A.H.M. Smets

Ultrahigh throughput plasma processing of free standing silicon nanocrystals with lognormal size distribution

We demonstrate a method for synthesizing free standing silicon nanocrystals in an argon/silane gas mixture by using a remote expanding thermal plasma. Transmission electron microscopy and Raman spectroscopy measurements reveal that the distribution has a bimodal shape consisting of two distinct groups of small and large silicon nanocrystals with sizes in the range 2–10u2009nm and 50–120u2009nm, respectively. We also observe that both size distributions are lognormal which is linked with the growth time and transport of nanocrystals in the plasma. Average size control is achieved by tuning the silane flow injected into the vessel. Analyses on morphological features show that nanocrystals are monocrystalline and spherically shaped. These results imply that formation of silicon nanocrystals is based on nucleation, i.e., these large nanocrystals are not the result of coalescence of small nanocrystals. Photoluminescence measurements show that silicon nanocrystals exhibit a broad emission in the visible region peaked at 725u2009nm. Nanocrystals are produced with ultrahigh throughput of about 100u2009mg/min and have state of the art properties, such as controlled size distribution, easy handling, and room temperature visible photoluminescence.

The hydride stretching modes of hydrogenated vacancies in amorphous and nanocrystalline silicon: A helpful tool for material characterization

A model is proposed to assign the hydrogen complexes in amorphous and nano/microcrystalline silicon to the hydride stretching modes in infrared spectra. We demonstrate that this analysis approach is a helpful tool to characterize the material properties of amorphous and microcrystalline silicon.

Ex situ and in situ defect density measurements of a-Si:H by means of the cavity ring down absorption technique

For the first time it is demonstrated that the surface defect density can be measured using the cavity ring down (CRD) absorption technique and it is shown that CRD is more sensitive for surface defects than dual beam photoconductivity (DBP) technique. Ex situ measurements have shown that the surface defects of the oxidized a-Si:H surface are distributed over a surface region with thickness W( d ). The obtained surface defect density is 1.0 × 10 12 up to 1.4 × 10 12 cm -2 . During growth the a-Si:H surface defect density region has at least a thickness of 15 nm. During deposition of 15 nm a-Si:H the surface density increases up to a not yet saturated value of 1×10 13 cm -2 .