Dmitri Daineka

Mechanical Loading Effects on the Resistivity of Thin Film Semiconductors

The influence of mechanical stress on PECVD thin film layers (250 to 500 nm) of hydrogenated amorphous and microcrystalline silicon (both intrinsic, pand n-doped) as well as indium tin oxide (ITO) and aluminum doped zinc oxide (ZnO:Al) was examined via uniaxial tension and compression tests and a simultaneous measurement of the resistivity both parallel and perpendicular to the applied stress (piezoresistivity). The resistivity for intrinsic hydrogenated amorphous layers is increasing for tensile strain whereas it is decreasing for intrinsic hydrogenated microcrystalline layers. P-doped layers of microcrystalline silicon have an increasing resistivity with increasing tensile strain which is in opposition to the behavior of n-type layers that show a decrease in resistivity for the same strain. Both ITO and ZnO:Al show a strong increase in resistivity with strain. The experiments for every material type show that the effect is reversible up to a certain strain and that a permanent damage remains if the sample is subjected to a strain exceeding this limit. In-situ mechanical tests in a scanning electron microscope demonstrate that such irreversible changes are due to crack formation when a certain strain is exceeded. These cracks can be observed perpendicular to the direction of the applied stress.

Aluminum recycling from reactor walls: A source of contamination in a-Si:H thin films

In this article, the authors investigate the contamination of hydrogenated amorphous silicon thin films with aluminum recycled from the walls and electrodes of the deposition reactor. Thin films of hydrogenated amorphous silicon were prepared under various conditions by a standard radio frequency plasma enhanced chemical vapor deposition process in two reactors, the chambers of which were constructed of either aluminum or stainless steel. The authors have studied the electronic properties of these thin films and have found that when using an aluminum reactor chamber, the layers are contaminated with aluminum recycled from the chamber walls and electrode. This phenomenon is observed almost independently of the deposition conditions. The authors show that this contamination results in slightly p-doped films and could be detrimental to the deposition of device grade films. The authors also propose a simple way to control and eventually suppress this contamination.