T. J. Belich

Experimental investigations into the formation of nanoparticles in a∕nc-Si:H thin films

Hydrogenated amorphous silicon thin films with nanocrystalline silicon inclusions (a∕nc-Si:H) have received considerable attention due to reports of electronic properties comparable to hydrogenated amorphous silicon (a-Si:H) coupled with an improved resistance to the light-induced formation of defects. In this study, a∕nc-Si:H thin films are synthesized via radio-frequency plasma-enhanced chemical-vapor deposition with helium and hydrogen diluted silane. The plasma conditions were chosen to simultaneously deposit both Si nanocrystallites and an amorphous silicon matrix. This structure has been confirmed by transmission electron microscopy (TEM) studies. Both plasma electronic diagnostics and TEM image analysis of a∕nc-Si:H films deposited with and without a temperature gradient between the capacitively coupled reactor electrodes suggest nanoparticle formation in the plasma, as opposed to solid-state nucleation of the nanoparticles in the film. Optical-absorption studies of the a∕nc-Si:H films indicate ele...

How Marketing Managers Use Market Segmentation: An Exploratory Study

Much of the previous market segmentation research has focused on methods of positioning total markets into segments and rarely on how marketing managers actually use market segmentation in practice. In contrast, this article first discusses the organizational environment in which marketing managers make segmentation decisions. Then it describes results of a survey of marketing managers about the segmentation variables they use, the criteria they choose to form segments and to select target market segments, and different marketing actions used to reach different segments. Suggestions are made for future research.

Non-Gaussian 1/f noise as a probe of long-range structural and electronic disorder in amorphous silicon

Measurements of the second spectra that characterize the non-Gaussian statistical nature of conductance fluctuations are reported for a series of hydrogenated amorphous silicon thin films. The deposition conditions used to synthesize the films were systematically varied in order to observe the effect that differing amounts of disorder have on the noise statistics. One series of n-type films were deposited at varying substrate temperatures, another n-type series was grown at varying rf powers, and a third series of compensated films was synthesized with varying ratios of phosphine to diborane. None of these series shows any significant change in the non-Gaussian noise statistics as the long-range disorder and deposition properties are changed. Measurements of the second spectra for a film synthesized in an inductively coupled plasma thermal growth system, which yields nano-particles of ~ 150 nm in diameter, are also reported. These results are discussed in terms of models for the non-Gaussian noise properties in amorphous silicon.

The Staebler-Wronski Effect and 1/f Noise in Amorphous Silicon

Experimental measurements of the Q-function (a comparison of the conductivity and thermopower activation energies) and the non-Gaussian statistical character of the 1/f noise in n-type doped a-Si:H as a function of light soaking (the Staebler-Wronski effect) are reported. There is a significant decrease in the non-Gaussian statistical character of the 1/f noise following light soaking of a device quality film, consistent with a slight increase in the long-range disorder. However, there is no change in the Q-function following light exposure, indicating that there is no significant increase in the long-range disorder.

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.

Hydrogenated Amorphous Silicon Thin Films with Nanocrystalline Silicon Inclusions

Thin films of hydrogenated amorphous silicon containing nanocrystalline silicon inclusions (a/nc-Si:H) have been synthesized in an RF capacitively coupled PECVD system using a mixture of hydrogen diluted silane and helium, under deposition conditions at the edge of powder formation within the plasma. High resolution TEM confirms the presence of nanocrystallites as small as 2 nm in these films. Measurements of the optical absorption spectrum using CPM and PDS indicates a broadening of the Urbach slope in the a/nc-Si:H, compared to a-Si:H films, but no appreciable increase in midgap absorption. Despite the deposition conditions for the a/nc-Si:H being very different from those associated with producing optimal quality a-Si:H, the dark conductivity and photoconductivity values, and the sensitivity to light-induced defect creation in the a/nc-Si:H films are comparable to those in a-Si:H.