Hydrogen semiconductor sensors

We indicate a possible use of semiconductor sensors in the studies of interaction of hydrogen ions and electrons with various energy with a... 

Fig.4.2. Relative concentration N/Na of hydrogen atoms in a reaction vessel as a function of relative discharge intensity (current) in the Wood tube J/Jg- The measurements were carried out by a semiconductor sensor (/), microcalorimeter (2), and by using the diffusion Wrede method (J).

Similarly, we used the method of semiconductor sensors (SS) to study heterogeneous recombination of NH2 and NH radicals [2, 3], as well as hydrogen [4], oxygen [5], and nitrogen [6] atoms. 

As an example of application of semiconductor sensors for this purpose, we consider photolysis of simplest olefines (ethylene, propylene, acetylene, etc.) occurring in the range of vacuum ultraviolet. It is well-known (e.g., see [11]) that photolysis of ethylene may result in detachment of either hydrogen molecules (detached in one act) or hydrogen atoms. Hydrogen atoms subsequently associate into molecules or interact with ethylene molecules. In what follows, we consider how this problem can be solved with the help of sensors. 

NH2 radicals, hydrogen atoms adsorbed on the surface of a semiconductor sensor more actively affect the electric conductivity of the sensor. 

Note that this method enables one to observe variation of electric conductivity of a sample due to adsorption of hydrogen atoms appearing as a result of the spillover effect, no more. In a S3rstem based on this effect it is rather difficult to estimate the flux intensity of active particles between the two phases (an activator and a carrier). The intensity value obtained from such an experiment is always somewhat lower due to the interference of two opposite processes in such a sample, namely, birth of active particles on an activator and their recombination. When using such a complicated system as a semiconductor sensor of molecular hydrogen (in the case under consideration), one should properly choose both the carrier and the activator, and take care of optimal coverage of the carrier surface with metal globules and effect of their size [36]. 

Atoms of metals are more interesting tiian hydrogen atoms, because they can form not only dimers Ag2, but also particles with larger number of atoms. What are the electric properties of these particles on surfaces of solids The answer to this question can be most easily obtained by using a semiconductor sensor which plays simultaneously the role of a sorbent target and is used as a detector of silver adatoms. The initial concentration of silver adatoms must be sufficiently small, so that growth of multiatomic aggregates of silver particles (clusters) could be traced by variation of an electric conductivity in time (after atomic beam was terminated), provided the assumption of small electric activity of clusters on a semiconductor surface [42] compared to that of atomic particles is true. 

The influence of other active components, such as 1, OH, H on a semiconductor sensor, with other conditions being the same, is comparable with the influence of atomic oxygen [50]. Contribution of N and OH is proportional to their relative contents (compared to that of atomic oxygen) in the atmosphere and may become essential at altitudes lower than 60 - 70 km. The use of selective detectors excludes the influence of atomic hydrogen. Studies of adsorption of water vapours on ZnO films [50] show that their influence is negligibly small at the film temperatures below 100°C. Variations of electric conductivity of the films under the influence of water vapours and of an atomic oxygen are comparable at the ratio of their concentrations [H20]/[0] = 10" . 

From general considerations it should be mentioned that only atoms of hydrogen can be present in gaseous phase in addition to atoms of antimony, molecules of antimony hydride and antimony hydride radicals in this system. Therefore, it is necessary to analyze plausible effects of each of above particles on conductivity of semiconductor sensor under experimental conditions. 

MedUn, J. W., McDaniel, A. H., Allendorf, M. D. and Bastasz, R. (2003), Effects of competitive carbon monoxide adsorption on the hydrogen response of metal-insulator-semiconductor sensors the role of metal film morphology,/ourna/ of Applied Physics, 93(4), 2267-74. 

Kang, B. S., Ren, E, Gila, B. R, Abernathy, C. R. and Pearton, S. J. (2004b) AlGaN/ GaN-based metal-oxide-semiconductor diode-based hydrogen gas sensor . Applied Physics Letters, 84(7), 1123-1125. 

Several types of semiconductor sensors were developed for analysis of toxic gases and vapors. They serve for detection and determination of hydrocarbons, alcohols, ethers, ketones, esters, nitrated compounds, ammonia, carbon monoxide, hydrogen, methane, etc. Their detection limit is often lower than 0.1 ppm. More details are given in [22]. The company Serna Electronics (Irvine, England) has sensors for about 200 different compounds on its production list and is prepared to "tailor a sensor on special demand. 

Fang, Y. K, Hwang, S. B., Lin, C.Y. Lee, C.C. (1997). Trench Pd/Si metal-oxide-semiconductor Schottky barrier diode for a high sensitivity hydrogen gas sensor. ]. Appl. Phys., Vol. 82, pp. 3143-3146... 

---