Shortened photoconductance lifetime of Si/SiGe heterostructures due to interfacial oxygen or carbon from incomplete in-situ hydrogen cleans

The photoconductance decay lifetime in pseudomorpically strained <100> Si/Si0.7Ge0.3 heterostructures grown by rapid thermal chemical vapor deposition is measured in heterostructures with and without oxygen and carbon at the interface between the silicon substrate and epitaxial Si0.7Ge0.3 layer. A standard ex-situ clean combined with an in-situ hydrogen cleaning step using different combinations of hydrogen flows (0-20 slpm), pressure (80-8.8×104 Pa), and temperature (760-865 °C) are used to produce high oxygen and or carbon concentrations at the interface, measured by secondary ion mass spectrometry. For all cases in which oxygen was detected at the interface the heterostructure's lifetime were significantly shorter, 55-113 μs, compared to that in device quality Si/Si0.7Ge0.3 heterostructures, 530 μs, grown using a 1 min, 900 °C in-situ hydrogen bake that regularly reduces oxygen and carbon contamination below SIMS detection limits. Numeric simulations of the Si/Si0.7Ge0.3 heterostructures indicate that increasing recombination at the interface leads to a saturation of the lifetime at approximately 55 μs due to electron transport limited recombination at the Si/SiGe interface, consistent with the experimental observations.