S. M. Nekorkin

Room-temperature intracavity difference-frequency generation in butt-joint diode lasers

We obtain, for the first time to our knowledge, the room-temperature intracavity difference-frequency generation in the mid-infrared range (around 10 mum wavelength) in a butt-joint GaAs/InGaAs/InGaP quantum-well dual-wavelength laser diode which supports lasing at two closely spaced wavelengths in the near-infrared range close to 1 mum. We employ a special asymmetric waveguide design (which makes it possible the different-order transverse-mode lasing) and a low-doped substrate that minimize mid-infrared losses and phase mismatch for the difference-frequency nonlinear-mixing process. We explain qualitatively the physics of the intracavity mode mixing and describe in detail the design of the butt-joint diode laser. We show how to scale the effect into the far-infrared (terahertz) range, to improve the phase-matching conditions, and to enhance further the difference-frequency generation efficiency (the latter is about 1 W/(kW)2 in our first experiment).

Nonlinear mode mixing in dual-wavelength semiconductor lasers with tunnel junctions

The authors demonstrate and study two- and three-wavelength generations in the semiconductor diode laser with a tunnel junction separating two different quantum-well active regions integrated within a single waveguide. To avoid resonant cross absorption of the modes at different frequencies and achieve phase matching, the laser waveguide is designed to generate the first-order transverse mode at a longer wavelength and the third-order mode at a shorter wavelength. Excellent agreement with the designed and measured device parameters is observed. Intracavity nonlinear mixing leading to sum-frequency and second-harmonic generation is demonstrated.

Non-linear wave mixing in GaAs/InGaAs/InGaP butt-joint diode lasers

We suggest and fabricate butt-joint diode lasers for efficient non-linear wave mixing in semiconductors. The first experimental demonstration of sum-frequency and second harmonic continuous-wave generation in InGaAs/GaAs/InGaP butt-joint diode lasers in the edge-emitting geometry is reported.

Waveguide effect of GaAsSb quantum wells in a laser structure based on GaAs

The waveguide effect of GaAsSb quantum wells in a semiconductor-laser structure based on GaAs is studied theoretically and experimentally. It is shown that quantum wells themselves can be used as waveguide layers in the laser structure. As the excitation-power density attains a value of 2 kW/cm2 at liquid-nitrogen temperature, superluminescence at the wavelength corresponding to the optical transition in bulk GaAs (at 835 nm) is observed.

Experimental study of nonlinear mode mixing in dual-wavelength semiconductor lasers

New schemes for the generation of the sum, difference, and double frequencies in dual-wavelength injection lasers, based on an intracavity nonlinear mode mixing owing to a bulk nonlinearity, are experimentally investigated. Namely, the operation of the dual-wavelength laser diodes at the TE0 and TE1 modes, butt-joint laser diodes, and interband cascade lasers with tunnel junction are described.

Stimulated emission from an InGaAs/GaAs/AlGaAs heterostructure grown on a Si substrate

High-perfection artificial Ge/Si substrates are created by hot-wire chemical-vapor deposition, and InGaAs/GaAs/AlGaAs quantum-well heterostructures are grown on these substrates by metalorganic chemical-vapor deposition. Photoluminescence spectra of these heterostructures are investigated. Stimulated emission in the near-infrared spectral range under optical pumping is observed. Threshold pump powers for the onset of stimulated emission are determined and the variation of the emission spectra with the optical-pump power is examined.

Emission properties of heterostructures with a (GaAsSb-InGaAs)/GaAs bilayer quantum well

The specific features of the emission characteristics of GaAs-based heterostructures with a GaAs1 − xSbx-InyGa1 − yAs bilayer quantum well are studied. The heterostructures are grown by metal-organic chemical vapor deposition (MOCVD). With an analysis of previously reported data on the MOCVD growth process taken into account, the temperature range (560–580°C), the relation between the fluxes emitted by the sources of Group-V and −III elements (≲1), and the order of layer growth for the production of the active region of a GaAs/InGaP laser heterostructure are determined experimentally. The active region is a GaAs0.75Sb0.25-In0.2Ga0.8As bilayer quantum well. For the structure, a 1075-nm electroluminescence signal attributed to indirect transitions between the valence band of the GaAs0.75Sb0.25 layer and the conduction band of the In0.2Ga0.8As layer is observed. An increase in the continuous-wave pump current yields a decrease in the 1075-nm emission intensity and initiates stable lasing at a wavelength of 1022 nm at a threshold current density of 1.4 kA cm−2 at room temperature. Lasing occurs at transitions direct in coordinate space.

Anomalous Characteristics of Lasers with a Large Number of Quantum Wells

Semiconductor lasers with an active region containing six quantum wells are investigated experimentally. The temperature dependences of working characteristics (threshold current density, external differential quantum efficiency, and directional pattern) are analyzed. Anomalous behavior of the temperature dependence of the threshold current and external differential quantum efficiency, associated with a negative characteristic temperature and a decrease in the quantum efficiency of radiation upon a decrease in temperature, is detected. A narrowing of the directional patterns in the plane perpendicular to the p-n junction upon an increase in temperature is revealed.

A Multifrequency Interband Two-Cascade Laser

Multifrequency lasing in a new class of injection heterolasers, i.e., in an interband two-cascade laser with a tunneling p-n junction separating two active regions of quantum wells located in the same waveguide is obtained and studied. The developed laser structure with pulsed pumping provided the simultaneous emission of two first-order modes with the wavelengths of 1.063 and 0.98 μm and two third-order modes with the wavelengths of 0.951 and 0.894 μm. Due to nonlinear mixing of the modes within the laser cavity, the generation of the second harmonics and sum frequencies was observed.

Electrical transport and persistent photoconductivity in quantum dot layers in InAs/GaAs structures

The conductivity of quantum dot layers is studied in InAs/GaAs structures in the temperature range from 300 to 0.05 K in the dark and using two types of illumination in magnetic fields up to 6 T. Depending on the initial concentration of current carriers, the conductivity of the structures varied from metallic (the Shubnikov-de Haas effect was observed) to hopping conductivity. At low temperatures, the temperature dependence of the resistance changed from the Mott dependence to the dependence described by the Shklovskii-Efros law for hopping conductivity in the presence of the Coulomb gap in the density of states. The conductivity of samples was studied upon their illumination at λ = 791 nm and λ > 1120 nm. All the samples exhibited a positive persistent photoconductivity at T < 250 K. The structures were also studied using photoluminescence and an atomic force microscope.