V. I. Kopchatov

Gain characteristics of quantum dot injection lasers

Gain characteristics of injection lasers based on self-organized quantum dots (QDs) were studied experimentally for two systems: InGaAs QDs in an AlGaAs matrix on a GaAs substrate and InAs QDs in an InGaAs matrix on an InP substrate. A ground-to-excited state transition was observed with increasing threshold gain. An empirical equation is proposed to fit the current density dependence of the QD gain. This fitting equation is shown to be valid for both the ground and excited state lasing in the systems under study in the 77-300 K temperature range. The effect of QD surface density on gain characteristics is calculated analytically.

Vertically coupled quantum dot lasers: First device oriented structures with high internal quantum efficiency

Main mechanisms of internal carrier losses and leakage from the ground state of quantum dots have been studied in heterostructure lasers based on vertically coupled quantum dots. It has been shown that the threshold current density may be reduced down to 15 A/cm 2 at room temperature by reducing the non-radiative recombination and improving the carrier localization.

Multi-Stacked InAs/InGaAs/InP Quantum Dot Laser (Jth=11 A/cm2, λ=1.9 µm (77 K))

Self-organized InAs quantum dots inserted in an (In, Ga)As matrix lattice matched to InP substrate were used as an active region of an injection laser. Low threshold (11 A/cm2) lasing at 1.9 nm (77 K) via the quantum dot states was realized. Temperature dependencies of the main laser parameters demonstrate the important role of the nonradiative recombination. An analysis of basic mechanisms of leakage shows that the Auger recombination share is negligible.

Collective resonance and form factor of homogeneous broadening in semiconductors

The superradiance model was recently successfully applied to describe semiconductor quantum well luminescence spectra at low temperature (77 K). In the present work, we expand and develop this approach for room-temperature spectra and compare results with optical autocorrelation data obtained earlier. Also, the convenience of the superradiance model has been proven for precise description of cryogenic spectra of quantum dot heterostructures. Numerical analysis of quantum dot spectra allows us to conclude that homogeneous line broadening dominates over inhomogeneous one.

Investigation of the device characteristics of a low-threshold quantum-dot laser emitting at 1.9 µm

InAs quantum dots in a InGaAs matrix grown on an InP substrate by molecular-beam epitaxy are employed as the active region of an injection laser. Lasing via quantum-dot states is observed in the temperature range 77–200 K. At the lowest threshold current density 11 A/cm2 the radiation wavelength is equal to 1.894 µm (77 K).

Improved degradation stability of blue-green II-VI light-emitting diodes with excluded nitrogen-doped ZnSe-based layers

Degradation characteristics of p-i-n BeZnSe/Zn(Be)CdSe light-emitting diodes were investigated. Undoped short-period superlattices, which provide efficient hole transport from the p+-BeTe:N near-contact region (hole injector) into the active region, were used instead of the p-doped BeZnSe:N emitter. It is demonstrated that this makes it possible to considerably lengthen the operating life of the light-emitting diodes at highest direct current densities (∼4.5 kA/cm2) at room temperature.

Superradiance in semiconductors

The dependences of the characteristic superradiance time in quantum well InGaAs/GaAs laser heterostructures on the pump current, temperature, and cross sections of the active region are studied by analyzing electroluminescence spectra. The number of dipoles involved in forming a superradiant pulse is estimated using elementary equations from the theory of superradiance in two-level systems. A mechanism is proposed for superradiance in semiconductors.

Low-threshold quantum dot injection laser emitting at 1.9 /spl mu/m

Self-organized InAs quantum dots inserted in an (In,Ga)As matrix lattice matched to an InP substrate were used as an active region of an injection laser. Laser action was observed up to 200 K. Low threshold (11.4 A/cm/sup 2/) lasing at 1.894 /spl mu/m (77 K) via the quantum dot states was realized. The ground-to-excited state transition with increasing threshold gain was observed. The quantum dot material gain of the order of 10/sup 4/ cm/sup -1/ was estimated.

Collective resonances and shape function for homogeneous broadening of the emission spectra of quantum-well semiconductor heterostructures

An analytic expression for the shape function for homogeneous broadening of the emission spectra of semiconductor heterostructure lasers is obtained on the basis of simple expressions from the theory of the superradiance of two-level systems. Good agreement between the theory and experimental data is achieved for an InGaAs/GaAs quantum-well heterostructure laser. An estimate of the duration of the superradiance pulse is given.

COLLECTIVE RESONANCE AND FORM-FACTOR OF HOMOGENEOUS BROADENING IN SEMICONDUCTORS

The concept of resonant carrier many body interaction during radiative recombination was applied to explain spectra of quantum well electroluminescence at 77 K. Extremely good (1%) agreement of the calculated and experimental spectra in the entire range of emission has been achieved. Estimations give a sub-picosecond characteristic time of such radiation process.