Spectral sensitivity enhancement by thin film of beta-FeSi2-Si composite prepared by RF-sputtering deposition

In reference to the application of photovoltaic cells, beta -FeSi2-Si compo site films were fabricated to increase the photo-generated carriers with en ergy below the bandgap of silicon. As beta -FeSi2-Si system composites, two types of films were prepared. One was a composite of a beta -FeSi2 thin-la yer sandwiched by a Si substrate and a-Si thin film and its photoyield was measured. The other was a composite film composed of a-Si and beta -FeSi2 n ano-particles fabricated by an alternate sputtering method and its photo re sponse was measured. The size of beta -FeSi2 was controlled to decrease the barrier height by the quantum effect to facilitate the movement of carrier s from beta -FeSi2. Photoelectric yield measurements on the thin-layer comp osite film showed that the barrier height Delta phi was found to decrease b y varying the thickness of the beta -FeSi2 layer. Delta phi decreased to 0. 12 eV at the beta -FeSi2 thickness of 5 nm. However, the spectral response increase was not detected because of a window effect of the a-Si layer. For the beta -FeSi2 nano-particle-a-Si composite films, the decrease of the ba rrier height between Si and beta -FeSi2 by the quantum size effect was also indicated by comparison with theoretical values. Moreover, the photoyield was increased in the range of 0.98-1.05 eV compared to that of noble a-Si f ilm. It was suggested that the carrier generated in the beta -FeSi2 nano-pa rticle was taken out as a photocurrent by moving to a-Si thin film and pass ing over the heterodiode side. (C) 2001 Elsevier Science B.V. All rights re served.