J. Phys. Colloques
Volume 50, Numéro C6, Juin 1989Beam Injection Assessment of Defects in Semiconductors
|Page(s)||C6-177 - C6-177|
J. Phys. Colloques 50 (1989) C6-177-C6-177
THICKNESS DEPENDENCE OF CATHODOLUMINESCENCE IN THIN FILMSJ. YUAN1, S. BERGER2 et L.M. BROWN1
1 Cavendish Laboratory, Madingley Road, GE-Cambridge CB3 OHE, Great-Britain
2 AT & T Laboratories, Murry Hill, NJ 07974, U.S.A.
Thin film samples have been increasingly used in high resolution imaging studies of cathodoluminescence (CL) from materials, in order to achieve the smallest CL source possible[1-3]. The analysis of the luminescence signals from thin film material is often hampered by the changes associated with the film thickness variation. This thickness effect has been analysed in a simple model which takes into account the diffusion of the excited states in thin films. The electron beam is assumed to provide a uniform excitation density over the entire film thickness appropriate to electron transparent films (the definition of which is also given). The intensity variation of CL signal as a function the foil thickness t is given by the formula I(t) =I0(t-(2L)/(coth(t/2L)+f) where L is the diffusion length of the energy carrier in a bulk sample ; f is the ratio of the bulk diffusion 'velocity' L/τ to that of the surface diffusion velocity s. Both physical parameters can be obtained from a plot of the CL intensity verses the film thickness. This has been applied to a number of materials such as Y2O3 : Eu3+, YAG : Ce3+, Diamond and InP. For the last two types of materials, the result of the analysis is consistent with those from other experiments[3, 4]. For phosphors with a relatively large doping of luminescent ions, the saturation effect caused by an intense excitation density must be taken into account in interpreting the physical parameters deduced[5, 6].