Interplay Between Strain and Thickness on the Effective Carrier Lifetime of Buffer-Mediated Epitaxial Germanium Probed by the Photoconductance Decay Technique

We report contactless effective minority carrier lifetimeof epitaxiallygrown unstrained and in-plane biaxially tensile-strained(001) germanium (epsilon-Ge) epilayers measured using microwave-reflectancephotoconductance decay measurements. Strained Ge epilayers were grownusing In x Ga1-x As linearly graded buffers on (001) GaAs substrates. Usinghomogeneous excitation of unstrained Ge epilayers, thickness-dependentseparation of minority carrier lifetime components under low injectionconditions yielded a bulk lifetime of 114 +/- 2 ns and low surfacerecombination velocity of 21.3 +/- 0.04 cm/s. More notably, aneffective minority carrier lifetime of >100 ns obtained from sub-50nm 1.6% tensile-strained Ge epilayers showed no degradation relativeto the unstrained counterpart. Detailed material characterizationusing X-ray diffractometry revealed successful strain transfer of0.61 and 0.89% to the Ge epilayers via In x Ga1-x As metamorphic buffers andconfirms pseudomorphic growth. Lattice coherence observed at the epsilon-Geepilayer and In x Ga1-x As buffer heterointerfaces via transmission electronmicroscopy substantiates the prime material quality achieved. Therelatively high carrier lifetimes achieved are an indicator of excellentmaterial quality and provide a path forward to realize low-thresholdGe laser sources.