Synthesis of Ge-Sn at high pressure and high temperature in a laser-heated diamond anvil cell

Abstract

Ge–Sn compound is predicted to be a direct band gap semiconductor with a tunable band gap. However, the bulk synthesis of this material by conventional methods at ambient pressure is unsuccessful due to the poor solubility of Sn in Ge. We report the successful synthesis of Ge–Sn in a laser-heated diamond anvil cell (LHDAC) at ~7.6 GPa & ~2000 K. In situ Raman spectroscopy of the sample showed, apart from the characteristic Raman modes of Ge TO (Г) and β-Sn TO (Г), two additional Raman modes at ~225 cm⁻¹ (named Ge–Sn₁) and ~133 cm⁻¹ (named Ge–Sn₂). When the sample was quenched, the Ge–Sn₁ mode remained stable at ~215 cm⁻¹, whereas the Ge–Sn₂ mode had diminished in intensity. Comparing the Ge–Sn Raman mode at ~225 cm⁻¹ with the one observed in thin film studies, we interpret that the observed phonon mode may be formed due to Sn-rich Ge–Sn system. The additional Raman mode seen at ~133 cm⁻¹ suggested the formation of low symmetry phase under high P–T conditions. The results are compared with Ge–Si binary system.

Keywords:

• semiconductors
• high pressure and high temperature synthesis
• Raman spectroscopy
• diamond anvil cell

Acknowledgements

The authors are grateful to P. Ch. Sahu and N. Subramanian for valuable discussions. We acknowledge L. Meenakshi Sundaram for technical help. We are grateful to P.R. Vasudeva Rao, C.S. Sundar, M.P. Janawadkar and A.K. Arora for support and encouragement. N.V. Chandrashekar, N.R. Sanjay Kumar and M. Sekar are also thanked for their help in various stages of the work. We gratefully acknowledge financial support from DAE, India. We acknowledge A.K. Sinha for his support for using INDUS-2 (BL12) synchrotron beam line at RRCAT, Indore.