Anisotropy and thickness effects on reflection coefficients and acoustic signatures of bulk and thin Ge and m-Ge deposited on SiO₂ substrates

Abdellaziz Doghmane^*, Nabil Bouziane and Zahia Hadjoub

Laboratoire des Semi-Conductors, LSC, Département de Physique, Faculté des Sciences,

 Université Badji-Mokhtar, BP 12, Annaba, DZ-23000, Algérie.

E-mail: a_doghmane@yahoo.fr

ABSTRACT

Over the last few decades, an increasingly larger fraction of electronics has become “microelectronics” which is, nowadays, approaching an era of “nanoelectronics”. Crystalline and microcrystalline germanium (Ge and m-Ge) is seen to be a good candidate for such purposes. Although its electrical, structural, optical properties are well understood, very little work is reported on its elastic behavior which is of great importance in several applications mainly surface acoustic wave, SAW, devices. Hence, it is our aim to investigate elastic properties of bulk and thin Ge<100>, Ge<110> Ge<111> and m-Ge on reflection coefficients, R(q), and acoustic signatures, V(z), choosing SiO₂ as the most widely used substrate. For all cases, we first deduced SAW velocities from elastic constants. Then, determined and plotted R(q),  from which V(z) periodic curves were calculated using the angular spectrum model to be finally analyzed via fast Fourier transform treatment. The deduced quantitative data put into evidence their great dependence on crystallographic orientations. Moreover, the effects of layer thickness on the value and the generation efficiency of Rayleigh wave velocity were found to be dispersive. This behavior was found to be typical of loading layer effects.

Keywords: Thin films, Reflection coefficient, Acoustic signature, thickness, Ge, SiO₂.

Corresponding author contact: Prof. A. Doghmane, LSC, Dept. Physics, BP 12 Annaba University, Algeria; Fax. + 213 38 86 21 29. Tel. + 213 774 47 35 20 .