In:
ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2021-01, No. 56 ( 2021-05-30), p. 1475-1475
Abstract:
Miniature O 2 sensors with low energy consumption are of practical interest for the chemical and metallurgical industries, development of systems for analyzing the performance of internal combustion engines and as functional elements of artificial lung ventilation devices. The requirements for miniaturization, high sensitivity, speed and relative cheapness are satisfied by O 2 sensors based on β-Ga 2 O 3 . The chemical and thermal stability of β-Ga 2 O 3 allows developing gas sensors with extremely high operating temperatures of 400-1100 °C ensuring high reproducibility of their characteristics and high speed of operation. In turn, the high operating temperatures of O 2 β-Ga 2 O 3 sensors are their drawback causing high energy consumption. Previously, we studied the effect of H 2 on the gas-sensitive properties of the α-Ga 2 O 3 /ε-Ga 2 O 3 structure with Pt contacts grown by the halide vapor phase epitaxy (HVPE) on the patterned sapphire substrates (PSS) [1]. Low operating temperatures, weak dependence of properties on the humidity and control of selectivity by means of voltage changes indicate that the research of α-Ga 2 O 3 /ε-Ga 2 O 3 structures as sensitive elements of gas sensors is promising. We presume that in addition to increasing the applied voltage to the structures, the sensitivity of α-Ga 2 O 3 /ε-Ga 2 O 3 to certain gases, in particular O 2 can be increased by reducing the level of doping with a donor impurity. Thus this work is devoted to research the effect of O 2 on gas-sensitive properties of α-Ga 2 O 3 /ε-Ga 2 O 3 structures doped with Sn. Ga 2 O 3 films were grown by the HVPE in Perfect Crystals LLC. PSS of (0001) orientation and 430 microns in thickness were used as substrates. During the synthesis, the films were doped with Sn. To measure the gas-sensitive properties of the α-Ga 2 O 3 /ε-Ga 2 O 3 structures Pt contacts were formed on their surface. The samples consisted of a mixture of α and ε phases with the orientation (0001). Using scanning and transmission electron microscopy, it was found that the α-phase forms columnar structures at the top of the sapphire cone, and the ε-phase fills the gaps between the columns. The characteristic triangular shape of columnar structures indicates that they consist of α-Ga 2 O 3 with trigonal symmetry. ɛ-Ga 2 O 3 has a grain but not polycrystalline structure taking into account the XRD results. Figure 1 shows the I-U characteristics of α-Ga 2 O 3 /ε-Ga 2 O 3 structures at the exposure of O 2 in a wide range of concentrations C O2 from 2 to 100 % at temperature T = 200 °C. The current through the samples decreases with C O2 increasing. In the range of the T = 180 - 200 °C, at T = 200 °C, the highest response to O 2 are observed. It is worth noting that the operating temperatures of the α-Ga 2 O 3 /ε-Ga 2 O 3 structures in the reaction to O 2 are significantly lower than the operating temperatures of O 2 β-Ga 2 O 3 sensors. These low values of T are an advantage in developing gas-analytical systems with low energy consumption. The concentration dependences of the response at the T = 180 - 200 °C are approximated fairly accurately by a power function : response ~ C O2 b , where b is the exponent that depends on the temperature. Figure 1-Effect of O 2 on I-U characteristics of α-Ga 2 O 3 /ε-Ga 2 O 3 . A decrease in the Sn impurity concentration in α-Ga 2 O 3 /ε-Ga 2 O 3 from ~4×10 18 cm -3 to ~1.5×10 17 cm -3 leads to a significant sensitivity to O 2 in the temperature range from 180 to 220 °C at low values of the applied voltage U ≤ 7.5 V. The I - U characteristics of α-Ga 2 O 3 /ε-Ga 2 O 3 structures in a dry gas mixture N 2 + O 2 are described by the model of MSM structures based on the theory of thermoelectronic emission in diode approximation with the resistance of the semiconductor layer exceeding the resistance of the space charge regions at the metal/semiconductor interface. The sensory effect consists in the chemisorption of oxygen molecules on the surface of ε-Ga 2 O 3 that according to SEM has a grain structure. As a result, the energy barrier at the grain boundaries of ε-Ga 2 O 3 increases leading to a decrease in the current. The studied structures showed high sensitivity to relatively low concentrations (0.745 %) of H 2 and CO at the T = 180-220 °C and practically did not react to the effects of NO 2 and CH 4 . This research was financially supported by the Russian Scientific Foundation, grant No 20-79-10043. [1] A V Almaev, V I Nikolaev, S I Stepanov, A I Pechnikov, A V Chikiryaka, N N Yakovlev, V M Kalygina, V V Kopyev and E V Chernikov. J. Phys. D: Appl. Phys. 53 (2020) 414004 (9pp) https://doi.org/10.1088/1361-6463/ab9c69 Figure 1
Type of Medium:
Online Resource
ISSN:
2151-2043
DOI:
10.1149/MA2021-01561475mtgabs
Language:
Unknown
Publisher:
The Electrochemical Society
Publication Date:
2021
detail.hit.zdb_id:
2438749-6
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