm, 60 nm) on the high electron mobility transistor (HEMT) are simulated by using silvaco, and furthermore, the differences in characteristic among the enhancement mode devices made from such double heterostructure materials with different F injection doses (150 W, 135 W) are also simulated. The simulation results show that the threshold voltage shifts towards positive direction and the saturation current decreases as the GaN channel thickness decreases. The two-dimensional electron gas (2 DEG) density could be reduced as GaN channel thickness decreases due to piezoelectric polarization weakened by backing AlGaN barrier. Combining F plasma treatment and double heterostructure material, the enhancement mode device with high positive threshold voltage is successfully developed. The DC characteristics of the enhancement mode devices with different GaN channel thickness values are analyzed comparatively, and the simulation results are validated by using the experimental results. The threshold voltages of these enhancement mode devices with GaN channel thickness values of 14 nm, 28 nm, and 60 nm reach 1.1 V, 0.8 V, and 0.3 V, respectively. The maximum transconductance values of these enhancement mode devices with GaN channel thickness values of 14 nm, 28 nm, and 60 nm reach 115 mS/mm, 137 mS/mm, and 198 mS/mm, respectively. The thinner GaN channel thickness in the double heterostructure could reduce the depth of quantum well and 2 DEG density, so that the device with a GaN channel thickness of 14 cm has a lower saturation current. The breakdown voltages and gate reverse leakage currents of the three kinds of devices are investigated, and the device with a thinner GaN channel has a lower leakage current and higher breakdown voltage due to weakened vertical electrical field in thinner channel double heterostructure. The damage of channel mobility in F plasma treatment is weakened by using a lower plasma power (135 W), and the enhancement mode device without annealing process demonstrates a better saturation current and transconductance characteristic. The results of the device with annealing confirm that the plasma damage is depressed at an F injection power of 135 W. The threshold voltage temperature stability of 14 nm GaN channel thickness device is studied, and Vth is only 0.4 V after 350 ℃ 2 min annealing process. Drain induced barrier lowering (DIBL) effects of the HEMTs with double heterostructures are investigated, and the DIBL value of the14 nm GaN channel device is 16 mV/V. The DIBL value indicates a good limiting property of the 2 DEG in double heterostructure device.

Superior material qualities and transport properties of InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition**Project supported by the National Natural Science Foundation of China (Grant Nos. 61306017, 61334002, 61474086, and 11435010) and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61306017).

Pulsed metal organic chemical vapor deposition is introduced into the growth of InGaN channel heterostructure for improving material qualities and transport properties. High-resolution transmission electron microscopy imaging shows the phase separation free InGaN channel with smooth and abrupt interface. A very high two-dimensional electron gas density of approximately 1.85 × 1013 cm−2 is obtained due to the superior carrier confinement. In addition, the Hall mobility reaches 967 cm2/V·s, owing to the suppression of interface roughness scattering. Furthermore, temperature-dependent Hall measurement results show that InGaN channel heterostructure possesses a steady two-dimensional electron gas density over the tested temperature range, and has superior transport properties at elevated temperatures compared with the traditional GaN channel heterostructure. The gratifying results imply that InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition is a promising candidate for microwave power devices.

Comparison of electrical characteristics between AlGaN/GaN and lattice-matched InAlN/GaN heterostructure Schottky barrier diodes

Lattice-matched Pt/Au–In0.17Al0.83N/GaN hetreojunction Schottky barrier diodes (SBDs) with circular planar structure have been fabricated. The electrical characteristics of InAlN/GaN SBD, such as two-dimensional electron gas (2DEG) density, turn-on voltage, Schottky barrier height, reverse breakdown voltage and the forward current-transport mechanisms, are investigated and compared with those of a conventional AlGaN/GaN SBD. The results show that, despite the higher Schottky barrier height, more dislocations in InAlN layer causes a larger leakage current and lower reverse breakdown voltage than the AlGaN/GaN SBD. The emission microscopy images of past-breakdown device suggest that a horizontal premature breakdown behavior attributed to the large leakage current happens in the InAlN/GaN SBD, differing from the vertical breakdown in the AlGaN/GaN SBD.

Growth of AlN/GaN HEMT structure Using Indium-surfactant

We have grown AlN/GaN heterostructure which is a promising candidate for mm-wave applications. For the growth of the high quality very thin AlN barrier, indium was introduced as a surfactant at the growth temperature varied from 750 to 1070 ℃, which results in improving electrical properties of two-dimensional electron gas (2DEG). The heterostructure with barrier thickness of 7 ㎚ grown at of 800 ℃ exhibited best Hall measurement results; such as sheet resistance of 215 Ω/□, electron mobility of 1430 ㎠/V·s, and two-dimensional electron gas (2DEG) density of 2.04 ｘ 10 13 /㎠. The high electron mobility transistor (HEMT) was fabricated on the grown heterostructure. The device with gate length of 0.2 ㎛ exhibited excellent DC and RF performances; such as maximum drain current of 937 ㎃/㎜, maximum transconductance of 269 mS/㎜, current gain cut-off frequency of 40 ㎓, and maximum oscillation frequency of 80 ㎓.

DC Characteristics of AlGaN/GaN HEMTs Using a Dual-Gate Structure.

Multiple techniques such as fluoride-based plasma treatment, a p-GaN or p-AlGaN gate contact, and a recessed gate structure have been employed to modulate the threshold voltage of AlGaN/GaN-based high-electron-mobility transistors (HEMTs). In this study, we present dual-gate AlGaN/GaN HEMTs grown on a Si substrate, which effectively shift the threshold voltage in the positive direction. Experimental data show that the threshold voltage is shifted from -4.2 V in a conventional single-gate HEMT to -2.8 V in dual-gate HEMTs. It is evident that a second gate helps improve the threshold voltage by reducing the two-dimensional electron gas density in the channel. Furthermore, the maximum drain current, maximum transconductance, and breakdown voltage values of a single-gate device are not significantly different from those of a dual-gate device. For the fabricated single- and dual-gate devices, the values of the maximum drain current are 430 mA/mm and 428 mA/mm, respectively, whereas the values of the maximum transconductance are 83 mS/mm and 75 mS/mm, respectively.

Enhanced two dimensional electron gas transport characteristics in Al2O3/AlInN/GaN metal-oxide-semiconductor high-electron-mobility transistors on Si substrate

The authors report on Al2O3/Al0.85In0.15N/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistor (MOS-HEMT) on Si fabricated by using atomic layer deposited Al2O3 as gate insulator and passivation layer. The MOS-HEMT with the gate length of 2 μm exhibits excellent direct-current (dc) characteristics with a drain current maximum of 1270 mA/mm at a gate bias of 3 V and an off-state breakdown voltage of 180 V for a gate-drain spacing of 4 μm. Also, the 1 μm-gate MOS-HEMT shows good radio-frequency (rf) response such as current gain and maximum oscillation cut-off frequencies of 10 and 34 GHz, respectively. The capacitance-voltage characteristics at 1 MHz revealed significant increase in two-dimensional electron gas (2DEG) density for the MOS-HEMT compared to conventional Schottky barrier HEMTs. Analyses using drain-source conductivity measurements showed improvements in 2DEG transport characteristics for the MOS-HEMT. The enhancements in dc and rf performances of the Al2O3/Al0.85In0.15N/GaN MOS-HEMT are attributed to the improvements in 2DEG characteristics.

Influence of PECVD deposited SiNx passivation layer thickness on In0.18Al0.82N/GaN/Si HEMT

The influence of plasma enhanced chemical vapour deposited (PECVD) silicon nitride (SiNx) passivation film thickness on In0.18Al0.82N/GaN/Si heterostructures and HEMTs has been investigated. The formation of Si3N4 was confirmed by x-ray photoelectron spectroscopy (XPS) measurements. X-ray reflectivity (XRR) measurements reveal that both the density and roughness of the SiNx film increase with increasing film thickness. With an increase in SiNx film thickness, a significant increase in two-dimensional electron gas (2DEG) density, drain current, extrinsic transconductance and negative threshold voltage shift of the In0.18Al0.82/GaN/Si HEMTs are observed. An optimal thickness of SiNx is ~100 nm and it yields a substantial increase in 2DEG density (~30%) with a minimum sheet resistance for In0.18Al0.82N/GaN/Si heterostructures. Furthermore, we correlate the observed SiNx film thickness-dependent electrical characteristics of In0.18Al0.82/GaN/Si HEMTs with the density of the SiNx film.

Tuning the conductivity threshold and carrier density of two-dimensional electron gas at oxide interfaces through interface engineering

The two-dimensional electron gas (2DEG) formed at the perovskite oxides heterostructures is of great interest because of its potential applications in oxides electronics and nanoscale multifunctional devices. A canonical example is the 2DEG at the interface between a polar oxide LaAlO3 (LAO) and non-polar SrTiO3 (STO). Here, the LAO polar oxide can be regarded as the modulating or doping layer and is expected to define the electronic properties of 2DEG at the LAO/STO interface. However, to practically implement the 2DEG in electronics and device design, desired properties such as tunable 2D carrier density are necessary. Here, we report the tuning of conductivity threshold, carrier density and electronic properties of 2DEG in LAO/STO heterostructures by insertion of a La0.5Sr0.5TiO3 (LSTO) layer of varying thicknesses, and thus modulating the amount of polarization of the oxide over layers. Our experimental result shows an enhancement of carrier density up to a value of about five times higher than that observed at the LAO/STO interface. A complete thickness dependent metal-insulator phase diagram is obtained by varying the thickness of LAO and LSTO providing an estimate for the critical thickness needed for the metallic phase. The observations are discussed in terms of electronic reconstruction induced by polar oxides.

Impact of pressure on transport properties of AlGaN/GaN high electron mobility transistor

The properties of AlxGa1−xN/GaN high electron mobility transistor (HEMT) impacted by pressure are characterized quantitatively. The results indicate that the dislocation density increases as the critical thickness decreases with increasing pressure. The two-dimensional electron gas density was found to be linearly changeable with the pressure. A simulation has been completed to verify the influence of electron mobility. The results show that the misfit dislocation scattering induced by the pressure is a major limiting factor for the properties of HEMT.

Numerical and experimental analyses of two-dimensional electron mobility in Al(In,Ga)N/AlGaN heterostructures

Two-dimensional electron mobilities in AlGaN-channel nitride heterostructures were numerically and experimentally analyzed. The calculation and experimental results indicated that mobility for InAlN/AlGaN heterostructures grown by metalorganic chemical vapor deposition was limited by interface roughness scattering as well as alloy disorder scattering. The mobility limits for AlGaN-channel heterostructures with a two-dimensional electron gas (2DEG) density of 3 × 1013/cm2 were estimated to be, for instance, 249 cm2 V−1 s−1 for an Al0.3Ga0.7N channel and 192 cm2 V−1 s−1 for an Al0.5Ga0.5N channel. The calculated values showed no major disagreement with the results reported on AlGaN-channel heterostructures.

Droop Improvement in InGaN/GaN Light-Emitting Diodes by Polarization Doping of Quantum Wells and Electron Blocking Layer

-Polarization doping in quantum wells and electron blocking layer is proposed to improve the emission intensity and efficiency droop of InGaN light-emitting diodes (LEDs). Band diagrams and the internal quantum efficiencies of LEDs are theoretically studied by the ATLAS simulation program. Numerical results show that the internal quantum efficiency of polarization doped LED structures are improved by 25% as compared to un-doped structures which can be due to accumulation of high density two-dimensional electron gas in quantum wells.

Impacts of recessed gate and fluoride-based plasma treatment approaches toward normally-off AlGaN/GaN HEMT.

We report two approaches to fabricating high performance normally-off AIGaN/GaN high-electron mobility transistors (HEMTs). The fabrication techniques employed were based on recessed-metal-insulator-semiconductor (MIS) gate and recessed fluoride-based plasma treatment. They were selectively applied to the area under the gate electrode to deplete the two-dimensional electron gas (2-DEG) density. We found that the recessed gate structure was effective in shifting the threshold voltage by controlling the etching depth of gate region to reduce the AIGaN layer thickness to less than 8 nm. Likewise, the CF4 plasma treatment effectively incorporated negatively charged fluorine ions into the thin AIGaN barrier so that the threshold voltage shifted to higher positive values. In addition to the increased threshold voltage, experimental results showed a maximum drain current and a maximum transconductance of 315 mA/mm and 100 mS/mm, respectively, for the recessed-MIS gate HEMT, and 340 mA/mm and 330 mS/mm, respectively, for the fluoride-based plasma treated HEMT.