Ge(Sn) growth on Si(001) by magnetron sputtering

Abstract

The semi-conductor Ge1―xSnx exhibits interesting properties for optoelectronic applications. In particular, Ge1―xSnx alloys with x ≥ 0.1 exhibit a direct band-gap, and integrated in complementary-metal-oxide-semiconductor (CMOS) technology, should allow the development of Si photonics. CMOS-compatible magnetron sputtering deposition was shown to produce monocrystalline Ge1―xSnx films with good electrical properties at low cost. However, these layers were grown at low temperature (< 430 K) and contained less than 6 % of Sn. In this work, Ge1―xSnx thin films were elaborated at higher temperature (> 600 K) on Si(001) by magnetron sputtering in order to produce low-cost and CMOS-compatible relaxed pseudo-coherent layers with x ≥ 0.1 exhibiting a better crystallinity. Ge1―xSnx crystallization and Ge1―xSnx crystal growth were investigated. Crystallization of an amorphous Ge1―xSnx layer deposited on Si(001) or Ge(001) grown on Si(001) leads to the growth of polycrystalline films. Furthermore, the competition between Ge/Sn phase separation and Ge1―xSnx growth prevents the formation of large-grain Sn-rich Ge1―xSnx layers without the formation of β-Sn islands on the layer surface, due to significant atomic redistribution kinetics at the crystallization temperature (T = 733 K for x = 0.17). However, the growth at T = 633 K of a highly-relaxed pseudo-coherent Ge0.9Sn0.1 film with low impurity concentrations (< 2 × 1019 at cm―3) and an electrical resistivity four orders of magnitude smaller than undoped Ge is demonstrated. Consequently, magnetron sputtering appears as an interesting technique for the integration of optoelectronic and photonic devices based on Ge1―xSnx layers in the CMOS technology.