IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Thin Films Wednesday Sessions
       Session TF-WeA

Paper TF-WeA6
In situ and Ex Situ Surface Dangling Bond Measurements on a-Si:H by Means of Surface Cavity Ring Down Absorption

Wednesday, October 31, 2001, 3:40 pm, Room 123

Session: Nucleation and Growth
Presenter: M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands
Authors: A.H.M. Smets, Eindhoven University of Technology, The Netherlands
J.H. van Helden, Eindhoven University of Technology, The Netherlands
M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
The study of surface dangling bonds during growth of hydrogenated amorphous silicon (a-Si:H) is of great importance because of their possible role as dominant growth sites. In this contribution we will introduce a new technique, surface cavity ring down absorption (SCRDA), which enables us to measure directly small absorptions (10@super -5@ - 10@super -2@) by surface dangling bonds. The sensitive SCRDA technique is based up on the rate of absorption of a light pulse confined between two highly reflective mirrors in an optical cavity configuration. Ex situ single wavelength measurements (@lambda@ = 1064 nm, @tau@@pulse@ = 10 ns, E@pulse in cavity@ = ± 1 µJ) on a-Si:H films (10-3000 nm) on Corning glass show that the SCRDA technique is able to detect the surface dangling bonds. The obtained surface defect density of the a-Si:H oxidized surface is around 10@super 12@ cm@super -2@ and is in agreement with electron spin resonance (ESR) and photothermal deflection spectroscopy (PDS) results. Furthermore, it is demonstrated that the surface roughness, as determined from AFM measurements, correlates with the surface defect density. In situ SCRDA measurements are performed using a mirror - prism (suprasil) - mirror cavity configuration in which the light pulse incidents perpendicular on the two 70° tilted prism surfaces and has a total internal reflection on the backside surface. The initial a-Si:H growth phase (approx. 20 nm) has been monitored. The surface defect density increases up to the not yet saturated value of about 10@super 13@ cm@super -2@ in agreement with reported results using in situ ESR measurements. This value is higher than expected from reported growth models (10@super 9@ - 10@super 12@ cm@super -2@) in which the defect density is determined by the creation and passivation of surface defects by weakly absorbed radicals. The implications for the growth mechanism of a-Si:H will be discussed.