Novel high quality GeSn and GePb alloys for mid-infrared photodetectors

by Prof. Jim Williams (Research School of Physics, Australian National University, ACT 2601, Australia)

Friday 5 Jun 2026, 10:00 → 10:45 Europe/Rome

1/3-1 - Sala R (Dipartimento di Fisica e Astronomia - Edificio Marzolo)

Jim Williams and Michael Eksteen

Research School of Physics, Australian National University, ACT 2601, Australia

GeSn and more recently GePb alloys have attracted attention as promising candidates for fabricating mid-infrared photodetectors operating up to 10 µm. However, the growth of both alloys on Ge or Si substrates is challenging since the equilibrium Sn solid solubility in Ge is less than 1% and the Pb solubility is in the parts per million range. Also, the lattice mismatch between Ge and GeSn or GePb causes threading dislocations during film relaxation to equilibrium lattice spacings. Both aspects have been found to severely degrade the photodetector performance.

This presentation covers the progress that we have made on overcoming the limitations of the current GeSn and GePb materials. Specifically, a main objective of our approach has been to pursue avenues for defect reduction in both remote plasma enhanced CVD (RPECVD)-grown GeSn films and also GeSn films produced by a combination of Sn-ion implanted Ge and pulsed laser melting (PLM), to provide suitable material for high performance photodetectors. A second objective has been to develop a satisfactory n-type doping procedure for GeSn films based on ion implantation and PLM. A further objective has involved characterising strained and relaxed Ge-GeSn superlattices grown by RPECVD, and a final objective has been to investigate the possible production of GePb films by ion implantation and PLM. Apart from a brief review of each of these areas, specific focus will be given to the following two areas.

Particular emphasis will be given to the following areas. i) Strained and strain-relaxed Ge-GeSn superlattices, where we have characterised superlattices of various compositions and thicknesses by a suite of analytical methods. Using strain engineering approaches, our results show that defect-free, fully-strained superlattices with more than 10 Ge-GeSn pairs can be grown for high Sn concentrations. ii) We have achieved around 0.5 atomic % of Pb in Ge which is 5 orders of magnitude above the equilibrium solubility limit. Pb segregation to the surface and Pb-rich filamentary behaviour during rapid solidification of molten Ge limit the Pb content in Ge. iii) Towards efficient n-type doping of Ge and GeSn, where we have found that compensating p-type centres that are present in both Ge and GeSn severely limit n-type doping.  Following implantation we have studied several annealing methods from RTA to PLM and used Rutherford backscattering and channelling and TEM, along with Hall effect and magnetoresistance, to characterise the samples.

Seminar organized by the Semiconductor Physics Group & Advanced Crystals

20260605 Jim Williams.pdf