HEMT Research Articles

Deep insight of inter-channel coupling in AlGaN/GaN double channel HEMT and its application in C-ERB2 sensing

AlGaN/GaN Double Channel High Electron Mobility Transistors (DCHEMTs) have emerged as promising biosensors, leveraging the unique properties of inter-channel coupling. This paper investigates the influence of mole fraction variations in the AlGaN layer on inter-channel coupling and explores its implications for C-ERB2 biosensing. The study reveals the potential of inter-channel coupling to enhance sensitivity in biosensing applications, particularly for detecting C-ERB2, a crucial protein associated with various cancers. The device architecture, simulation models, electrostatics, and sensitivity analysis are comprehensively examined. The findings underscore the significance of inter-channel coupling in optimizing biosensor performance, offering valuable insights for the advancement of biosensing technologies.

Metal‐Organic Chemical Vapor Deposition Grown Low‐Temperature Aluminum Nitride Gate Dielectric for Gallium Nitride on Si High Electron Mobility Transistor

Gate dielectrics for gallium nitride (GaN) high electron mobility transistor (HEMT) technology have always been challenging because of the nonideal semiconductor–dielectric interface, which leads to electronic traps. Plasma‐enhanced chemical vapor deposition and atomic layer deposition are standard techniques, but they require surface treatment and post‐annealing to control these traps. This article explores metal organic chemical vapor deposition‐grown in situ aluminum nitride (AlN) as a gate dielectric. The interface is expected to be pristine as there is no change in the chamber environment. A thin (10 nm) AlN layer is deposited at a low temperature to minimize strain and prevent the formation of an unwanted conductive channel within the device. The electrical and structural properties of this AlN‐capped HEMT are compared to a standard GaN‐capped HEMT, including temperature‐dependent studies. The results show that the AlN‐capped HEMT retains a higher charge in the channel while having an order of magnitude lower gate leakage than the GaN‐capped sample. Furthermore, the AlN‐capped HEMT performs similarly to the GaN‐capped HEMT in terms of temperature‐dependent leakage, dynamic on‐resistance, and temperature coefficient of resistance.

Effect of hydrogen poisoning on p-gate AlGaN/GaN HEMTs

In this work, we investigate the degradation behavior and mechanism of p-gate AlGaN/GaN high-electron mobility transistors (HEMTs) for the first time under hydrogen (H2) atmosphere. The experimental results reveal significant decrease in drain-to-source current, negative drift in threshold voltage, increase in off-state gate leakage current, and deterioration of subthreshold swing in the p-gate AlGaN/GaN HEMT after H2 treatment. The degradation of the electrical parameters is considered to hydrogen poisoning phenomenon. Through secondary ion mass spectrometry and variable temperature photoluminescence spectroscopy, we observe the increase in hydrogen concentration in the p-GaN layer and the formation of electrically inactive Mg–H complexes after H2 treatment. As results, the effective hole concentration decreases and the trap density of the device increases, which are confirmed by Hall effect measurement and low-frequency noise analysis, respectively. The detrimental effect of hydrogen on p-gate AlGaN/GaN HEMTs can be attributed primarily to the compensation of Mg doping and the generation of defects.

Solid-mechanics analysis and modeling of the alloyed ohmic contact proximity in GaN HEMTs using µRaman spectroscopy

This study explores the impact of alloyed ohmic contact separation on ungated GaN high electron mobility transistors (HEMTs) lattice stress by employing Raman spectroscopy and solid mechanics simulations for comprehensive analysis. Focusing on the substantial stresses exerted by ohmic contacts, our research introduces a novel mechanical calibration procedure. The proposed procedure demonstrates that the stress in the GaN buffer can be precisely modelled using Raman measurements taken from patterns of varying length, which in return reveals the impact of ohmic contacts on stress. We show that this technique shows a good alignment to the Raman measurement results. Moreover, we identify ohmic contact edges as potential sites for defect generation due to the accumulation of substantial elastic energy, a finding supported by experimental observations of crack formations in related studies. Our calibrated mechanical model not only enhances the understanding of stress distributions within GaN HEMTs but also lays the groundwork for future improvements in electro-thermo-mechanical simulations.

The Dynamic Modulation Doping Effect of Gas Molecules on an AlGaN/GaN Heterojunction Surface.

AlGaN/GaN high-electron-mobility transistors (HEMTs) are widely used in high-frequency and high-power applications owing to the high two-dimensional electron gas (2DEG) concentration. However, the microscopic origin of the 2DEG remains unclear. This hinders the development of device fabrication technologies, such as threshold voltage modulation, current collapse suppression, and 2DEG concentration enhancement technologies, as well as AlGaN/GaN sensors with very high sensitivity to polar liquids. To clarify the 2DEG microscopic origin, we studied the effects of gas molecules on AlGaN/GaN surfaces through various experiments and first-principles calculations. The results indicated that the adsorption of gas molecules on the AlGaN/GaN surface is an important phenomenon, clarifying the microscopic origin of the 2DEG. This study elucidates the properties of AlGaN/GaN heterojunctions and promotes the development of new fabrication technologies for AlGaN/GaN devices.

Threshold voltage modulation on a CTL-based monolithically integrated E/D-mode GaN inverters platform with improved voltage transfer performance

This work demonstrates a high-performance monolithically integrated GaN inverters platform, which incorporates enhancement-mode (E-mode) and depletion-mode (D-mode) GaN high-electron-mobility transistors (HEMTs) simultaneously using an Al:HfOx-based charge trapping layer. The developed E-mode HEMT exhibits a positive threshold voltage of 2.6 V, a high ON–OFF current ratio of 1.9 × 108, a current density of 376 mA/mm, and an ON-resistance of 15.31 Ω·mm. Moreover, the direct-coupled field-effect-transistor logic (DCFL) GaN inverter was characterized with and without D-mode device threshold voltage (VTH) modulation, demonstrating improved output swing and switching threshold shift by proposed VTH modulation. The optimized DCFL GaN inverter manifests a switching threshold of 2.34 V, a logic voltage output swing of 4.98 V, and substantial logic-low and logic-high noise margins of 2.16 and 2.49 V, respectively, at a supply voltage of 5 V. These results present a promising approach toward realizing monolithically integrated GaN logic circuits for power IC applications.

Investigation of High-Sensitivity pH Sensor Based on Au-Gated AlGaN/GaN Heterostructure

A high-sensitivity pH sensor based on an AlGaN/GaN high-electron mobility transistor (HEMT) with a 10 nm thick Au-gated sensing membrane was investigated. The Au nanolayer as a sensing membrane was deposited by electron-beam evaporation and patterned onto the GaN cap layer, which provides more surface-active sites and a more robust adsorption capacity for hydrogen ions (H+) and hydroxide ions (OH−) and thus the sensitivity of the sensor can be significantly enhanced. A quasi-reference electrode was used to minimize the sensing system for the measurement of the microliter solution. The measurement and analysis results demonstrate that the fabricated sensor exhibits a high potential sensitivity of 58.59 mV/pH, which is very close to the Nernstian limit. The current sensitivity is as high as 372.37 μA/pH in the pH range from 4.0 to 9.18, under a 3.5 V drain-source voltage and a 0 V reference-source voltage. Comparison experiments show that the current sensitivity of the Au-gated sensor can reach 3.9 times that of the SiO2-gated sensor. Dynamic titration experiments reveal the pH sensor’s ability to promptly respond to immediate pH variations. These findings indicate that this pH sensor can meet most application requirements for advanced medical and chemical analysis.

Low contact resistance and high breakdown voltage of AlGaN/GaN HEMT grown on silicon using both AlN/GaN superlattice and Al0.07Ga0.93N back barrier layer

In this study, the growth of a high-quality AlGaN/GaN high electron mobility transistor (HEMT) heterostructure on silicon (Si) by metal–organic chemical vapor deposition was investigated by utilizing both the AlN/GaN superlattice (SL) and Al0.07Ga0.93N back barrier (BB) techniques. An atomic force microscope and high-resolution x-ray diffractometer confirm a low surface roughness of 0.26–0.34 nm and the formation of a high-quality AlN/GaN SL and GaN channel. The AlGaN/GaN heterostructures exhibit a high electron mobility of up to 1700 cm2 V−1∙s and a high carrier concentration density of (1.02–1.06 × 1013 cm−2) for both heterostructures. The AlGaN/GaN HEMT devices demonstrate a low specific contact resistivity (ρ c) of 2.7 × 10−6 Ω·cm2 and a low contact resistance (RC ) of 0.3 Ω·mm for the heterostructure with a BB layer. Furthermore, the DC characteristics demonstrate that incorporating Al0.07Ga0.93N BB in the heterostructure results in a 19.2% increase in lateral breakdown voltage (with a 10 µm spacing) and a 27.5% increase in vertical breakdown voltage (at 1 mA cm−2) compared to heterostructures without Al0.07Ga0.93N BB within the AlN/GaN SL structure. Moreover, an improvement of 10.6% in the maximum saturation current (I DS) and 15.2% in on-resistance (R ON) has been achieved for the device fabricated on an Al0.07Ga0.93N BB structure. The insertion loss of the buffer layer improves to −1.40 dB mm−1 at 40 GHz. Consequently, the proposed heterostructure investigated in this study demonstrates suitability for electronic device applications.

Structural and interface band alignment properties of transparent p-type α-GaCrO3:Ni/α-Al2O3 heterojunction

Herein, we report epitaxial growth of p-type Ni doped gallium chromium oxide thin film on Al2O3 substrates and studied its band alignment properties with that of the substrate. Thin films are grown using the magnetron-sputtering technique. Synchrotron-based XRD measurements, performed in the coplanar and non-coplanar geometries, confirm high-quality single domain epitaxial growth of p-type α-GaCrO3:Ni. Pendellosung oscillations around the Bragg peak and transmission electron microscopy reveal the high interfacial quality of p-type α-GaCrO3:Ni films with the substrate. Thin film, thickness ∼200 nm, shows around 70% average transmission. The values of valence band and conduction band offsets are determined to be 2.79 ± 0.2 and 0.51 ± 0.2 eV, respectively, which confirm straddling gap band alignment at the heterojunction. This type of alignment creates a threshold barrier for the selective charge carriers and is useful in enhancing the performance of a wide range of devices, including UV photodetectors, metal oxide semiconductor high electron mobility transistors, and light emitters.

Compact Internally Matched High-Power Power Amplifier with a Wide Frequency Band of 0.8–2 GHz

In this paper, a GaN high-electron-mobility transistor (HEMT) compact high-power wide-band power amplifier with an operation frequency from 0.8 GHz to 2 GHz is proposed. In order to realize a compact design, an internally matched method is employed. A wide-band matching strategy with an LC network and a multi-stage wide-band power combiner/divider is introduced in this design to achieve a wide bandwidth. A power combination structure is applied to have high output power. Wire-spiral inductance and film capacitors are employed to construct the compact matching network. The equivalent inductance of the bonding wire is also involved in the matching network. Experimental results show that the PAE (power-added efficiency) during the whole operation’s bandwidth (0.8 GHz to 2.0 GHz) is from 40% to 57%. The output power can reach from 48.3 dBm to 49.8 dBm with a circuit size of 30.8×27.4mm2.

Device and Noise Performances of AlGaN/GaN High Electron Mobility Transistors with Various GaN Channel Layers Grown on AlN Buffer Layer

AlGaN/GaN high electron mobility transistors (HEMTs) with different GaN channel layers grown on AlN buffer layer are fabricated and investigated in order to optimize the device performances and to study the noise properties. To investigate the strain effect of the GaN channel layer grown on the AlN buffer layer, the positive shift of Raman peak is observed as the GaN channel becomes thinner. The threshold voltages (Vth) of the fabricated devices shift to positive direction according to the decreased GaN channel layer due to the decreased 2‐dimensional electron gas (2DEG) and deteriorated crystal quality of GaN channel layer. All devices demonstrated 1/f noise properties and the dominance of the carrier number fluctuations (CNF) noise mechanism. The largest trap density (Nt) value in the narrowest GaN channel device is because of the degraded crystal quality and the enhanced strain effect of the GaN channel layer. However, the lowest noise levels at the drain current (Id) > 10−6 A for the device with the GaN channel thickness of 30 nm grown on AlN buffer layer are observed to be due to the fully depleted GaN channel layer although its poor crystal quality.

Gallium arsenide octave-bandwidth microwave voltage-controlled oscillator having discrete varicap

Modern reconfigurable communication systems demand microwave voltage-controlled oscillators (VCOs) possessing an octave-wide bandwidth. Many advanced applications require also a low phase noise and a low current consumption for such VCOs. To meet an octave-bandwidth specification in combination with a low phase noise and a low current consumption it is desirable to implement a microwave monolithic integrated circuit (MMIC) technology. In-house gallium arsenide (GaAs) MMIC technology is implemented to build VCOs in this work. At the same time, in order to achieve a high-Q wide frequency tuning range, we implemented also a discrete variable capacitance diode (varicap). The discrete varicap is stacked above MMIC oscillator chip. A vertical design structure of the discrete varicap guarantees a high overlap capacitance ratio (K>20) along with reduced affect of the parasitic reactance. A high overlap capacitance ratio is needed for an octave-wide frequency tuning, while reduced affect of the parasitic reactance increases Q-factor of the VCO resonator. Hence, a sequential integration of the discrete varicap over monolithic oscillator chip resolves referred tough challenges in the design of VCO. Integrated VCO is finally packaged as a surface-mount device (SMD). At that SMD ceramic package is sealed with the metal lid. The oscillator circuitry is based on the conventional negative resistance approach with a positive feedback realized by common-source capacitance. An active element of the oscillator is a pseudomorphic high electron-mobility transistor (pHEMT). The gate length of a transistor is 0.15 µm. The width of the gate varies from 240 µm to 360 µm depending on working frequencies of the VCO. The varicap is built on the GaAs epitaxial heterostructure having customized gradient doping profile with abrupt junction. Nonlinear behavioral model of the varicap is extracted from the diode measurements and is further used for VCO simulation. Two types of VCO have been designed, fabricated and tested. First (second) type of VCO provides a tuning range from 5 to 10 GHz (from 10 GHz to 20 GHz), respectively. The measurement results demonstrate an output power of 3.9 dBm; a current consumption of 30 mA at a supply voltage of 5 V; a phase noise of minus 90 dBc/Hz at 100 kHz offset (minus 85 dBc/Hz at 100 kHz offset) for the first (second) type of VCO, respectively.

Degradation analysis of GaN-based high–electron-mobility transistors under different stresses in semi-on state conditions

The large numbers of high-energy carriers that occur in semiconductor devices under semi-on state conditions can cause significant device degradation. The effects of different stresses on the electrical and trapping characteristics of GaN-based high-electron-mobility transistors (HEMTs) are investigated. Test results for GaN HEMTs under semi-on state conditions show that the electrical characteristics of these devices degrade to a certain extent after they are subjected to electrical pulse stress cycles with different drain voltage, frequencies, and duty cycles; a degree of degradation also occurs in the electrical characteristics of the devices when they are subjected to direct current electrical stresses. After electrical stress is applied, the absolute amplitude of the traps in the device increases, thus indicating an increase in the trap density. The results show that voltage is the main driver for device damage, with the current playing an accelerating role through its effects on device temperature or by supplying hot electrons; therefore, the drain voltage has the most significant effect on device degradation, which is mainly due to channel high-energy hot electron injection.

Electronic Properties of Group-III Nitride Semiconductors and Device Structures Probed by THz Optical Hall Effect.

Group-III nitrides have transformed solid-state lighting and are strategically positioned to revolutionize high-power and high-frequency electronics. To drive this development forward, a deep understanding of fundamental material properties, such as charge carrier behavior, is essential and can also unveil new and unforeseen applications. This underscores the necessity for novel characterization tools to study group-III nitride materials and devices. The optical Hall effect (OHE) emerges as a contactless method for exploring the transport and electronic properties of semiconductor materials, simultaneously offering insights into their dielectric function. This non-destructive technique employs spectroscopic ellipsometry at long wavelengths in the presence of a magnetic field and provides quantitative information on the charge carrier density, sign, mobility, and effective mass of individual layers in multilayer structures and bulk materials. In this paper, we explore the use of terahertz (THz) OHE to study the charge carrier properties in group-III nitride heterostructures and bulk material. Examples include graded AlGaN channel high-electron-mobility transistor (HEMT) structures for high-linearity devices, highlighting the different grading profiles and their impact on the two-dimensional electron gas (2DEG) properties. Next, we demonstrate the sensitivity of the THz OHE to distinguish the 2DEG anisotropic mobility parameters in N-polar GaN/AlGaN HEMTs and show that this anisotropy is induced by the step-like surface morphology. Finally, we present the temperature-dependent results on the charge carrier properties of 2DEG and bulk electrons in GaN with a focus on the effective mass parameter and review the effective mass parameters reported in the literature. These studies showcase the capabilities of the THz OHE for advancing the understanding and development of group-III materials and devices.

Study on a p-GaN HEMT with composite passivation and composite barrier layers

A novel structure of p-GaN high-electron-mobility transistor (HEMT) is proposed and studied. It features two composite layers. One is the composite passivation (CP) layer consisting of Si3N4 and high-permittivity (HK) film. The other is a composite barrier (CB) layer consisting of Al x Ga1−x N/AlN/Al0.23Ga0.77N. Due to the coordinated effect of CP and CB, the specific on-resistance (R ON, SP) can be reduced under the premise of ensuring breakdown voltage (BV). Meanwhile, since the HK film in CP introduces a mechanism to automatically compensate the hot electrons trapped by surface states, the current collapse effect could be suppressed. According to the simulation results, in comparison with the conventional p-GaN HEMT, the proposed one using TiO2 as the HK material and using Al-component of 0.35 for Al x Ga1−x N gains a 29.5% reduction in R ON, SP while getting a 9.8% increase in BV, which contributes to a 50.5% decrease in the energy loss during one cycle at 200 kHz. It is also demonstrated by the simulation results that the current collapse in the proposed device is reduced by 28.6%. Thereby, a promising p-GaN HEMT with improved performance and reliability is invented.

Strain‐Engineered Unified SiNx Deposition for Device Passivation and Capacitance Dielectric in GaN Monolithic Microwave Integrated Circuit

Silicon nitride (SiNx) is used for device passivation and capacitance dielectric in GaN monolithic microwave integrated circuits. However, this is a conflicting requirement as passivation requires SiNx to cause tensile strain, and capacitance dielectric primarily demands a high breakdown voltage and large dielectric constant for SiNx, leading to a damaged AlGaN surface during deposition. Two independent SiNx depositions under two different conditions (silicon‐ and nitrogen‐rich) are usually carried out to meet both requirements. Herein, a solution for a unified deposition through interfacial strain analysis on an AlGaN/GaN heterostructure grown on 6H‐SiC imposed by thin film silicon nitride (SiNx), deposited using inductively coupled plasma chemical vapor deposition system is proposed. The strain analysis is done using Raman spectroscopy. The surface morphology of the SiNx is studied using atomic force microscopy. The breakdown characteristics are ascertained from measurements on high electron mobility transistors and metal–insulator–metal capacitors.

Millimeter-Wave GaN High-Power Amplifier MMIC Design Guideline Considering a Source via Effect

A millimeter-wave (mmWave) gallium nitride (GaN) high-power amplifier (HPA) monolithic microwave-integrated circuit (MMIC) was implemented, considering a source via effect. In this paper, we introduce guidelines for designing GaN HPA MMICs, from device sizing to meeting high-power specifications, power matching considering source via effects, schematic design of three-stage amplifier structures, and electromagnetic (EM) simulation. Based on the results of load pull simulation and small-signal maximum stable gain (MSG) simulation, the GaN high-electron-mobility transistor (HEMT) size was selected to be 8 × 70 μm. However, since the source via model provided by the foundry was significantly different from the EM results, it was necessary to readjust the power matching considering this. Additionally, when selecting the source via size, the larger the size, the easier the matching, but since the layout of the peripheral bias circuit is not possible, a compromise was required considering the actual layout. To prevent in-band oscillation, an RC parallel circuit was added to the input matching circuit, and low-frequency oscillation was solved by adding a gate resistor on the PCB module. The proposed PA was fabricated with a commercial 0.1 μm GaN HEMT MMIC process. It exhibited 38.56 to 39.71 dBm output power (Pout), 14.2 to 16.7 dB linear gain, and 14.1% to 18.2% power-added efficiency (PAE) in the upper Ka band. The fabricated GaN power amplifier MMIC shows competitive Pout in the upper Ka band above 33 GHz.

18 A/1020 V p-GaN-gated HEMTs with Isosceles Trapezoidal-Shaped Multi-Finger Structure

In this article, we investigate the effects of gate and drain field plates and isosceles trapezoidal-shaped multi-finger structures on the characteristics of high current p-GaN-gated high-electron-mobility transistors (HEMTs). By optimizing the lengths of gate and drain field plates, the p-GaN-gated HEMTs with 200 μm have a breakdown voltage of 1893 V, a specific on-resistance of 7.0 mΩ-cm2, and a Baliga figure of merit (BFOM) value of 511 MW cm−2. Using the optimized isosceles trapezoidal-shaped multi-finger metallization on the source and drain, the p-GaN-gated HEMT with a 100 mm gate width can reach a current of 2.3 A. Combining all the optimum parameters of field plates and isosceles trapezoidal-shaped multi-finger, the fabricated 600 mm p-GaN-gated HEMT exhibits an output current of 18 A, an on-resistance of 0.7 Ω, and a breakdown voltage of 1020 V. Furthermore, the device also exhibits good thermal stability at high temperatures. These results demonstrate the potential and advantages of p-GaN-gated HEMT for power applications.

N‐polar deep‐recess GaN MISHEMT with enhanced ft·LG by gate dielectric thinning

AbstractThe authors report a novel structure to improve the high‐frequency performance of nitrogen‐polar GaN deep‐recess high electron mobility transistors (HEMTs) wherein a timed plasma etch was used to tailor the profile of the gate dielectric. A favourable trade‐off between gate fringing capacitance and transconductance was established, resulting in an improved current gain cutoff frequency times gate length (ft·LG) figure of merit compared to standard Schottky‐gate and metal‐insulator‐semiconductor (MIS) HEMTs. The etched gate dielectric MISHEMT demonstrated a maximum ft·LG of 15.0 GHz·µm for an LG of 100 nm.

Current-collapse suppression and leakage-current decrease in AlGaN/GaN HEMT by sputter-TaN gate-dielectric layer

In this paper, we explore the electrical characteristics of high-electron-mobility transistors (HEMTs) using a TaN/AlGaN/GaN metal insulating semiconductor (MIS) structure. The high-resistance tantalum nitride (TaN) film prepared by magnetron sputtering as the gate dielectric layer of the device achieved an effective reduction of electronic states at the TaN/AlGaN interface, and reducing the gate leakage current of the MIS HEMT, its performance was enhanced. The HEMT exhibited a low gate leakage current of 2.15 × 10−7 mA/mm and a breakdown voltage of 1180 V. Furthermore, the MIS HEMT displayed exceptional operational stability during dynamic tests, with dynamic resistance remaining only 1.39 times even under 400 V stress.