Ž . Thin Solid Films 383 2001 185188 Correlation between a-Si:H surface oxidation process and the performance of MIS structures ´ a,  b a b b a H. Aguas , Y. Nunes , E. Fortunato , P. Gordo , M. Maneira , R. Martins a Department of Materials Science and CEMOP UNINOVA, Faculty of Sciences and Technology of the New Uni  ersity of Lisbon, 2825-114 Caparica, Portugal b Department of Physics, Faculty of Sciences and Technology of the New Uni  ersity of Lisbon, 2825-114 Caparica, Portugal Abstract In order to correlate the MIS devices performance with different surface oxidation methods, AFM, spectroscopic ellipsometry and infrared spectroscopy measurements were performed in a-Si:H films, before and after surface oxidation, using different Ž . Ž . Ž oxidation techniques and oxides: thermal dry in air , wet in H O and by oxygen plasma, while MIS metal-insulator-semicon- 2 2 . ductor devices were characterised by I  V curves, under dark and AM1.5 illumination conditions. The a-Si:H films were grown by the PECVD technique, in a modified triode configuration reactor to allow a precise control of the ion bombardment during the film deposition. We found that the growth of a thin layer of oxide by chemical processes on the top of the a-Si:H surface can cause changes on the surface morphology that are reflected in the electrical behaviour of the devices. The oxygen plasma treatment, cause the rearrangement of the surface atoms leading to a change of their morphology and to the improvement of the electrical properties of the surface for a MIS applications.  2001 Elsevier Science B.V. All rights reserved. Ž . Keywords: a-Si:H films; Metal-insulator-semiconductor MIS ; I V curves 1. Introduction Ž . Hydrogenated amorphous silicon a-Si:H has been used in a wide variety of optoelectronic applications such as solar cells, image sensors, position sensors, gas  sensors and thin film transistors 1 . In all of these applications, surface and interface states play an im- portant role in determining the final performances of the devices. In the particular case of a metal-insulator- Ž . semiconductor MIS structure, the incorporation of a thin oxide layer can drastically modify the electrical  properties of such interfaces 2 by reducing the density of surface states. The thin oxide layer between the a-Si:H and the Pd  Corresponding author. Tel.: 351-21-294-83-00; fax: 351-21- 295-7810. ´ Ž . E-mail address: hma@mail.fct.unl.pt H. Aguas . plays also a main role in the device performance by providing the passivation of the a-Si:H surface defects and by providing a barrier between the metal and the  semiconductor 3. The surface morphology of the a-Si:H films is essentially dependent on the growth  process 4 , once it is not expected that the growth of a Ž . few nm  2 of oxide in the surface by a chemical process, affect drastically the surface morphology. In spite of this we believe that some rearrangements can occur leading to slightly changes of the surface mor- phology that can be related to the oxide growth process and to the MIS structure performances. To correlate these properties, AFM and spectroscopic ellipsometry measurements have been performed on the a-Si:H surface after different surface oxidations. 2. Experimental details Several oxidation processes were used with the ob- 0040-609001$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 0 - 6 0 9 0 00 01605-9