A. Yu. Luk’yanov

Optical monitoring of technological parameters during molecular-beam epitaxy

It is shown that one can use low-coherence tandem interferometry to measure the substrate temperature during the course of molecular-beam epitaxy in the case of oblique incidence of the probing light onto the surface. The temperature conditions in the Ob’-M installation for growing heteroepitaxial structures of cadmium and mercury tellurides and in the RIBER SIVA-21 installation for the growth of silicon-germanium structures are investigated. Calibration curves relating the readings of the standard thermocouple fixed within the heater to the true substrate temperature in the range 0–500°C are created.

Optical monitoring of technological parameters in metal-organic vapor-phase epitaxy

The possibility of applying low-coherent tandem interferometry to optical monitoring of the temperature of a semiconductor substrate and the thickness of a deposited layer in metal-organic vapor-phase epitaxy (MOVPE) is demonstrated for the first time. The absolute accuracy in the temperature measurements of Si, GaAs, and sapphire substrates under MOVPE conditions is limited by the calibration accuracy and is ±1°C. The accuracy in the measurement of the deposited layer thickness is 2 nm. A considerable (10–100°C) deviation of the temperature measured by a thermocouple placed inside a susceptor from the actual substrate temperature is found. A significant temperature gradient along the susceptor depending on the gas flow rate and other factors is revealed. It is shown that, owing to the high heating efficiency of sapphire substrates, there is no need to coat their reverse with absorbing layers upon heating up to 300°C or in the presence of hydrogen pressure of higher than 100 mbar.

Luminescence of phthalocyanine thin films

The near-IR luminescence in thin films of metal-free phthalocyanine and phthalocyanine complexes is investigated at room temperature. It is shown that the intensity of the luminescence peaks depends on the polymorphic modification and the structure of the complexes, whereas the peak positions remain virtually unchanged.

Compact photothermal-refractometric detector for high performance liquid chromatography based on a polarization interferometer

A combined photothermal-refractometric detector for high-performance liquid chromatography is proposed. Five metal complexes as 4-pyridylazo-2-naphthol chelates and three sugars were investigated as model substances. For these compounds, detection limits, repeatability, and reproducibility of determination were calculated. Obtained results were compared with results for traditional detectors, which show that photothermal detection has higher sensitivity than photometric and other absorption detectors.

The sensitivity of thermal-lens and phase-shift (interferometric) techniques in photothermal spectroscopy: A comparative study

The thermal-lens and phase-shift (interferometric) techniques of photothermal spectroscopy are studied theoretically for the coaxial and mutually orthogonal propagations of probing and pumping beams. Respective expressions for the amplitude of detected signals are derived for the case of the volume absorption of pumping radiation. The sensitivities of the two techniques are numerically analyzed for different parameter values. It is demonstrated that the phase technique offers higher sensitivity especially if the size of the region with a perturbed temperature field is much larger than the probing beam radius.

Quantitative measurements of optical absorption in CVD-grown ZnS with the phase-shift photothermal method

A technique of measuring weak bulk optical absorption at a wavelength of 10.6 μm in polished plates made of CVD-grown polycrystalline ZnS was developed on the basis of the phase-shift photothermal method. The results obtained are in good agreement with the data on the absorption of the samples under investigation, calculated from calorimetric and transmittance measurements. The possibility of highly sensitive local quantitative measurements of the optical-absorption coefficient using the phase-shift photothermal method is demonstrated.

Growing InN films by plasma-assisted metalorganic vapor-phase epitaxy on Al2O3 and YSZ substrates in plasma generated by gyrotron radiation under electron cyclotron resonance conditions

Hexagonal indium nitride (InN) films on (111)- and (100)-oriented yttria-stabilized zirconia (YSZ) substrates and (0001)-oriented Al2O3 substrates have been grown for the first time at a rate of 1 μm/h by the method of metalorganic vapor-phase epitaxy with plasma-assisted nitrogen activation in an electron cyclotron resonance discharge generated by gyrotron radiation at low-temperature (350°C) growth. InN films grown without buffer layers possess a textured polycrystalline structure. Using an InN/GaN double buffer layer, single-crystalline InN films have been obtained on Al2O3(0001) substrates. Data on the morphology, structure, and photoluminescent properties of the obtained InN films are presented.

Thin-film photovoltaic cells based on vanadyl phthalocyanine and fullerene

Prototypes of organic photovoltaic cells containing a planar phthalocyanine-fullerene hetero-junction are fabricated. The main parameters of photoconversion in such structures are measured in relation to deposition conditions of a photoactive molecular layer (vanadyl phthalocyanine) and to the material of a subcathode interface layer. It is shown that morphological changes in the vanadyl phthalocyanine layer due to a decrease in the deposition rate in vacuum improve the efficiency of the cells roughly by an order of magnitude.

Phase (interferometric) photothermal method for separate measurements of surface and volume absorption

The possibility of separately measuring the surface and volume absorption by a phase photothermal method is demonstrated with ZnSe polished samples. A theory developed allows us to directly relate the signal amplitude to the coefficients of surface and volume absorption. From the experimentally found dependence of the temperature oscillation amplitude at the sample surface on the angle of incidence, the position of the absorbing surface layer relative to the interface is determined and a mechanism of interaction between the pumping radiation and the target material is assessed.

High-rate growth of InN films on fianite and sapphire substrates by metalorganic vapor phase epitaxy with plasma-assisted nitrogen activation

Hexagonal single-crystalline indium nitride (InN) films on (0001)-oriented sapphire (Al2O3) and (111)-oriented fianite (yttria-stabilized zirconia, YSZ) substrates and on (0001)-oriented GaN/Al2O3 templates have been grown at a record high rate of 10 μm/h by the method of metalorganic vapor phase epitaxy with nitrogen activation in plasma of electron cyclotron resonance discharge generated by gyrotron radiation. It is established that the use of fianite substrates significantly improves the structural perfection and photoluminescent properties of InN films as compared to those grown on sapphire and templates. Undoped InN films exhibit n-type conductivity with electron concentrations within n = 8.0 × 1019–4.9 × 1020 cm−3 and room-temperature mobilities up to 180 cm2/(V s).