Dependence of saturation effects on electron confinement and injector doping in GaAs∕Al0.45Ga0.55As quantum-cascade lasers

Abstract

We report on a detailed experimental and theoretical analysis of the role of injector doping density on both the threshold current density (Jth) and the saturation current density (Jsat), determining the dynamic range of the quantum cascade lasers. The experimental results were obtained from two growth series of λ≈9μm GaAs∕Al0.45Ga0.55As quantum-cascade lasers based on single and double phonon resonance depopulation mechanisms. We derive a quasilinear dependence of Jth on the injector doping density of both designs for doping range as wide as (4–10)×1011cm−2. Despite threshold current increase the faster rise of saturation current with doping results in an enhanced dynamic range for injector doping up to ∼8×1011cm−2. For higher doping levels, Jsat itself saturates. Furthermore, our investigations yield that single phonon resonance devices exhibit clear current saturation simultaneously with a decrease of the optical power, whereas two phonon resonance devices show only power saturation, which we attribute to increased leakage currents. These deteriorate the laser performance of the latter design at higher operational temperatures.

Genetic algorithm applied to the optimization of quantum cascade lasers with second harmonic generation

“…When calculating g, we must take into account the value of the expression given in the square brackets in Eq. (12), which is not the same for the optimized and reference structure, as well as the value of jv (2) j and the calculated wavelength. The differences are not significant, but can still lead to an evident difference of the nonlinear conversion efficiencies.…”

“…We can notice that the relative increase of the nonlinear conversion efficiency is larger than the relative increase of the nonlinear susceptibility. The reason for this lies in the fact that g is not dependent solely on jv (2) j, but on other variables as well. When calculating g, we must take into account the value of the expression given in the square brackets in Eq.…”

“…1,2 This feature, combined with room temperature operation and a wide range of emission wavelengths, has earned them the flattering title of being one of the most sophisticated and reliable light sources in the infrared and terahertz region of the electromagnetic spectrum. [3][4][5][6][7][8][9] Their fast development in the past decade led to high performance devices, which have been commercialized by several companies, such as Nanoplus and Alpes Lasers.…”

GaAs/AlGaAs (~9.4 μm) quantum cascade lasers operating at 260 K

“…The meaning of the remaining parameters is as typically used. The analysis of the above equation with numerical values of parameters as given in [9] shows that to provide modal gain at least 20 cm −1 at room temperature we need inversion ∼3×10 10 cm −2 (Fig. 8), which should allow for threshold current densities in the range (3-4) kA/cm −2 at 77 K in good quality devices (γ 32 = (12 − 14) meV) -see Fig.…”

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.…”