ISSN 10637397, Russian Microelectronics, 2011, Vol. 40, No. 8, pp. 616–619. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © I.A. Kurova, N.N. Ormont, 2010, published in Izvestiya Vysshikh Uchebnykh Zavedenii. Materialy Elektronnoi Tekhniki, 2010, No. 3, pp. 45–48.
The high photosensitivity and stability to light
exposure are the required properties of material for its
widescale commercial application in photoelectric
converters. In recent years, in order to improve these
properties, modified materials have been developed on
the basis of hydrogenated silicon aSi:H: microcrys
talline and protocrystalline films, amorphous films,
including the nanocrystalline phase. These modified
films include, among others, layered aSi:H films,
obtained at the Saint Petersburg State Electrotechni
cal University by cyclic deposition with bylayer
annealing in hydrogen plasma. Earlier, it was estab
lished that layered aSi:H films are characterized by
high photosensitivity . However, the core of this
property is not clear.
Below, we discuss research on temperature depen
dences of dark conductivity
, as well as photoconductivity as a function of
of light exposure of layered aSi:H films in
a wide range of temperatures and intensities. For com
parison purposes, similar measurements are given of
) for nondoped regular (non
layered) aSi:H films, obtained by deposition in glow
ing discharge plasma. Such investigations make it pos
sible to reveal the peculiarities of the distribution of
electron state densities in the energy gap and electron
recombinations in the studied films.
The article is based on the report presented at the SILICON
2010 Seventh International Conference on actual problems of
physics, material science, technology and diagnostics of silicon,
nanometer structures and instruments based on them.
Layered and regular aSi:H films were studied, with
a thickness of 1
m and aluminum contacts in planar
configuration. All measurements were conducted at a
monotonous temperature increase ranging from 130
to 450 K after annealing of the films at
= 463 K in
1 h and slowly cooling to 130 K. The films were in a
vacuum chamber of nitrogen cryostat with a cooler
and heater. The temperature was measured using a
thermocouple located on the film.
The films were illuminated by halogen lamp with an
IR filter. The intensity of light exposure was varied in the
range from 75 to 0.085 mW cm
using a set of neutral
filters. The measurements of
) were performed at
short light exposure of the film in the course of a slow
temperature increase. This prevented photoinduced
variations in its properties during measurements.
RESULTS AND DISCUSSION
Figure 1 illustrates the temperature dependences of
the dark conductivity and photoconductivity of lay
ered and regular aSi:H films at various intensities of
light exposure. It can be seen in Figure 1, that the dark
dark conductivity of layered and regular films depends
exponentially on temperature, but with different acti
(0.95 and 0.8 eV, respectively). A
for a layered film indicates a deeper posi
tion of the equilibrium Fermi level in the energy gap.
The temperature dependences of the photoconductiv
ity of the layered and regular films differ: the photo
conductivity of the layered film monotonously
increases with temperature at any intensity of light
exposure, and, for regular films, there exists a region of
temperature quenching of photoconductivity (TQP).
Moreover, the temperature of the start of quenching,
On the Essence of the High Photosensitivity of aSi:H Layered Films
I. A. Kurova and N. N. Ormont
Moscow State University, Moscow, Russia
—It is established that layered aSi:H films grown by cyclic deposition with bylayer annealing in
hydrogen plasma are characterized by high photosensitivity, which, at room temperature, exceeds by more
than an order of magnitude the photosensitivity of regular nondoped aSi:H films grown by deposition in the
plasma of an HF glowing discharge. The high photosensitivity is determined by small dark conductance and
the high photoconductance of layered films in the range of room temperature. It is demonstrated that this can
be stipulated by the existence of sensitizing levels, related with higher oxygen concentrations at layer’s inter
face and the low concentration of broken silicon bonds in the depth of layers with a more ordered structure.
: amorphous hydrogenated silicon (aSi:H), layered aSi:H films, photoconductivity, photosensitiv
AND MULTILAYER COMPOSITIONS