Germanium-tin (GeSn) is a novel group-IV semiconductor with strong potential for infrared photodetectors. Conventional germanium has an indirect bandgap, but adding Sn lowers the energy of the direct Γ conduction-band valley relative to the indirect L valley. With sufficient Sn content and appropriate strain control, GeSn can become a direct-bandgap semiconductor with a tunable response across the short- and mid-infrared ranges, while remaining compatible with silicon technology.

Realising this potential is challenging because Sn has a low equilibrium solubility in Ge, while lattice mismatch generates strain. Sn segregation, strain relaxation, dislocations and other defects can strongly affect optical absorption, carrier recombination and mobility.

This project investigates two linked areas: materials characterisation and n-type doping. GeSn films and multilayer structures fabricated by remote plasma-enhanced chemical vapour deposition or ion implantation followed by pulsed-laser melting will be studied using X-ray diffraction, Raman spectroscopy, Rutherford backscattering spectrometry and channeling, electron microscopy, and optical measurements. These techniques reveal how fabrication conditions, Sn composition, strain and defects determine material quality.

The project will also examine n-type doping using phosphorus, arsenic and antimony. Hall effect and magnetoresistance measurements, supported by multi-carrier transport modelling and defect spectroscopy, will distinguish electrically active donors from parallel conduction and compensating defects. The goal is to establish clear structure-defect-property relationships and identify processing conditions for high-quality GeSn infrared photodetectors.

Basic knowledge of solid state pahysics (equivalent to PHYS3032) including crystal structures, semiconductor bandgaps, doping and electrical properties.