The near-IR light absorption oscillations in 2D macroporous silicon structures with microporous silicon layers, CdTe
surface nanocrystals and SiO<sub>2</sub> nanocoatings are investigated. The electro-optical effect was taken into account within the
strong electric field approximation. Well-separated oscillations with giant amplitude were observed in the spectral ranges
of surface level absorption. This process is because of resonance electron scattering on the surface impurity states with
the difference between two resonance energies equal to the Wannier-Stark ladder due to big scattering lifetime as
compared to the electron oscillation period in an electric field. The electron transitions and free electron motion are
realized due to additional change of local electric field as a result of grazing light incidence and quasi-guided mode
Photonic membranes are widely used kind of 2D photonic crystals in signal processing. We develop the
approach uniting both in-plane and out-of-plane geometries as well as resonator properties of membrane-like
photonic crystals (MPC). The resonator standing modes are excited by an external source through the special
inputs and may be controlled due to nonlinear coating. We study typical 1D and 2D photonic membrane
resonators of rectangular form with nonlinear inclusions as an important element of logical devices. The drastic
change of the reflectivity due to so-called nonlinear band shift effect is investigated and two main signal
processing schemes are analyzed for Si/SiO<sub>2</sub> MPC covered with nonlinear doped glasses. General design of alloptical
logic gates and adder design are discussed. Novel calculation method based on the analytical basis of
resonator's eigenstates is used to obtain dependencies for reflectivity, modal spectrum and field distribution for
chosen working frequencies.
Mechanisms of the negative and imaginary parts of the permittivity formation in 2D photonic macroporous silicon
structures are investigated. Negative part of permittivity in 2D photonic macroporous silicon structures is determined by
the polaritonic and surface electromagnetic mode formation. One of mechanisms of the imaginary permittivity formation
is the electro-optical effect realized clearly in 2D photonic macroporous silicon structures in the near-IR area (impurity
absorption). We investigated the "out-of-plane" optical absorption of 2D photonic macroporous silicon structures taking
into account the optical mode formation and the electro-optical effect. The reflected electromagnetic waves at grazing
angle of light incidence onto macropore surface change effectively the local surface electric field.
Polaritonic resonancies are investigated in 2D silicon photonic crystals. Theoretically unpredicted
reduction in the transmittance of electromagnetic radiation and the step formation are observed for
wavelengths less than optical period of structures due to directed and decay optical modes formed by
macroporous silicon as a short waveguide structure. Prevalence of absorption over reflection of light
testify to the polaritonic type band formation. Surface polaritons are formed on decay modes in a silicon
matrix or macropore at formation of directed optical modes relatively on macropore or silicon matrix.
Absorption, photoconductivity and Raman scattering maxima are determined by a corresponding
maximum of a longitudinal component of electromagnetic waves in macroporous silicon structure as
short waveguide with a specific surface. Longitudinal component of electromagnetic waves in
investigated structure interacts effectively with surface oscillators, and polaritonic resonances in 2D
silicon photonic crystals are observed.
Charge carrier transport mechanism in barrier "In-macroporous silicon" structures has been investigated. Currentvoltage, capacitance-voltage, photoelectrical and noise characteristics were analyzed comparatively in structures of macroporous and single-crystal silicon. There has been designed manufacture technology of ohmic and barrier contacts on 2D macroporous silicon as well as single-crystal silicon in the same technological cycle. The contacts
were found to exhibit stable characteristics during six month period of time. The saturation of the reverse current at 0.2 ≤ U ≤ 1.0 V was observed at high temperatures. The carrier transport mechanism in the investigated structures are determined by thermal activation mechanisms at room temperature and tunneling of carriers through the transient region at temperatures T ≤ 180 K. Capacitance-voltage characteristics are similar to those observed in the metal-oxide-semiconductor structures and are included capacitance of the oxide layer and the depletion region. The presence of the transient region between metal and silicon was confirmed by the photoresponse spectra of "Inmacroporous Si" structures contained two pronounced peaks at the wavelengths 0.56 and 1.1 μm. The longwavelength peak was observed for In contacts on single n-Si crystal prepared by the same method.
Out-of-plane optical transmission spectra of 2D photonic macroporous silicon structures are investigated. By the plane wave expansion method all possible 2D lattice symmetries are considered and analyzed both in general case and for p-, s-polarizations. Sharp increase of absorption and formation of photonic band gaps is measured for wavelengths between one and two optical periods of macroporous silicon structure. Thus, for periodic structures one photonic band gap is formed, and some narrow peaks of density of states are formed for structure with the arbitrary macropore distribution. Theoretically unpredicted reduction in the transmittance of electromagnetic radiation and the step formation are observed for wavelengths less than optical period of macropores. Transmission spectra of macroporous silicon as well as steps were explained by a model of directed and decay optical modes formed by macroporous silicon as a short wave-guide structure. Prevalence of absorption over reflection of light, dependence of photoconductivity on incidence angle of the electromagnetic radiation testify to formation of the polaritonic type band formation.
In this paper we analyze theoretically how introduction of the third component into the two-dimensional photonic crystal influences on the photonic band structure and the density of states of the system. We consider the periodic array of cylindrical air rods in a dielectric and the third medium is introduced as an intermediate layer of the thickness d and the dielectric constant εi between the air pores and the dielectric background. Various combinations of the parameters R (pores radius), d, and εi which allow the band gap to appear were considered. Using the plane wave method we have obtained the band structures and density of states for the triangular lattice 2D photonic crystals. The dependencies of the band gaps width and gaps edges position on the interlayer dielectric constant and interlayer thickness were analyzed. In the framework of this approach we have estimated the influence of the surface oxide layer on the band structure of macroporous silicon. We observed the shift of the gap edges to the higher or lower frequencies depending on the interlayer thickness and dielectric constant. We have shown that the existence of a native oxide surface layer should be taken into consideration to understand the optical properties of 2D photonic crystals, particularly in macroporous silicon structures.
Effects of increase in absorption of electromagnetic radiation, enhancement of photoconductivity and surface wave formation in 2D photonic macroporous silicon were investigated. Dependence of photoconductivity on a corner of the falling of the electromagnetic radiation, prevalence of absorption over reflection of light, as well as enhancement of the photoconductivity in comparison with the monocrystalline silicon testify to formation of surface waves (surface polaritons) in illuminated macroporous silicon structures. For wavelengths less than optical period of macropores there is an essential reduction in transmittance of electromagnetic radiation to (2-3)•10<sup>-2</sup> (in comparison with the homogeneous material) and the polaritonic band formation. Conformity of spectra of photoconductivity of macroporous silicon to spectra of intrinsic photoconductivity of monocrystal silicon testifies the enrichment of a macropore surface by photocarriers and formation of a surface electromagnetic wave of plasmon type. Elecrtroreflectance spectroscopy of macroporous silicon surface showed an intrinsic electric field near 10<sup>6</sup> V/cm due to positive charge built in oxide layer on the walls of the macropores. Thus, electronic gas is quantified in a surface layer of the macroporous silicon structure. Polariton frequencies in long-wave part of the macroporous silicon optical transmittance are commensurable with experimental values of the surface plasmon frequency in the two dimensional electronic gas on Si-SiO<sub>2</sub> boundary.
Effects of the enhancement of photoconductivity in 2D photonic macroporus silicon structures were investigated. Dependence of photoconductivity on the angle of incidence of the electromagnetic radiation is observed with maxima at normal incidence of electromagnetic radiation, in the region of the angle of full internal reflection respective to macropore walls and at a grazing angle of incidence respective to the surface of structure. The absolute maximum of photoconductivity is measured at distance between macropores, corresponding to two lengths of the electron free run, i.e. by the maximal transfer of the amplified electric components from a macropore surface in a silicon matrix. Angular dependences of photoconductivity, as well as enhancement of the photoconductivity in comparison with monocrystal silicon, primary absorption p-component of electromagnetic radiation testified to formation of surface electromagnetic waves in illuminated macroporous silicon structures. Its effects result in amplification of a local electric field on a surface of macroporous silicon structure and a macropore surface. The measured value of the built-in electric field on a macropore surface achieves 10<sup>6</sup> V/cm, the signal photoconductivity amplifies 10<sup>2</sup> times, and Raman scattering -- up to one order of value.
Local chemical states and structure of microporous layers on macropore walls were investigated before and after KOH etching using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy. Micropore layers of the thickness 100 - 700 nm were formed on macropore walls of two-dimensional silicon structures. Higher current densities gave the thinner microporous. FTIR spectroscopy results showed content strong peak 465 cm<sup>-1</sup> attributed to SiO<sub>2</sub> structures and Si-Si peak 650 cm<sup>-1</sup> observed due to high porosity and big total surface of microporous layers. After KOH etching Si-O peak is presented in FTIR spectra of all investigated structures. Macroporous silicon structures fabricated at low initial bias <i>U<sub>0</sub></i> less of 1-st peak in <i>I-V</i> characteristic after KOH etching content mainly OH, Si-O and Si-Si peaks.
The light-assisted method of electrochemical etching of n-Si allows the formation of cylindrical macropores with a high ratio of pore depth to pore diameter and with strong periodicity. Such structures are highly promising for modification of the electromagnetic wave spectra in semiconductor devices. In this work, the method of macropore formation on low resistance silicon plates was improved. Photoluminescence (PL), peaking near 600 nm with an intensity of 10 (mu) W/cm<SUP>2</SUP>, was measured on macroporous silicon, which had evolved microporous layers containing nanocrystals. For higher current densities during pore formation the intensity of the orange light emission decreased, and a blue PL shift was observed due to a reduction in the sizes of the Si nanoparticles. Anomalous coefficients of light absorption allow the development of thermal- and photo-sensors on the basis of macroporous silicon. The investigated macroporous silicon structures are a promising material for multi-element thermal sensor fabrication due to a high temperature coefficient of electrical resistance (1 - 4%), low noise level (2 (DOT) 10<SUP>-9</SUP> VHz<SUP>-1/2</SUP>) and good radiation absorption in the spectral region (lambda) equals 2 - 20 micrometers .
Photoluminescence (PL) in complex micropore-macropore silicon structures consisted of 100 - 700 nm micropore layers on macropore walls have been studied. Scanning electron microscopy observations and Fourier transform infrared spectroscopy results have been performed to identify structure and local chemical states. For higher current densities during pore formation the intensity of orange PL peaking near 600 nm decreased, and the PL lifetime was grown. The blue PL shift was observed due to reduction of Si nanoparticle sizes, and micropore-macropore structures showed the lower PL intensity dealing with the small hydride concentration and thin microporous layers. Obtained results suggest arising of orange PL from microporous layers on the macropore walls that widened optoelectronic functions of two-dimensional macroporous silicon structures.
Model of the influence of the shallow and deep impurity level profiles on the capacitance relaxation curves was made using the optimal parameter choice method. There were established that the shallow impurity profile decay and the deep impurity profile growth increase the dimensionless time. Besides it the shallow impurity profile growth and the deep impurity profile decay decrease. Such effects give rise the undervalue of the dimensionless capacitance (omega) for the first case and overvalue (omega) for the second one. The received expressions for increment d may be used for the quantitative estimation of the shallow and deep impurity profiles without procedure of the differentiation of the experimental C-t-curves. That permit to increase the accuracy of the impurity profile determination.
Electrochemical process of the n-Si macroporous photonic structure formation has been investigated. The stationary distribution of the nonequilibrium hole concentration through the depth of n-Si plates after the intrinsic backside illumination was calculated. The light intensity and the electrical field regimes were determined for the macropore formation with the constant hole concentration on the tips. The stationary current regime is not equal to the electrochemical process stability. It was found that the stabilization of the hole concentration due to the light intensity change is more effective relatively the electrical field variation. The hole concentration stability and the cylindrical pore formation are possible for the high photosensitive samples only.
For technological optimization of CdHgTe crystals used widely in IR-photodetectors the mechanisms of principal (theoretical) limitation of carrier concentration, mobility, and lifetime were investigated in the result of thermo and ultrasonic treatments. Next new phenomena and peculiarities of non-equilibrium processes were determined. Experimentally and theoretically minimum of lifetime concentration dependence was obtained when equilibrium carrier concentration was variated due to modification of acceptor (mercury vacancies) concentration. For 'weak' p-type conductivity crystals in low for holes magnetic fields the simple analytical Hall coefficient magnetofield dependence was justified. That permitted us to control electron and hole concentrations and mobilities for practically intrinsic material. Recombination-sized effect dealt with dependence of characteristic diffusion length on macrodefect size and configuration was obtained. Thermoacoustic processes of mercury vacancy generation and 'cure' were investigated.
Mechanisms of macrodefect's and isovalent admixture's influence on photoluminescence spectra and halvanomagnetic parameters of HgCdTe/CdTe heterostructures were investigated. Profiles of electrical and structural parameter distributions through the depth of epilayers HgCdTe (x approximately equal to 0.2, p-type and with mixed conductivity), on CdTe substrates ('clean' and with 4% of Se or Zn components) were measured. There was detected substantial increase of well-known in CdTe donor-acceptor photoluminescence band 1.43 eV (T equals 77 K) in transition layers and CdTe substrates with increased macrodefect concentration (dislocations, subgrain boundaries, Te precipitates). It was established that such elevation was dealing with the donor component of conductivity in substrates and corresponding epilayers. The donor's nature was dealing with the substrate's defect structure. So photoluminescence band intensity may characterize CdTe defect level and permit us to reject such substrates.