Design of three-well indirect pumping terahertz quantum cascade lasers for high optical gain based on nonequilibrium Green's function analysis

Tao Liu, Nanyang Technological University; National Institute of Education (NIE)
Tillmann Kubis, Birck Nanotechnology Center, Purdue University
Qi Jie Wang, Nanyang Technological University; National Institute of Education (NIE)
Gerhard Klimeck, Network for Computational Nanotechnology, Birck Nanotechnology Center, Purdue University

Date of this Version

3-19-2012

Citation

Appl. Phys. Lett. 100, 122110 (2012)

Comments

Copyright 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Appl. Phys. Lett. 100, 122110 (2012) and may be found at http://dx.doi.org/10.1063/1.3697674. The following article has been submitted to/accepted by Applied Physics Letters. Copyright 2012 Tao Liu, Tillmann Kubis, Qi Jie Wang, and Gerhard Klimeck. This article is distributed under a Creative Commons Attribution 3.0 Unported License.

Abstract

The nonequilibrium Green's function approach is applied to the design of three-well indirect pumping terahertz (THz) quantum cascade lasers (QCLs) based on a resonant phonon depopulation scheme. The effects of the anticrossing of the injector states and the dipole matrix element of the laser levels on the optical gain of THz QCLs are studied. The results show that a design that results in a more pronounced anticrossing of the injector states will achieve a higher optical gain in the indirect pumping scheme compared to the traditional resonant-tunneling injection scheme. This offers in general a more efficient coherent resonant-tunneling transport of electrons in the indirect pumping scheme. It is also shown that, for operating temperatures below 200 K and low lasing frequencies, larger dipole matrix elements, i.e., vertical optical transitions, offer a higher optical gain. In contrast, in the case of high lasing frequencies, smaller dipole matrix elements, i.e., diagonal optical transitions are better for achieving a higher optical gain. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697674]

Discipline(s)

Nanoscience and Nanotechnology

 

Share