In this paper, electric field induced Pockels effect and optical rectification were demonstrated in the space charge regions of surface layers of (001)- and (110)-cut silicon crystals. The Pockels signals were much larger than the Kerr signals. These effects were considerable that they should be taken into account when designing silicon devices. Dependence of the optical rectification on various depth of the silicon crystal was investigated which could be used as a simple and nondestructive method to detect distribution of electric field of silicon devices.
The current-voltage (I-V) characteristics and phenomena of electroluminescence of cubic boron nitride (cBN) single crystal flakes with color-zoning under extremely non-uniform electric fields (ENUEFs) induced by needle-plate electrodes were observed. When a cBN flake with sizes of 0.3×0.3×0.1 mm3 was tightly fixed between the tungsten needle and brass plate electrodes in the atmosphere, the I-V relationship exhibited nonlinearity, and peculiar phenomena of electroluminescence with bright blue-violet light appeared at the bias voltage in a range of 700-1200 V. The current-controlled differential negative resistance was synchronously observed. The electroluminescent phenomena were somewhat different for cases of the needle electrode respectively contacting to the amber and transparent zones. The electroluminescent radiations of cBN flakes biased at voltages with a range of 600-1550 V were also investigated in vacuum. In a vacuum chamber, the green emitting phosphor spread around the cBN flake might be excited by the vacuum ultraviolet (VUV) emission from the cBN crystal, and the green fluorescence was observed by naked eyes. The VUV radiation spectrum with a peak wavelength of 149 nm was measured. In the atmosphere, the blue-violet light emission may be the gas discharge resulted from the air ionization induced by the VUV emission from the cBN crystal under the ENUEF, and the ENUEF subsequently keeps the air discharging. The VUV emission from the cBN crystal under the ENUEF can be caused by the original interband transition and the subsequent intraband transfer for electrons, and the final electron-hole direct recombination.
The characteristics of photo-current-voltage and dark-current-voltage for two-photon-response semi-insulating GaAs photodetectors responding to near-infrared wavelengths of 1.31 μm and 1.55μm are investigated. The semi-insulating GaAs photodetectors were fabricated into hemisphere on whose bottom two types of electrodes were deposited. In experiments, the incident laser was adjusted to travel normally to the photodetector and focus at the center of the bottom so as to improve the nonlinear photo-responsivity markedly. It is observed that the photocurrent dependent on bias exhibits quadratic nonlinearity for both lasers and both electrode configurations, which reflects frequency-doubled absorption responsible for the physical mechanisms of the photodetectors; and the reasonable analysis demonstrates the important role of the electric-field-induced frequency-doubled absorption in two-photon response. Furthermore, it is found that the photocurrent is quite more greater when the electrode positioned at the bottom center of the photodetectors (central electrode for short) is negatively charged than that in the case of it positively charged under the conditions of the identical bias voltage and the same incident optical power; while the dark-current varies in exactly the opposite mode compared to the photocurrent. The aforementioned disparate variations of the photocurrent and the dark-current are well interpreted by the theory of surface band-bending of semi-insulating GaAs, and such variations result in a large ratio of photo-current to dark-current in the case of the central electrode negatively charged. The investigated results also indicate that the optimization of electrode structure is essential to improve the photo-responsivity of the photodetector.
Silicon crystal is a kind of centrosymmetric materials, which has no second-order optical effects at dipole approximation.
However, the inversion symmetry of silicon crystals will be broken by the built-in field or the DC electric field applied to
it. We theoretically studied the response of the third-order susceptibility to the electric field and deduced the effective
second-order susceptibility tensors when the electric fields applied to silicon are along the [111], [110] and [001]
directions, respectively. The results show that the forms of the effective second-order susceptibilities of Si are consistent
with those of C3V, C2V and C4V symmetry groups of crystals which indicate that silicon crystals should belong to C3V, C2Vand C4V symmetry groups instead of Oh symmetry group, respectively. So silicon crystals will exhibit some second-order
nonlinear optical properties corresponding to related symmetric crystals under the corresponding incident electric fields.
This research method of the electric field-induced second-order nonlinear optical processes can also be used to other
centrosymmetric materials.
By observing two-photon response and anisotropy of the light-induced voltage in Si-Al Schottky barrier potential of the Si MSM (Metal-Semiconductor-Metal) planar structure two-photon response optical detector. It is certified from the experimental and theoretical analysis that the built-in electric field generated by the Schottky barrier potential will induce the phenomena of optical rectification in Si photodiode. Thus, it is deduced that there must be double-frequency absorption (DFA) caused by phase-mismatch in the mechanism of two-photon response of Si photodiode. If the intensity of the built-in electric field is strong enough, the DFA will be the main feature of the two-photon response.
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