Research

My research focuses on ultra-wide bandgap semiconductor devices, including GaN electronics, and optoelectronics, Ga2O3 electronics.

Gallium oxide electronics

• Record electron mobility – 180 cm2/Vs at room temperature, 2790 cm2/Vs at 50 K – in β-(AlxGa1-x)2O3/Ga2O3 modulation doped field effect transistors (MODFETs).
• First demonstration of Shubnikov-de Haas oscillations in β-Ga2O3.
• Extraction of electron effective mass and quantum scattering lifetime in β-Ga2O3.
• Small signal radio-frequency measurements on β-(AlxGa1-x)2O3/Ga2O3 MODFETs.

Tunnel injected UV LEDs

• P-AlGaN has long been critical problem for the application in optoelectronic devices, because of the low hole conductivity and high contact resistance, arrised from the high acceptor activation energy.
• My research focused on non-equilibrium hole injection into UV LEDs.
• Holes are supplied using interband tunneling injection through a AlGaN/ InGaN tunnel junction interconnected to the p-AlGaN cladding layer.
• This could potentially solve multiple problems in UV LED applications which are caused by poor p-type AlGaN layers.

Links:

1) Yuewei Zhang, Chandan Joishi, Zhanbo Xia, Mark Brenner, Saurabh Lodha, Siddharth Rajan, “Demonstration of β-(AlxGa1-x) 2O3/Ga2O3 double heterostructure field effect transistors”, Applied Physics Letters 112, 233503 (2018). (Featured in Editor’s Picks)

2) Yuewei Zhang, Adam Neal, Zhanbo Xia, Chandan Joishi, Jared M Johnson, Yuanhua Zheng, Sanyam Bajaj, Mark Brenner, Donald Dorsey, Kelson Chabak, Gregg Jessen, Jinwoo Hwang, Shin Mou, Joseph P. Heremans, and Siddharth Rajan, “Demonstration of high mobility and quantum transport in modulation-doped β-(AlxGa1-x)2O3/Ga2O3 heterostructures”, Applied Physics Letters 112, 173502 (2018). Featured article. News release in AIP News on this article.

3) Y. Zhang, S. Krishnamoorthy, J. M Johnson, F. Akyol, A. Allerman, M. W Moseley, A. Armstrong, J. Hwang, S. Rajan, ''Interband tunneling for hole injection in III-nitride ultraviolet emitters'' Appl. Phys. Lett. 106, 141103 (2015).

4) Yuewei Zhang, Andrew A Allerman, Sriram Krishnamoorthy, Fatih Akyol, Michael W Moseley, Andrew M Armstrong, Siddharth Rajan, "Enhanced light extraction in tunnel junction-enabled top emitting UV LEDs", Applied Physics Express 9 (5), 052102 (2016).

5) Yuewei Zhang, Sriram Krishnamoorthy, Fatih Akyol, Andrew A Allerman, Michael W Moseley, Andrew M Armstrong, Siddharth Rajan, "Design and demonstration of ultra-wide bandgap AlGaN tunnel junctions", Appl. Phys. Lett. 109, 121102 (2016).

6) Yuewei Zhang, Sriram Krishnamoorthy, Fatih Akyol, Andrew A Allerman, Michael W Moseley, Andrew M Armstrong, Siddharth Rajan, "Design of p-type cladding layers for tunnel-injected UV-A light emitting diodes", Appl. Phys. Lett. 109, 191105 (2016).