R. Q. Yang, W. Huang, L. Li, L. Lei, J. A. Massengale, T. D. Mishima, and M. B. Santos, “Gain and resonant tunneling in interband cascade IR photodetectors” (Invited ), talk 10543-13 at Quantum Sensing and Nanophotonic Devices XV at Photonics West, San Francisco, CA, Jan. 27- Feb.1, 2018 (in Proc. SPIE. 10540, 105400E).