Impact of Plasma Postoxidation Temperature on the Electrical Properties of Al₂ O₃/ GeOₓ/ Ge pMOSFETs and nMOSFETs

GeOx/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 GeOx/Ge interface roughness and a slight increase of the interface trap density. The Ge p- and n-channel MOSFETs with the GeOx/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 GeOx/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 1013cm-2in MOSFETs fabricated by the RT plasma post oxidation.