Photosensitive Region Research Articles

Effects of the Preparation Procedure and In2O3Thickness on the Electrical and Photovoltaic Properties of In2O3 /CuInSe2Heterostructures

In2O3 /CuInSe2 heterostructures were produced by growing indium oxide layers on bulk single-crystal and polycrystalline p-type CuInSe2 substrates using thermal oxidation and magnetron sputtering. The substrates were prepared by cleaving or abrasive polishing and chemical etching. The resistivity of the In2O3 layers was measured as a function of temperature and layer thickness, and the current–voltage characteristics and spectral response of the heterostructures were analyzed. The results indicate that the structures exhibit reduced reflection losses at oxide thicknesses below 0.5 μm. The reduced thickness of interfacial layers owing to the low process temperature in the case of magnetron sputtering makes it possible to extend the spectral region of photosensitivity of the heterostructures.

Tunnel Currents in the Photo-Field Detectors and the Auger Transistor under Strong Electric Field

ABSTRACTThe photo-field emission properties of semiconductors at a very strong electric field together with tunnel electron emission in metal-insulator-semiconductor heterostructures with a tunneltransparent layer of an insulator was studied. It was found that a self-consistent quantum well near the surface of semiconductor emitter tips can change the spectral region of photosensitivity of the radiation semiconductor field emitter detectors, and leads to the significant increase in their photosensitivity [1]. Also the appearance of a self-consistent quantum well near the semiconductor surface is the key factor which allows to use the metal-insulator heterojunction in the development of an Auger transistor based on the Al-SiO2-n-Si structure - the fastest operation semiconductor bipolar transistor [2–4]. Conditions for appearance of a self-consistent quantum well under strong electric field in both the near-surface region of a vacuum semiconductor field-emitter and metal-insulator-semiconductor heterostructures (Auger transistor) were studied also.

Microstructured optical fiber devices

We present several applications of microstructured optical fibers and study their modal characteristics by using Bragg gratings inscribed into photosensitive core regions designed into the air-silica microstructure. The unique characteristics revealed in these studies enable a number of functionalities including tunability and enhanced nonlinearity that provide a platform for fiber device applications. We discuss experimental and numerical tools that allow characterization of the modes of the fibers.

Fabrication and photoelectronic properties of ZnTe single crystals and Schottky diodes

n-and p-ZnTe single crystals were grown by the method of the gaseous-phase reactions using various halogen-containing agents (NH4Cl, NH4Br, and NH4I) as the carrier gases. Luminescent properties of the crystals were studied in relation to the type of the carrier gas. In/ZnTe Schottky barriers were formed. The photovoltaic effect was studied in the obtained structures for cases of natural and linearly polarized radiation. It was ascertained that the induced photopleochroism of the Schottky barriers is controlled by the angle of incidence of radiation and remains unchanged in the region of high photosensitivity. It is concluded that the obtained barriers may be used as broadband photosensors of linearly polarized radiation.

Cladding-mode-resonances in air-silica microstructure optical fibers

We present a comprehensive study of mode propagation in a range of different air-silica microstructured fibers. The inscription of both Bragg and long-period gratings (LPGs) into the photosensitive core region of microstructured air-silica fibers has allowed us to generate complex transmission spectra from a range of fibers with various fill fractions and with increasing air-clad hole diameters. The spectral characteristics for typical air-hole geometry's are explained qualitatively and modeled using beam propagation simulations, where the numerical modeling corroborates the experimental measurements. Specifically, the data reveal the propagation of higher order leaky modes in fibers with periodically spaced air-holes, and relatively small air-fill fraction. And as the air-hole diameter increases, spectra show cladding modes defined solely by the inner air-clad region. We describe these measurements and corresponding simulations and discuss their implications for the understanding of such air-hole structures.

Up and down UV-trimming of planar directional waveguide couplers: modeling

In contrast to etched channel waveguide couplers, directional couplers UV-written into a photosensitive layer can be both down and up trimmed by UV post-illumination of the waveguide cores and of the separating photosensitive region, respectively. Theoretically, the coupling length can be corrected by 10%-40% several times, before the third supermode starts to propagate.

Design of Matched Cladding Fiber with UV-Sensitive Cladding for Minimization of Cladding-Mode Losses in Fiber Bragg Gratings

The effect on the Bragg-grating-induced cladding-mode coupling of varying the extent of the photosensitive region in a step-index fiber is analyzed. We introduce a figure of merit for the suppression of cladding-mode loss and compare different matched cladding fiber designs. It is found to be advantageous to increase the extent of the photosensitive region. However, no significant improvement is obtained by extending the photosensitive region more than approximately 10 μm into the cladding. This result is not in agreement with a simple analysis that neglects UV absorption, which suggests that the radius of the photosensitive region should be close to twice as large.

Evidence for a photosensitive region in the caudal mesencephalon of the turtle brain.

Using an in vitro brainstem-cerebellum preparation from the turtle Chrysemys picta, burst discharge was recorded from the abducens nerve when light was directed on the brainstem. This burst discharge likely represents a neural correlate of the eye-blink reflex. Increasing the intensity of the light stimulus reduced the response latency from a duration of many seconds to approximately 1-2 s. No response was recorded when the light source was covered. The response was present when infrared light was blocked, and it could only be produced when the light spectra contained wavelengths below approximately 550 nm. Lesion experiments reveal that the photosensitive area is located caudal to the trochlear nerve and rostral to the trigeminal nerve. Single-unit microelectrode recordings demonstrate that this region is tonically active in the dark and that activity is suppressed by light. Pharmacological results show that the light response is blocked by application of compounds that act as serotonergic antagonists, and that antagonists of noradrenergic receptors (alpha or beta) either have no effect or their actions are variable. Taken together, these data suggest that an isthmo-optic-like area in the turtle brain is photosensitive to direct light and activates neural circuits that control eye movements.

Identification of rhodopsin in the pigeon deep brain

We detected rhodopsin gene expression in the pigeon lateral septum, a photosensitive deep brain region that is responsible for the photoperiodic gonadal response. The nucleotide sequence of the deep brain rhodopsin cDNA clone exactly matched that of the retinal one, indicating that a single rhodopsin gene is transcribed in the two tissues. Immunohistochemical analysis localized rhodopsin in the cerebrospinal fluid-contacting neurons, which have been assumed to be photoreceptive cells in the deep brain. Pigeon rhodopsin seems to play dual important roles in the visual and non-visual systems, the latter of which contributes to the photoperiodic response.

Localization of Blepharismin Photosensors and Identification of a Photoreceptor Complex Mediating the Step‐up Photophobic Response of the Unicellular Organism, Blepharisma

Abstract— Photosensitivity for the step‐up photophobic response of Blepharisma is localized in the anterior 1/5 of the cell body. Blepharismin pigment, which is believed to be a photoreceptor pigment mediating the step‐up photophobic response of the cells, was separated into five types of blepharismin (BL‐1, ‐2, ‐3, ‐4 and ‐5). Blepharismin‐1, ‐3, ‐4 and ‐5 were localized in the posterior 4/5, while BL‐2 was located over the entire cell body; the anterior end, which is the photosensitive region, contained only BL‐2. The results indicate that a functional photoreceptor pigment mediating the step‐up photophobic response is BL‐2. Hydroxylapatite chromatography revealed that BL‐2 was bound to a 200 kDa membrane protein. We concluded that a photoreceptor mediating the step‐up photophobic response was a BL‐2/200 kDa protein complex.

Photoinduced polarization reversal jumps in ferroelectric-semiconductor SbSI

The results of a study of photoinduced polarization reversal processes in SbSI single crystals are presented. Simultaneous switching current and Barkhausen effect measurements were used in the experiment. It is shown that the illumination of the SbSI crystal with electric field applied results in an occurrence of Barkhausen jumps provided the light corresponds to the photosensitive spectral region. In crystals with constricted hysteresis loop the illumination causes polydomainization on a level with poling, whereas in crystals without loop constriction only poling processes are initiated. It is established that illumination accelerates the processes of poling and depoling, quantitative characterization of which is presented. The phenomena connected to the influence of the illumination on polarization processes (poling in weak fields, depoling in strong fields, acceleration of the attainment of the polarization steady state) depend to a large extent on the instant of illumination switching on as related to...

Transmitted radiation through a subwavelength-sized tapered optical fiber tip

The far-field angular intensity dependence of the λ = 633 nm radiation transmitted through a 60 nm circular aperture located at the apex of an aluminum-coated tapered optical fiber tip is mapped as a function of the angle θ spanning the tip axis and the detector direction. Measurements are performed for polarized radiation with its electric field oriented (a) in the scan plane or (b) perpendicular to it. The existing predictions for a subwavelength-sized circular aperture in a thin perfectly conducting planar screen fails massively to describe the far-field measurements results. The photon intensity of the evanescent wave near the tip is measured by approaching the photosensitive region of a cleaved p-n GaAs photodetector in the near field of the tip aperture.

A silicon ultraviolet detector

A selective photodetector for ultraviolet light has been developed. The detector consists of an integrated combination of a selective photodiode and an interference filter. The doping profile of the diode was devised in such a way that a sharp potential barrier for holes appears at a depth of about 100 nm. The photosensitive region of the diode is located between the surface and this barrier. The diode surface was covered by a Fabry-Perot-type Al-SiO2-Al interference filter. The detector was fabricated using the methods of silicon IC technology. The ratio of the photoresponsivities at 300 nm and 1 μm was about 104.

Nonlinear current-voltage characteristics in MeBi2O3Me structure

The current-voltage (I–U) characteristics, both under illumination from the photosensitivity region and the dark I–U characteristics, are studied in MeBi2O3Me structures at different temperatures versus sample thickness and the configuration and material of electrodes. In the I–U characteristics four distinct regions are observed: ohmic I ∼ U, superlinear I ∼ Un > 1, the region of reverse bend where the degree of nonlinearity decreases and approximates the value of n = 1, and the second superlinear region I ∼ Un > 1. With increasing temperature of the samples the degree of nonlinearity decreases, the voltage in the beginning of the superlinear region increases slightly. In MeBi2O3Me structures the nonlinear I–U characteristics are explained in terms of a semiconductor model with intergrain barriers. The height of intergrain barriers (φ0 = (0.19 to 0.24) eV) and the average size of crystallites (h = (0.25 to 0.35) μm) for δ-Bi2O3 films are determined from the experimental I–U characteristics. [Russian Text Ignored].

Control of structural rhythms in the lateral eye of Limulus: interactions of natural lighting and circadian efferent activity

The structure of the Limulus polyphemus retina changes with the time of day. The structural changes exhibit a circadian rhythm when the animal is kept in constant darkness. During subjective night, the aperture of each visual unit (ommatidium) widens and flattens, allowing more photons to impinge on the underlying photoreceptors. In addition, the photosensitive region (rhabdom) of the photoreceptors widens and shortens. During subjective day, these changes reverse: both the aperture and rhabdom elongate and narrow, reducing the number of photons caught by the photoreceptors. The endogenous structural rhythm is mediated by efferent optic nerve activity generated from a circadian clock located in the brain. Eliminating the efferent input by cutting the optic nerve blocks the rhythm and shocking the cut nerve restores it. Natural lighting magnifies the structural rhythm. Daylight induces photomechanical movements, enhancing the endogenous daytime changes that decrease photon catch. The onset of darkness enhances endogenous nighttime changes that increase photon catch. Cutting the optic nerve blocks all structural changes, both endogenous and photomechanical. In the animal's natural environment, the effects of circadian efferent input and natural lighting are thus reciprocal: The evening onset of efferent activity pushes retinal structure in one direction; the morning onset of daylight pulls it in the other. The 2 processes, however, are not equivalent. In the absence of cyclic lighting, circadian efferent input produces an attenuated structural rhythm, but cyclic lighting alone produces no rhythm.

Characterization of InP/GaInAs/InP heterostructures grown by organometallic vapor phase epitaxy for high-speed p-i-n photodiodes

Organometallic vapor phase epitaxy at atmospheric pressure is used to grow InP/Ga 0.47In 0.53As/InP p-i-n photodiode structures designed for high speed operation. Growth of high purity Ga 0.47In 0.53As and abrupt InP/GaInAs heterointerfaces is combined to make the fastest reported front-side illuminated GaInAs p-i-n detectors. High resolution transmission electron microscopy (HRTEM) examination of the InP/GaInAs interfaces indicates that the transitions are abrupt to about 4 monolayers or less. No misfit dislocations are detected at the InP substrate/GaInAs epitaxial layer interface or the GaInAs/InP epitaxial interface. The purity of n −-GaInAs is evaluated using photoluminescence at 1.5 K and Hall measurements at 77 K. The full width at half maximum (FWHM) of the GaInAs photoluminescence is 1.5 MeV at 1.4 K, the best value reported to date. The Hall mobility is as high as 64,000 cm 2/V·s for n = 5×10 14 cm −3 at 77K. The lowest dark current measured is 0.15 nA at −4 V for a 50 μ m diameter photodiode with a 25 γm bonding pad or 6×10 −6 A/cm 2. This is among the best values reported to date. The bandwidth of a packaged photodiode with a 25 γm diameter photosensitive region is 17–20 GHz.

Influence of Unsymmetrical Electrode structure on a-Si Photodiode Characteristics

ABSTRACTAmorphous silicon(a-Si) stripe p-i junction photodiode array for contact-type image sensor of a facsimile has been developed and investigated especially with regard to its unsymmetrical electrode structure. This sensor consists of a p-i a-Si stripe layer, Cr separate electrodes, and an ITO common electrode. As a result, it is found that the photosensitive region of a-Si stripe type photodiode exists not only in a-Si sub-region having both upper and lower electrodes but also in a-Si sub-regions having upper or lower one-sided electrode. It is considered that photocarrier collecting mechanisms in the a-Si sub-regions are different and result to the different photodiode characteristics.

Stationary photoconductivity of mixed Tl 1−xAg xInSe 2 crystals

Tl 1−xAg xInSe 2 ( x = 0 to 0.03) single crystals of solid solution were grown by Bridgeman-Stockbarger techniques. Photoelectric measurements were taken at 300 and 77 K. With an increase in the value of x, the equilibrium concentration is increased 10 to 100 times. At 77 K a region of impurity photosensitivity has been detected which is bordered by the fundamental absorbtion edge. The photosensitivity ( R d R p ) of the solid solution crystals at 77 K increases from 8.2 ( x = 0) to 55.2 ( x = 0.03) the conclusion is made that when Tl is replaced by Ag then the sensitization of semiconductor.

Sm-base barrier structures

The electrical and photoelectrical characteristics of Sm–p-GaSe barrier structures produced by the method of vacuum deposition are investigated. The structures of interest is shown to have a pronounced diode structure (rectification factor amounts to 103 to 104 at U = (1 to 3) V), in this case the prevailing mechanism of current passage is connected with thermionic emission. The photosensitivity region extends from 1.1 to 3.5 eV, short circuit photocurrent density (at P = 400 mW/cm2), and open circuit voltage amount to js.c. = 3.4 mA cm−2 and Uo.c. = 0.42 V, respectively. Due to the formation of boundary states the surface treatment of GaSe substrate is observed to have a bearing upon the Sm–GaSe characteristics. To discuss the observed experimental results the band energy diagram of the SmGaSe structure is constructed. [Russian Text Ignored]

Measurement of the parameters of a linear CCD structure as a one-dimensional X-ray imaging detector

The basic parameters of linear charge-coupled devices (CCD) as one-dimensional X-ray imaging detectors are measured in the 5.4−19.6 keV photon energy range. Within this range, the sensitivity-wavelength dependence is obtained. At the maximum of this dependence, the threshold flux density of photons for such a device attains 3×10 6 cm −2 s −1 for a storage time of ∼ 150 ms. This is equivalent to the incidence of single photons on a CCD cell with dimensions of 15 υm×15 υm during a storage time which varies from 120 μs–30 s. Within the photon energy range mentioned above, the sensitivity varies from 0.3 to 3 mV·photon −1·cell. The linearity of the dependence of signal amplitude on flux density of photons remains up to 7 × 10 8 cm −2 s −1 Any dependence of the sensitivity on the flux density of photons is not revealed. The spatial resolution is better than 100 μm and must be measured with micron accuracies. In addition to the photosensitive region, the shift register one is successfully tried. The ways of improving the CCD parameters for registration of X-rays are discussed.