We have investigated junction surface treatments of SiGe/Si/Si pin diodes by using leakage current measurements under the reverse bias condition and X-ray photoelectron spectroscopy. HF-acid dipping followed by H2SO4 + H2O2 treatment resulted in the highest breakdown voltages (exceeding 300 V) at a leakage current of 100 mu A/cm(2). Low-temperature oxidation with UV ozone treatment resulted in lower breakdown voltages (less than 200 V), and Si and Ge oxides appeared on the junction surface. Chemical shift analysis of Si 2p and Ge 3d on the SiGe junction surface revealed that the leakage characteristics are independent of the nonstoichiometric components of the surface oxides. Elimination of the Ge oxide in the surface oxide is necessary to achieve a high breakdown voltage. (c) 2006 The Electrochemical Society.