Влияние интерфейсных эффектов на электронный спектр структур GaAs/AlGaAs, используемых для создания фотоприемных устройств среднего ИК-диапазона

The effect of transition processes arising in the growth chamber of the molecular beam epitaxy unit on the interfaces structure and electronic spectrum of GaAs /AlxGa1-xAs quantum wells used for MID IR photodetectors was investigated. It is shown that such processes lead to (1) low-frequency shift of the photosensitivity spectrum; (2) reduction of energy shift between the fundamental and first excited hole levels in quantum wells; (3) the appearance of the symmetry forbidden transition in the absorption spectra. These effects provide a simple approach for non-destructive assessment of the interfaces quality in GaAs/AlxGa1-xAs heterostructures for MID IR photodetectors.

Combined Sensitisation of Benzaldehyde Diphenylhydrazones: Effect of Hydrazone Structure on Sensitization Efficiency

Injection, spectral and combined (injection-spectral) sensitisations of several benzaldehyde diphenylhydrazones have been studied using the layers of amorphous selenium and complex compounds based on<br />pyril dyes to broaden photosensitivity spectrum of electrophotographic carrier and to study sensitisation mechanism. Two photogeneration mechanisms for charge carriers have been shown to exist at a combined<br />sensitisation, i.e. generation in the injection layer followed by the injection into a transport layer and generation in a transport layer on a dye. The excited dye molecules have been established to create hole strapping sites in a transport layer: it is exhibited in a different nature of photodischarge curves in selenium- and dye-absorbing regions at the negative surface potential. The effect of the substituent in a benzaldehyde fragment on the efficiency of injection, spectral and combined sensitisations of benzaldehyde diphenylhydrazones<br />has been studied. The ionization potentials of hydrazones were determined by the two following methods: according to the charge transfer band of hydrazone-chloranil charge transfer complexes and<br />by means of quantum-chemical calculations of hydrazone molecules to interpret the results obtained. In the course of quantum-chemical calculations the conjugation character was also determined in the molecules of benzaldehyde diphenylhydrazones.

Polarimetric sensors on the basis of CdS/CuInSe2 heterocontact: Influence of the heat treatment on photosensitivity spectrum

CuInSe2 thin films were grown by vacuum evaporation of presynthesized material from a single source. The room-temperature photoconductivity spectra of the film show a strongly dependence on the evaporation conditions and, especially, on the evaporation temperature. A shift of the long-wavelenght photoactive absorption edge and the evolution of the photoconductivity spectra of the films were observed. The influence can be explained by allowing for deviations of the compositions of the condensed phase from CuInSe2 stoichiometry.

Photosensitivity spectrum of crayfish rhodopsin measured using fluorescence of metarhodopsin.

Discrepancies exist among spectral measurements of sensitivity of crayfish photoreceptors, their absorption in situ, and the number and absorption spectra of crayfish photopigments that are extracted by digitonin solutions. We have determined the photosensitivity spectrum of crayfish rhodopsin in isolated rhabdoms using long wavelength fluorescence emission from crayfish metarhodopsin as an intrinsic probe. There is no measurable metarhodopsin in the dark-adapted receptor, so changes in the emission level are directly proportional to metarhodopsin concentration. We therefore used changes in metarhodopsin fluorescence to construct relaxation and saturation ("photoequilibrium") spectra, from which the photosensitivity spectrum of crayfish rhodopsin was calculated. This spectrum peaks at or approximately 530 nm and closely resembles the previously measured difference spectrum for total bleaches of dark-adapted rhabdoms. Measurements of the kinetics of changes in rhabdom fluorescence and in transmittance at 580 nm were compared with predictions derived from several model systems containing one or two photopigments. The comparison shows that only a single rhodopsin and its metarhodopsin are present in the main rhabdom of crayfish, and that other explanations must be sought for the multiple pigments seen in digitonin solution. The same analysis shows that there is no detectable formation of isorhodopsin in the rhabdom.

The contribution of a sensitizing pigment to the photosensitivity spectra of fly rhodopsin and metarhodopsin.

Most of the photoreceptors of the fly compound eye have high sensitivity in the ultraviolet (UV) as well as in the visible spectral range. This UV sensitivity arises from a photostable pigment that acts as a sensitizer for rhodopsin. Because the sensitizing pigment cannot be bleached, the classical determination of the photosensitivity spectrum from measurements of the difference spectrum of the pigment cannot be applied. We therefore used a new method to determine the photosensitivity spectra of rhodopsin and metarhodopsin in the UV spectral range. The method is based on the fact that the invertebrate visual pigment is a bistable one, in which rhodopsin and metarhodopsin are photointerconvertible. The pigment changes were measured by a fast electrical potential, called the M potential, which arises from activation of metarhodopsin. We first established the use of the M potential as a reliable measure of the visual pigment changes in the fly. We then calculated the photosensitivity spectrum of rhodopsin and metarhodopsin by using two kinds of experimentally measured spectra: the relaxation and the photoequilibrium spectra. The relaxation spectrum represents the wavelength dependence of the rate of approach of the pigment molecules to photoequilibrium. This spectrum is the weighted sum of the photosensitivity spectra of rhodopsin and metarhodopsin. The photoequilibrium spectrum measures the fraction of metarhodopsin (or rhodopsin) in photoequilibrium which is reached in the steady state for application of various wavelengths of light. By using this method we found that, although the photosensitivity spectra of rhodopsin and metarhodopsin are very different in the visible, they show strict coincidence in the UV region. This observation indicates that the photostable pigment acts as a sensitizer for both rhodopsin as well as metarhodopsin.