ACCUMULATION LAYER MODEL FOR GA(2)O(3) THIN-FILM GAS SENSORS BASED ON THE VOLKENSTEIN THEORY OF CATALYSIS

In the framework of the phenomenological electron theory of chemisorption (Volkenstein model) the pressure dependence of the thin-film conductivity for the case of donor-like chemisorption is derived for the first time, solving self-consistently the 1D Poisson equation. As the experiments for H-2 and CO chemisorption on Ga2O3 thin films indicate (carrier density approximately 10(11) cm-3) the finite case, xi=D/L(D) approximately (D=film thickness, L(D)=Debye length) has to be considered. It is shown that only the finite case yields the principal features of thin-film gas sensors, e.g. the power law behaviour over a wide pressure region and the temperature dependence of the power. The 1D accumulation layer model is able to explain the experimental results for H-2 chemisorption on Ga2O3 thin films in a sufficient and consistent manner. For reasonable parameters and xi=0.5 the model yields in the temperature region between 850 and 950 K a universal power law behaviour of the average electron density with the power of 1/3. This power 1/3 is also obtained for different film thicknesses D=1, 2 and 4 mum.