535 research outputs found
Abnormal Character of the Diffusivity-mobility Ratio in Doping Superlattices
The influence of high level of doping in type n-i-p-i crystal structures on electron and hole state distributions is examined. Abnormal behaviour in the diffusivity- mobility ratio due to shortening of the density
state tails under excitation of doping Superlattices is described
Production of broadband modal gain spectra in asymmetric multiple quantum-well Ga0.47In0.53As/Ga0.18In0.82As0.4P0.6 heterostructures
The modal gain spectra of asymmetric multiple
quantum-well Ga0.47In0.53As/Ga0.18In0.82As0.4P0.6 hetero-
structures are theoretically analysed within the framework
of the four-band kp method. An efficient procedure for
obtaining the broadband and almost êat gain spectrum is
proposed. The designs of semiconductor radiation sources
with different sets of nonuniformly excited quantum wells
producing broadband amplification in spectral ranges from
1.28 to 1.525 \mu m and from 1.36 to 1.6 \mu m are calculated
Calculation of energy characteristics for Si1-xGex-Si strucrures with single quantum wells
Energy characteristics of Si1–xGex–Si quantum-size structures with single quantum wells were calculated numerically
based on a four-band k⋅p method. Analytical expressions for the Luttinger parameters are obtained
as functions of the component composition of Si1–xGex compounds. Analytical expressions for the energy h−ω
of optical band-to-band transitions are obtained in an effective mass approximation and agree well with numerical
calculations by the k⋅p method. This allows one to determine accurately a range of changes while
varying the component compositions and thickness of the active and barrier layers
Carrier transport and screening in n-i-p-i crystals
The variation of the energy spectrum of n-i-p-i crystals under excitation was examined and the
influence of the reduction of the screening length on the ratio between the coefficient of diffusion
and the mobility of the current carriers was established. It is shown that the filling of subband
states by carriers results in an anomalous behaviour of the diffusivity-mobility ratio. The effect
occurs in the electric quantum limit and at room temperature as well
Nonlinear gain and bistability in photonic crystal heterostructures with compositional and doping superlattices
Optical properties of photonic crystal heterostructures with embedded n–i–p–i superlattices are studied. Nonlinear
behavior of the transmission and reflection spectra near the defect mode is investigated. Self-consistent calculations of
the output performance characteristics are performed using the transfer-matrix method and taking into account the gain
saturation. Features and characteristic parameters of the nonlinear gain in active n–i–p–i layers are determined. Detail
analysis of the gain saturation and accompanying nonlinear refraction effects is carried out for one-dimensional photonic
crystal heterostructure amplifiers in the GaAs–GaInP system having at the central part an active “defect” from the
doubled GaAs n-i-p-i crystal. The gain saturation in the active layers in the vicinity of the defect changes the index
contrast of the photonic structure and makes worse the emission at the defect mode. Spectral bistability effect which can
be exhibited in photonic crystal heterostructure amplifiers is predicted and the hysteresis loop and other attending
phenomena are described. The bistability behavior and modulation response efficiency demonstrate the potential
possibilities of the photonic crystal heterostructures with n-i-p-i layers as high-speed optical amplifiers and switches
Nonlinearities in the reflection and transmission spectra of the photonic bandgap heterostructures with n–i–p–i crystals
Nonlinear optical properties of photonic crystal heterostructures with embedded
n–i–p–i superlattices are investigated. Self-consistent calculations of the transmission and
reflection spectra near the defect mode are performed using the transfer-matrix method and
taking into account the gain saturation. Analysis of features and output characteristics is carried
out for one-dimensional photonic crystal heterostructure amplifiers in the GaAs–GaInP
system having at the central part an active “defect” from doubled GaAs n–i–p–i crystal layers.
The gain saturation in the active layers in the vicinity of the defect changes the index
contrast of the photonic structure and makes worse the emission at the defect mode. Spectral
bistability effect, which can be exhibited in photonic crystal heterostructure amplifiers, is
predicted and the hysteresis loop and other attending phenomena are described. The bistability
behavior and modulation response efficiency demonstrate the potential possibilities of
the photonic crystal heterostructures with n–i–p–i layers as high-speed optical amplifiers and
switches
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
Multiple-wavelength lasing in one-dimensional bandgap structures: implementation with active n–i–p–i layers
We study the optical localized states in a one-dimensional system of strongly coupled defect microcavities for the case when a tight-binding approximation is not valid. Transmission and electromagnetic mode density spectra as well as the distribution of light intensity inside the bandgap material are investigated. We report on the effect of splitting the fundamental coupled-cavity mode into several high-Q submodes to support perfect transmission of light at low group-velocity values. New types of laser microcavities that provide low-threshold lasing at multiple wavelengths and in opposite directions are proposed. Possible implementation of the laser systems with active n–i–p–i layers is discussed
Current carrier lifetime in doping superlattice crystals
It is shown, that the lifetime of nonequilibrium current carriers in the luminescence process in doping superlattice structures
changes in a wide range with increasing the excitation level of the crystal. Two effects are important, i. e., (a) lowdimensional
character of the carrier distribution and (b) change in the overlap of electron and hole wave functions. At low
excitation, non-radiative recombination can play principal cause in the stabilization of the effective lifetime of current
carriers. At high excitation, the effective lifetime of current carriers approaches the value in the bulk crystal. The major
attention was given to the compensated GaAs doping superlattices with i-layers (n-i-p-i crystals) and to the structures with
no i-layers (n-p-n-p structures). The layer thickness of n-, p-, and i-type were 20, 40, or 60 nm and the concentrations of the
dopants Te and Zn made up to 1018 cm3. Photoluminescence spectra and the decay time of the spontaneous emission
intensity in the superlattices were measured at the temperature interval from 1 1 to 300 K. The influence of u-particle
irradiation and thermal annealing on the luminescence spectra and the carrier lifetime was also investigate
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