Effect of free-carrier absorption on the threshold current density of GaAs∕(Al,Ga)As quantum-cascade lasers

Abstract

GaAs/ Al 0.33 Ga 0.67 As quantum-cascade lasers with plasmon-assisted waveguides exhibit a decreasing threshold current density j th with increasing wave number 0 of the laser line, which changes as a function of the injector doping density. We have developed an analytical approach based on the effective dielectric tensor component for the p-polarized light emitted from a quantum-cascade laser, which explains the observed dependence of j th ͑ 0 ͒ in terms of losses due to free-carrier absorption predominantly in the doped waveguides ␣ WG ͑ 0 ͒. A contribution to the losses by free-carrier absorption in the quantum-cascade structure itself and subsequently to j th can be neglected except for very high injector doping densities. The calculated values for ␣ WG ͑ 0 ͒ are in good agreement with the experimental data. Our approach quantitatively predicts the observed decrease of j th from 17 to 7 kA cm −2 with increasing 0 between 900 and 1100 cm −1. In addition to achieving a direct physical insight into the influence of free-carrier absorption on the laser performance, the proposed analytical approach provides a simple tool for the determination of the waveguide losses for any quantum-cascade laser without adopting a numerical solver.

Free-carrier absorption in quantum cascade structures

“…[17][18][19] Such large free-carrier absorption would jeopardize the future use of QCLs. It was, however, shown 20 in a midinfrared QCL that the free-carrier absorption plays a small role in the actual laser losses. A calculation 21 of FCA induced by interface roughness in single quantum wells does predict a small absorption coefficient.…”

Influence of doping density on electron dynamics in GaAs∕AlGaAs quantum cascade lasers

“…40,41 The doping level in the active region is an important parameter with particular influence on the dynamic working range of QCLs. Until now, very few experimental investigations have been presented including the influence of the injector doping on InP-based [42][43][44] and GaAs-based [45][46][47][48] QCL threshold currents.…”

Aspects of the internal physics of InGaAs∕InAlAs quantum cascade lasers

“…Until now, very few experimental investigations have been presented that have discussed the influence of the injector doping on QCL threshold currents. [17][18][19] In this work we report on such a theoretical investigation of a recent four-quantum-well design, 9 in which the influence of the injector doping density on the electron dynamics and on the carrier heating is analyzed.…”