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To improve the stability and sensitivity of pH sensors based on AlGaN/GaN high electron mobility transistors (HEMTs), we proposed a modified sensing structure by integrating a reference HEMT device. This structural pH sensor exhibits a typical Nernstian behavior with a sensitivity of 54.38 mV/pH, which is higher than the value of 49.43mV/pH derived from the AlGaN/GaN HEMT-based sensor without integrating the reference HEMTs device. Furthermore, the stability of the new structural sensor is enhanced by approximately 19.2% in comparison with that of its traditional counterpart. The improved performances are analyzed using an electrical double-layer model together with an equivalent circuit model, and we find that the new sensor structure has a larger capacitor and exhibits a better rectification effect, hence decreasing the electrical noise and enhancing the stability of the testing signal. Meanwhile, the new sensor structure displays a smaller equivalent resistance and results in a larger available output current, hence exhibiting a higher sensitivity. [ABSTRACT FROM AUTHOR]

We have successfully grown AlGaN/GaN high electron mobility transistor (HEMT) structure on the high-quality undoped thick AlN buffer layer with large band offset to replace the conventional high-resistivity GaN buffer layer. The AlGaN/GaN HEMT fabricated on this AlN buffer layer exhibits low OFF-state leakage current with high ION/IOFF of ~106 due to enhanced confinement of the electrons in the 2-D electron gas (2-DEG) channel. The undoped AlN buffer layer is responsible for suppressing the trapping effects to greatly reduce the current dispersion in pulsed ID – VD characteristics, which is hardly avoided in conventional deep acceptor-doped GaN buffer layer. The device also demonstrates high breakdown voltage of 2154 V with very high figure of merit (FOM) of ~1.8 GV2-1 cm−2, one of the highest ever reported, suggesting that the AlGaN/GaN-based Hemts WITH AlN buffer layer are promising for high-performance RF and power applications. [ABSTRACT FROM AUTHOR]

AlGaN/GaN FinMISHFETs with m-plane sidewall surface channel and various fin widths ($\text{W}_{\textsf {fin}}$) were fabricated and characterized. The investigated devices have much higher current drivability due to the uniform and smooth surface of m-plane than those with the a-plane sidewall surface channel. The AlGaN/GaN FinMISHFETs with $\text{W}_{\textsf {fin}}$ smaller than 36 nm exhibit normally-off operation, high Ion/Ioff ratio of 108, and remarkable subthreshold swing (SS) smaller than 40 mV/decade in the wide current range of at least three orders. Combined with a positive threshold voltage, SS values smaller than 60 mV/decade in a wide current rage of at least three orders are among the world’s best subthreshold characteristics. Furthermore, when $\text{W}_{\textsf {fin}}$ is 31 nm, the off-state drain current is as low as 10–12 A. We show that this sharp switch is due to the simultaneous turn-on of the 2-D electron gas and the m-plane sidewall surface channel. The simulation results are carried out to show the gate-induced variation of the electron concentration within the fin structure, and the assumption of considering gate width as a function of gate bias is also developed to explain the reason for deep sub-60mV/decade in the demonstrated devices. [ABSTRACT FROM AUTHOR]

Two different lateral GaN-based nanowire gate-all-around transistors with and without 2-D electron gas (2-DEG) channel were fabricated using top-down approach, and their noise characteristics were investigated. The nanowire transistor with 2-DEG channel had a relatively larger channel cross section, which consists of regrown AlGaN/GaN plateau on the trapezoidal GaN layer, and exhibited negative threshold voltages (${V} _{\textsf {th}}$). The transistor without 2-DEG channel consisted only GaN layer with triangular-shaped smaller channel cross section and exhibited a positive ${V} _{\textsf {th}}$. Both nanowire transistors clearly demonstrated typical $1/{f}$ noise characteristics, but the AlGaN/GaN nanowire transistor with 2-DEG channel showed larger noise magnitude. The noise characteristics of both devices are well explained by the carrier number fluctuation with correlated mobility fluctuation model. Using this model, the interface trap densities and the remote Coulomb scattering parameters were extracted, revealing a worse interface quality for the AlGaN/GaN device on the one hand, but stronger scattering for the narrow GaN transistor on the other hand. [ABSTRACT FROM AUTHOR]

We have proposed a method of surface passivation with high-temperature atomic layer-deposited (ALD) Al2O3 layer on the fully recessed anode AlGaN/GaN-based Schottky-barrier diode (SBD) and systematically analyzed the cause of the lateral and the vertical leakage component in the SBD. The forward turn-on voltage of the recessed SBD decreased to 0.38 V from the value of 0.8 V of the nonrecessed SBD due to the lowered barrier height. Application of the ALD Al2O3 surface passivation layer to the recessed SBD, which was deposited at higher temperature (550 °C), significantly improved the performances of the proposed SBD such as high on-current of 12 A at 1.5 V and increased breakdown voltage of 780 V with greatly decreased reverse leakage current (at least 3 orders lower in magnitude), compared to the corresponding on-current of 6 A at 1.5 V and breakdown voltage of 510 V of the reference SBD. [ABSTRACT FROM AUTHOR]

In0.08Al0.92N/GaN fin-type high-electron mobility transistors (fin-HEMTs) with different gate-to-drain lengths (${L} _{\text {gd}}$) are fabricated and characterized by dc and low-frequency noise (LFN) measurements. The fabricated device with the largest ${L} _{\text {gd}}$ exhibits the degradation of the maximum drain current and transconductance with a positive shift of the threshold voltage. LFN measurements of the In0.08Al0.92N/GaN fin-HEMTs reveal clear 1/ ${f}$ behavior of the noise spectra, and the minimum value is observed in the device at ${L} _{\text {gd}} = {20}\,\,\mu \text{m}$. The devices with smaller ${L} _{\text {gd}}$ follow a carrier number fluctuation noise model owing to electron trapping/detrapping into the In0.08Al0.92N barrier layer from the 2-D electron gas (2DEG) channel. In contrast, the device with the largest ${L} _{\text {gd}}$ shows correlated mobility fluctuations due to the large 2DEG mobility fluctuations in the large access area. [ABSTRACT FROM AUTHOR]

Three types of bufferless GaN‐based FETs are fabricated on GaN‐on‐insulator (GaNOI) wafer: i) recessed‐gate AlGaN/GaN MOSFET with threshold voltage (Vth) of 4 V; ii) AlGaN/GaN nanowire gate‐all‐around (GAA) MOSFET with Vth of −2 V; and iii) GaN nanowire GAA‐MOSFET with Vth of 3.5 V. These devices are characterized and compared. The nanowire GAA‐MOSFET can be easily fabricated by simply removing buried oxide layer of GaNOI wafer. The recessed‐gate AlGaN/GaN MOSFET presents poor on‐current characteristic. On the other hand, the nanowire GAA‐MOSFETs show improved on‐current, reduced subthreshold swing (SS), good pinch‐off characteristics, and negligible current collapse phenomenon. [ABSTRACT FROM AUTHOR]

The radiation hardness of AlGaN/GaN high-electron-mobility transistors (HEMTs) is found to improve with increasing GaN channel thickness. Epitaxial MgCaO shows promise as a radiation-tolerant gate dielectric, with only small shifts in operating parameters of metal–oxide–semiconductor HEMTs observed at doses up to 1 Mrad(SiO2). Bias-induced electron trapping and radiation-induced-hole trapping can occur in the MgCaO, depending on the applied bias during stress and/or irradiation. AC transconductance measurements are used to help understand charge trapping in these devices. [ABSTRACT FROM PUBLISHER]

DC and 1/ f noise performances of the AlGaN/GaN fin-shaped field-effect transistor (FinFET) with fin width of 50 nm were analyzed. The FinFET exhibited approximately six times larger normalized drain current and transconductance, compared to those of the AlGaN/GaN planar metal-insulator-semiconductor heterostructure field-effect-transistor (MISHFET) fabricated on the same wafer. It was also observed that the FinFET exhibited improved noise performance with lower noise magnitude of 8.5 \times 10^-15~\textA^2 /Hz when compared to the value of 8.7 \times 10^-14\textA^2 /Hz for the planar MISHFET. An intensive analysis indicated that both devices follow the carrier number fluctuation model, but the FinFET suffers much less charge trapping effect compared to the MISHFET (two orders lower charge trapping was observed). Moreover, the FinFET did not exhibit the Lorentz-like components, which explains that the depleted fin structure effectively prevents the carriers from being trapped into the underlying thick GaN buffer layer. On the other hand, the slope of the noise is 2 irrespective of drain voltage and apparently showed the Lorentz-like components, especially at high drain voltage in MISHFET device. This explains that the carrier trapping/detrapping between the 2-D electron gas channel and the GaN buffer layer is significant in MISHFET. [ABSTRACT FROM PUBLISHER]

We have grown an AlIn(Ga)N/GaN heterostructure which is a promising alternative to the AlGaN/GaN heterostructure. The mobility and the carrier concentration of the two-dimensional electron gas (2DEG) formed at the AlIn(Ga)N/GaN heterointerface were strongly dependent on both the growth temperature and pressure. Two optimized growth conditions for the heterostructure with a low sheet resistance less than 300 Ω/sq were obtained by varying the growth temperature and pressure from 750 to 1070 °C and 100 to 300 torr, respectively: (i) AlIn(Ga)N/GaN heterostructure with high 2DEG carrier concentration of 2.4 × 1013 cm−2 with mobility of 1010 cm2 V−1s−1 (grown at 900 °C and 100 torr); (ii) AlIn(Ga)N/GaN heterostructure with high 2DEG mobility of 1910 cm2 V−1s−1 with carrier concentration of 1.13 × 1013 cm−2 (grown at 900 °C and 300 torr). Both structures would be useful for different purpose of device application. [ABSTRACT FROM AUTHOR]

We propose graphene as a Schottky metal electrode material for an AlGaN/GaN heterostructure layer-based metal–insulator–semiconductor–insulator–metal (MISIM)-type UV sensor. The fabricated AlGaN/GaN MISIM UV sensor showed two distinguishable sensing windows, namely, a UV-A and a UV-B region with sharp cutoff characteristic. The graphene-electrode UV sensor had a lower dark current density and better UV-to-visible rejection ratio than that of a Ni-electrode UV sensor. [ABSTRACT FROM PUBLISHER]

The low-frequency noise (LFN) characteristics of AlGaN/GaN FinFETs with omega-gate and combined two-dimensional electron gas (2DEG) and MOS conduction are investigated. It is found that LFN is dominated by carrier number fluctuations whatever the width of the fin. Charge trapping in narrow devices is one order of magnitude lower than in wide fin device. In narrow devices, the sidewall conduction prevails and the noise mainly stems from the carrier trapping in the sidewall Al2O3 gate dielectric. Instead, in wide fin devices, the top gate AlGaN/GaN HEMT structure dominates and the LFN is mostly governed by the carrier trapping in the GaN layer close to 2DEG channel. [ABSTRACT FROM PUBLISHER]

Two types of fin-shaped field-effect transistors (FinFETs), one with AlGaN/GaN heterojunction and the other with heavily doped heterojunction-free GaN layer operating in junctionless mode, have been fabricated and characterized. The threshold voltages of both devices shift toward positive direction from large negative value as the fin width decreases. Both devices exhibit high ON-state performance. The heterojunction-free GaN FinFETs show superior OFF-state performance because the current flows through the volume of the GaN channel layer, which can be fully depleted. The proposed GaN nanochannel FinFETs are very promising candidates not only for high performance, but also for high power applications. [ABSTRACT FROM AUTHOR]

We have demonstrated the lateral multifinger-type Schottky barrier diode (SBD) with bonding pad over active structure fabricated on the AlGaN/GaN heterostructure prepared on sapphire substrate. The fabricated GaN-SBD with size of 9 mm^2 exhibited excellent device characteristics such as forward current of 4.5 A at 1.5 V, leakage current of 6 \muA at 600 V, and high breakdown voltage of 747 V. The temperature variations of GaN-SBD for the reverse recovery characteristics are negligible and the value of reverse-recovery charge (Q)rr of GaN-SBD is one twentieth of Si-diode at 175^\circC. [ABSTRACT FROM AUTHOR]

High-quality \SiO2 is deposited on GaN by radio frequency (RF) magnetron sputtering at room temperature. Adding oxygen to the sputtering gas effectively compensated for the oxygen vacancies and resulted in a breakdown field of 9.6 MV/cm for the sputtered- \SiO2 film on GaN. The reduced electron concentration and mobility of the 2-D electron gas due to the sputtering-induced surface damage were effectively removed by an optimized postannealing treatment. A sputtered-\SiO2\/ \AlGaN/GaN metal–oxide–semiconductor high-electron-mobility transistor (HEMT) (MOSHEMT) was demonstrated with the lowest thermal energy requirement among all the dielectric deposition techniques, which exhibited a saturation drain current of 621 mA/mm and a breakdown voltage of 205 V at the gate–drain distance of 2 \mu\m. More than four orders of magnitude lower gate leakage current than conventional HEMT of the same dimension was achieved. These characteristics demonstrate excellent potential of using RF magnetron sputtering to produce gate insulators for GaN-based MOSHEMTs. [ABSTRACT FROM PUBLISHER]

We demonstrate high-performance InGaN–based light-emitting diodes (LEDs) with tunneling-junction-induced 2-D electron gas (2-DEG) at n-AlGaN/GaN heterostructure, inserted in the middle of the \p^++-GaN contact layer of a conventional LED structure. The LED with a 2-DEG layer exhibits about 20% enhancement in output power, as compared with that of the conventional LED at 350 mA, which is believed to be due to enhanced hole-injection efficiency and better lateral current spreading by the presence of 2-DEG at the AlGaN/GaN heterostructure. [ABSTRACT FROM PUBLISHER]

AlGaN/GaN-based fin-shaped field-effect transistors with very steep side-wall have been fabricated by utilizing electron-beam lithography and subsequent anisotropic side-wall wet etch in tetramethyl ammonium hydroxide solution. The investigate device demonstrated extremely broad transconductance ( gm) ranging from \sim 0 to \sim 8 V at VD = 10 V, which is essential for high linearity device performance. Pulse measurement showed that the device exhibits negligible gate lag, but still suffers from drain lag. The device with L\mathrm {GD} of 17~\mu \textm exhibited excellent OFF-state characteristic with subthreshold swing of \sim 58 mV/decade, low OFF-state leakage current of \sim 10^{-12} A, and breakdown voltage of \sim 400$ V at V_{G}=- 9 V. [ABSTRACT FROM PUBLISHER]

Heavily doped GaN nanochannel fin-shaped field-effect transistors (FinFETs) without heterojunction have been fabricated and characterized for the first time. Simplified pragmatical technology for GaN epitaxial growth and FinFET process was used to achieve nanodevices with a channel width from 40 to 100 nm and a gate length of 1 \mu\m. They exhibit excellent on-state performance, such as maximum drain current of 670 mA/mm and maximum transconductance of 168 mS/mm. Record off-state performance was measured: extremely low leakage current of \sim\!\!\10^-11\ \mA and source–drain breakdown voltage of \sim280 V. The subthreshold slope of 68 mV/decade is close to the theoretical limit (60 mV/decade, so far achieved only in SOI MOSFETs) and leads to very high Ion/Ioff ratio of \10^8 - \10^9. The proposed heterojunction-free nanochannel GaN FinFET is a very promising candidate not only for high-performance and high-speed integrated circuits but also for high-power applications. [ABSTRACT FROM PUBLISHER]

A single-nanoribbon \Al2\O3\/GaN metal–insulator–semiconductor field-effect transistor (MISFET) has been fabricated. The fabricated device exhibits normally off operation with a threshold voltage of 2.1 V. The device also exhibits superior performances such as a maximum drain current density of 1.51 A/mm, a maximum transconductance of 580 mS/mm, and a field-effect mobility of 293 \cm^2\cdot \V^-1\cdot \s^-1. This is because the electron concentration in the GaN channels can be increased due to the enhanced gate controllability, which, thus, effectively screens the field lines from the interface traps or the defects near the channels to improve the electron mobility in the channel. The nanoribbon \Al2\O3\/GaN MISFET is a very promising candidate for high-performance normally off GaN FETs. [ABSTRACT FROM PUBLISHER]

A high-performance normally off GaN-based MOSFET was fabricated. The buffer layer of the MOSFET was grown by varying the growth temperature to control the size of nucleation sites which results in an extremely high buffer resistance (> \10^12\ \Omega/\sq). The fabricated small-area MOSFET exhibited excellent normally off device characteristics, such as a threshold voltage of 2 V, maximum drain current of 253 mA/mm, on–off current ratio of \5.5 \times \10^7, destructive breakdown voltage of 830 V, and leakage current of 0.7 \mu\A/mm at a VDS of 600 V. The corresponding values of the large-area MOSFET with a multifinger pattern were 0.6 V, 6 A, \1.3 \times \10^7, 670 V, and 50 \mu\A (0.28 \mu \A/mm). [ABSTRACT FROM AUTHOR]

Multifinger lateral-type AlGaN/GaN Schottky barrier diode (SBD) with bonding pad over active (BPOA) structure was fabricated and exhibited excellent device performances, such as forward current of 6 A at 1.5 V, leakage current of 16 \mu\A at -600 V, reverse-recovery time (Trr) of 18 ns, breakdown voltage of 840 V, and low specific on-resistance (Ron) of 9 \m\Omega \cdot \cm^2, resulting in the figure-of-merit (VBR^2/Ron) as high as 78 \MW/cm^2, which demonstrates that the AlGaN/GaN SBD with BPOA structure has a great potential application to the high-power electronics. [ABSTRACT FROM AUTHOR]

AlGaN/GaN Schottky barrier diodes (SBDs) with and without the in situ silicon carbon nitride (SiCN) cap layer were investigated. The fabricated SBD with the SiCN cap layer exhibited improved electrical characteristics, such as the forward turn-on voltage of about 0.7 V, the forward current of 4.1 A at 1.5 V, and the reverse breakdown voltage of 630 V, as compared with the corresponding values of 0.8 V, 3.8 A, and 580 V for the reference SBD without the SiCN cap layer. This improvement in the device performance of the SiCN-SBD is because the in situ SiCN cap layer not only lowers the barrier height but also effectively passivates the surface of the device with better surface morphology. [ABSTRACT FROM AUTHOR]

Normally off \Al2\O3\/\GaN MOSFETs are fabricated by utilizing a simple tetramethylammonium hydroxide (TMAH) treatment as a postgate-recess process. The TMAH-treated device with a gate length of 2.5 \mu\m exhibited excellent device performances, such as a threshold voltage of 3.5 V, a maximum drain current of 336 mA/mm, and a breakdown voltage of 725 V, along with extremely small gate leakage current of about \10^-9\ \A/mm at Vgs = \15\ \V, which is approximately six orders lower in magnitude compared to that of the device without TMAH treatment. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated using a gate recess process and a surface treatment with tetramethylammonium hydroxide (TMAH) prior to gate metal deposition. Electrical characterizations show improved extrinsic transconductance and saturation current, as well as more uniform off-state behavior with reduced off-current by a factor of 3.5 and gate leakage current by a factor of 4.2 in the devices with TMAH treatment. The analyses based on atomic force microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy show that the TMAH treatment effectively reduces the roughness of the recess-etched AlGaN surface and removes the native oxide layer on the AlGaN surface, suggesting a simple and viable route towards the fabrication of gate-recessed HEMTs based on AlGaN/GaN heterostructure with improved controllability and uniformity. [ABSTRACT FROM AUTHOR]

Novel AlGaN/GaN omega-shaped nanochannel FinFETs with fin width of 50 nm were successfully fabricated using TMAH lateral wet etching with ALD HfO 2 sidewall spacer. This fin structure apparently exhibited the current spreading in the access region, which results in the suppression of the drain lag effect at high drain voltage and sharp switching performance with subthreshold swing of 57–65 mV/decade. Excellent on- and off-state state performances for the fabricated device prove that the omega-shaped gate structure not only exhibits excellent gate controllability, but also decouples the active nano-channel region from the underlying thick buffer. The proposed device is very promising candidate for high-performance device applications. [ABSTRACT FROM AUTHOR]

Abstract: AlGaN/GaN heterostructure was grown on semi-insulating 6H–SiC substrate. The effect of the thickness of the initial AlN buffer layer on the crystalline quality and the stress of the grown GaN layer were investigated. The semi-insulating characteristic of the undoped GaN layer, which is very important for obtaining low device leakage current, was analyzed by photoluminescence measurement. Modulation doping of Si during the growth of AlGaN barrier layer was also introduced to increase the concentration of the two-dimensional electron gas density and hence to improve the device performance. The fabricated AlGaN/GaN heterostructure field effect transistor with gate length of 0.2μm and SiO2 passiviation layer exhibited good small-signal characteristics such as current gain cut-off frequency of 47GHz and the maximum oscillation frequency of 121GHz. [Copyright &y& Elsevier]

Highlights: [•] Normally-off dual gate AlGaN/GaN MISFET with a selective area-recessed floating gate was proposed. [•] The proposed device showed the enhanced off-state blocking voltage, corresponding to the simulation data. [•] The device showed the negligible degradation of the on-state performance. [•] The device showed a low subthreshold slope and a low gate leakage current. [Copyright &y& Elsevier]

Highlights: [•] The pulse measurements for the AlGaN/GaN FinFETs with normally-off operation. [•] The proposed FinFET exhibits the reduced gate/drain lag. [•] The device also shows high on-state performances for high current operation. [ABSTRACT FROM AUTHOR]