Tesis
Sensores baseados em nanofios semicondutores de SnO2: fotodetector de luz UV e sensor de gás
Fecha
2022-04-11Registro en:
Autor
Araujo, Estacio Paiva
Institución
Resumen
In this work, sensors employing SnO2 semiconductor nanowires as active layer for gas
and light detection were built. SnO2 nanowire samples were grown by VLS (VapourLiquid-Solid) method and morphological and structural properties were analyzed. XRD
results exhibited SnO2 tetragonal rutile phase, within space group P42/mnm and lattice
parameteres of a = b = 4.73 Å and c = 3.18 Å (JCPDS 41-1445). SEM images confirmed
the desired morphology and TEM images revealed monocristaline character. Two
different sensors’ architecture were chosen: a Metal-Semiconductor-Metal (MSM) with
a nanowire network and a Field Effect Transistor with a single nanowire (NWFET).
Current-voltage measurements of the SnO2 nanowire network devices with and without
ultraviolet (UV) and visible (VIS) irradiation ranges were studied. Results indicated that
a barrier is formed between the nanowire network and metallic contact when in
absence of light, whereas under UV illumination there was an appreciable
photoconductive gain and a small one under VIS illumination. NWFET’s values of charge
density and mobility were estimate, of 1.6x1019 cm-3 and 3.7x10-4 cm2/Vs, respectively.
Under UV illumination, the NWFET presented an ambipolar behavior, while under VIS
illumination a unipolar response. SnO2 nanowire network’s photoresponse had a ION/IOFF
ratio of 170 and 8.2 for UV and VIS light, respectively. In addition, response time was 2.8
s for UV light and 98s for VIS light, althought UV light measurements presented multiple
decay times of 0.55 s and 145.84 s and for VIS light only one decay time of 153 s. NWFET
photodetector response curves displayed a ION/IOFF ratio of 309 and 57 for VDS = + 1 V
and VDS = - 1 V, respectively. For a positive voltage, VDS = + 1 V, the rise time was about
0.59 s and decay time was 0.63 s. Under a negative applied voltage, VDS = - 1 V, rise and
decay times were 0.68 s and 0.75 s, respectively, were obtained. For the VIS light
condition, no photocurrent variation in the NWFET was observed. The SnO2 nanowire
network device was also used to study gas sensoring at room temperature. Sensor
response, (), was found to be about 32 % and 9 % for acetone concentrations of 970
ppm and 50 ppm, respectively. In order to optimize and enhance the reponse, differentvii
values of applied voltage were tested, resulting in a response of 32 % for V = + 9 V and
49 % for V = + 0.1 V. Given that, smaller values of applied voltage improved our sensor’s
response.