A phonon scattering assisted injection and extraction based terahertz quantum cascade laser

Abstract

A novel lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the GaAs/Al 0.25 Ga 0.75 As material system that maximizes the product of population inversion and oscillator strength at 150 K. The fabricated devices using Au double-metal waveguides show lasing at 3.2 THz up to 138 K. The electrical characteristics display no sign of differential resistance drop at lasing threshold, which suggests -thanks to the rate equation model -a slow depopulation rate of the lower lasing state, a hypothesis confirmed by non-equilibrium Green's function calculations.

Simulating terahertz quantum cascade lasers: Trends from samples from different labs

“…They will be referenced in the text by a shorthand notation containing first author name, journal, and year, e.g., DupontJAP2012 for the device considered in Ref. 33.…”

“…33 These designs use LO phonon scattering to populate the upper laser state, which is fundamentally different to the RT injection but requires a larger bias to operate. Here, we present results for DupontJAP2012, 33 RazavipourJAP2013, 50 and KhanalOE2015. 51 …”

Two-well quantum cascade laser optimization by non-equilibrium Green's function modelling

“…However, to date, their operation is limited to ∼200 K 4 and the necessity of cryogenic cooling hinders a widespread use of these devices. In the last decade, significant scientific effort has been directed towards identifying the main temperaturedegrading mechanisms [5][6][7][8] , as well as finding optimized QCL designs [9][10][11][12][13][14] . The degrading mechanisms include thermal backfilling 3,15 , thermally activated LO phonon emission [6][7][8]16 , increased broadening [17][18][19] , and carrier leakage into continuum states 20 .…”

“…In contrast, in this work we will employ an advanced model directly at the optimization stage. Specifically, we shall use a NEGF model 27 , capable of accurately simulating experimental devices 13,26,28 and including the most general treatment of scattering, from all relevant processes.…”

“…In addition, we limit the escape of carriers into continuum states by employing barriers with a high (25%) AlAs concentration [12][13][14]20 . An example of a design is shown in Fig.…”