Query: SHENG ZHANG gan

Candidate papers:

abstract: Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state of the art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.
author_names: Hiroshi Amano

Y Baines

Matteo Borga

T Bouchet

Paul R Chalker

Matthew Charles

K J Chen

Nadim Chowdhury

Rongming Chu

Carlo De Santi

Maria Merlyne De Souza

Stefaan Decoutere

Lea Di Cioccio

Bernd Eckardt

Takashi Egawa

Patrick J Fay

Joseph J Freedsman

Louis Guido

Oliver Haberlen

Geoff Haynes

Thomas Heckel

Dilini Hemakumara

Peter A Houston

Jie Hu

Mengyuan Hua

Qingyun Huang

Alex Q Huang

Sheng Jiang

Hiroji Kawai

Daniel M Kinzer

Martin Kuball

Ashwani Kumar

Kean Boon Lee

Xu Li

Denis Marcon

Martin Marz

Robert McCarthy

Gaudenzio Meneghesso

Matteo Meneghini

Erwan Morvan

Akira Nakajima

E M Sankara Narayanan

Stephen Oliver

Tomas Palacios

Daniel Piedra

Marc Plissonnier

Rekha Reddy

Min-Chul Sun

Iain G Thayne

A Torres

Nicola Trivellin

Vineet Unni

Michael J Uren

Marleen Van Hove

David J Wallis

Jingshan Wang

Jinqiao Xie

Shuichi Yagi

Shu Yun Yang

C Youtsey

Ruiyang Yu

Enrico Zanoni

Stefan Zeltner

Yuhao Zhang
title: The 2018 GaN power electronics roadmap
year: 2018

abstract: Wide bandgap gallium nitride (GaN) based devices have attracted a lot of attention in optoelectronics, power electronics, and sensing applications. AlGaN/GaN based sensors, featuring high density and high mobility two dimensional electron gas (2DEG) have been demonstrated to be effective chemical sensors and biosensors in the liquid environment. One of the key factors limiting the wide adoption of the AlGaN/GaN liquid sensor is the package reliability issue. In this paper, the reliability of three types of sensor packaging materials (SiO2/Si3N4, PI, and SiO2/Si3N4/PI) on top of 5 mm metal are tested in Phosphate buffer saline (PBS) solution. By analyzing the I V characteristics, it is found that the leakage currents within different regimes follow distinct leakage models, whereby the key factors limiting the leakage current are identified. Moreover, the physical mechanisms of the package failure are illustrated. The failure of the SiO2/Si3N4 package is due to its porous structure such that ions in the solution can penetrate into the packaging material and reduce its resistivity. The failure of the PI package at a relatively low voltage <3 V) is mainly due to the poor adhesion of PI to the AlGaN surface such that the solution can reach the electrode by the "lateral drilling" effect. The SiO2/Si3N4/PI package achieves less than 10 mA leakage current at 5 V voltage stress because it combines the advantages of the SiO2/Si3N4 and the PI packages. The analysis in this work can provide guidelines for the design and failure mechanism analysis of packaging materials.
author_names: Hanyuan Zhang

Shu Yang

Kuang Sheng
title: The Leakage Mechanism of the Package of the AlGaN/GaN Liquid Sensor
venue: Materials
year: 2020

abstract: Open gated AlGaN/GaN high electron mobility transistor (HEMT) based sensor can inherently deliver a high current sensitivity (SI) in response to the pH change. However, it remains a challenge to further improve the performance of the packaged AlGaN/GaN based sensor, due to a lack of investigation on the device design optimization. In this paper, the influence of the gate geometry on the device sensitivity is investigated through theoretical analysis and experiments. It has been found that the key factor limiting the current sensitivity is the series resistance (RS) of the packaged sensor. There are two cases: (1) when the aspect ratio of the gate structure (W/L) is small, the channel resistance dominates the total resistance and the current sensitivity increases with W/L; (2) when W/L is large, the RS dominates the total resistance, the sensitivity decreases with W/L. Therefore, there is an optimal W/L which can be approximately reached when W/L r2DEG/RS. Based on the guidelines, the current sensitivity of the AlGaN/GaN sensor with an optimized geometry in our experiment can reach 157 mA/pH, which is the highest value among the packaged AlGaN/GaN based pH sensors in literature, to our best knowledge. The comparison with the Si based ISFET and the impact of the gate membrane on the sensitivity of AlGaN/GaN based sensor have also been analyzed and discussed.
author_names: Hanyuan Zhang

Jiawei Tu

Shu Yang

Kuang Sheng

Ping Wang
title: Optimization of gate geometry towards high sensitivity AlGaN/GaN pH sensor.
venue: Talanta
year: 2019

abstract: The InGaN/GaN multi quantum wells (MQWs) are prepared at the same condition by metal organic chemical vapor deposition (MOCVD) except the thickness of cap layers additionally grown on each InGaN well layer. The photoluminescence (PL) intensity of the thin cap layer sample is much stronger than that of thicker cap layer sample. Interestingly, the thick cap layer sample has two photoluminescence peaks under high excitation power, and the PL peak energy temperature curves show an anomalous transition from reversed V shaped to regular S shaped with increasing excitation power. Meanwhile, it exhibits a poorer thermal stability of thick cap layer sample under higher excitation power than that under lower excitation power. Such an untypical phenomenon is attributed to carrier redistribution between the two kinds of localized states which is induced by the inhomogeneous distribution of indium composition in thick cap layer sample. Furthermore, the luminescence of deep localized states has a better thermal stability, and the luminescence of shallow localized states has a poor thermal stability. In fact, such a severer inhomogeneous indium distribution may be caused by the degradation of subsequent epitaxial growth of InGaN/GaN MQWs region due to longer low temperature GaN cap layer growth time.
author_names: Yao Xing

Degang Zhao

De-sheng Jiang

Zongshun Liu

Jian-jun Zhu

Ping Chen

Jing Yang

Feng Liang

Shuangtao Liu

Liqun Zhang
title: Carrier Redistribution Between Two Kinds of Localized States in the InGaN/GaN Quantum Wells Studied by Photoluminescence
venue: Nanoscale Research Letters
year: 2019

abstract: A high linearity and high gain AlGaN/GaN HEMTs with a 100 nm gate were demonstrated. The device employs transitional recessed gate (TRG) along the gate width for millimeter wave power application. The gradually changing gate recess depth was created using transitional dosed photoetching. Accurate etching ensured that the FET elements have a continued <inline formula> <tex math notation="LaTeX"\text{V}_{\mathrm {ts} /tex math>/inline formula> offset in the local equivalent threshold voltage <inline formula> <tex math notation="LaTeX"\text{V}_{\mathrm {th} /tex math>/inline formula> in different areas. The device exhibits a high <inline formula> <tex math notation="LaTeX"\text{I}_{\mathrm {d,max} /tex math>/inline formula> of 1.12 A/mm and a high peak extrinsic <inline formula> <tex math notation="LaTeX"\text{g}_{\mathrm {m} /tex math>/inline formula> of 374 mS/mm with an improved gate swing >2.6 V, much higher than that of Fin HEMT. Excellent RF performance was shown, including <inline formula> <tex math notation="LaTeX"\text{f}_{\mathrm {T}\text{f}_{\mathrm {max} =61.8$ /tex math>/inline formula>/148.8 GHz, <inline formula> <tex math notation="LaTeX"\text{G}_{\mathrm {as}\text{G}_{\mathrm {linear} {9.98} /tex math>/inline formula> 12dB at 30 GHz. To the best of our knowledge, this is the best associated gain and linearity performance reported to date for AlGaN/GaN HEMTs. This letter has great potential for high gain and linearity millimeter wave power applications, which are needed for future communication systems.
author_names: Sheng Wu

Xiao-hua Ma

Ling Yang

Minhan Mi

Meng Zhang

Mei Wu

Yang Lu

Hengshuang Zhang

Chupeng Yi

Yue Hao
title: A Millimeter Wave AlGaN/GaN HEMT Fabricated With Transitional Recessed Gate Technology for High Gain and High Linearity Applications
venue: IEEE Electron Device Letters
year: 2019

abstract: This work evaluates the switching performance of 1.2 kV vertical GaN power FinFETs using the mixed mode device circuit TCAD simulation. The device simulation is calibrated with the I V and C V characteristics of experimental devices. A double pulse circuit is implemented in the mixed mode simulation and subsequently used to evaluate the device turn on/turn off times and switching losses under hard switching. To improve the switching performance of vertical power FinFETs, a novel inter fin design is proposed based on the split gate geometry. This structure removes the gate metal in the inter fin region and exposes the drift layer to the source metal. During the device turn (on)off transients, the drift layer underneath the inter fin gap region is (dis)charged by the drain to source current instead of gate current, leading to shorter switching times and lower switching losses. By utilizing this split gate structure, over 47% superior switching figure of merit (FOM) and over 30% lower switching losses have been demonstrated in 1.2 kV vertical GaN power FinFETs. The 1.2 kV, 80 mO split gate vertical GaN power FinFETs show over 30% superior switching FOM and over 50% smaller switching losses when compared to commercial 1.2 kV SiC MOSFETs under similar switching conditions. These results provide important guidelines for the design of vertical GaN power FinFETs and show their great potentials for high frequency medium voltage power applications.
author_names: Hengyu Wang

Ming Xiao

Kuang Sheng

Tomas Palacios

Yuhao Zhang
title: Switching Performance Evaluation of 1200 V Vertical GaN Power FinFETs
venue: 2019 IEEE 7th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
year: 2019

abstract: Abstract Optical field leakage to the GaN substrate in GaN based green laser diodes (LDs) can reduce the peak optical gain and weaken the output performance of LDs. In this study, a graded indium composition n InxGa1 xN lower waveguide (LWG) structure is proposed which should be more feasible to grow with high material quality and at the same time can effectively reduce the optical field leakage in GaN based green LD, avoiding to use thick n type Al0.08Ga0.92N cladding layer or thick n InxGa1 xN LWG with high indium content. According to the optical and electrical characteristics of LDs calculated by LASTIP, it is found that the optical field has been concentrated around the active area and the optical field leakage has been eliminated effectively using graded indium composition LWG in green LDs, which results in an obvious improvement of optical and electrical performance.
author_names: Feng Liang

Degang Zhao

De-sheng Jiang

Zongshun Liu

Jian-jun Zhu

Ping Chen

Jing Yang

Shuangtao Liu

Yao Xing

Liqun Zhang
title: Suppression of optical field leakage in GaN based green laser diode using graded indium n InxGa1 xN lower waveguide
venue: Superlattices and Microstructures
year: 2019

abstract: Unpaired image to image translation problem aims to model the mapping from one domain to another with unpaired training data. Current works like the well acknowledged Cycle GAN provide a general solution for any two domains through modeling injective mappings with a symmetric structure. While in situations where two domains are asymmetric in complexity, i.e. the amount of information between two domains is different, these approaches pose problems of poor generation quality, mapping ambiguity, and model sensitivity. To address these issues, we propose Asymmetric GAN (AsymGAN) to adapt the asymmetric domains by introducing an auxiliary variable (aux) to learn the extra information for transferring from the information poor domain to the information rich domain, which improves the performance of state of the art approaches in the following ways. First, aux better balances the information between two domains which benefits the quality of generation. Second, the imbalance of information commonly leads to mapping ambiguity, where we are able to model one to many mappings by tuning aux, and furthermore, our aux is controllable. Third, the training of Cycle GAN can easily make the generator pair sensitive to small disturbances and variations while our model decouples the ill conditioned relevance of generators by injecting aux during training. We verify the effectiveness of our proposed method both qualitatively and quantitatively on asymmetric situation, label photo task, on Cityscapes and Helen datasets, and show many applications of asymmetric image translations. In conclusion, our AsymGAN provides a better solution for unpaired image to image translation in asymmetric domains.
author_names: Yu Li

Sheng Tang

Rui Zhang

Yongdong Zhang

Jintao Li

Shuicheng Yan
title: Asymmetric GAN for Unpaired Image to Image Translation
venue: IEEE Transactions on Image Processing
year: 2019

abstract: In this paper, AlGaN/GaN Fin HEMTs with different fin configurations are theoretically and experimentally investigated. A simple physical based threshold voltage model for AlGaN/GaN Fin HEMTs is built for qualitative analysis. It is shown that the threshold voltage of AlGaN/GaN Fin HEMTs depends on the width and height of the fin structure. The peak value and linearity of transconductance and current gain cutoff frequency are improved by reducing the fin length. It is also found that the linearity of transconductance is sensitive to the fin height, which can be attributed to the capacitance control from sidewalls.
author_names: Meng Zhang

Xiao-hua Ma

Ling Yang

Minhan Mi

Bin Hou

Yunlong He

Sheng Wu

Yang Lu

Heng-shuang Zhang

Qing Zhu

Jun Yin

Jiafeng Wu

Lin-An Yang

Yue Hao
title: Influence of Fin Configuration on the Characteristics of AlGaN/GaN Fin HEMTs
venue: IEEE Transactions on Electron Devices
year: 2018

abstract: Both yellow luminescence (YL) and blue luminescence (BL) bands of GaN films have been investigated for decades, but few works report the relationship between them. In this study, two sets of GaN samples grown via metalorganic chemical vapor deposition (MOCVD) were investigated. A close relationship was found between the YL and BL bands for unintentionally doped GaN and Si doped GaN samples, both of which were grown without intentional acceptor doping. It was found that the intensity ratio of blue luminescence to yellow luminescence (IBL/IYL) decreases sharply with the increase in carbon impurity concentration, even though both IBL and IYL increase obviously. It was also found that IBL/IYL decreases sharply with the increase in Si doping concentration. It is suggested that the C and Si impurities play important role in linkage and competition of the blue and yellow luminescence.
author_names: Feng Liang

Degang Zhao

De-sheng Jiang

Zongshun Liu

Jianjun Zhu

Ping Chen

Jing Yang

Shuangtao Liu

Yao Xing

Liqun Zhang
title: Role of Si and C Impurities in Yellow and Blue Luminescence of Unintentionally and Si Doped GaN
venue: Nanomaterials
year: 2018