Published online by Cambridge University Press: 01 February 2011
Demand for low cost and high density near infrared (NIR) detection has motivated the development and use of germanium on silicon (Ge/Si) heterostructures to extend the optoelectronic application of Si technology. Ge/Si structures are currently being considered for NIR p/n detectors that can be integrated with Si CMOS [1]. Various research demonstrations of integrated Ge/Si diodes with CMOS have been made including using sputtered poly-Ge to form Ge/Si photodiodes after the CMOS transistors were complete. Poly-crystalline germanium (poly-Ge) may be formed by various methods including the use of plasma enhanced chemical vapor deposition. In this work, the formation of poly-Ge/Si heterostructures by inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) is examined as an alternative method to integrate poly-Ge into a CMOS process flow. In this work, 25 nm poly-Ge on Si heterostructures are formed by either recrystallization of ICP-CVD hydrogenated amorphous germanium (α-Ge:H) or direct deposition of ICP-CVD poly-Ge. A rapid measure of the suitability for detectors of the different poly-Ge films is the minority carrier recombination lifetime, which can affect dark current, quantum efficiency and overall detector detectivity. Recombination lifetimes were measured, therefore, in α-Ge:H that was recrystallized using rapid thermal annealing between 400 – 1050 °C in nitrogen ambient. Lifetimes were measured using a non-contact inductively coupled photo-conductance setup and an effective surface recombination velocity is subsequently extracted for each Ge/Si heterostructure that describes the integrated recombination in the Ge layer and at the Ge/Si interface, which separates the Ge contribution from recombination in the bulk silicon and at the silicon surface. The effective recombination velocities for the 25 nm Ge layers are found to be ∼103−104 cm/s.