Simultaneous measurement of the electronic and lattice temperatures in GaAs/Al0.45Ga0.55As quantum-cascade lasers: Influence on the optical performance

Abstract

We measured the electronic and lattice temperatures in steady-state operating GaAs/AlGaAs\ud quantum-cascade lasers, by means of microprobe band-to-band photoluminescence. Thermalized\ud hot-electron distributions with temperatures up to 800 K are established. The comparison of our data\ud with the analysis of the temperature dependence of device optical performances shows that the\ud threshold current is determined by the lattice temperature

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

“…This was confirmed by calculating the ratio between the relative increase in electron temperature and power of each individual electron ͑T e − T L ͒ / ͑P E / N s ͒ which shows almost constant behavior for all doping levels. Consequently, the coupling constant drops with increased doping from 10.3 K / kA cm −2 at 4.1 ϫ 10 11 cm −2 to 7.1 K / kA cm −2 at 6.5ϫ 10 11 cm −2 at 80 K and from 22.2 K / kA cm −2 at 4.1ϫ 10 11 cm −2 to 14.2 K / kA cm −2 at 6.5ϫ 10 11 cm −2 at 240 K. The value at 4.1ϫ 10 11 cm −2 at 240 K is in excellent agreement with recently published experimental value of ϳ28 K/kA cm −2 determined from microprobe photoluminescence measurements, 51 but somewhat larger ͑ϳ50% ͒ than the first theoretical prediction reported earlier, 50 due to more scattering mechanisms taken into account in this calculation. The maximal value of the electron temperature, which corresponds to the current density just before saturation, is found to increase linearly with doping.…”

“…Equations ͑9͒ and ͑1͒ form a system of 2N nonlinear equations yielding N subband concentrations and N electron temperatures. However, recent experimental 51 and theoretical work 50 justified the use of a single ͑average͒ electron temperature ͑T e ͒ in the midinfrared QCLs. Furthermore, this considerably reduces the computational cost of solving of a nonlinear problem.…”

Towards automated design of quantum cascade lasers

“…[13][14][15][16][17] However, the output characteristics of these devices are still poor in comparison to InP based mid-infrared QCLs, demanding further optimization of layer structures and investigations of the influences of relevant physical and technological parameters. 18,19 As the GaAs/ AlGaAs system is lattice matched, the alloy composition and layer width can be varied independently. In midinfrared devices, the separations between the energy states in the active region are set by the desired emission wavelength ͑between the active laser levels͒ and the longitudinal optical ͑LO͒ phonon energy ͑between the ground and lower laser level͒, which facilitates the population inversion by allowing the fast emptying of the lower laser state by means of nonradiative transitions.…”

Spectroscopy of GaAs∕AlGaAs quantum-cascade lasers using hydrostatic pressure

“…11 Achieving cw operation in MIR GaAs-based QCLs is a very challenging task due to the relatively high threshold current densities ͑I th ͒. Influence of the injector doping, 14 the lattice temperature, 15 and carrier escape via weakly localized ⌫ states 16 were attributed as major limiting factors, for the high temperature operation and attainable gain, that determine the increase of I th and dynamic working range of ϳ9 m GaAs-based QCLs. Nevertheless, cw operation has been reported 10,17 with operating temperatures up to 150 K. However, the output characteristics are still inferior compared to InP MIR QCL.…”