Impact of Oxygen Concentration on Hole Mobility in Undoped Ge Quantum Wells

Abstract We demonstrate that oxygen-related impurities significantly limit hole mobility in Ge quantum wells (QWs) and show that the use of purified precursors substantially mitigates this effect. Samples grown without precursor purification exhibit peak hole mobilities below 5.0×10 5 cm 2 /Vs, whereas those grown with purified precursors consistently achieve mobilities exceeding 1.0×10 6 cm 2 /Vs, with a maximum near 2.25×10 6 cm 2 /Vs. Precursor purification reduces the oxygen concentration in the QWs by roughly a factor of five. By fitting the density-dependent mobility with a model that includes remote-charge, background-charge, and interface-roughness scattering (following Huang and Sarma), we find that the background charge density N b is reduced by about one order of magnitude, from (5.7 ± 0.7)×10 14 to (4.9 ± 1.3)×10 13 cm -3 , when using the purified precursor. This reduction correlates with the observed mobility enhancement and identifies oxygen-related defects as the dominant source of background scattering. Although oxygen control is a key pathway to improve mobility in Ge QWs, interface-roughness and remote-charge scattering remain significant and together limit the achievable peak mobility.