The Dynamic Uultrasound Influence on the Diffusion and Drift of the Charge Carriers in Silion p-n Structures
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The Dynamic Uultrasound Influence on the Diffusion and Drift of the Charge Carriers in Silion p-n Structures Roman M. Burbelo1, Oleg Y. Olikh1, and Mark K. Hinders2 1 Faculty of Physics, T. Shevchenko Kyiv National University, Volodimirska 64, Kyiv, 01033, Ukraine 2 Applied Science Faculty, The College of William & Mary, McGlothlin 330, Williamsburg, VA, 23187-8795
ABSTRACT Study of the current-voltage (I-V) characteristics of silicon solar cells, treated by MHz ultrasound with intensity up to 3 W/cm2 have been carried out. It is revealed that under such nonequilibrium conditions, the minority carriers’ diffusion process changes, which leads to the increase of the photocurrent (up to 15 %). An acoustostimulated reduction (down to 40 %) of the saturation current of the p-n junction is also observed. It is determined, that the observed changes depend nonlinearly on ultrasound power density, and the efficiency of the ultrasound influence increases with the vibration frequency. We consider that the ultrasound induced effects are connected with nonequilibrium processes of ionization and reorientation of structural defects in the acoustic field.
INTRODUCTION Recent time much attention is paid to the study of ultrasound influence on the defect structure and electrophysical properties of semiconductor structures [1-8]. In particular, it is revealed, that the broadering of a solar cell (SC) spectral sensitivity range [2], low-temperature annealing of radiating defects [3-5] and passivation of grain boundary defects [6] can be realized by the intensification of the defects diffusion and restructuring in a ultrasound field. At the same time processes which occur in material under the acousto-induced nonequilibrium conditions are not clear till now and attract enhanced interest of researchers [7, 8]. For instance, investigation of changes of the characteristics of semiconductor devices, caused by the ultrasound treatment, may create preconditions for development of a new class of devices dynamically controlled by an "active" sound. In this paper, results of investigation of the influence of dynamic (in situ) ultrasound on the charge transfer in silicon solar cells are presented.
EXPERIMENT DETAILS The measured SC consists of a 300-µm-thick p-type silicon substrate (doped with boron; p=1.3·1015 cm-3); and a 0.5-µm-thick Si layer of electron conductivity (thickness d n = 0.5 µm, n=1019 cm–3) was formed on its surface by implantation of P ions.
Longitudinal ultrasound waves have been excited by means of LiNbO3 piezoelectric transducers. The excitation frequency fUS was assigned by two resonant modes of the transducers — 4 MHz and 13.6 MHz. Intensity WUS of the excited US (up to 3 W/cm2 ) depends on amplitude of RF voltage (URF), applied to transducer. A soundwaveguide, which includes metallic (served for piezoelectric field shielding) and dielectric interlayers, was placed between the transducer and the semiconductor structure. Scheme of the sample arrangement is shown in Figure 1. I-V characteristics of the sola
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