Greetings. I have a mesa structure with a top Si layer and the side walls have SiGe and a Ge quantum well exposed. I want to make Al contacts to this well but native oxides prevent good ohmic contact formation. I considered a HF acid cleaning, but the literature on this wet etching method suggests HF, although excellent for native Si oxide cleaning, doesn't work as well in Ge. Besides that, since I can't do the cleaning in situ as soon as I remove my sample from the acid bath the oxide layers start to grow again. I've read a paper that employs in situ Ar plasma etching which seems to be good at removing both oxides and carbon contamination. The paper, however, only mentions the technique, since it's not its main objective. Do you know which parameters of pressure, power and time should I employ for this kind of cleaning?

Thank you very much.