On the Low-Temperature Response of Semiconductor Gas Sensors (original) (raw)
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Gas Sensing Properties of Hydrogenated Amorphous Silicon Films
IEEE Sensors Journal, 2000
Gas sensing experiments on hydrogenated amorphous silicon (a-Si:H) films have been performed. We show that a-Si:H exhibits a low-temperature gas response that is distinctly different from the more familiar combustive gas response operative on heated metal-oxide surfaces. In particular, we show that at room temperature and above, a-Si:H samples exhibit a dissociative gas response which has first been observed on hydrogenated diamond (HD) samples. Whereas this dissociative gas response disappears at HD surfaces upon evaporation of the adsorbed surface electrolyte layer, a gas response with a similar cross sensitivity profile is observed on a-Si:H surfaces that persists up to the original deposition temperature of the a-Si:H films. We argue that this latter kind of gas response is due to a coordinative gas response that takes place when surface H-atoms of the a-Si:H film enter the coordination sphere of adsorbed analyte gas molecules.
The sensitization of semiconductor gas sensors
Sensors and Actuators B: Chemical, 1992
In this paper the sulphur dioxide response on a CdS-based thin-film gas sensor, deposited by spray pyrolysis, has been studied. It is found that for S-30 ppm of sulphur dioxide the sensitivity of the films increases considerably with the applied electric field E = 2 x lo* V/cm between the electrodes. Such behaviour cannot be explained in terms of a simple adsorption theory. The increase of sensitivity is pointed out to be closely connected with the relaxation processes, which destroy the electrical homogeneity of a sample. A phenomenological theory of the observed sensitization of the semiconductor film to acceptor gas, based on the creation of a negative charge region near the anode and the occurrence of adsorption-desorption processes on the charge surface, is suggested. The breakdown of electrical homogeneity is confirmed by potential probe experiments. The experiments show that the sensitivity increases by a factor of 5 to 10 in comparison with the characteristic sensitivity in the region of low electric field and Ohmic current-voltage relationship. The results obtained can be used in the manufacture of a semiconductor gas sensor.
Receptor Function and Response of Semiconductor Gas Sensor
Journal of Sensors, 2009
Theoretical approaches to receptor function and response of semiconductor gas sensor are described, following the illustrations of some relevant key issues such as tunneling transport. Depletion in small semiconductor crystals is characterized by the occurrence of new type depletion (volume depletion) after conventional one (regional depletion), and inclusion of both types makes it possible to formulate the receptor function and response to oxygen (air base), oxidizing gas (nitrogen dioxide), and reducing gas (hydrogen). The equations derived theoretically using physical parameters of the semiconductor side and chemical parameters of the gases side appear to reproduce satisfactorily the sensing behavior to the aforementioned gases as well as the influence of changes in physical parameters such as grain size and donor density. Extension to the semiconductor crystals dispersed with surface electron-traps shows that the traps act as a sensitizer to promote sensor response.
Gas sensing properties of hydrogen-terminated diamond
Sensors and Actuators B: Chemical, 2008
Hydrogen-terminated diamond (HD) samples possess a p-type surface conductivity (SC) which is caused by transfer doping to an adsorbed liquid electrolyte layer. We report on gas sensing experiments on such samples and show that these selectively respond to analyte gases that can undergo electrolytic dissociation in the surface electrolyte layer. These gas sensing interactions occur at room temperature and are far more selective than sensing interactions at heated metal oxide layers. Successive substitution of surface hydrogen atoms by oxygen atoms causes the sensor baseline resistance and the gas-induced resistance changes to increase. This latter observation suggests that a small number of O-termination sites may have a catalytic effect on the gas sensing interactions. Increased temperature, O 3 and UV light exposure all reduce the sensor recovery time constants. Heating beyond the water evaporation threshold (∼200 • C) causes the surface electrolyte layer to disappear and the gas sensing effect to vanish. Re-adsorption of the surface electrolyte layer re-establishes both the sensor baseline resistance and the gas sensing effect. A model for the dissociative gas response is proposed that accounts for the observed experimental facts.
IEEE Transactions on Electron Devices, 1999
This paper presents the results from analysis and modeling of the gas sensing performance, current conduction and gas detection mechanisms, and adsorption effects on device parameters of a Pt/SnOx x x/diamond-based gas sensor. The sensor is sensitive and demonstrates high, repeatable, and reproducible reaction. The sensor response in seconds to small concentrations of O2, CO, and H2 gases. The current conduction mechanism of the diamond-based CAIS (catalyst/adsorptive-oxide/intrinsicdiamond/semiconductor-diamond) diode was found to be dominated by space charge limited conduction in the forward bias region and tunneling in the reverse bias region, distinctively different from silicon based sensors. While gas adsorption causes a change in the barrier height and tunneling factor, no significant change was observed in the ideality factor over the temperature range investigated. The detection mechanism of the sensor is attributable to the change in occupancy ratio of the oxygen vacancies of the adsorptive oxide layer upon oxygen exposure, increasing the contact potential between adsorptive-oxide and intrinsic-diamond.
New approaches for improving semiconductor gas sensors
Sensors and Actuators B: Chemical, 1991
It is demonstrated that the sensing characteristics of a semiconductor gas sensor using SnO, can be improved by controlling fundamental factors which affect its receptor and transducer functions. The transducer function is deeply related with the microstructure of the elements, i.e., the grain size of SnO, (D) and the depth of the surface space-charge layer (15). The sensitivity is drastically promoted when D is made comparable to or less than 2L, either by control of D for pure SnO, elements or by control of the Debye length for impurity-doped elements. On the other hand, the receptor function is drastically modified by the introduction of foreign receptors on the surface of SnO,. In the particular cases of Pd and Ag promoters, the oxides (PdO and Ag,O) formed in air interact with the SnO, surface to produce an electron-deficient space-charge layer, and this contributes much to promoting the gas sensitivity. For a test gas having a specific reactivity, such specificity can be utilized for exploiting gas-selective receptors, as exemplified by CuO-SnO, and La,O,-SnO, elements, which detect H,S and ethanol gas respectively very sensitively.
Water adsorbate mediated accumulation gas sensing at hydrogenated diamond surfaces
Sensors and Actuators B: Chemical, 2013
Hydrogenated diamond (HD) specimens feature a peculiar form of gas response which occurs at room temperature and which is mediated by a thin layer of water that tends to accumulate on HD surfaces as these are exposed to normal atmospheric conditions. HD specimens are known to be sensitive to gases and vapours that are capable of forming acid-base reactions in liquid water. In this paper we show that HD sensors feature a novel kind of accumulating gas response which -under favourable conditions -comes close to an integrator-like behaviour. In this integrator-limit of operation, the HD gas response becomes proportional to the total flow of reactive gases that had been interacting with the water adsorbate layer on top of the HD sensors.
Investigation of gas–surface interactions at self-assembled silicon surfaces acting as gas sensors
Applied Surface Science, 2003
This paper reports the results of an investigation aimed at using self-assembled monolayers to modify the supramolecular interactions between Si surfaces and gaseous molecules. The specific goal is that of employing molecularly imprinted silicon surfaces to develop a new class of chemical sensors capable to detect species with enhanced selectivity. Single-crystal p-type (0 0 1) silicon has been modified by grafting organic molecules onto its surface by using wet chemistry synthetic methods. Silicon has been activated toward nucleophilic attack by brominating its surface using a modified version of the purple etch, and aromatic fragments have been bonded through the formation of direct Si-C bonds onto it using Grignard reagents or lithium aryl species. Formation of self-assembled monolayers (SAMs) was verified by using vibrational spectroscopy. Porous metal-SAM-Si diodes have been successfully tested as resistive chemical sensors toward NO x , SO x , CO, NH 3 and methane. Current-voltage characteristics measured at different gas compositions showed that the mechanism of surface electron density modulation involves a modification of the junction barrier height upon gas adsorption. Quantum-mechanical simulations of the interaction mechanism were carried out using different computational methods to support such an interaction mechanism. The results obtained appear to open up new relevant applications of the SAM techniques in the area of gas sensing. #
Nanoscale Research Letters, 2016
We propose a novel technique to investigate the gas sensitivity of materials for implementation in field-effect transistor-based gas sensors. Our technique is based on the measurement of the surface charge induced by gas species adsorption, using an electrometer. Platinum sensitivity to hydrogen diluted in synthetic air has been evaluated with the proposed charge measurement technique in the operation temperature range from 80 to 190°C at constant H 2 concentration of 4 % and for different concentrations ranging from 0.5 to 4 % at 130°C.