Georgy G. Zegrya

Theoretical study of thresholdless Auger recombination in compressively strained InAlAsSb/GaSb quantum wells

The effect of strain on thresholdless Auger recombination in quantum wells has been studied theoretically. A detailed analysis of overlap integrals between the initial and final states of carriers has been carried out. It is shown that the strain affects both qualitatively and quantitatively the overlap integral between the electron and hole states. The Auger recombination coefficient is calculated for InAlAsSb quantum well and its dependence on quantum well parameters, strain, and temperature is analyzed.

Observation of the biexponential ground-state decay time behavior in InAs self-assembled quantum dots grown on misoriented substrates

Biexponential behavior of the time-resolved photoluminescence decay from the ground state has been studied over a temperature range of 77–300 K on samples with varying sized self-assembled InAs∕GaAs quantum dot ensembles controlled by substrate misorientation alone. The slower second decay component is considerably longer than the first one, and has been measured to be as long as 300 ns. This slow component is attributed to carrier recapturing and indirect radiative recombination processes.

Study of high-power GaAs-based laser diodes operation and failure by cross-sectional electrostatic force microscopy

One of the important factors that restricts the power limit of semiconductor lasers is a catastrophic optical mirror damage. This process is significantly suppressed through decreasing the optical power density due to its redistribution over the broad transverse waveguide (BW). Recently it was shown that record-breaking values of the quasicontinuous and continuous-wave (QWC and CW) output power for 100-μm-wide-aperture devices can be achieved by incorporating a broad transverse waveguide into 0.97 μm emitting Al-free InGaAs(P)/InGaP/GaAs and Al-containing InGaAs/AlGaAs/GaAs separate confinement heterostructure quantum-well lasers (SCH-QWL). Another important factor limiting the CW output power is the Joule overheating of a laser diode due to an extra serial resistance. Traditionally, a decrease in the resistance is achieved by development of the contacts, whereas a voltage distribution across the device structure is not analyzed properly. At high operating currents the applied voltage can drop not only across the n-p-junction, but also at certain additional regions of the laser structure depending on a particular design of the device. Electrostatic force microscopy (EFM) provides a very promising method to study the voltage distribution across an operating device with a nanometer space resolution. An application of EFM for diagnostics of III-V laser diodes without and under applied biases have been recently demonstrated. However, the most interesting range of the biases, the lazing regime, has not been studied yet.

Suppression of intrinsic bistability in resonant-tunneling diode by in-plane magnetic field

Using the Bardeen formalism, we calculated the electron tunneling through a double barrier structure with an in-plane magnetic field. It is shown that the in-plane magnetic field has two effects on the current–voltage characteristics. First, it reduces the width of the bistable region. At high magnetic fields, the bistability can be completely suppressed. This can provide a method for tuning the bistable region in a double barrier structure. Second, it modifies the peak current. The dependence of the peak current on the magnetic field is different in the cases of high and low electron concentrations in the quantum well.

Power rise in broad-waveguide diode laser with inclined facet

A method of transverse mode selection in high-power broad-waveguide separate confinement heterostructure quantum-well lasers by placing the front mirror at the angle other than the normal to the radiation propagation direction is proposed. Optimal values of facet inclination angles and widths and the refractive indices of the dielectric coating at which the fundamental guided mode dominates are found. The possibility of increasing the output power 1.2 times of a broad-waveguide separate confinement heterostructure quantum-well diode laser with inclined facet is shown.

Application of semiconductor quantum dots for a study of biological systems

Advantages of semiconductor quantum dots (QDs) for study and diagnostics of biological systems are discussed A new method for amino acid diagnostics using semiconductor QDs is proposed. Interaction of isolated QDs with charged amino acids is studied in detail. It is shown that such interaction results in a shift of the QD luminescence spectra by several dozens of meV. This effect provides new possibilities for identification of biological objects using QDs.

Time-resolved photoluminescence measurements of InAs self-assembled quantum dots (Invited Paper)

Time-resolved photoluminescence decay measurements have been performed on samples with varying sized self-assembled InAs/GaAs quantum dot ensembles, formed by substrate mis-orientation alone, but otherwise under identical growth conditions. Ground-state radiative recombination lifetimes from 0.8 to 5.3 ns in the incident energy density range of 0.79 pJcm-2 - 40 nJcm-2 at a temperature of 77 K were obtained. It was found that a reduction of the quantum dot size led to a corresponding reduction of the radiative lifetime. The evident bi-exponential decay was obtained for the ground state emission of the quantum dot array, with the slower second component attributed to a carrier re-capturing and indirect radiative recombination processes. Also experimental evidence of the effect of the AlGaAs barrier in InAs QDs emitting in the wavelength range 1200-1300nm is presented. Time-resolved photoluminescence measurements have been performed on samples with different compositions of Al in the barrier. A full discussion of the lifetimes of these near infra-red emitting dots will be presented.

Time-resolved photoluminescence measurements of InAs self-assembled quantum dots

Time-resolved photoluminescence decay measurements have been performed on samples with varying sized self-assembled InAs/GaAs quantum dot ensembles, formed by substrate mis-orientation alone, but otherwise under identical growth conditions. Ground-state radiative recombination lifetimes from 0.8 to 5.3 ns in the incident energy density range of 0.79 pJcm-2 - 40 nJcm-2 at a temperature of 77 K were obtained. It was found that a reduction of the quantum dot size led to a corresponding reduction of the radiative lifetime. The evident bi-exponential decay was obtained for the ground state emission of the quantum dot array, with the slower second component attributed to a carrier re-capturing and indirect radiative recombination processes. Also experimental evidence of the effect of the AlGaAs barrier in InAs QDs emitting in the wavelength range 1200-1300nm is presented. Time-resolved photoluminescence measurements have been performed on samples with different compositions of Al in the barrier. A full discussion of the lifetimes of these near infra-red emitting dots will be presented.

Time-resolved photoluminescence measurements of in As self-assembled quantum dots

Time-resolved photoluminescence decay measurements have been performed on samples with varying sized self-assembled InAs/GaAs quantum dot ensembles, formed by substrate mis-orientation alone, but otherwise under identical growth conditions. Ground-state radiative recombination lifetimes from 0.8 to 5.3 ns in the incident energy density range of 0.79 pJcm-2 - 40 nJcm-2 at a temperature of 77 K were obtained. It was found that a reduction of the quantum dot size led to a corresponding reduction of the radiative lifetime. The evident bi-exponential decay was obtained for the ground state emission of the quantum dot array, with the slower second component attributed to a carrier re-capturing and indirect radiative recombination processes. Also experimental evidence of the effect of the AlGaAs barrier in InAs QDs emitting in the wavelength range 1200-1300nm is presented. Time-resolved photoluminescence measurements have been performed on samples with different compositions of Al in the barrier. A full discussion of the lifetimes of these near infra-red emitting dots will be presented.

Theoretical and experimental study of the effect of carrier relaxation on threshold and power-current characteristics of quantum well lasers

In this paper, the effect of intraband relaxation processes of non-equilibrium carriers on the threshold and power-current characteristics of quantum-well lasers is studied both theoretically and experimentally. Special attention is paid to the study of physical mechanisms, which affect the maximum laser power. It is shown that at high excitation levels, the maximum laser power gets affected, apart from lattice and carrier heating, by the phenomenon of gain saturation. Power-current characteristics of a quantum well laser are calculated with gain saturation effect being taken into account. It is shown that at high excitation levels the characteristic becomes non-linear. Calculated behavior of power-current characteristics agrees well with experimental observations.