Download The properties of p-type cuprous oxide films prepared by reactive

The properties of p-type cuprous oxide films
prepared by reactive sputtering
S.H. Wu *
T.C. Lin**
Department of Electrical Engineering
Kun Shan University
Abstract
Cuprous oxide (Cu2O) is a direct-gap semiconductor and has a very high absorption
coefficient in visible light region. Transparent conducting oxides (TCO) film appling
in solar cells to product semitranslucent glass, have some beneficial heat insulation
and electronic generation layers. Cuprous oxide (Cu2O) is a direct bend gap and is
p-type semiconductor at without doping. To understand Cu2O characteristics can
provide useful and foundamental datum to promote the efficiency of solar cells.
In this study, we concentrated on the effect of deposition conditions of Cu2O film
grown by reactive rf-magnetron sputtering, Cu was used as the sputtering target. The
RF power and the O2 flow rate was changed in order to obtain a cuprous oxide film
with different characteristics. In addition, the influence of film growing characteristics
depended on bias voltage was discussed. Based on n-TCO/p-Cu2O structure, the
different n-TCO materials was used to study the influence of solar cell properties. An
α-step equipment was used to detect film thicknesses. A 4-points probe was used to
measure a sheet resistivity and the Hall measurement was used to detect the carrier
concentration and mobility. The structure could be characterized by X-ray diffraction
(XRD).The surface morphologies were observed by SEM and AFM. The
transmittance was measured by UV-VIS spectrophotometer. I-V measurement was
used to analyzed the opens-circuit voltage and short-circuit current.
According to experimental results knew that to growing a single phases of Cu2O
films was not easy to handle. The crystal surface, superficial morphologies and
photoelectronic properties of cuprous oxide film were close relationship with RF
power and oxygen flow rate. The oxygen flow rate was varied from0.7sccm to
0.9sccm and the rf power was changed from 120W~140W. A single phase of Cu2O
films can be obtained. At RF power of 130W and oxygen flow rate of 0.7sccm, the
best photoelectronic properties, which resistivity is 50.6Ω-cm and average reflection
is 14% in visible light, were obtained. The preferred orientation of (200) and surface
morphologies were significantly changed depending on bias voltages, therefore, the
results showed the growth mechanism was also closely relative to bias voltages.
When the bias voltage increased from zero to 200V, the roughness in rms value fell
from 24.6nm to 13.4nm. The lowest resistivity of 7.5Ω-cm in our experiments was
gotten at the substrate bias of 200V, and average reflection was 14% in visible light
region at this condition. Due to high carrier concentration in p+-Cu2O layers, the
depletion region at P/N junction is very narrow which will be influence photoelectric
current. Therefore, the photoelectric current can not be detected, in our experiments.
* Author
** Advisor