Heteroepitaxy of High-Mobility Germanium on Sapphire (0001) with Magnetron Sputtering

Abstract

As an excellent semiconductor material with low band gap and high carrier mobility, germanium is widely used in the semiconductor industry in photoelectronic devices, high-frequency radio frequency (rf) circuits and devices, etc. Compared to bulk germanium wafer and silicon-based germanium on insulator (GOI) materials, the germanium on sapphire (GOS) substrate offers a highly cost-effective solution with several important advantages, including low thermal expansion coefficient mismatch, high insulator resistivity, lower rf losses, and superior crosstalk suppression. In this work, we present a method to grow a high-quality thin germanium epitaxial film on a sapphire (0001) substrate using direct-current (DC) sputtering at an elevated temperature of 600 °C. We demonstrate that thermal annealing at 850 °C reduced the germanium (111) twinning, increased the size of crystalline domains in the germanium film and thus further improved the crystalline quality. For a film with a thickness of 500 nm, the hole Hall mobility increased to 440 cm2/V·s after thermal annealing, which is about 10 times more than that of the as-sputtered film. For a 2.0 μm film, the hole Hall mobility increased to 824 cm2/V·s, which has not been reported in the literature for a GOS film. This method offers a simple but efficient way to fabricate a GOS substrate for optical electronic device applications.

Single crystalline Ge thin film growth on c-plane sapphire substrates by molecular beam epitaxy (MBE)

“…That is, twin-free Ge (111) should give three (220) peaks separated by 120° in the phi-scan. 22 Since at T G = 400 °C and 500 °C, 18 peaks are observed, this indicates that there are three different growth domains which we indicated by A, B and C and are rotated from each other. Each of the three domains have the expected three family members and three twins which are separated by 120° and 60° respectively.…”