Impact of Plasma Postoxidation Temperature on the Electrical Properties of ${\rm Al}_{2}{\rm O}_{3}/{\rm GeO}_{x}/{\rm Ge}$ pMOSFETs and nMOSFETs

GeO_x/Ge interfaces are fabricated by plasma post oxidation of Al₂O₃/Ge (100) structures at 300 °C and room temperature (RT). It is found that reduction of oxidation temperature results in a significant decrease of the GeO_x/Ge interface roughness and a slight increase of the interface trap density. The Ge p- and n-channel MOSFETs with the GeO_x/Ge interfaces oxidized at the RT provide 20% and 25% enhancement, respectively, of high field hole and electron mobilities than those of MOSFETs oxidized at 300 °C. This mobility enhancement is attributable to the reduction of GeO_x/Ge interface roughness, which has been proven by theoretical calculation of surface-roughness-limited mobility using the real MOS interface roughness directly extracted from transmission electron microscopy results. As a result, high hole and electron mobility of 179 and 378 cm²/Vs, respectively, have been obtained at a Ns of 10¹³ cm^-2 in MOSFETs fabricated by the RT plasma post oxidation.