Photoeffects in cobalt doped pyrite (FeS2) films

By indiffusion of a thin metallic cobalt layer into a pyrite film deposited by metal organic chemical vapour deposition (MOCVD), cobalt doped pyrite ( FeS2) films have been prepared. The cobalt in these films acts as a donor a nd transforms the originally p-type into n-type conductivity. To our knowle dge this is the first time that n-type pyrite films have been prepared. Com pared to the undoped p-type pyrite films, the cobalt-diffused films exhibit a much higher photoconductivity, as revealed by time resolved microwave co nductivity analysis. From Hall and conductivity measurements a charge carrier concentration of a bout 10(20) cm(-3) and a Hall mobility of about 1.5 cm(2)/(V s) was calcula ted. This has to be compared with p-type pyrite films which do not show a H all mobility above 0.1 cm(2)/(V s), the detection limit of our Hall system. By analytical techniques (Rutherford backscattering and photoelectron spec troscopy) it was confirmed that the increase of the photoactivity is a bulk property of the pyrite films and not merely due to a surface passivation ( for instance, due to metallic CoS2). The presented results stimulate furthe r experiments on in-situ-doping of pyrite by MOCVD and open the opportunity for the preparation of pn-junctions and pn-solar cells with pyrite. (C) 19 99 Elsevier Science Ltd. All rights reserved.