Role of interface states and depletion layer in NO2 sensing mechanism of n-InP epitaxial layers

Abstract The electronic properties of n-type InP epitaxial layers covered by their native oxides have been investigated in order to explain the NO 2 gas sensing mechanism. The impact of interface states on the interface Fermi level, E F , carrier concentration in-depth profiles, n ( x ), and resistance, R , of n-InP layers has been studied by means of numerical analysis. The U-shaped interface state continuum, with the density minimum, N SS0 , from 10 10 to 10 13  eV −1  cm −2 , has been assumed at the InP interface according to the disordered-induced gap state model. Moreover, the surface fixed charge, Q FC , representing adsorbed ions at the semiconductor surface has been introduced. Also the influence of temperature on the electron distribution n ( x ) has been analysed. The n-InP layer resistance and Hall-effect measurements (using the Van der Pauw method) have been performed for the InP sensors before and upon NO 2 action in order to assess the influence of gas adsorption on the electron concentration and mobility as well as on the depletion layer width, W . On this basis the influence of interface states and near-surface region on the InP layer response to NO 2 adsorption has been determined. In addition, the conclusions for optimising the InP-based resistive sensor structure (in terms of the layer thickness and doping) have been obtained.