Huaxing Jiang

Characterization of in situ SiNx thin film grown on AlN/GaN heterostructure by metal- organic chemical vapor deposition

We report an investigation of in situ SiNx gate dielectric grown on AlN/GaN heterostructures by metal-organic chemical vapor deposition. It is revealed that the in situ SiNx is Si-rich, with a N/Si ratio of 1.21 and a relatively high effective dielectric constant of ∼8.3. The 7 nm in situ SiNx film exhibited a large resistivity of >1014 Ω · cm and a breakdown field of 5.7 MV/cm. Furthermore, interface trapping effects in the in situ SiNx/AlN/GaN heterostructures were investigated by frequency dependent conductance analysis.

Low trap states in in situ SiNx/AlN/GaN metal-insulator-semiconductor structures grown by metal-organic chemical vapor deposition

We report the use of SiNx grown in situ by metal-organic chemical vapor deposition as the gate dielectric for AlN/GaN metal-insulator-semiconductor (MIS) structures. Two kinds of trap states with different time constants were identified and characterized. In particular, the SiNx/AlN interface exhibits remarkably low trap state densities in the range of 1011–1012 cm−2eV−1. Transmission electron microscopy and X-ray photoelectron spectroscopy analyses revealed that the in situ SiNx layer can provide excellent passivation without causing chemical degradation to the AlN surface. These results imply the great potential of in situ SiNx as an effective gate dielectric for AlN/GaN MIS devices.

In situ growth of SiNx as gate dielectric and surface passivation for AlN/GaN heterostructures by metalorganic chemical vapor deposition

SiNx grown in situ by metalorganic chemical vapor deposition (MOCVD) has shown great potential as a high-quality gate dielectric and surface passivation for AlN/GaN heterostructure transistors. In this paper, we present a thorough study on how the growth conditions affect the film quality of SiNx and correlate the observed material properties with the electrical characteristics of the heterostructures. Lowering the growth pressure and SiH4/NH3 ratio can improve the SiNx/AlN interface roughness, leading to a reduced interfacial trap state density. The gate leakage current can be suppressed by increasing the resistivity of SiNx, which can be tailored with growth temperature and SiH4/NH3 ratio.

Fabrication and Characterization of Gate-Last Self-Aligned AlN/GaN MISHEMTs With In Situ SiN x Gate Dielectric

This paper reports on the fabrication and characterization of gate-last self-aligned in situ SiN_x/AlN/GaN MISHEMTs. The devices featured in situ grown SiN_x by metal-organic chemical vapor deposition as a gate dielectric and for surface passivation. Selective source/drain regrowth was incorporated to reduce contact resistance. SiNx sidewall spacers and low-κ benzocyclobutene polymer (κ = 2.65) supporting layers were employed under the gate head to minimize the parasitic capacitance for high-frequency operation. The device with a gate length (L_G) of 0.23 μm exhibited a maximum drain current density (I_DS) exceeding 1600 mA/mm with a high ON/OFF ratio (I_ON/I_OFF) of over 107. The current gain cutoff frequency (f_T) and maximum oscillation frequency (f_max) were 55 and 86 GHz, respectively. In addition, the effect of temperature, from room temperature up to 550 K, on the dc and RF performances of the gate-last self-aligned MISHEMTs was studied.

Monolithic integration of enhancement-mode vertical driving transistorson a standard InGaN/GaN light emitting diode structure

In this letter, monolithic integration of InGaN/GaN light emitting diodes (LEDs) with vertical metal-oxide-semiconductor field effect transistor (VMOSFET) drivers have been proposed and demonstrated. The VMOSFET was achieved by simply regrowing a p- and n-GaN bilayer on top of a standard LED structure. After fabrication, the VMOSFET is connected with the LED through the conductive n-GaN layer, with no need of extra metal interconnections. The junction-based VMOSFET is inherently an enhancement-mode (E-mode) device with a threshold voltage of 1.6 V. By controlling the gate bias of the VMOSFET, the light intensity emitted from the integrated VMOSFET-LED device could be well modulated, which shows great potential for various applications, including solid-state lighting, micro-displays, and visible light communications.

Off-state leakage current reduction in AlGaN/GaN high electron mobility transistors by combining surface treatment and post-gate annealing

We report on the reduction of off-state leakage current in AlGaN/GaN high electron mobility transistors (HEMTs) by a two-step process combining pre-gate surface treatment and post-gate annealing (PGA), which suppressed the two leakage paths, namely, lateral surface leakage and vertical tunneling leakage, separately. The lateral surface leakage current, which was mainly induced by the high-density trap states generated during the device isolation etching process, was significantly reduced by a low power O2-plasma and HCl surface treatment process. The PGA process reduced the vertical tunneling leakage current by improving the Schottky contact quality of the transistor gate. Consequently, the device off-state leakage current was decreased by about 7 orders of magnitude and no degradation was introduced to the on-state performance, leading to a high on/off current ratio of 1010 and steep subthreshold slope (SS) of 62 mV/dec. The origin and leakage suppression mechanisms are also investigated and discussed in detail.

Ultralow reverse leakage current in AlGaN/GaN lateral Schottky barrier diodes grown on bulk GaN substrate

We report on a study of AlGaN/GaN heterostructure lateral Schottky barrier diodes (L-SBDs) grown on a bulk GaN substrate. The L-SBDs exhibited an ultralow reverse leakage current below 10−6 A/cm2 without employing any extra treatments, which was over 4 orders of magnitude lower than that of a reference device on a sapphire substrate. The superior performance was attributed to the high crystalline quality of the heterostructure achieved by homoepitaxy. The comparison also revealed that the absence of high-density trap states in the homoepitaxial L-SBD grown on the bulk GaN substrate played a key role in achieving a low reverse leakage current.

Fabrication and improved performance of AlGaN/GaN HEMTs with regrown ohmic contacts and passivation-first process

This work reports the fabrication of AlGaN/GaN HEMTs with regrown ohmic contacts using either a passivation-last or a passivation-first process, where the order of surface passivation and gate metallization processes is different. An improved performance is demonstrated using the passivation-first process, achieving a maximum current/power gain cutoff frequency (fT/fmax) around 60/127 GHz with an 80-nm gate length. The ohmic contacts were regrown with highly doped n-GaN, resulting in a contact resistance of ~0.2 Ω·mm. The RF performance can be further enhanced by reducing the extrinsic gate capacitance and short channel effects.

Monolithic integration of III-nitride voltage-controlled light emitters with dual-wavelength photodiodes by selective-area epitaxy

We report for the first time on-chip integration of III-nitride voltage-controlled light emitters with visible and ultraviolet (UV) photodiodes (PDs). InGaN/GaN and AlGaN/GaN heterostructures were grown in specific regions by selective-area epitaxy, allowing monolithic integration of versatile devices including visible light emitting diodes (LEDs), visible-light PDs, AlGaN/GaN high electron mobility transistors (HEMTs), and UV-light Schottky barrier (SB) PDs. A serial connection between the LED and HEMT through the epitaxial layers enables a three-terminal voltage-controlled light emitter (HEMT-LED), efficiently converting voltage-controlled signals into visible-light signals that can be coupled into an adjacent visible-light PD generating electrical signals. While the integrated blue HEMT-LED and PD transmits signals carried by visible light, the visible-blind SB-PD on a chip receives external UV light control signals with negligible interference from the on-chip visible-light source. This integration scheme can be extended to open an avenue for developing a variety of applications, such as smart lighting, on-chip optical interconnect, optical wireless communication, and opto-isolators.

High Performance Monolithically Integrated GaN Driving VMOSFET on LED

This letter reports the monolithic integration of GaN-based driving vertical metal–oxide–semiconductor field-effect transistor (VMOSFET) on light-emitting diode (LED) with high output current density and bright-ness. By selectively regrowing a simple p- and n-GaN bilayer on top of an LED wafer, the VMOSFET was realized with an n/p/n structure and intrinsically connected with the LED through the bottom conductive n-GaN layer. During the fabrication, a tetramethylammonium hydride wet etch technique was employed to smoothen the sidewall channel surface of the VMOSFET and to enhance its channel electron mobility, consequently achieving a high output current density exceeding 1.4 kA/cm2. The integrated VMOSFET-LED exhibited a high light output power of 8.5 mW or 9.4 W/cm2 with a modulated injection current of 10 mA through the VMOSFET, showing a great potential of such integration scheme for a variety of smart-lighting applications.