Photoconductivity transient response from the steady state in amorphous semiconductors

AbstractWe present analysis, computer modelling and experimental measurements of the photoconductive decay which occurs on cessation of illumination, in amorphous semiconductors. We explore the processes of relaxation of the excess carrier distributions, and examine the relative rôles of re-trapping and recombination in a model case of an exponential trapping state profile, with monomolecular recombination. A variety of possible decay behaviour is revealed. We examine several plausible intuitive explanations of the decay process, including (a) the assumption that the rate limiting step in the decay process is the thermal release of trapped carriers from the vicinity of the quasi - Fermi level, and (b) multiple re-trapping at the quasi -Fermi level prior to recombination. Actual decay rates, however are often much faster than that predicted by these assumptions, and the generation rate dependencies do not follow the relation expected. These explanations are shown in detail to be largely erroneous. Results of experimental measurements of the decay from steady state and TPC in films of a-Si1-xCx:H are presented. While these appear initially to be at variance with the predictions of the present work, we demonstrate that the observations can be reconciled fully with theory.</jats:p

Conductive nanoscopic ion-tracks in diamond-like-carbon

Highly energetic heavy ions with energies of 1 MeV/nucleon or more (e.g. 350 MeV Au ions) result in material modification in matter. The extremely high local energy deposition along the path leads to a material change within a nanoscopic cylinder of about 10 nm throughout the film thickness (up to 30 µm). In diamond-like carbon the material change results in conducting tracks embedded in the insulating material. This is due to a change in the bond structure to a higher sp2 bonding content in the tracks and results in a conductivity change of up to four orders of magnitude. This paper discusses the conductivity mechanism in the 10 nm thick wires and presents a study of the conductivity dependence on the sp3-content in the diamond-like carbon and the used ion species. The conductive tracks are the basis of nanoscopic electronic devices made by irradiation of layered structures

Conductivity of ion tracks in diamond like carbon films

High-energy heavy ions (e.g. 1 GeV uranium ions) passing through a diamond-like carbon (DLC) film create conducting tracks along their path. The conductivity of these channels is due to a conversion of diamond sp3 bonds to graphite sp2 bonds caused by the large energy deposited along the ion track. The tracks have a diameter of approximately 10 nm and represent conducting filaments embedded in the insulating diamond-like matrix. They might be used as electron field emitters in vacuum electronic devices