Istituto dei materiali per l'elettronica ed il magnetismo     
Frigeri C., Serényi M., Khánh N. Q., Csik A., Nasi L., Erdélyi Z., Beke D. L., Boyen H. Hydrogen behaviour in amorphous Si/Ge nano-structures after annealing. In: ACSIN 2011 - 11th International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures (St. Petersburg (RU), 3-7 October 2011). Abstract, pp. 202 - 202. Ioffe Physical Technical Institute, 2011.
The H behaviour in a-Si, a-Ge, a-SiGe is still debated, also thanks to their employment in photovoltaic solar cells whose performance depends on dangling bonds passivation by H doping. a-SiGe can be obtained by depositing alternating nano-layers of a-Si and a-Ge and intermixing the 2 atoms by annealing. Here results on H behaviour upon annealing of nano-structures made of 50 couples of very thin (3 nm each) alternating layers of a-Si and a-Ge are given. The superlattice nano-structures were deposited by sputtering. Hydrogen was added at flow rates of 0.4 to 6 ml/min. ERDA of a-Si and a-Ge single layers showed that for flows ≥1.5ml/min the incorporated H saturates at 16 at% and 7 at% in Si and Ge, respectively. IR optical absorbance showed that H is mostly incorporated as Si and Ge monohydrides. Annealing was done at 673 K for times between 1 and 10 h. The H behaviour in nano-structures as a function of annealing and H content was followed by IR optical absorbance, AFM and ERDA. With increasing annealing temperature/time the surface morphology degrades with formation of bumps and craters whose size and density increase with increasing H content. Upon annealing the signals of Ge-H and Si-H complexes disappear in the IR spectra indicating that H is released to the lattice. This supports the conclusion that it is the released H that produces bumps and craters when the bumps blow up because of the high internal pressure of H. ERDA of a-Si and a-Ge single layers, showing a faster H release in a-Ge than in a-Si, suggests that in the superlattice nano-structures H is first released from the a-Ge layers upon annealing. This agrees with literature reporting on the lower binding energy of Ge-H with respect to Si-H. It also shows that H is unstable against annealing.
Subject Amorphous Si
Amorphous Ge
IR absorbance

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