Cfo. Graeff et al., EFFECTS OF THERMAL ANNEALING ON THE OPTOELECTRONIC PROPERTIES OF HYDROGENATED AMORPHOUS-GERMANIUM, Philosophical magazine. B. Physics of condensed matter. Structural, electronic, optical and magnetic properties, 69(2), 1994, pp. 387-396
In this work we investigate the effect of thermal annealing above the
deposition temperature (200 degrees C) on the optoelectronic propertie
s of hydrogenated amorphous Ge thin films. For this purpose, visible a
nd infrared transmission spectroscopy, photothermal deflection spectro
scopy (PDS), Raman scattering, dark conductivity and electron spin res
onance (ESR) spectroscopy have been used. For thermal treatments below
350 degrees C, the defect density increases with increasing anneal te
mperature T-a, but the sample remains amorphous. In this case the abso
rption coefficient at 0.7 eV determined by PDS can be used as a measur
e of the dangling-bond spin density (obtained by ESR). For 350 degrees
C < T-a < 420 degrees C, crystallites are formed and grow, up to T-a
= 430 degrees C, when the sample becomes microcrystalline. The crystal
lization process is best described by a surface-induced crystallizatio
n with nucleation occurring at the film-substrate interface.