AlGaN Barrier Layer Research Articles

Development of UV light-emitting diodes based AlGaN/GaN heterojunction utilizing thermal oxidation annealing

Ultraviolet (UV) irradiation has a significant impact on enhancing the performance of sensors. Currently, there is still an urgent need for devices that are simple and easy to fabricate. In this work, a cost-effective and convenient method was employed to fabricate a UV light emitting diode. A four-inch silicon based AlGaN/GaN heterojunction substrate was used. The Ni/Au (20/20 nm) layer was deposited on the AlGaN barrier layer, followed by thermal oxidation to prepare the UV diode. The diode annealed in oxygen can emit UV light at a wavelength of 365 nm and is visible, and no light is emitted from the device in nitrogen annealing. The I–V and C–V characteristics of the device are tested to explore the mechanism. Transmission electron microscopy and technology computer aided design simulation methods were used to analyze the device luminescence mechanism.

On the coupled effect of a MIS-based anode and AlGaN-polarized super-junction to reduce the local electric field for AlGaN/GaN Schottky barrier diodes

This work employs advanced physical models with the help of technology computer-aided design tools to systematically design and investigate AlGaN/GaN Schottky barrier diodes (SBDs), focusing on enhancing forward conduction and reverse blocking characteristics. A recessed metal/insulator/III-nitride (MIS) anode is demonstrated to manage electric field distribution. The incorporation of a 1 nm thick Al2O3 layer enables a reduced leakage current and a significant increase in breakdown voltage (BV). Subsequently, tailored field plates (FPs) further improve the BV of the MIS SBD to ∼1650 V but strong electric field magnitude will be found at the edge of the FP. Hence, a MIS SBD with a graded AlGaN barrier layer (MIS-GA SBD) is designed, featuring a gradient decrease in Al content along the [0001] direction. The generation of negative polarization charges within the barrier functions as a super-junction, significantly homogenizing the electric field. As a result, the MIS-GA SBD achieves a remarkable BV exceeding 3500 V, highlighting its strong potential for high-voltage power electronic applications.

Charge trapping gate stack enabled non-recessed normally off AlGaN/GaN HEMT with high threshold voltage stability

This paper reports a non-recessed normally off AlGaN/GaN high-electron-mobility transistor (HEMT) with a charge trapping gate dielectric stack. The charge trapping gate dielectric stack featuring a low density of fixed positive charges consists of an O3-based Al2O3 tunneling layer and an O3-based HfO2 blocking layer, both deposited via atomic layer deposition. For HEMT with a 15 nm AlGaN barrier layer, a threshold voltage of 2.57 V and an on-resistance of 8.50 Ω × mm are achieved. For positive bias temperature instability (PBTI) testing, the electric field provided by the 15 nm AlGaN layer serves as a barrier to channel carriers, significantly enhancing the PBTI test stability. The optimized gate dielectric stack enables the fabrication of the non-recessed normally off metal–insulator–semiconductor-HEMT with enhanced threshold voltage (Vth) stability.

Enhanced device performance of GaN high electron mobility transistors with in situ crystalline SiN cap layer

In this paper, a ∼2 nm in situ SiN cap layer on AlGaN barrier layer is grown, which is revealed to be crystalline using high-resolution cross-sectional transmission electron microscopy. Benefitting from superior interface quality of epitaxial crystalline SiN/AlGaN interface, the gate diodes with in situ SiN cap layer feature lower interface trap state density than that with GaN cap layer. By comparing the GaN high electron mobility transistors (HEMTs) with the conventional GaN cap layer, the GaN HEMTs with in situ SiN cap layer exhibit improved device performance, showing higher electron mobility, higher drain current, larger on/off current ratio, and higher transconductance. For breakdown characteristics, the devices with in situ crystalline SiN cap layer show prominent advantages over the GaN cap layer with a 30% breakdown voltage increase to 810 V.

Capacitance reduction in AlGaN/GaN heterojunction diodes through thermally oxidized NiO anode

In this study, a thin barrier AlGaN/GaN heterojunction diode with a NiO anode is proposed. NiO as an anode combined with a 5 nm AlGaN barrier layer can significantly deplete two-dimensional electron gas in the anode region of the device. Combined with the etching-free technology, the damage caused by etching the AlGaN barrier layer is successfully avoided. The capacitance of the device was reduced from 28 pF mm−1 (Schottky) to 966 fF/mm (NiO) which reduced 97%. At the same time the NiO anode devices with a reverse current leakage of ~10−8 A/mm@−100V achieved a high current ON/OFF ratio of ~10-8. NiO not only reduces the capacitance and leakage of the device but also enhances its anti-collapse ability. Without using the structure of field plates, the breakdown voltage of the device was also increased compared with the Schottky diode.

Effect of temperature on the stability and performance of III-nitride HEMT magnetic field sensors

The study aimed to investigate the underlying physics limiting the temperature stability and performance of non-surface passivated Al0.34Ga0.66N/GaN Hall effect sensors, including contacts, under atmospheric conditions. The results obtained from analyzing the microstructural evolution in the Al0.34Ga0.66N/GaN Hall sensor heterostructure were found to correlate with the electrical performance of the Hall effect sensor. High-resolution x-ray photoelectron spectroscopy studies revealed the signature of surface oxidation in the GaN cap layer, as well as a slight out-diffusion of “Al” from the AlGaN barrier layer. To prevent the formation of a bumpy surface morphology at the Ohmic contact, we investigated the impact of “Pt” top Ohmic contacts. The application of a top “Pt” contact stack resulted in a smooth Ohmic contact surface and provided evidence that the bumpy surface morphology in Au-based Ohmic contacts is due to the formation of an Al-Au viscous alloy during rapid thermal annealing. In the early stages of thermal aging, the small drop in contact resistivity stabilized with subsequent thermal aging past the initial 550 h at 200 °C. The outcome is that the Al0.34Ga0.66N/GaN Hall effect sensors, even without surface passivation, exhibited a stable response to applied magnetic fields with no sign of significant degradation after 2800 h of thermal aging at 200 °C under atmospheric conditions. This observed stability in the Hall sensor without surface passivation can be attributed to a self-imposed surface oxidation of the cap layer during the early stages of aging, which serves as a protective layer for the device during subsequent extended periods of thermal aging at 200 °C.

A Novel high-voltage DMG Fe-doped AlGaN/AlN/GaN HEMTs with sheet charge density model

In this work, two-dimensional electron gas of the dual material gate Fe doped AlGaN/AlN/GaN High Electron Mobility Transistors (HEMTs) device, sheet charge density model is demonstrated. The model is constructed by considering the electron charge in the barrier layer and the quasi triangular quantum well. This sheet charge density is calculated by Fermi-Dirac statistics by the formation of various sub energy bands and it is valid for all bias voltages. Higher carrier densities are produced and the introduction of the Fe-doped AlN layer reduces the electrons penetration to pass through the AlGaN barrier layer. The model's transcoductance variation is basically constant over an extensive variety of gate source voltages, thereby rendering it perfect regarding high-performance amplifications. The developed analytical model is demonstrated and the simulation results are validated with TCAD simulation. A good agreement is achieved with both analytical and simulation results for all of the voltages employed and device geometries.

Effect of lateral inhomogeneous AlGaN barrier layer on electronic properties of GaN HEMTs

In this study, an AlGaN/GaN high electron mobility transistor with lateral inhomogeneous AlGaN barrier layer (LI-AlGaN HEMT) is proposed and studied systematically. The LI-AlGaN HEMT comprises three AlGaN regions with varying Al content, connected to the source, gate, and drain, respectively. With the increase of Al content in each region, the saturation current of the LI-AlGaN HEMT increases gradually, while the on-resistance (Ron) and breakdown voltage (BV) decrease. The threshold voltage (Vth) of the LI-AlGaN HEMT depends only on the Al content of AlGaN beneath the gate. By introducing the source field plate (FP), the calculated output current of the conventional FP-HEMT is consistent with the experimental data. After optimizing Al content, the LI-AlGaN FP-HEMT has the same Vth compared with conventional FP-HEMT. However, the saturation current is increased by approximately 20 % and the Ron is decreased by approximately 30 %. Additionally, the BV is increased to 1008 V. So the optimized lateral inhomogeneous AlGaN HEMT has better DC characteristics and is suitable for high power GaN device applications.

The Effect of the Barrier Layer on the Uniformity of the Transport Characteristics of AlGaN/GaN Heterostructures on HR-Si(111).

The high transport characteristics of AlGaN/GaN heterostructures are critical components for high-performance electronic and radio-frequency (RF) devices. We report the transport characteristics of AlGaN/GaN heterostructures grown on a high-resistivity (HR) Si(111) substrate, which are unevenly distributed in the central and edge regions of the wafer. The relationship between the composition, stress, and polarization effects was discussed, and the main factors affecting the concentration and mobility of two-dimensional electron gas (2DEG) were clarified. We further demonstrated that the mechanism of changes in polarization intensity and scattering originates from the uneven distribution of Al composition and stress in the AlGaN barrier layer during the growth process. Furthermore, our results provide an important guide on the significance of accomplishing 6 inch AlGaN/GaN HEMT with excellent properties for RF applications.

A high-performance terahertz detector based on a graded channel GaN high-electron-mobility transistor with a recessed gate

A novel recessed gate graded AlGaN high-electron-mobility transistor (RGGA HEMT) for high-sensitivity terahertz (THz) detectors is reported, which exhibits significant potential for high-sensitivity THz detectors, and consequently. The simulation results indicate the exceptional field-effect factor of the proposed RGGA HEMT, which is largely attributed to the three-dimensional electron gas generated by the graded AlGaN barrier layer and the subsequent enhancement of channel conductance. The responsivity and noise equivalent power reach 58mA/W and 43pW/Hz respectively at 227GHz by utilizing a technical computer-aided design platform. As compared to conventional structure GaN HEMT experimental data, the current responsivity is improved by 2.64 times, and the NEP is reduced by 43.4%. The unprecedented improvement in detection performance renders the RGGA HEMT a highly promising approach for future THz real-time single-pixel imaging applications at room temperature.

Research on a High-Threshold-Voltage AlGaN/GaN HEMT with P-GaN Cap and Recessed Gate in Combination with Graded AlGaN Barrier Layer

Research on a High-Threshold-Voltage AlGaN/GaN HEMT with P-GaN Cap and Recessed Gate in Combination with Graded AlGaN Barrier Layer

Improvement of AlGaN/GaN High-Electron-Mobility Transistor Radio Frequency Performance Using Ohmic Etching Patterns for Ka-Band Applications.

In this paper, AlGaN/GaN high-electron-mobility transistors (HEMTs) with ohmic etching patterns (OEPs) "fabricated to improve device radio frequency (RF) performance for Ka-band applications" are reported. The fabricated AlGaN/GaN HEMTs with OEP structures were used to reduce the source and drain resistances (Rs and Rd) for RF performance improvements. Within the proposed study using 1 μm hole, 3 μm hole, 1 μm line, and 3 μm line OEP HEMTs with 2 × 25 μm gate widths, the small signal performance, large signal performance, and minimum noise figure (NFmin) with optimized values were measured for 1 μm line OEP HEMTs. The cut-off frequency (fT) and maximum oscillation frequency (fmax) value of the 1 μm line OEP device exhibited optimized values of 36.4 GHz and 158.29 GHz, respectively. The load-pull results show that the 1 μm line OEP HEMTs exhibited an optimized maximum output power density (Pout, max) of 1.94 W/mm at 28 GHz. The 1 μm line OEP HEMTs also exhibited an optimized NFmin of 1.75 dB at 28 GHz. The increase in the contact area between the ohmic metal and the AlGaN barrier layer was used to reduce the contact resistance of the OEP HEMTs, and the results show that the 1 μm line OEP HEMT could be fabricated, producing the best improvement in RF performance for Ka-band applications.

Optimization of Gate-Head-Top/Bottom Lengths of AlGaN/GaN High-Electron-Mobility Transistors with a Gate-Recessed Structure for High-Power Operations: A Simulation Study.

In this study, we propose an optimized AlGaN/GaN high-electron-mobility transistor (HEMT) with a considerably improved breakdown voltage. First, we matched the simulated data obtained from a basic T-gate HEMT with the measured data obtained from the fabricated device to ensure the reliability of the simulation. Thereafter, to improve the breakdown voltage, we suggested applying a gate-head extended structure. The gate-head-top and gate-head-bottom lengths of the basic T-gate HEMT were symmetrically extended by 0.2 μm steps up to 1.0 μm. The breakdown voltage of the 1.0 μm extended structure was 52% higher than that of the basic T-gate HEMT. However, the cutoff frequency (fT) and maximum frequency (fmax) degraded. To minimize the degradation of fT and fmax, we additionally introduced a gate-recessed structure to the 1.0 μm gate-head extended HEMT. The thickness of the 25 nm AlGaN barrier layer was thinned down to 13 nm in 3 nm steps, and the highest fT and fmax were obtained at a 6 nm recessed structure. The fT and fmax of the gate-recessed structure improved by 9% and 28%, respectively, with respect to those of the non-gate-recessed structure, and further improvement of the breakdown voltage by 35% was observed. Consequently, considering the trade-off relationship between the DC and RF characteristics, the 1.0 μm gate-head extended HEMT with the 6 nm gate-recessed structure was found to be the optimized AlGaN/GaN HEMT for high-power operations.

Barrier and channel thickness engineering to optimize fin height for enhancement mode Al0.3Ga0.7N/GaN FinHEMT

AbstractIn this work, a thorough analysis of the Al0.3Ga0.7N/GaN FinHEMT structure has been performed using three‐dimensional numerical simulations to achieve enhancement mode (E‐mode) operation. In the proposed optimized structure, the fin height (HFin) is comprised of 7 nm critical strained AlGaN barrier layer with 30% Al mole fraction and 63 nm GaN channel layer having a fixed fin width (WFin) of 160 nm. The two‐dimensional electron gas (2DEG) concentration near the hetero interface is found to vary inversely with HFin of the proposed structure. The 2DEG variation was compared between fin‐shaped full tri‐gate approach and variable side gate length tri‐gate design counterpart for a fixed HFin of 70 nm. We achieved an improved threshold voltage of −0.2 V in the optimized HFin structure as compared to −1.45 V obtained in the unoptimized structure as reported earlier. Further, upon decreasing WFin to 40 nm in the same structure having optimized HFin of 70 nm, an E‐mode operation was achieved with a positive threshold voltage of 0.4 V. The positive shift in threshold voltage is explained with the help of necessary energy band diagram.

Extraction of device parameters from capacitance-voltage characteristics of p-GaN/AlGaN/GaN HEMT

This article presents unique methods for extracting essential device parameters of p-GaN/AlGaN/GaN HEMT from its gate capacitance-voltage characteristics. These parameters encompass p-GaN layer doping, AlGaN barrier layer thickness, threshold voltage, effective interface charge at AlGaN/GaN, and UID-GaN layer doping. Detailed step-by-step extraction techniques are elucidated, and their accuracy is rigorously validated against experimental and simulation data. The suggested methods are analytical and straightforward to comprehend. Furthermore, it enables the determination of trap density and its distribution at the AlGaN/GaN interface. These extraction processes play a crucial role in the comprehensive characterization of p-GaN/AlGaN/GaN HEMTs. The extracted device parameters can subsequently be used to improve device optimization, modelling, fabrication, and process control for normally-OFF p-GaN-gated HEMTs.

Drain current sensitivity analysis using a surface potential-based analytical model for AlGaN/GaN double gate MOS-HEMT

In this research, a surface potential-based drain current model for an AlGaN/GaN symmetrical double-gate metal oxide semiconductor high electron mobility transistor (DG-MOSHEMT) is proposed and used to detect label-free biomolecules for the first time. The model is applied for a nanocavity-based DG-MOSHEMT and works on the concept of dielectric modulation to detect biomolecules like uricase, urease, streptavidin, protein, biotin, ChOx, and APTES(3-aminopropyltriethoxysilane). The performance indicators, such as a change in drain ON current (ΔION), drain current sensitivity (SION), transconductance sensitivity (Sgm), and output conductance sensitivity (Δgd), are used to assess the device's efficacy. Numerical simulations are conducted to verify the model's accuracy and quantify its sensitivity. The DG-MOSHEMT device elicited exceptional sensitivity towards the uricase biomolecule, surpassing all other analytes tested, with SION = 0.328, Sgm = 0.197, and Δgd = 28.1 mS/mm. Furthermore, the model considers the contribution of the first two sub-bands of the quantum well and competently captures the fluctuation in drain ON current and sensitivity. A comprehensive sensitivity analysis of the drain current is conducted by altering physical parameters such as cavity length, thickness, gate length and barrier layer thickness. Notably, the sensitivity SION is significantly improved with cavity length and thickness for the optimized AlGaN barrier layer.

Crack-Free High-Composition (>35%) Thick-Barrier (>30 nm) AlGaN/AlN/GaN High-Electron-Mobility Transistor on Sapphire with Low Sheet Resistance (<250 Ω/□)

In this article, a high-composition (>35%) thick-barrier (>30 nm) AlGaN/AlN/GaN high-electron-mobility transistor (HEMT) structure grown on a sapphire substrate with ultra-low sheet resistivity (<250 Ω/□) is reported. The optimization of growth conditions, such as reduced deposition rate, and the thickness optimization of different epitaxial layers allowed us to deposit a crack-free high-composition and thick AlGaN barrier layer HEMT structure. A significantly high two-dimensional electron gas (2DEG) density of 1.46 × 1013 cm−2 with a room-temperature mobility of 1710 cm2/V·s was obtained via Hall measurement using the Van der Pauw method. These state-of-the-art results show great potential for high-power Ga-polar HEMT design on sapphire substrates.

Terahertz Radiation from High Electron Mobility Avalanche Transit Time Sources Prospective for Biomedical Spectroscopy

A Schottky barrier high-electron-mobility avalanche transit time (HEM-ATT) structure is proposed for terahertz (THz) wave generation. The structure is laterally oriented and based on AlGaN/GaN two-dimensional electron gas (2-DEG). Trenches are introduced at different positions of the top AlGaN barrier layer for realizing different sheet carrier density profiles at the 2-DEG channel; the resulting devices are equivalent to high–low, low–high and low-high–low quasi-Read structures. The DC, large-signal and noise simulations of the HEM-ATTs were carried out using the Silvaco ATLAS platform, non-sinusoidal-voltage-excited large-signal and double-iterative field-maximum small-signal simulation models, respectively. The breakdown voltages of the devices estimated via simulation were validated by using experimental measurements; they were found to be around 17–18 V. Under large-signal conditions, the series resistance of the device is estimated to be around 20 Ω. The large-signal simulation shows that the HEM-ATT source is capable of delivering nearly 300 mW of continuous-wave peak power with 11% conversion efficiency at 1.0 THz, which is a significant improvement over the achievable THz power output and efficiency from the conventional vertical GaN double-drift region (DDR) IMPATT THz source. The noise performance of the THz source was found to be significantly improved by using the quasi-Read HEM-ATT structures compared to the conventional vertical Schottky barrier IMPATT structure. These devices are compatible with the state-of-the-art medium-scale semiconductor device fabrication processes, with scope for further miniaturization, and may have significant potential for application in compact biomedical spectroscopy systems as THz solid-state sources.

Threshold voltage shift model for p-GaN gate enhancement mode HEMT

In this paper, we based on the gate structure of p-GaN HEMT connected with Schottky diode and PIN diode and analyzed the threshold voltage shift mechanism under the influence of gate voltage. Based on the carrier transport mechanism, the electron injection current and hole injection current of the p-GaN layer is discussed and calculated, while the gate current model and threshold voltage shift model of the p-GaN HEMT are analyzed. The accuracy of the model is verified by comparing with the experimental data. The effects of p-GaN doping concentration, AlGaN barrier layer thickness and Al component on the gate current and VTH shift are discussed based on the model. By optimizing the device structure and process parameters, the gate current of HEMT can be reduced and the stability of VTH can be improved.

Development of a novel immunoFET technology-based POC assay for detection of Leishmania donovani and Leishmania major.

Leishmaniasis is considered as one of the 20 neglected tropical diseases. Current methods of leishmanial diagnosis depend on conventional laboratory-based techniques, which are time-consuming, costly and require special equipment and trained personnel. In this context, we aimed to provide an immuno field effect transistors (ImmunoFET) biosensor that matches the conventional standards for point-of-care (POC) monitoring and detection of Leishmania (L.) donovani/Leishmania major. Crude antigens prepared by repeated freeze thawing of L. donovani/L. major stationary phase promastigotes were used for ELISA and ImmunoFETs. Lesishmania-specific antigens were serially diluted in 1× PBS from a concentration of 106 -102 parasites/mL. A specific polyclonal antibody-based sandwich ELISA was established for the detection of Leishmania antigens. An immunoFET technology-based POC novel assay was constructed for the detection of Leishmania antigens. Interactions between antigen-antibody at the gate surface generate an electrical signal that can be measured by semiconductor field-effect principles. Sensitivity was considered and measured as the change in current divided by the initial current. The final L. donovani/L. major crude antigen protein concentrations were measured as 1.50 mg/mL. Sandwich ELISA against the Leishmania 40S ribosomal protein detected Leishmania antigens could detect as few as 100 L. donovani/L. major parasites. An immunoFET biosensor was constructed based on the optimization of aluminium gallium nitride/gallium nitride (AlGaN/GaN) surface oxidation methods. The device surface was composed by an AlGaN/GaN wafer with a 23 nm AlGaN barrier layer, a 2 μm GaN layer on the silicon carbide (SiC) substrate for Leishmania binding, and coated with a specific antibody against the Leishmania 40S ribosomal protein, which was successfully detected at concentrations from 106 to 102 parasites/mL in 1× PBS. At the concentration of 104 parasites, the immunoFETs device sensitivities were 13% and 0.052% in the sub-threshold regime and the saturation regime, respectively. Leishmania parasites were successfully detected by the ImmunoFET biosensor at a diluted concentration as low as 150 ng/mL. In this study, the developed ImmunoFET biosensor performed well. ImmunoFET biosensors can be used as an alternative diagnostic method to ELISA. Increasing the sensitivity and optimization of immuno-FET biosensors might allow earlier and faster detection of leishmaniasis.