Journal
PHYSICAL REVIEW B
Volume 79, Issue 11, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.79.115306
Keywords
electron-phonon interactions; elemental semiconductors; high-speed optical techniques; hopping conduction; hot carriers; localised states; photoconductivity; semiconductor thin films; silicon; terahertz wave spectra; time resolved spectra
Funding
- Ministry of Education [LC06040]
- Academy of Sciences of the Czech Republic [A100100902, AVOZ10100520, AVOZ10100521]
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We present the results of optical-pump-terahertz probe experiments applied to a set of thin-film microcrystalline silicon samples, with structures varying from amorphous to fully microcrystalline. The samples were excited at wavelengths 800 and 400 nm and studied at temperatures down to 20 K. The character of nanoscopic electrical transport properties markedly change on a subpicosecond time scale. The initial transient photoconductivity of the samples is dominated by hot free carriers with a mobility of similar to 70 cm(2)/Vs. These carriers are rapidly (within 0.6 ps) trapped into weakly localized hopping states. The hopping process dominates the terahertz spectra on the picosecond and subnanosecond time scales. The saturated high-frequency value of the hopping mobility is limited by the sample disorder in the amorphous sample and by electron-phonon interaction for microcrystalline samples.
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