Surface termination and roughness of Ge(100) cleaned by HF and HCl solutions

Oxide removal from Ge(100) surfaces treated by HCl and HF solutions with different concentrations are systematically studied by synchrotron radiation photoelectron spectroscopy (SR-PES). SR-PES results show that clean surfaces without any oxide can be obtained after wet chemical cleaning followed by vacuum annealing with a residual carbon contamination of less than 0.02 monolayer. HF etching leads to a hydrogen-terminated Ge surface whose hydrogen coverage is a function of the HF concentration. In contrast, HCl etching yields a chlorine-terminated surface. Possible etching mechanisms are discussed. Surface roughness after HF and HCl treatments is also investigated by atomic force microscopy which shows that HF treatment leaves a rougher surface than HCl.