Photovoltages Larger than the Band Gap in Zinc Sulfide Crystals

Ellis, S. G.; Herman, Frank; Loebner, E.E.; Merz, W. J.; Struck, C. W.; White, John

doi:10.1103/physrev.109.1860

Cited by 72 publications

(31 citation statements)

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“…Soon afterwards the non-conservation of parity in π → µ → e decay was reported by Garwin et al [18], and Friedman and Telegdi [19], following their observation of large decay-electron anisotropies. Parity non-conservation is now codified in the V -A structure of the weak currents [20,21] which imparts a distinctive angle-energy correlation on the decay electrons with the muon polarization. Since this early work, the precision measurement of angle-energy correlations has enabled increasingly precise tests of V -A theory.…”

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confidence: 99%

Precision muon physics

Gorringe

Hertzog

2015

Progress in Particle and Nuclear Physics

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a b s t r a c tThe muon is playing a unique role in sub-atomic physics. Studies of muon decay both determine the overall strength and establish the chiral structure of weak interactions, as well as setting extraordinary limits on charged-lepton-flavor-violating processes. Measurements of the muon's anomalous magnetic moment offer singular sensitivity to the completeness of the standard model and the predictions of many speculative theories. Spectroscopy of muonium and muonic atoms gives unmatched determinations of fundamental quantities including the magnetic moment ratio µ µ /µ p , lepton mass ratio m µ /m e , and proton charge radius r p . Also, muon capture experiments are exploring elusive features of weak interactions involving nucleons and nuclei.We will review the experimental landscape of contemporary high-precision and highsensitivity experiments with muons. One focus is the novel methods and ingenious techniques that achieve such precision and sensitivity in recent, present, and planned experiments. Another focus is the uncommonly broad and topical range of questions in atomic, nuclear and particle physics that such experiments explore.

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confidence: 99%

Precision muon physics

Gorringe

Hertzog

2015

Progress in Particle and Nuclear Physics

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“…In a crystal, the electron is not set free, ' but remains associated with the neutral halogen atom, or alternatively speaking, with the p 5 hole present in the halogen ion. If the direct interaction of the electron t and hole is small compared to the spin-orbit interaction of the hole, one may have conditions somewhat similar 1 to jj coupling in an atom, i.e., there exist two neighboring states which differ essentially only in the j-value assigned to the hole (J or f). As in the atom, both of these states may be reached by optical transitions from the p 6 ground state, provided the electron is in an s-like state (y=i).…”

Section: Acknowledgmentsmentioning

confidence: 98%

“…1 Hilsch and Pohl and their collaborators measured the spectra up to energies corresponding to 1600 A in the vacuum uv region, and, somewhat later, Schneider and O'Bryan extended the measurements to 1100 A. More recently, the alkali iodides have been studied extensively, 2 ' 3 since the first peak of their fundamental absorption lies in the vicinity of 2000 A, a region of the spectrum which can be reached with conventional uv apparatus.…”

Section: Introductionmentioning

confidence: 98%

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Effects of Polarized Light on Photocurrents and Photovoltages in ZnS

1959

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The anomalous short circuit photocurrents in ZnS have been measured using polarized light. In spite of the fact that for a given wavelength, light polarized perpendicular to the c axis is more strongly absorbed than light polarized parallel to the c axis, there are wavelength regions in which the absolute magnitude of the short circuit photocurrents are smaller for perpendicularly polarized light. The data are consistent with a double valence band model. P HOTOVOLTAGES larger than the energy gap have been reported for hexagonal ZnS. [1][2][3][4] In addition, the sign of the open circuit photovoltage (and the short circuit current) reverses with wavelength. 2,4 Similar reversals have been reported for CdS. 5 From measurements of the pyroelectric effect made in this laboratory and by Lempicki, 4 it has been definitely established that the sign of the photovoltage at a given wavelength is associated with the polarity of the c axis. These phenomena are related to general effects of the crystal symmetry on interactions with light.Another type of measurement falling into this category involves the polarization of light absorbed or emitted by the crystal. As an example we cite the work done on the dichroic optical absorption of ZnS and CdS 6-8 as well as the work on fluorescent measurements. 7,9 The results of the absorption measurements show that light polarized perpendicular to the c axis is more strongly absorbed than light polarized parallel. This is consistent with the optical selection rules derived theoretically by Birman 10 and Casella. 11 Since the electrical and optical properties are related to the crystal symmetry, it is reasonable to measure the electrical properties with polarized light. This has been done for the photoconductivity of CdS 12 with externally applied fields. We have measured the short circuit photocurrent as a function of the wavelength of incident light for the two directions of light polarization for ZnS. This communication presents the results. EXPERIMENTAL RESULTS AND DISCUSSIONThe measurements have been made by adding a polarizer to instrumentation which together with the sample preparation has been described in reference 2. It is important to discuss in some detail the nature of our crystal samples. Among workers in the field 2-4 there is some difference of opinion as to the role that crystalline disorder plays in the various properties of hexagonal ZnS. In an attempt to relate crystal disorder, such as inclusions of stacking faults and cubic phase, we have examined many samples for these inclusions. Sixty-five single crystals of hexagonal ZnS (40 unactivated and 25 activated with various combinations of Cu, Al, and Mn) were analyzed by x-ray diffraction techniques. (The x-ray radiation had no effect on the electrical properties.) Most of the crystals were about 4 mm long and exhibited uniform birefringent banding. With these, a one-mm spot in the middle of the crystal was chosen for x-ray examination. With crystals that exhibited heavy banding at one or more points, the one-mm spot in...

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“…Photovoltages, much larger than the band-gap energy ͑E g ͒ of the semiconductor, have been observed in obliquely deposited thin films of a large number of semiconductors [1][2][3][4][5][6][7][8][9][10][11][12][13][14] on transparent substrates under normal illumination. This effect is commonly known as the anomalous photovoltaic effect ͑APV͒.…”

Section: Introductionmentioning

confidence: 99%

Phenomenological model of anomalously high photovoltages generated in obliquely deposited semiconductor films

Singh

Kumar

2008

Journal of Applied Physics

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Photovoltage in obliquely deposited films of semiconductors is found to be much higher in magnitude than the corresponding band gap of the semiconductor. Also, the magnitude of the photovoltage depends on the angle of deposition, the separation between the electrodes, the wavelength of the incident light, the intensity of the illumination and temperature, but this behavior is not understood well. In this work a phenomenological model of the generation of photovoltage along the horizontal plane of the obliquely deposited films on transparent substrates is presented for the first time. The model is based on the presence of obliquely grown grains separated by parallel grain boundaries and the existence of grain boundary potential barriers across the grain boundaries. In the case of semiconductor films with a high absorption coefficient for short wavelengths in the visible range, there occurs a relatively large photogeneration of carriers on the front side of the grain boundaries rather than on the back side, and this gives rise to a net photocurrent and a photovoltage across each grain boundary. The horizontal components of this photovoltage get added up due to a large number of grain boundaries lying between the electrodes on the front surface and produce a large photovoltage due to the series combination. An expression has been derived based on this model which shows that for low intensities of illumination the horizontal component V och of the photovoltage increases linearly with electrode separation, resistivity of the film, and the incident light intensity. It depends on the angle of deposition and under certain conditions it is expected to be maximum when the angle of deposition is 45°. The analysis can be applied to study the effect of increase in intensity or decrease in temperature on V och . It also shows that the photovoltage across the thickness of the obliquely deposited film V ocv is minimum for normal deposition and increases with the increase in the angle of oblique deposition.

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Photovoltages Larger than the Band Gap in Zinc Sulfide Crystals

Cited by 72 publications

References 3 publications

Precision muon physics

Precision muon physics

Effects of Polarized Light on Photocurrents and Photovoltages in ZnS

Phenomenological model of anomalously high photovoltages generated in obliquely deposited semiconductor films

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