Dmitrii V. Ushakov

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.

Effects of energy-spectrum broadening in alloyed semiconductor superlattices

The density of energy states is calculated for alloyed semiconductor superlattices for different excitation levels with cllowance for the effects of screening and fluctuations of impurity concentrations. The influence of the state density tails on spontaneous-emission spectra is investigated for cross-over transitions and in a model without a selection rule for the electron wave vector. Account for the state density tails allows one to describe the longwave wing and shape of spontaneous-emission spectra in accordance with experimental data.

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 .

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.

NONLINEAR OPTICAL PROCESSES IN DOPED SEMICONDUCTOR SUPERLATTICES

For doped semiconductor superlattices we have analyzed the effects of absorption saturation and change in the refractive index depending on the level of their excitation and structure parameters. The calculations were carried out with account for the tails of the density of states and screening of the electrostatic potential. It is shown that doped superlattices may display “shading,” i.e., the increase in the absorption coefficient at a fixed frequency with increase in light intensity. For δ–doped superlattices a stronger nonmonotonicity of the change in the refractive index with increase in the excitation level in comparison with typical structures can manifest itself.

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.

Temperature dependence of the threshold and Auger recombination in asymmetric quantum-well heterolasers

The temperature dependence of the lasing threshold in the GaInAs-GaInAsP-InP bi-quantum-well heterolasers with different widths of the quantum wells (4 and 9 nm) has been determined. Processes of non-radiative Auger recombination which occur in the active region of the quantum-well lasers have been included into consideration. The analytical approach for the evaluation of the characteristic temperature of the lasing threshold is presented. For described asymmetric quantum-well heterostructure lasers, it is shown that the influence of Auger recombination processes on the temperature behavior of the lasing threshold is not essential until the temperature of the active region is lower than 360 K and the cavity losses do not exceed 80 cm-1.

Photonic bandgap structures with n-i-p-i layers

Optical properties of one-dimensional heterostructures having optical forbidden gap are described and photonic structures with n-i-p-i superlattices are designed for laser 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.

Photonic crystal heterostructures with controllable active layers

Properties of one-dimensional photonic crystal heterostructures having a photonic band gap in the near infra-red spectrum are examined and photonic crystals with n-i-p-i superlattices are designed for information technologies. For the first time, the availability of n-i-p-i crystals in photonic band gap heterostructures is considered and different configurations of microcavities are described. Optical properties and output characteristics of the photonic crystals in the GaAs-AlGaAs and GaAs-GaInP systems are determined and possible applications for optical switchers, filters, single-mode laser sources, and amplifiers are discussed.