Photo-induced Electromotive Force Research Articles

Speckle Measurement for Small In-Plane Vibration Using GaAs.

In this study, the measurement characteristics of speckles based on the photoinduced electromotive force (photo-emf) effect for high-frequency, small-amplitude, and in-plane vibration were theoretically and experimentally studied. The relevant theoretical models were utilized. A GaAs crystal was used as the photo-emf detector for experimental research, as well as to study the influence of the amplitude and frequency of the vibration, the imaging magnification of the measuring system, and the average speckle size of the measuring light on the first harmonic of the induced photocurrent in the experiments. The correctness of the supplemented theoretical model was verified, and a theoretical and experimental basis was provided for the feasibility of using GaAs to measure in-plane vibrations with nanoscale amplitudes.

Interface recombination feature in metal–semiconductor junction at high photo-excitation

A theory of the photo-induced electromotive force in a p-type semiconductor accounting for the energy band bending and interface recombination dependence on excitation level is developed. It is shown that at high photo-excitation the effective interface recombination velocity in the metal-semiconductor junction is negligible compared with the volume one, when the surface potential is less than its critical value. The photo-induced electromotive force value is maximal at this condition.

Plasmon drag effect in metal nanostructures

In order to better understand the mechanism of the photon drag effect in plasmonic nanostructures, photo-induced electric signals have been studied in gold and silver films and various plasmonic nanostructures. The spectral dependence of the effect points to the primary role of individual localized plasmon resonances in the photo-induced electromotive force (emf) generation responsible for the photon drag effect. We demonstrate the potential to engineer both the magnitude and polarity of the emf with nanoscale geometry and provide a simple model based on the intrinsic nonlinearity of metal in defining this effect.

The influence of energy band bending on the photo-induced electromotive force in extrinsicsemiconductors

A theory of the photo-induced electromotive force in extrinsic semiconductors accountingfor the energy bands bending is developed. The non-equilibrium space charge layer and theboundary conditions in the real metal–semiconductor junction have been taken intoaccount. It is shown that photo-induced electromotive force in an n-type semiconductor atany photo-excitation volume essentially depends on the surface potential for certain surfaceparameters.

A new approach for investigation of photo-induced electromotive force in semiconductors

A new method for photo-induced electromotive force theoretical study of bipolarsemiconductors accounting for the distortion of energy bands near the semiconductorsurface is presented. This method is based on the exact solution of the continuityequations and the Poisson equation and on the boundary conditions derived for thereal metal–semiconductor junction. It is shown that photo-induced electromotiveforce essentially depends on the surface potential for certain surface parameters.

ULTRASONIC DETECTION BY PHOTO-EMF SENSOR AND BY WIDEBAND AIR-COUPLED TRANSDUCER

Two non-contact remote ultrasonic detection systems are compared. The first consists of a continuous wave (CW) Nd:YVO4 laser operating at 532 nm used in conjunction with a photo-induced electromotive-force (EMF) sensor. The second system employs an air-coupled capacitance transducer that has a bandwidth from 100 kHz up to 2 MHz. Both systems exhibit higher sensitivity to out-of-plane than in-plane measurements of stress wave signals. Ultrasound generation is carried out by an Nd:YAG pulsed laser at 532 nm in the thermoelastic regime in a 1.6 mm aluminum plate. A0 Lamb mode is generated at frequency-thickness product with strong out-of-plane displacements. Ultrasonic waveforms acquired are reported and the performance advantages of the two remote non-contact detectors are compared with each other. For lower frequency tests (up to 2 MHz), better results have been achieved with the air-coupled transducer that also has superior overall performance and benefits. The tests enabled direct comparison of air-coupled transducer and photo-EMF detector.

Improved Responsivity of Non-Steady-State Photoinduced Electromotive Force Sensors Using Asymmetric Interdigitated Contacts for Laser-Based Ultrasound Detection

Improved Responsivity of Non-Steady-State Photoinduced Electromotive Force Sensors Using Asymmetric Interdigitated Contacts for Laser-Based Ultrasound Detection

Enhanced responsivity of non-steady-state photoinduced electromotive force sensors using asymmetric interdigitated contacts

The responsivity at a constant detection area of non-steady-state photoinduced electromotive force (photo-emf) detectors is improved by a factor equal to the number of contact pairs contained in asymmetric interdigitated surface contacts. The polar nature of photo-emf current generation requires contact asymmetry in which one increases the total signal by blocking the illumination between alternate contact pairs, in distinct contrast to the behavior of conventional interdigitated contacts fabricated upon isotropic photoconductors.