Abstract
Silicon thin
films are finding use in various kinds of electronic devices, most
significantly in flat panel displays and photovoltaic solar cells. Thin film devices
can be prepared in large area and on inexpensive substrates (glass, stainless
steel or polymer foils).
At
present, thin films of hydrogenated microcrystalline silicon (mc-Si:H) are intensively studied for application
in photovoltaic solar cells. They exhibit optical absorbtion higher than in
monocrystalline silicon and efficient light trapping. However, complicated
microstructure of mc-Si:H (grains, grain boundaries,
amorphous tissue) makes interpretation of electronic transport in the devices
difficult.
We have used
atomic force microscope (AFM) with conductive cantilevers for detection of
local currents in parallel with surface morphology [1]. In contact mode AFM,
surface corrugation is followed independently of electronic properties (in
contrast to studies by scanning tunnelling microscopy). In this manner, el.
transport and microstructure are correlated with very high lateral resolution
of 5 nm.
Thin film
transistor applications require high electron mobility, a prerequisite for
which are large grain size and low defect density. We have used pulsed
intereference laser crystallization (ILC) for spatially selective melting of
the films. In this manner, crystalline grains much larger than their thickness
were grown in well ordered patterns [2]. Laser beam induced current technique
(LBIC) was employed to probe photo-electronic properties of individual grains.
Grain boundaries were identified from phase shifts of the photocurrent.
Focusing of laser beam enabled lateral resolution of 0.3 mm.
[1] B. Rezek
et al., J. Appl. Phys. 92
(2002), p. 587-593
[2] B. Rezek
et al., J. Appl. Phys. 91
(2002), p. 4220-4227