Co-optimization of spin coherence and valley splitting in Si/SiGe heterostructures

• URL: http://arxiv.org/abs/2605.31342v1
• Date: Fri, 29 May 2026 14:20:52 GMT
• Title: Co-optimization of spin coherence and valley splitting in Si/SiGe heterostructures
• Abstract summary: We use density functional theory to optimize the valley splitting and spin dephasing time in realistic Si/SiGe heterostructures.<n> sharper Si/SiGe interfaces in general result in larger valley splittings and longer spin dephasing times.
• Score: 1.1549572298362782
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Single electron spins can be used to encode and process information in semiconductor quantum devices. Progress has been hindered by materials challenges, such as the small energy splitting between low-lying valley states and hyperfine coupling to nuclear spins. Here we use density functional theory to optimize the valley splitting and spin dephasing time in realistic Si/SiGe heterostructures. Reductions in the Si quantum well width generally increase the valley splitting. However, in narrow quantum wells, a larger fraction of the electronic wavefunction resides in the SiGe buffer layers, which increases the hyperfine coupling with spinful $^{73}$Ge. Our work shows that Si/SiGe heterostructures with 3~--~4~nm wide quantum wells and $^{73}$Ge and $^{29}$Si concentrations of 50 ppm should support average valley splittings $E_{v}$~$>$~500~$μ$eV and spin dephasing times $T_2^*$ exceeding 15~$μ$s assuming an effective quantum dot area of 700 nm$^2$. In addition, sharper Si/SiGe interfaces in general result in larger valley splittings and longer spin dephasing times.

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