We have studied the optimum oxide structure on the SiGe surface to suppress the leakage current in the mesa diode with the SiGe and Si pn-junction. The germanium oxide such as GeO2, on the junction surface causes the leakage current. The HF acid treatment followed by the H2SO4 and H2O2 acid treatment generates the pure SiO2, terminated surface on the SiGe film with suppressing the germanium oxide. This treatment minimizes the leakage current in the SiGe/Si diodes. (C) 20021 Elsevier Science Ltd. All rights reserved.