Recent progress in THz quantum cascade lasers and nitride deep UV LEDs Prof. Ke Wang Nanjing University

Terahertz (THz) quantum cascade lasers (QCLs) are semiconductor-based compact coherent THz sources，which employ inter-subband transitions and carrier recycling in periodically stacked multiple quantum wells. The operation frequency of traditional GaAs THz QCLs have covered 1.2 -5.4 THz range since invented in 2002. However, the operation temperature has been stuck at ~200 K for a decade, which is the main difficulty for a portable THz QCL and hinder its potential wide applications. The major temperature degradation mechanisms, various carrier leakage channels, and methods to improve THz QCL performance will be discussed. 

More important, the potential of the GaN/AlGaN system for next generation THz QCL will be discussed. GaN has much larger phonon energies (91 meV vs 36 meV for GaAs), and can in principle allow THz QCLs to operate at room temperature or even higher. They would be key coherent sources in the unexplored terahertz frequency range of 5.4~12 THz, in which GaAs THz-QCLs are not able to work due to the Reststrahlen band. 

For DUV LEDs, low hole densities in p-type AlGaN layers are the main obstacle for achieving high efficient devices. In contrast to the widely used MOCVD method, we have adopted molecular beam epitaxy (MBE) to grow high Al content p-type AlGaN:Mg and DUV LEDs. Recent progress will be discussed. 

Short bio:

Prof Ke Wang received the B. Sc degree from Nanjing University, China, in 2000, the M.Phil degree from the University of Hong Kong in 2003, and the PhD degree from the University of Strathclyde, Glasgow, United Kingdom, in 2007, respectively, all in physics. He joined Nanishi-Araki Lab at Ritsumeikan University, Japan, in 2008, and there he received JSPS Fellowship, and started works on III nitride MBE technologies. In 2013 he joined Chiba University, Japan, as a special associate professor, working together with Prof Akihiko Yoshikawa. Since 2016 he had been a research scientist in RIKEN, Japan, and working on DUV-LEDs and III-nitride based new type quantum cascade lasers. He is now a professor in Nanjing University. He has been engaged in the fields of III nitride semiconductor material growth, devices, and MBE technologies.