Thin Solid Films 436 (2003) 101–106 0040-6090/03/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0040-6090(03)00519-4 Rigorous analysis of the electronic properties of InP interfaces for gas sensing B. Adamowicz *, M. Miczek , C. Brun , B. Gruzza , H. Hasegawa a, a b b c Department of Microelectronics, Institute of Physics, Silesian University of Technology, Krzywoustego 2, Gliwice 44-100, Poland a LASMEA, Blaise Pascal University, Aubiere, Cedex 63177, France b Research Center for Integrated Quantum Electronics and Graduate School of Electronics and Information Engineering, Hokkaido University, c Sapporo 060-8628, Japan Abstract A theoretical analysis of the surface Fermi level position (E ) at n-InP interfaces with different surface state density (N (E)) FS SS and surface fixed charge (Q ) representing adsorbed ions or surface d-doping has been performed in order to understand the FC InP-based gas sensor behaviour. Furthermore, the in-depth profiles of the potential barrier in equilibrium and under illumination (surface photovoltage) have been rigorously calculated. A U-shaped interface state continuum has been assumed in accordance with the Disorder Induced Gap State model. From the simulated dependencies of E vs. the minimum surface state density N , FS SS0 the movement of E in the energy band gap as well as its pinning position have been investigated. In addition, the analysis of FS the E sensitivity to the negative and positive Q has revealed the remarkable charge detection sensitivity of InP interfaces FS FC within different dynamic ranges.  2003 Elsevier Science B.V. All rights reserved. Keywords: InP; Interfaces; Electronic properties; Surface states; Fermi level; Gas sensing 1. Introduction Microstructured devices utilising Si and III–V surfac- es yinterfaces, including metal-insulator-semiconductor field-effect transistors (MISFETs) and metal-semi- conductor Schottky diodes are largely used for detection of ions in liquid phase (OH ,H , cations), and of y q particular molecular species in gas phase, mainly hydro- genated compounds (H , H S, unsaturated hydrocar- 2 2 bons) as well as reducing gases (NH ) w1–4x. Recently, 3 Talazac et al. w5,6x have reported on new epitaxial InP- based sensors for detection of oxidising gases (NO 2, O,O ) whose sensing is crucial for environmental 2 3 protection. The basic principle of these types of devices is a modification of the potential barrier height at semiconductor interfaces in the presence of gases. This effect is mainly caused by: (i) the diffusion of adsorbed species into the semiconductor interfacial region and modification of the interface state density and band bending; and (ii) the change of the work function of *Corresponding author. Tel.: q48-32-237-2057; fax: q48-32-237- 2216. E-mail address: adamowic@polsl.gliwice.pl (B. Adamowicz). the catalytic metal due to the gas adsorption in the case of Schottky diodes. It should be stressed that the metal- semiconductor barrier strongly depends itself on the interface state density. Thus the interfacial states decide about the entire sensitivity of different types of semi- conductor structures against ionygas adsorption. In the case of III–V-based structures, the interface states—due to their high density—are responsible for the interface Fermi level pinning, making the barrier height almost insensitive against ions and gas molecules. Such a situation is still difficult to overcome in the technology of III–V-based MIS structures and Schottky diodes used as gas sensors w1–4,6x. Moreover, this drawback leads to difficulties in the determination of the surface state density and surface band bending by means of the standard electrical C – V technique, because of the strong screening of the external electrical field by the charge captured in the interface states. In such cases, one of the powerful methods for determination of the electronic interface parameters is the surface photovoltage (SPV). The SPV technique consists of the optical excitation of the semiconductor and measurement of the change in the contact potential difference between the semi-