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We present a systematic study of the impact of CF4 plasma treatment on GaN. It was found that CF4 plasma etches GaN at a slow rate and yields a smooth etched surface. The effect of CF4 plasma on electrical characteristics of GaN metal-semiconductor field-effect-transistor structures shows that the CF4 plasma introduces acceptors into the near surface region of the GaN, which depletes mobile electrons. It was further demonstrated that leakage current of AlGaN/GaN (or GaN) Schottky diodes can be significantly suppressed by proper CF4 plasma treatment. These unique properties of CF4 plasma can be utilized for the advanced processing of GaN transistors.

This letter reports AlGaN/GaN high-electron mobility transistors with capless activation annealing of implanted Si for nonalloyed ohmic contacts. Source and drain areas were implanted with an Si dose of I x 10(16) cm(-2) and were activated at similar to 1260 degrees C in a metal-organic chemical vapor deposition system in ammonia and nitrogen at atmospheric pressure. Nonalloyed ohmic contacts to ion-implanted devices showed a contact resistance of 0.96 Omega (.) mm to the channel. An output power density of 5 W/mm was measured at 4 GHz, with 58% power-added efficiency and a gain of 11.7 dB at a drain bias of 30 V.

In this letter, unpassivated high power deeply recessed GaN-based high electron mobility transistors (HEMTs) are reported. The introduction of a thick graded AlGaN cap layer and a novel fluorine-plasma surface treatment reduced the gate-leakage current and increased breakdown voltage significantly, enabling the application of much higher drain biases. Due to excellent dispersion suppression achieved at an epitaxial level, an output power density of more than 17 W/mm with an associated power added efficiency (PAE) of 50% was measured at 4 GHz and V-DS = 80 V without SiNx passivation. These results demonstrate the great potential of this novel epitaxial approach for passivation-free GaN-based HEMTs for high-power applications.

We report on the fabrication and high-frequency characterization of AlGaN/GaN high-electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). In devices with a gate length of 160 nm, a record power density of 10.5 W/mm with 34% power added efficiency (PAE) has been measured at 40 GHz in MOCVD-grown HEMTs biased at V-DS = 30 V. Under similar bias conditions, more than 8.6 W/mm, with 32% PAE, were obtained on the MBE-grown sample. The dependence of output power, gain, and PAE on gate and drain voltages, and frequency have also been analyzed.

We report AlGaN-GaN high electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) on SiC substrates with excellent microwave power and efficiency performance. The GaN buffers in these samples were doped with carbon to make them insulating. To reduce gate leakage, a thin silicon nitride film was deposited on the AlGaN surface by chemical vapor deposition. At 4 GHz, an output power density of 6.6 W/mm was obtained with 57% power-added efficiency (PAE) and a gain of 10, dB at a drain bias of 35 V. This is the highest PAE reported until now at 4 GHz in AlGaN-GaN HEMTs grown by MBE. At 10 GHz, we measured an output power density of 7.3 W/mm with a PAE of 36% and gain of 7.6 dB at 40-V drain bias.

High-voltage Al0.22Ga0.78N-GaN high-electron mobility transistors have been fabricated using multiple field plates over dielectric passivation layers. The device breakdown voltage was found to increase with the addition of the field plates. with two field plates, the device showed, a breakdown voltage as high as 900 V. This technique is easy to apply, based on the standard planar transistor fabrication, and especially attractive for the power switching applications.

N-p-n Al0.05GaN/GaN heterojunction bipolar transistors with a common emitter operation voltage higher than 330 V have been demonstrated using selectively regrown emitters. Devices were grown by metalorganic chemical vapor deposition on sapphire substrates. The n-type emitter was grown selectively on a 100-nm-thick p-base with an 8 mum n-collector structure using a dielectric mask. The shallow etch down to the collector mitigates damages induced in the dry etch, resulting a low leakage and a high breakdown. The graded AlGaN emitter results in a common emitter current gain of similar to18 at an average collector current density of up to 1 kA/cm(2) at room temperature.

This paper reports on the hot-carrier effects and semi-on-state behavior of nitrogen-polar GaN MIS-HEMTs at cryogenic temperatures (from 300 K down to 100 K). In the semi-on-state $(\text {V}_{\text {G}} \approx -{2}\,\,\text {V})$ , holes are generated by impact ionization in the high field region at the drain-side of the gate-edge. At room temperature, holes overcome the SiN/AlGaN stack and are collected at the gate-terminal, resulting in measurable hole gate-current (~11 nA/mm). Conversely, at cryogenic temperatures, the top SiN/AlGaN stack confines the holes within the GaN channel, thus inducing a negative threshold voltage shift (−0.4 V) and a sharp increase in drain current (0.18 A/mm). This behavior, referred to as “kink,” is readily observable on the $\text {I}_{\text {D}} - \text {V}_{\text {D}}$ characteristics. We demonstrated that the kink is related to impact ionization and follows a non-monotonic behavior maximized in the semi-on-state. Our interpretation is supported by a quantitative analysis based on the latest experimental impact-ionization coefficients available in the literature. [ABSTRACT FROM AUTHOR]

This letter presents an analysis of N-polar metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with a 40 nm MOCVD SiNx passivation and a trench-gate design. A device with a 50 nm gate-length (Lg) demonstrates a 313 GHz power gain cutoff frequency (fmax) at a quiescent drain bias (V $_{{DS,Q}} ) of 26 V. The high fmax\cdot VDS,Q of 8.1 THz \cdot V exhibits great potential of the device in high-frequency power applications. Investigation on small-signal parameters shows that fmax improves with V $_{{DS,Q}}$ due to a reduction of gate-drain capacitance (cgd) and an increase of output resistance (rds). When comparing with the previously reported planar HEMT design, the shorter Lg enabled by the trench-gate design enhances the intrinsic current gain cutoff frequency (f $_{{T,int}}$ ) leading to a higher peak fmax at a higher V $_{{DS,Q}}$ . [ABSTRACT FROM PUBLISHER]

In this letter, a novel device design to achieve both low ON-resistance and enhancement mode operation in a vertical GaN FET is demonstrated. In the traditional trench MOSFET structure, a dielectric is deposited on an n-p-n trenched structure and the channel forms via p-GaN inversion at the dielectric/p-GaN interface. However, this results in a relatively high ON-resistance due to poor electron mobility in the channel. By changing the structure to include a metal-organic chemical vapor deposition (MOCVD)-regrown Un-intentionally Doped (UID)-GaN interlayer followed by an in-situ dielectric (MOCVD Al2O3) cap on the n-p-n trenched structure, a pathway (channel) for enhanced electron mobility is created, resulting in reduced ON-resistance. Preliminary results for this device design demonstrated almost 60% reduction in the ON-resistance and similar breakdown voltage compared with a traditional trench MOSFET structure while maintaining normally off operation with a threshold voltage of 2 V. [ABSTRACT FROM PUBLISHER]

The kink effect has been studied in deep submicron AIGaN/GaN high-electron mobility transistors by measuring their DC, RFI and pulsed performance at cryogenic temperatures. In these devices, the kink effect is mainly due to traps: it appears at T < 260 K and can be removed either by applying UV light or biasing the gate with short pulses. Its appearance is related to the fluorine-based treatment (CF4/O2 plasma) used for etching the passivant, treatment which creates traps below and around the gate. This link between the kink and the etching treatment has also been confirmed in optically defined gate devices with different fluorine plasma exposure times. [ABSTRACT FROM AUTHOR]

We present a high-performance SiN/AIGaN (cap)/GaN (channel)/AIN (barrier)/GaN (buffer) metal-insulator-semiconductor high-electron-mobility transistor grown on the N-face, in which the 2-D electron gas (2DEG) is induced at the top GaN/AIN interface. The use of AIN eliminates alloy disorder scattering to the 2DEG and provides strong back-barrier confinement of the 2DEG under high electric fields for device scaling. Devices with 0.7-μm gate length showed a current-gain cutoff frequency (f[subT]) of 17 GHz and a power-gain cutoff frequency (f[submax]) of 37 GHz. A continuous-wave output power density of 7.1 W/mm was measured at 4 GHz, with 58% power-added efficiency and a large-signal gain of 15.3 dB at a drain bias of 35 V. [ABSTRACT FROM AUTHOR]

This letter studies the effect of access resistance on the high-frequency performance of AlGaN/GaN high-electron. mobility transistors. To systematically reduce the sheet access resistance, the transistors were measured at different temperatures. The increase of mobility at lower temperatures allowed more than four-fold reduction in the sheet access resistances. Both the current- and power-gain cutoff frequencies are observed to increase at low temperatures. Also, the intrinsic effective velocity has been estimated in these devices, as well as the parasitic delays involved in the final performance. Channel charging delay, which was expected to be most sensitive to parasitics, is observed to decrease at low temperatures. However, the drain delay, intrinsic delay, and effective electron velocity remain unaffected by temperature. [ABSTRACT FROM AUTHOR]

A GaN/ultrathin InGaN/GaN heterojunction has been used to provide a back-barrier to the electrons in an AlGaN/GaN high-electron mobility transistor (HEMT). The polarization-induced electric fields in the InGaN layer raise the conduction band in the GaN buffer with respect to the GaN channel, increasing the confinement of the two-dimensional electron gas under high electric field conditions. The enhanced confinement is especially useful in deep-submicrometer devices where an important improvement in the pinchoff and 50% increase in the output resistance have been observed. These devices also showed excellent high-frequency performance, with a current gain cut-off frequency (fT) of 153 GHz and power gain cut-off frequency (fmax) of 198 GHz for a gate length of 100 nm. At a different bias, a record fmax of 230 GHz was obtained. [ABSTRACT FROM AUTHOR]

Transistor operation by common emitter (CE) current modulation is shown for the first time in III-N hot electron transistors (HETs). The emitter and collector barriers ( \phi \mathrm {\mathbf {BE}} and \phi \mathrm {\mathbf {BC}} ) are implemented using Al0.45 Ga0.55N and In0.1Ga0.9N layers as polarization dipoles, respectively. CE modulation is achieved by increasing the E-B barrier height beyond the B-C barrier height by increasing the Al0.45Ga0.55N thickness ( $t$ ). Similar CE performance is seen in the identical HET structures grown on both bulk GaN and sapphire. A maximum $\alpha $ of $\sim 0.3$ is achieved using a GaN base thickness of 10 nm. The InGaN dipole used as the collector barrier is shown to be instrumental in enabling ohmic base contacts, low base sheet resistance, and low collector leakage, simultaneously. [ABSTRACT FROM PUBLISHER]