PHILOSOPHICAL MAGAZINE B, 2000, VOL. 80, NO. 10, 1811±1832 Visible photoluminescence and electroluminescence in wide-bandgap hydrogenated amorphous silicon K . LUTEROVA í, I. P ELANTy, P . FOJTI í K, M. NIKL, I. G REGORA , J . KOC Ï KA Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka  10, 162 53, Praha 6, Czech Republic J . D IAN, J . V ALENTA, P . M ALY  , J. KUDRNA , J. S Ï TE Ï PA í NEK Charles University, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Praha 2, Czech Republic A. PORUBA and P . H ORVA íTH Faculty of Chemistry, Technical University of Brno, Purkyn Ïova 118, 637 00 Brno, Czech Republic [ Received 4 April 2000 and accepted 6 June 2000 ] ABSTRACT The work describes basic photoluminescence (PL) and electroluminescence (EL) properties of wide-bandgap (2.0 eV or greater) hydrogenated amorphous silicon (a-Si :H). Thin ®lms of wide-bandgap (high-hydrogen-content) a-Si : H were prepared by microwave electron cyclotron resonance plasma-enhanced chemical vapour deposition from SiH 4 under high dilution with He. The ®lms exhibit spectrally broad (full width at half-maximum, 0.4 eV or greater) visible PL at room temperature, peaked at about 1.5 eV. On the basis of measurements of the PL temperature dependence, PL dynamics, infrared absorption spectra, picosecond pump-and-probe experiments and hydrogen thermal desorption spectroscopy the dominant microscopic mechanism of visible PL has been revealed to be the radiative de-excitation of oligosilane (- …SiH 2 † 2 - † units or of a speci®c defect in their close vicinity. EL has been investigated in sandwich p ‡ - i- n ‡ and p ‡ - p- n- n ‡ structures with (Cr±Ni)/indium tin oxide contacts. The as-grown structures exhibit good rectifying properties, low conductivity and no EL. After being subjected to a `forming’ procedure (application of a suciently high voltage), the current ¯owing through the structures increases abruptly by several orders of magnitude, up to about 10 mA, and the structures begin to emit weak EL at room temperature. The EL occurs in reverse bias only and its external quantum eciency is about 10 ¡5 %. It is concluded that the forming procedure leads to partial crystallization of a-Si : H between the contacts and impact lattice ionization can participate in the light emission. } 1. INTRODUCTION Intensive research of various forms of light-emitting silicon in the past 10 years has been stimulated by a vision of novel small optoelectronic sources based exclu- Philosophical Magazine B ISSN 1364±2812 print/ISSN 1463±6417 online # 2000 Taylor & Francis Ltd http://www.tandf.co.uk /journals yEmail: pelant@fzu.cz