Modern Power Devices

In recent years, ultrawide bandgap semiconductor materials represented by aluminum nitride (AlN) have attracted worldwide attention due to their excellent high-frequency power characteristics, stable high-temperature performance, low energy loss, and good ultraviolet (UV) transmittance. They have great application prospects in the fields of high-efficiency optoelectronic devices, high-power and high-frequency electronic devices, ultra-high voltage power electronic devices, deep UV warning and guidance, and deep UV-LED disinfection. The physical vapor transport (PVT) method has the advantages of a simple growth process, fast growth rate, and high crystal integrity, and has gradually become one of the most effective methods for growing bulk AlN crystals. This review systematically summarizes the latest research progress in AlN crystals grown by the PVT method in recent years, and introduces their applications in deep UV-LEDs, UV lasers and Schottky barrier diodes (SBDs). Finally, the challenges and application prospects of AlN crystals are discussed. As an important new type of direct bandgap ultrawide bandgap semiconductor material, AlN crystals have shown extremely important strategic application value. The output power of deep UV-LED devices meets practical requirements, and high-power electronic power devices are still in the verification stage. From the perspective of material superiority, they have considerable development potential.

Ultrawide-bandgap semiconductor AlN crystals: growth and applications

Vertical gallium nitride (GaN) power devices are enabling next-generation power electronic devices and systems with higher energy efficiency, higher power density, faster switching, and smaller form factor. In Part I of this review, we have reviewed the basic design principles and physics of building blocks of vertical GaN power devices, i.e., Schottky barrier diodes and p-n diodes. Key topics such as materials engineering, device engineering, avalanche breakdown, and leakage mechanisms are discussed. In Part II of this review, several more advanced power rectifiers are discussed, including junction barrier Schottky (JBS) rectifiers, merged p-n/Schottky (MPS) rectifiers, and trench metal–insulator–semiconductor barrier Schottky (TMBS) rectifiers. Normally- OFF GaN power transistors have been realized in various advanced device structures, including current aperture vertical electron transistors (CAVETs), junction field-effect transistors (JFETs), metal–oxide–semiconductor field-effect transistors (MOSFETs), and fin field-effect transistors (FinFETs). A detailed analysis on their performance metrics is provided, with special emphasis on the impacts of key fabrication processes such as etching, ion implantation, and surface treatment. Lastly, exciting progress has been made on selective area doping and regrowth, a critical process for the fabrication of vertical GaN power devices. Various materials characterization techniques and surface treatments have proven to be beneficial in aiding this rapid development. This timely and comprehensive review summarizes the current progress, understanding, and challenges in vertical GaN power devices, which can serve as not only a gateway for those interested in the field but also a critical reference for researchers in the wide bandgap semiconductor and power electronics community.

Vertical GaN Power Devices: Device Principles and Fabrication Technologies—Part II

Vertical heterojunction NiO/β n-Ga2O/n+ Ga2O3 rectifiers employing NiO layer extension beyond the rectifying contact for edge termination exhibit breakdown voltages (VB) up to 4.7 kV with a power figure-of-merits, VB2/RON of 2 GW·cm−2, where RON is the on-state resistance (11.3 mΩ cm2). Conventional rectifiers fabricated on the same wafers without NiO showed VB values of 840 V and a power figure-of-merit of 0.11 GW cm−2. Optimization of the design of the two-layer NiO doping and thickness and also the extension beyond the rectifying contact by TCAD showed that the peak electric field at the edge of the rectifying contact could be significantly reduced. The leakage current density before breakdown was 144 mA/cm2, the forward current density was 0.8 kA/cm2 at 12 V, and the turn-on voltage was in the range of 2.2–2.4 V compared to 0.8 V without NiO. Transmission electron microscopy showed sharp interfaces between NiO and epitaxial Ga2O3 and a small amount of disorder from the sputtering process.

Demonstration of 4.7 kV breakdown voltage in NiO/β-Ga2O3 vertical rectifiers

The optimization of mesa etch for a quasi-vertical gallium nitride (GaN) Schottky barrier diode (SBD) by inductively coupled plasma (ICP) etching was comprehensively investigated in this work, including selection of the etching mask, ICP power, radio frequency (RF) power, ratio of mixed gas, flow rate, and chamber pressure, etc. In particular, the microtrench at the bottom corner of the mesa sidewall was eliminated by a combination of ICP dry etching and tetramethylammonium hydroxide (TMAH) wet treatment. Finally, a highly anisotropic profile of the mesa sidewall was realized by using the optimized etch recipe, and a quasi-vertical GaN SBD was demonstrated, achieving a low reverse current density of 10−8 A/cm2 at −10 V.

https://www.mdpi.com/2079-4991/10/4/657/pdf

Optimization of Mesa Etch for a Quasi-Vertical GaN Schottky Barrier Diode (SBD) by Inductively Coupled Plasma (ICP) and Device Characteristics

Gallium nitride (GaN)-based vertical power Schottky barrier diode (SBD) has demonstrated outstanding features in high-frequency and high-power applications. This paper reviews recent progress on GaN-based vertical power SBDs, including the following sections. First, the benchmark for GaN vertical SBDs with different substrates (Si, sapphire, and GaN) are presented. Then, the latest progress in the edge terminal techniques are discussed. Finally, a typical fabrication flow of vertical GaN SBDs is also illustrated briefly.

/pdf/review-of-the-recent-progress-on-gan-based-vertical-power-26nivt99go.pdf

Review of the Recent Progress on GaN-Based Vertical Power Schottky Barrier Diodes (SBDs)

In this brief, a high-performance quasi-vertical GaN Schottky barrier diode (SBD) on sapphire substrate with post-mesa nitridation process is reported, featuring a low damaged sidewall with extremely low leakage current. The fabricated SBD with a drift layer of ${1}~\mu \text{m}$ has achieved a very high ON/ OFF current ratio ( ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}{)}$ of $10^{{12}}$ with a low leakage current of $\sim 10^{-{9}}$ A/cm2@-10 V, high forward current density of 5.2 kA/cm2 at 3 V in dc, a low differential specific ON-resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}}{)}$ of 0.3 $\text{m}\Omega \cdot $ cm2, and ideality factor of 1.04. In addition, a transmission-line-pulse (TLP) ${I}$ – ${V}$ test was carried out and 53 kA/cm2 at 30 V in pulsed measurement was obtained without device failure, exhibiting a great potential for high power applications.

/pdf/low-leakage-and-high-forward-current-density-quasi-vertical-2qisz92f21.pdf

Low Leakage and High Forward Current Density Quasi-Vertical GaN Schottky Barrier Diode With Post-Mesa Nitridation

In this study, novel AlGaN/GaN Schottky barrier diodes (SBDs) are fabricated with thin-barrier (5 nm) AlGaN/GaN heterostructures, featuring recess-free technology, eliminating bombardment plasma damage, and leading to high device uniformity. Combining a gated-edge termination (GET) design and assistance with high-quality low-pressure chemical vapor deposition SiN x , a low reverse leakage current (∼10 nA mm−1@−600 V) and a high reverse breakdown voltage of over 1.78 kV (@1 μA mm−1) are obtained. At the same time, we achieve a low turn-on voltage of 0.57 V and a low differential on-state resistance R on,sp of 1.49 mΩ cm2 for thin-barrier GET SBDs with an anode-to-cathode distance (L AC) of 15 µm, yielding a Baliga’s figure of merit of 2120 MW cm−2. Moreover, this proposed diode process flow is compatible with AlGaN/GaN high-electron-mobility transistors, which is promising for its integration in the smart GaN platform.

Thin barrier gated-edge termination AlGaN/GaN Schottky-barrier-diode with low reverse leakage and high turn-on uniformity

In this letter, the reverse leakage mechanism of thin-barrier AlGaN/GaN Schottky barrier diode (SBD) with recess-free technology is reported for the first time. Two types of SBD were fabricated with different AlGaN barrier thickness (5 and 7 nm). It is found that trap-assisted tunneling is the dominant mechanism for area-related leakage current in the Schottky region at low reverse bias, which attributed to the traps introduced by fluorine-based dry etch during opening the LPCVD SiN x cap. When it is highly reverse biased, Schottky edge leakage current becomes dominant for 7 nm SBD, but not for the 5 nm SBD. The suppression of edge leakage in the 5 nm SBD is due to the reduction of the Schottky edge electric field caused by the thinning of the barrier, which was verified by simulation. These findings will help to further optimize the performance of AlGaN/GaN SBD.

https://iopscience.iop.org/article/10.35848/1347-4065/abd86f/pdf

Analysis of reverse leakage mechanism in recess-free thin-barrier AlGaN/GaN Schottky barrier diode

Gallium nitride (GaN) has attracted increased attention because of superior material properties, such as high electron saturation velocity and high electrical field strength, which are promising for high-power microwave applications We report on a high-performance vertical GaN-based Schottky barrier diode (SBD) and its demonstration in a microwave power limiter for the first time The fabricated SBD achieved a very low differential specific on-resistance (RON,sp) of 021 mΩ·cm2, attributed to the steep-mesa technology, which assists in reducing the spacing between the edge of the anode and cathode to 2 µm Meanwhile, a low leakage current of ~10−9 A/cm2@−10 V, a high forward current density of 94 kA/cm2 at 3 V in DC, and an ideality factor of 104 were achieved Scattering parameter measurements showed that the insertion loss (S21 ) was lower than −3 dB until 3 GHz In addition, a microwave power limiter circuit with two anti-parallel diodes was built and measured on an alumina substrate The input power level reached 40 dBm (10 watts) in continuous-wave mode at 2 GHz, with a corresponding leakage power of 272 dBm (05 watts) at the output port of the limiter, exhibiting the great potential of GaN SBD in microwave power limiters

/pdf/first-demonstration-of-l-band-high-power-limiter-with-gan-25u1tiuolk.pdf

Hao Wu

Papers

Review of the Recent Progress on GaN-Based Vertical Power Schottky Barrier Diodes (SBDs)

Low Leakage and High Forward Current Density Quasi-Vertical GaN Schottky Barrier Diode With Post-Mesa Nitridation

Thin barrier gated-edge termination AlGaN/GaN Schottky-barrier-diode with low reverse leakage and high turn-on uniformity

Analysis of reverse leakage mechanism in recess-free thin-barrier AlGaN/GaN Schottky barrier diode

First Demonstration of L-Band High-Power Limiter with GaN Schottky Barrier Diodes (SBDs) Based on Steep-Mesa Technology