Presentation Information
[17p-PA5-10]Mobility Enhancement in Strained Germanium Quantum Wells via In-Situ Al2O3 Passivation
〇Tanbhir Hasan1, Kentarou Sawano1 (1.Tokyo City Univ.)
Keywords:
Quantum Wells,Quantum Computing,In-situ Alumina deposition
The holes in Germanium (Ge) are attractive in semiconductor quantum computing due to the strong spin-orbit coupling interaction, large and tunable g-factors, and weak hyperfine interaction. Compressively strained Ge quantum well (QW) is well known for confining holes, and the high-mobility undoped QWs are a leading candidate for up to four-qubit quantum processors. However, different scattering mechanisms make it challenging to achieve high mobility. When the defects or charged particles are trapped at the interface, particularly originating from the surface states, Remote Impurity Scattering (RIS) becomes a dominant mobility-limiting factor. A high-quality gate insulator (Al2O3 passivation layer) can suppress the surface states. In this research, we fabricated strained Ge QWs on a Si1-xGex buffer with in-situ, ex-situ, and without Al2O3 passivation, and the hole mobilities were evaluated. The strained Ge QW structures shown were fabricated by using a solid-source molecular beam epitaxy (MBE) and an atomic layer deposition (ALD) joint system. The sample without Al2O3 passivation shows very poor mobility, and electrons were observed as a carrier between the temperature range 100K and 150 K. This clearly indicates the presence of parasitic parallel conduction, which probably originated from the surface states. The hole density for Al2O3 passivated samples is seen to saturate below 50 K, indicating the formation of the two-dimensional hole gas in the strained Ge QWs. The in-situ Al2O3 passivated strained Ge QW shows the highest hole Hall mobility, indicating the significant suppression of the surface states. The mobility can be further improved by enhancing the Al2O3 quality, minimizing other RISs, annihilating the defects, etc.