Showing papers by "Norman S. Kopeika published in 1984"
TL;DR: In this article, surface effects stemming simply from photodiode operation in vacuum environment are seen to improve quantum efficiency significantly, attributed to desorption of surface impurities and consequent reduction of surface recombination and Debye length.
Abstract: Surface effects stemming simply from photodiode operation in vacuum environment are seen to improve quantum efficiency significantly. This is attributed to desorption of surface impurities and consequent reduction of surface recombination and Debye length. Effective depletion layer width, because of junction shallowness, can also be noticeably affected by changes in surface potential and free charge redistribution stemming from desorption of surface impurities. Quantum efficiency enhancement here in vacuum is greatest at visible wavelengths, thus suggesting application in solar cell technology, particularly since I sc , V oc , and fill factor are all increased in vacuum.
10 citations
10 citations
TL;DR: In this paper, a mathematical model is developed to relate wavelength tuning with surface potential and forward voltage shift, which suggests the possibility of wavelength tuning via surface band-bending changes deriving from surface electric field changes, as is done with MIS devices.
Abstract: Wavelength tuning via shallow junction GaAs LED's as a result of gamma irradiation is increased significantly when the irradiated LED's are operated in vacuum. Vacuum operation is seen to be essentially equivalent to increased gamma ray dosage for low irradiation levels as a result of desorptive processes common to both phenomena. They give rise to decreased nonradiative and increased radiative components of surface recombination photon emission. It is this spectrum which is shifted according to changes in surface potential and forward voltage deriving from alterations in surface state populations. A mathematical model is developed to relate wavelength tuning with surface potential and forward voltage shift. This technique is, in principle, a general technique independent of semiconductor material. It suggests the possibility of wavelength tuning via surface band-bending changes deriving from surface electric field changes, as is done with MIS devices. Examination of irradiated diode properties in vacuum and under pressure permits greater insight into the basic nature of surface phenomena long suspected to play a significant role in the diode electronic property changes brought about by nuclear irradiation.
9 citations
09 Jan 1984
TL;DR: In this paper, it is shown that the spectrum shifts according to changes in surface potential and forward voltage deriving from alterations in surface state populations, and suggests the possibility of wavelength tuning via surface band bending changes derived from surface electric field changes, as is done with MIS devices.
Abstract: Wavelength tuning via shallow junction GaAs LEDs as a result of y-irradiation is increased significantly when the irradiated LEDs are operated in vacuum Vacuum operation is seen to be essentially equivalent to increased y-ray doseage for low irradiation levels as a result of desorptive processes common to both phenomena They give rise to increased radiative surface recombination photon emission It is this spectrum which is shifted according to changes in surface potential and forward voltage deriving from alterations in surface state populations This technique is, in principle, a general technique independent of semiconductor material It suggests the possibility of wavelength tuning via surface band bending changes deriving from surface electric field changes, as is done with MIS devices Examination of irradiated diode properties in vacuum and under pressure permits greater insight into the basic nature of surface phenomena long suspected to play a significant role in the diode electronic property changes brought about by nuclear irradation© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only
TL;DR: In this paper, it is reported that glass-metal seals give rise to photocurrents as a result of light illumination, and the detection performance is of the order of 10 mA·W−1.
Abstract: Ordinary glass–metal seals are reported here to give rise to photocurrents as a result of light illumination. Responsivity observed here is of the order of 10 mA·W−1. Signal-polarity results suggest that the seal acts as a Schottky barrier. Photoionization of impurities, particularly iron oxide, in the glass energy gap is believed to be the detection mechanism. A method is suggested for increasing responsivity. Development of glass optical detectors may be advantageous for many applications involving optics and glass, including integrated optics, particularly in view of the low cost, the completely negligible dark current, and the guiding capabilities of glass fibers. The detection properties of glass–metal seals should be considered when evaluating experimental results, such as the optogalvanic effect, involving discharges as detectors of light.
09 Jan 1984
TL;DR: Kopeika et al. as discussed by the authors showed that photodiode operation in vacuum environment is seen to improve quantum efficiency significantly, attributed to desorption of surface impurities and consequentreduction of surface potential, recombination, and Debye length.
Abstract: Photodiode Quantum Efficiency Improvement through Vacuum Surface EffectsN. S. Kopeika, I. Hirsh and E. HazoutDept. Electrical and Computer EngineeringBen -Gurion University of the Negev, Beer -Sheva, Israel 84120AbstractSurface effects stemming simply from photodiode operation in vacuum environment are seen to improvequantum efficiency significantly. This is attributed to desorption of surface impurities and consequentreduction of surface potential, recombination, and Debye length. Effective depletion layer width can also benoticeably affected by free charge redistribution after desorption of surface impurities. Quantum efficiencyhere in vacuum is greatest at longer wavelengths because of decreased surface depth in vacuum.IntroductionAssuming all current carriers photo -generated in the junction depletion layer are collected, net photo-diode quantum efficiency n is limited by light reflectivity r of the device entrance face and the loss ofphotons absorbed between the front surface and the junction depletion layer. We call this d. Then, for adevice using a single pass of the incident light1 -3
26 Dec 1984
TL;DR: In this article, it is reported that glass-metal seals are reported to give rise to currents as a result of light illumination, and the sensitivity observed is of the order of 10 mA. Signal-polarity results suggest that the seal acts as a Schottky barrier.
Abstract: Ordinary glass-metal seals are reported here to give rise to currents as a result of light illumination. Responsivity observed here is of the order of 10 mA.W . Signal-polarity results suggest that the seal acts as a Schottky barrier. Photoionization of impurities, particularly iron oxide, in the glass energy gap is believed to be the detection mechanism. A method is suggested for increasing responsivity. Development of glass optical detectors may be advantageous for many applications involving optics and glass, including integrated optics, particularly in view of the low cost, the negligible dark current, and the guiding capabilities of glass fibers. The detection properties of glass-metal seals should be considered when evaluating experimental results, such as the optogalvanic effect, involving discharges as detectors of light.
TL;DR: The authors showed that vacuum desorption of minority surface impurities increases barrier height and decreases tunneling probability, thus increasing diode nonlinearity and making the diodes more nearly ideal.
Abstract: Desorption of air atoms from point contact diode surfaces via exposure to vacuum can give rise to significant changes in electronic characteristics. In the example considered, exposure of an X-band detector to a modest vacuum gives rise to a responsivity increase of about 80 percent for video and heterodyne detection. Experiments indicate that vacuum desorption of minority surface impurities increases the barrier height and decreases tunneling probability, thus increasing diode nonlinearity and making the diodes more nearly "ideal." The resulting relative increase of the thermionic emission current should decrease the effective shot-noise temperature, thus increasing the signal-to-noise ratio (SNR) even further.
TL;DR: In this article, relative scattering coefficients have been measured over the 400-900 nm wavelength range under various weather conditions in the northern Negev desert, and the wavelength dependence is seen to be quite variable, befitting bimodal aerosol conditions as predicted by Patterson.
Abstract: Relative scattering coefficients have been measured over the 400–900 nm wavelength range under various weather conditions in the northern Negev desert. Wavelength dependence is seen to be quite variable, befitting bimodal aerosol conditions as predicted by Patterson. However, wavelength dependence in the near-infrared region is observed to be much sharper than the negligible dependence predicted in the literature for this spectral range under conditions where dust is noticeably present in the atmosphere. The sharp degree of dependence is attributed to an additive effect of the separate scattering coefficients of each of the two aerosol modes, both of which decrease with wavelength in the near-infrared region.
11 Dec 1984
TL;DR: In this paper, regression coefficients for relative humidity, air temperature, and windspeed, with respect to atmospheric contrasts in various wavelength bands over visible and near IR wavelengths as measured over a 3-year period were made of regression coefficients.
Abstract: Calculations are made of regression coefficients for relative humidity, air temperature, and windspeed, with respect to atmospheric contrasts in various wavelength bands over visible and near IR wavelengths as measured over a 3 year period. Significant changes are noted between summer and winter, including some sign changes and opposing wavelength dependences. Analysis of spatial frequency data indicates in the rainy season, when the atmosphere is freer of airborne soil-derived particulates, turbulence is dominant in limiting imaging resolution through the atmosphere, with wavelength dependence determined primarily by background and forward scattering effects associated with humidity. Resolution is best in the near infrared. However, in the dry season image quality is limited primarily by large airborne particulates and their effects on atmospheric background and spatial frequency-dependent multiple forward scattering phenomena. As a result, resolution is best at short wavelengths. The strong wavelength dependences on small and large radii aerosol related effects suggest the possibility of predicting imaging resolution spectral dependence in advance in accordance with meteorological predictions. Analysis of regression coefficients in the spatial frequency domain permits quantitative determination of effects of each meteorological parameter on each type of atmospheric MTF, i.e., background, aerosol, and turbulence MTF's separately. In this way insight is gained as to not only the extent to which each meteorological parameter effects imaging resolution, but also the mechanism of the effect.