C. Blackwell

Conduction mechanisms in doped mixed-phase hydrogenated amorphous/nanocrystalline silicon thin films

A detailed description of the microscopic nature of electronic conduction in mixed-phase silicon thin films near the amorphous/nanocrystalline transition is presented. A conduction model utilizing both the conductivity and the reduced activation energy data, involving the parallel contributions of three distinct conduction mechanisms, is shown to describe the data to a high accuracy, providing a clear link between measurement and theory in these complex materials.

Conductance fluctuations in free-standing hydrogenated amorphous silicon nanoparticles

Measurements of the electronic current fluctuations of free-standing hydrogenated amorphous silicon nanoparticles are described. The nanoparticles are synthesized by high-density plasma chemical vapor deposition and are deposited onto conducting substrates. An insulating matrix, either silicon oxide or silicon nitride is then grown in order to electrically isolate the particles. Electronic measurements are performed in this transverse geometry, and underneath a top electrode of area 1mm x 1mm are typically 10,000 nanoparticles with an average diameter of 150 nm in parallel. The spectral density of the current fluctuations in the a-Si:H nanoparticles is well described by a 1/f frequency dependence for frequency f, as in the case of bulk a-Si:H films. The variation of the correlation coefficients with frequency octave separation of the noise power fluctuations in bulk a-Si:H films indicates serial interactions between fluctuators. In contrast, the octave separation dependence of the correlation coefficients for the nanoparticles are very well described by an ensemble of fluctuators whose amplitudes are independently modulated in parallel.