Atomic layer deposition of crystalline SrHfO₃ directly on Ge (001) for high-k dielectric applications

The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO₃ (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700°C for 5min. The 2×1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets (>2eV), low leakage current (<10^-5 A/cm² at an applied field of 1 MV/cm) at an equivalent oxide thickness of 1nm, and a reasonable dielectric constant (k∼18). The interface trap density (D_it) is estimated to be as low as ∼2×10¹²cm^-2eV^-1 under the current growth and anneal conditions. Some interfacial reaction is observed between SHO and Ge at temperatures above ∼650°C, which may contribute to increased D_it value. This study confirms the potential for crystalline oxides grown directly on Ge by atomic layer deposition for advanced electronic applications.