2.07-kV AlGaN/GaN Schottky Barrier Diodes on Silicon With High Baliga’s Figure-of-Merit

Significance Statement

Recently, GaN-based Schottky Barrier Diodes (SBDs) grown on silicon substrate have attracted significant attention for power electronics applications. The SBDs play a critical role in many power conversion system. To achieve a small form factor of the system, an increased operating speed is inevitable, while it is also a great challenging to maintain the conversion efficiency. GaN has a superior material such as the large bandgap (Eg = 3.4 eV), high electron saturation velocity (vsat ∼ 2.5 × 107 cm/s), high carrier density (n ∼ 1 × 1013 cm−2), and excellent breakdown field (Ec ~ 3.3 MV/cm), which is an excellent candidate for the SBDs to operate at high speed with low loss. In addition, growth of a high-quality GaN epitaxial layer on large silicon substrates has shown substantial progress, which allows the Ga-on-Si devices to be realized on large-scale silicon substrates (8 inch and above), and makes it possible to hove low cost and high performance GaN-based Schottky Barrier Diodes.

  One issue remains challenging for the GaN Schottky Barrier Diodes is the relatively high turn-on voltage VON due to the large bandgap of the material, which can increase the conduction loss and lower the efficiency. Different approaches have been proposed to reduce VON of AlGaN/GaN Schottky Barrier Diodes. Among them, using the anode recess technology is the most straightforward and effective way to reduce VON while maintaining high reverse breakdown capability. The recessed structure allows the current flows from the etched sidewall with an increased tunneling probability, resulting in a reduced VON. By employing the recess technology in the GaN Schottky Barrier Diodes, it is important to understand and control of the surface condition of etching, which is closely related to the channel/buffer leakage current and premature breakdown.

  In this work, we found a low-damage process using ICP-RIE to obtain optimized semiconductor/anode interface. The experimental results indicate that the pressure is critical during the recess process for low surface roughness. At increased pressures, the mean energy of ion bombardment becomes lower due to the increased collisions. Consequently, the reduced etching rate leads to clearly improved surface roughness. The measured results demonstrate the VON of GaN Schottky Barrier Diode is successfully reduced to ~ 0.7 V from a typical device of 1.2 V without anode recess. The improved surface roughness leads to an obvious leakage current suppression. Also, an excellent reverse breakdown voltage up to 2070 V for the SBD with LAC = 21 mm (anode-cathode distance) can be achieved, which is an evidence of the high quality surface condition after recess process. The Baliga’s Figure-of-Merit (B-FOM) is often used to evaluate the power devices in terms of power handling capability and conduction loss. The achieved B-FOM in this work is up to 1127 MW/cm2, which is among the highest compared with the published GaN-on-Si Schottky barrier diodes up to date.

2.07-kV AlGaN/GaN Schottky Barrier Diodes on Silicon With High Baliga’s Figure-of-Merit. Advances in Engineering

About the author

Chuan-Wei Tsou received the Ph.D. degree from the Institute of Electronics Engineering at National Tsing Hua University, Hsinchu, Taiwan, in 2016. In the summer of 2013, he was awarded with excellence in the summer intern competition of Taiwan Semiconductor Manufacturing Company (TSMC), Hsinchu, Taiwan. He is currently a device engineer with Industrial Technology Research Institute (ITRI), Hsinchu, Taiwan. His main research interests include simulation, design, fabrication, and characterization of the GaN-based diodes and High Electron Mobility Transistors (HEMTs) for high power and high frequency applications.  

About the author

Shawn S. H. Hsu received the B.S. degree from National Tsing Hua University, Hsinchu, Taiwan, in 1992, and the M.S. and Ph.D. degrees from the University of Michigan, Ann Arbor, in 1997 and 2003, respectively. He is currently a Professor with the Institute of Electronics Engineering and the Electrical Engineering Department, National Tsing Hua University, Hsinchu, Taiwan. His current research interests include the design, fabrication, and the modeling of GaN-on-Si power and microwave devices. He is involved in the design of MMICs and RFICs using Si/III–V-based technologies. He is also interested in heterogeneous integration using system-in-package (SiP) and 3D IC technology for high speed wireless/optical communications. Prof. Hsu has been appointed as a distinguished professor of National Tsing Hua University since 2014. 

Journal Reference

IEEE Electron Device Letters  (Volume:37 ,  Issue: 1 ), 2015.

Chuan-Wei Tsou; Kai-Pin Wei ; Yi-Wei Lian ; Shawn S. H. Hsu.

Electr. Eng. Dept., Nat. Tsing Hua Univ., Hsinchu, Taiwan

Abstract

In this letter, we demonstrate high-performance AlGaN/GaN Schottky barrier diodes (SBDs) on Si substrate with a recessed-anode structure for reduced turn-on voltage VON. The impact of the surface roughness after the recessed-anode formation on device characteristics is investigated. An improved surface condition can reduce the leakage current and enhance the breakdown voltage simultaneously. A low turn-on voltage of only 0.73 V can be obtained with a 50-nm recess depth. In addition, the different lengths of Schottky extension acting like a field plate are investigated. A high reverse breakdown voltage of 2070 V and a low specific ON-resistance of 3.8 mΩ · cm2 yield an excellent Baliga’s figure of merit of 1127 MW/cm2, which can be attributed to the low surface roughness of only 0.6 nm and also a proper Schottky extension of 2 μm to alleviate the peak electric field intensity in the SBDs.

Go To IEEE Electron Device Letters 

 

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