Growth of Ge/Si Amorphous Superlattices by Dual-Target DC Magnetron Sputtering

Abstract

ABSTRACTAmorphous Ge/Si superlattices have been grown by dual-target dc magnetron sputtering at ambient temperature under different negative substrate bias voltages Vs. The films were studied with cross-sectional transmission electron microscopy (XTEM). All films were amorphous, but for Vs ≤ 110 V the superlattices exhibited a columnar structure. Within each column, the compositional modulation was clearly resolved except in the vicinity of the column boundaries. For 110<VS≤250V, dense films with homogeneous and well-defined layers were obtained. High-resolution XTEM studies showed that superlattices with individual layer thicknesses less than 1.5 nm and smooth interfaces could be fabricated. Increasing Vs > 250 V resulted in ion induced intermixing such that at Vs ≥ 450 no compositional modulation was observed. The obtained structural results are discussed in terms of available models for ion-irradiation effects during low-temperature ballistic growth.