Metastable states in hydrogenated amorphous carbon

Abstract

Hydrogenated amorphous carbon ͑a-C:H͒ films were fabricated by the low-frequency ͑60 Hz͒ glow discharge of the mixture of methane and hydrogen, and their electrical properties were investigated. We observed that a-C:H films show the persistent photoconductivity ͑PPC͒ by illumination of heat-filtered white light for a few seconds and the quenching-induced excess conductivity ͑QEC͒ by fast cooling from the above-preparation temperature. The PPC and QEC were about 10 times larger than the annealed dark conductivity. The samples clearly showed metastable characteristics. With increasing illumination times from 1 to 100 min, the annealing activation energy of the PPC was about 0.39 eV. The annealing temperature at which the PPC disappeared increased from 100°C to 130°C. Illumination longer than 80 min leads to the formation of defects and to the decrease of PPC. From these results, we tentatively propose that the states in the band act as deep trap centers, generating the metastabilities. ͓S0163-1829͑96͒00336-0͔

Mesoscopic Kondo Effect in an Aharonov-Bohm Ring

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Effect of illumination on hydrogenated amorphous silicon thin films doped with chalcogens

“…A metastable excess conductance, which can be enhanced by a brief light exposure up to several orders of magnitude compared to the initial dark conductivity, has been observed in compensated aSi:H films [34][35][36][37][38][39] as well as in doping modulated multilayers of aSi:H [35,38,[40][41][42][43]. This metastable excess conductance, called persistent ph (PPC), decays slowly over several days at room temperature and disappears by annealing near 100°C in multilayered films and 200°C in compensated films [24].…”