Highly strained and heavily doped germanium thin films by non-equilibrium high-speed CW laser annealing for optoelectronic applications

Abstract

The integration of light transmitters into electronic circuits is essential for the development of optical communication systems. A direct bandgap semiconductor with excellent electrical properties is preferable for a cost-effective and high-performance device. Germanium is considered a promising candidate for CMOS-compatible optoelectronics, even though the light emission is inefficient due to its indirect bandgap property. It has been reported that applying tensile strain modifies the energy band structure thus making quasi-direct bandgap emission possible. In addition, n-type doping has been expected to improve this emission. We have realized high tensile strain in polycrystalline germanium grown on a quartz substrate by employing continuous wave laser annealing (CWLA). In this study, we investigated the implementation of a similar annealing technique with antimony doped samples to combine both tensile strain and n-type doping in a Ge-on-insulator (GeOI) structure. We investigated various samples with different interfaces to achieve large-grained polycrystalline films on insulator. Characterizations of the CWLA processed samples revealed the successful introduction of both tensile strain and n-type doping in GeOI. The properties were confirmed by the enhancement of direct Γ-LH emission that observed even for room-temperature optical measurements. These results provide an important insight that will assist the feasible and large-scale development of germanium-based optoelectronic devices.