GaInAs/AlInAs Heteropair Quantum Cascade Laser Operating at a Wavelength of 5.6 μm and Temperature of Above 300K

A quantum cascade laser based on a strain-compensated Ga0.4In0.6As/Al0.58In0.42As heteropair is developed, which operates in a pulse mode in the wavelength range of 5.5–5.6 µm at a temperature of up to 350 K. Such characteristics are obtained due to increased quantum well depth and a two-phonon depopulation mechanism for the lower laser level. The laser epitaxial heterostructure was grown by the MOVPE method. Investigation by the high-resolution X-ray diffraction technique confirmed a high quality of the heterostructure. The threshold current density is 1.6 kA/cm2 at 300 К. The characteristic temperature is T0 = 161 K for the temperature range of 200–350 K. For a laser of size 20 µm × 3 mm with cleaved mirrors, the maximum pulse power is 1.1 W at 80 K and 130 mW at 300 K.     Keywords: quantum cascade laser, GaInAs/AlInAs heteropair, MOVPE, the middle IR spectru

Experimental study of negative photoconductivity in n-PbTe(Ga) epitaxial films

We report on low-temperature photoconductivity (PC) in n-PbTe(Ga) epitaxial films prepared by the hot-wall technique on -BaF_2 substrates. Variation of the substrate temperature allowed us to change the resistivity of the films from 10^8 down to 10_{-2} Ohm x cm at 4.2 K. The resistivity reduction is associated with a slight excess of Ga concentration, disturbing the Fermi level pinning within the energy gap of n-PbTe(Ga). PC has been measured under continuous and pulse illumination in the temperature range 4.2-300 K. For films of low resistivity, the photoresponse is composed of negative and positive parts. Recombination processes for both effects are characterized by nonexponential kinetics depending on the illumination pulse duration and intensity. Analysis of the PC transient proves that the negative photoconductivity cannot be explained in terms of nonequilibrium charge carriers spatial separation of due to band modulation. Experimental results are interpreted assuming the mixed valence of Ga in lead telluride and the formation of centers with a negative correlation energy. Specifics of the PC process is determined by the energy levels attributed to donor Ga III, acceptor Ga I, and neutral Ga II states with respect to the crystal surrounding. The energy level corresponding to the metastable state Ga II is supposed to occur above the conduction band bottom, providing fast recombination rates for the negative PC. The superposition of negative and positive PC is considered to be dependent on the ratio of the densities of states corresponding to the donor and acceptor impurity centers.Comment: 7 pages, 4 figure