Valerii K. Kononenko

Optoelectronic properties and characteristics of doping superlattices

Optical and electric properties of doping superlattices, or n-i-p-i crystals, can be varied in a wide range under excitation and through the choice of the thicknesses and doping of the crystal layers. Some basic results concerned the transformation of the electron energy spectrum of doping superlattices are summarized. Parameters and characteristics of doping superlattices related to optoelectronics devices, such as photodetectors, laser diodes, and optical modulators, are presented.

How to restrain Auger recombination predominance in the threshold of asymmetric bi-quantum-well lasers

Both radiative and nonradiative processes which occur in the active region of GaInAs–GaInAsP–InP asymmetric multiple quantum-well (AMQW) heterolasers with two quantum wells of different width (4 and 9 nm) are described. Several possible processes of non-radiative Auger recombination which affect the temperature sensitivity of the lasing threshold are analyzed and the temperature dependencies of the investigated processes are presented. For the above-mentioned AMQW heterostructure, it is shown that the influence of the Auger recombination processes on the temperature behaviour of the lasing threshold can be restrained by operation at temperatures lower than 340 K and the cavity losses which do not exceed 60 cm K1 .

Quantum-well heterostructure laser diodes with flat widely tunable gain spectra

For a novel type of asymmetric multiple-quantum-well heterostructure lasers it is shown that a flat modal gain spectrum is obtained in a wide spectral range. It occurs since the quantum wells varied in widths and chemical compositions give a definite contribution to the total gain in different intervals of the spectrum. A certain design of the laser structures (chemical composition, thickness, doping, and arrangement of active and barrier layers) provides the conditions of non-uniform excitation of the quantum wells that results in the broad-band flat gain spectrum. Output power characteristics of the tunable laser diodes with a grating external cavity are examined in detail. For the spectral interval near the wavelength of 820 nm, the GaAs-AlGaAs system is preferred. In this case, the width of the gain band reaches up 50 nm and the tuning curve is practically flat at the output power about 10 mW in a single-mode regime without mode hops. Use of the other ternary or quaternary semiconductor compounds transfers the tuning range to a necessary spectral region. The described quantum-well heterostructures are suitable to make effective tunable laser diodes for a wide variety of applications, such as WDM optical networks, coherent spectroscopy, chemical analysis, metrology, and environment monitoring.

Polarization characteristics of quantum-well semiconductor structures

For low-dimensional semiconductor systems, matrix elements of optical dipole transitions versus different directions of the radiation polarization vector have been analyzed in detail. Analytical and numerical calculations are performed for quantum-well heterostructures in III-V semiconductor compounds. An influence of the spectral broadening due to intrasubband relaxation of current carriers on the transformation of light emission spectra in TE and TM modes with excitation has been studied. Distributions of electromagnetic wave fields and the optical confinement factor for TE and TM modes in multiple quantum-well layer structures, including a novel type of asymmetric heterostructures, have been determined. For quantum-wire structures, including a novel type of asymmetric heterostructures, have ben determined. For quantum-wire structures, the degree of light emission polarization has been examined and effects in porous Si luminescence are explained.

Amplification in photonic crystal heterostructures with active media from doping superlattice layers

Computer simulation demonstrates that asymmetric photonic crystal heterostructures with defect layers provides lasing at two different wavelengths and in opposite output directions. The light field distribution and radiation transport in the photonic structures are strongly affected by the n-i-p-i layers periodicity, dispersion characteristics of the components, and. conditions at the interfaces. Described photonic crystal. heterostructures can be attractive for a wide variety of applications. In particular, they can be used as single-mode laser sources or amplifiers at the near-infrared spectral region.

Saturation of absorption in n-i-p-i crystals

Peculiarities of the absorption saturation in doping superlattices with n-i-p-i crystal type structure are established. Calculations are performed in the k-selection rule model taking into account the screening of the electrostatic potential by current carriers and the density state tails.

Design and characteristics of widely tunable quantum-well heterostructure lasers in the Littman and Metcalf cavity configuration

Analysis of light-current and tuning characteristics of a quantum-well laser in an external cavity is performed. The band diagram of the proposed tunable asymmetric multiple quantum-well heterostructure laser source under the forward bias is shown. The heterostructure consists of the GaAs-AlGaAs system.

Current injection and recombination processes in asymmetric triple quantum well lasers

For lasers based on asymmetric quantum-well heterostructures comprising three different quantum wells and barrier layers with a complex potential profile, current carrier injection and radiation emitting processes have been considered. The analysis performed by using rate equations has shown that a regime of regular pulse generation at remote wavelengths is practicle. The radiation pulsation process is accompanied by oscillations of the carrier injection efficiency into quantum wells. At certain parameters of the laser structures it is possible to realize radiation bistable switching-on or the regime where relative powers at different wavelengths change with increasing the pump current. The injection efficiency has been determined by solving the Poisson equation and continuity conditions for electron and hole currents. Carrier tunneling through potential barriers between the quantum wells has been taken into account. Calculations have been performed for the GaAs - AlxGa1- xAs system.

Nonlinear response of quantum-well heterostructure lasers at current modulation and cavity detuning

The influence of cavity detuning on the nonlinear dynamics of quantum-well heterostructure lasers with harmonic modulation of the pump current is analyzed. Four different models of the active medium which allow us to simulate different practical situations with respect to the modulation frequency and cavity detuning are used. As shown, different nonlinear regimes, including period doubling, chaos, and generalized bistability, can be obtained either with the cavity detuning from the maximum gain band or near the laser threshold. Effects of the radiation polarization on the laser performance are studied too. Parameters of the current modulation and spectral detuning of laser diodes are considered in relation to optical communication and optoelectronic applications.

Control of transmission in photonic structures with n-i-p-i layers

Structures with a tunable photonic band gap can be used as effective optical switches. In this paper, the availability of n-i-p-i crystal layers in such periodic structures is considered. The dispersion and transmission characteristics of the GaAs-AlGaAs structures are examined for different excitation levels up to where light amplification occurs, The main feature of the switches is the control of the photonic band gap edge near 1.5 /spl mu/m by light at the shorter wavelengths due to the change in the refraction index of the active layers.