From Solid-State Dewetting of Ultrathin, Compressively Strained Silicon–Germanium-on-Insulator Films to Mastering the Stoichiometry of Si_1–xGe_x Nanocrystals

Abstract

The mastering of material composition at the nanoscale is of prime importance for many applications. In this context, we developed a simply implementable and fast germanium enrichment method allowing the control of the germanium fraction within silicon− germanium nanocrystals. In our process, the tuning of the stoichiometry is achieved in the background of thermally induced solid-state dewetting, followed by a solid−solid interfacial reaction step between nanocrystals issued from dewetting and the silicon dioxide substrate. At first, we show by scanning transmission electron microscopy and scanning Auger microscopy that homogeneous silicon−germanium nanocrystals are successfully formed by means of solid-state dewetting of silicon− germanium-on-insulator ultrathin films. Then, we demonstrate that an interfacial reaction between the silicon−germanium of the nanocrystals and the silicon dioxide of the substrate can be thermally induced under ultrahigh vacuum conditions. The reaction, entailing almost exclusively silicon, permits us to modify the germanium fraction within silicon−germanium nanocrystals by controlling its advancement. Finally, we highlight the possibility to control the stoichiometry of silicon−germanium nanostructures simply by using thermal effects.

Solid-State Dewetting Dynamics of Amorphous Ge Thin Films on Silicon Dioxide Substrates

“…Only nanowires with a diameter greater than 55 nm show a crystallization temperature of 500 °C, in agreement with that of bulk germanium [ 26 ]. The proposed interpretation is that oxygen atoms hinder both the formation and growth of crystallites by penetrating the nanowire more than the typical thickness of the native oxide, of the order of a few nm [ 28 , 29 ], thus interfering deeply with the crystallization dynamics in thin nanowires. The thickness of native oxide is typically not very stable under thermal treatments, being easily removed during annealing.…”