Nonequilibrium electron leakage in terahertz quantum cascade structures

Abstract

The nonequilibrium absorption of longitudinal-optical phonons by hot electrons are studied in terahertz quantum cascade structures. We present a method for including electron leakage to the continuum that takes into account the mobility of the electrons. This is incorporated into a density matrix Monte Carlo method that includes the optical field within the resonant cavity. The effects of electron leakage to the continuum as a function of lattice temperature are discussed. Results are compared with experiment and found to be consistent. It is shown that using only confined wave functions and thereby neglecting the leakage via tunneling is inadequate for describing the electron transport.

Experimental investigation of terahertz quantum cascade laser with variable barrier heights

“…16 Due to the practical limitations of the EMC simulations, these effects have been neglected. Instead, we took a special care to keep the position of higher minibands and energy separation of the lasing states from high miniband states in the new structures to be similar to that in the reference structure.…”

Modeling techniques for quantum cascade lasers

“…125 A special challenge in hybrid quantum-semiclassical simulations will be a selfconsistent description of dephasing going beyond phenomenological dephasing time models. 125 Furthermore, free carrier absorption 239,240 and electron leakage into the continuum of states 241,242 can have an effect and thus should be adequately implemented into the simulations.…”

Density matrix Monte Carlo modeling of quantum cascade lasers

“…21,22 For these, the use of localized wavefunctions has proven advantageous, as can be obtained from a tight binding approach. 22,[45][46][47] Rather than determining the extended eigenstates for the actual potential V as in semiclassical simulations [see Fig. 1(a)], the active region structure is divided into modules separated by thick barriers, where each module is described by a separate potential V tb , as indicated in Fig.…”

“…43,44 Furthermore, the DM formalism has been combined with EMC to describe the incoherent tunneling transport across thick injection barriers. 22,[45][46][47] This hybrid approach overcomes the main weakness of semiclassical transport simulations, which treat the carrier transport through a barrier as instantaneous since electrons scattered into states extending over the barrier see no resistance. 22 For biases where narrow anticrossings occur, this can result in excessive current spikes, indicating the breakdown of the semiclassical description.…”

“…48 In this paper, we extend EMC to include incoherent tunneling transport, building upon the pioneering work of Callebaut and Hu. 22 As in previous related approaches, 22,[45][46][47] we use localized basis states to describe the incoherent tunneling mechanism. However, here this effect is not considered by solving the von Neumann and the Boltzmann transport equations in parallel, but rather directly built into EMC as an additional "scattering-like" mechanism derived from the DM formalism.…”