High-electron-mobility (370 cm²/Vs) polycrystalline Ge on an insulator formed by As-doped solid-phase crystallization

Area of Science:

• Materials Science
• Semiconductor Physics
• Nanotechnology

Background:

• High-electron-mobility polycrystalline germanium (poly-Ge) thin films are challenging due to poor crystallinity and dopant solubility.
• Defect-induced acceptors and grain boundary scattering limit electron mobility in conventional poly-Ge.

Purpose of the Study:

• To investigate the effect of arsenic (As) doping on the solid-phase crystallization of amorphous germanium (Ge).
• To enhance the electron mobility and crystallinity of n-type poly-Ge thin films for electronic applications.

Main Methods:

• Amorphous Ge films were doped with varying concentrations of As.
• Solid-phase crystallization was induced at 375°C.
• Post-annealing was performed at 500°C.
• Electron mobility and concentration were measured.

Main Results:

• Appropriate As doping (~10^20 cm^-3) promoted lateral growth, increasing Ge grain size to ~20 μm.
• Neutral As atoms reduced trap-state density and grain boundary energy barriers.
• Achieved electron mobility of 370 cm²/Vs at 5 × 10^18 cm^-3 electron concentration.
• Electron mobility surpassed other n-type poly-Ge and n-type single-crystal Si.

Conclusions:

• As doping is a viable strategy to improve the quality of poly-Ge films.
• Low-temperature synthesis of high-mobility n-type poly-Ge enables monolithic integration with Si-based technologies.
• This advancement paves the way for high-performance Ge-CMOS on Si-LSIs and displays.