Y2O3/Ge gate stacks with ultrathin GeOx interlayer were fabricated by two-step rf sputtering using a Y2O3 target followed by a vacuum-annealing, which were carried out in the same chamber without vacuum breaking. TiN-gate Ge metal-insulator-semiconductor (MIS) capacitors were fabricated with equivalent oxide thicknesses in the range of 2.1-2.3 nm. The highest temperature was 400 degrees C for the entire fabrication process. Interface states density (D-it) was characterized using a deep-level transient spectroscopy method with optimized injection pulse and quiescent reverse-bias voltages at each temperature. Dit values were approximately 4 x 10(13), 5 x 10(11), and 3 x 10(12) cm(-2) eV(-1) at energy positions around valence band, mid- gap, and conduction band, respectively. The slow trap contribution was also small in the upper half of the band-gap, implying a potential application of the Y2O3/Ge gate stack to the fabrication of high-performance Ge-n-MIS field effect transistors. (c) 2013 Elsevier B.V. All rights reserved.