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<p>We investigate a trench-gated quantum point contact (QPC) formed in a GaAs/AlGaAs two-dimensional electron gas (2DEG), where the trench-gate is positioned above the side gates and electrically insulated by an HfO₂ layer. This geometry enables enhanced electrostatic confinement and reduced side-gate gaps. Low-temperature transport measurements at 50 mK show that increasing the positive trench-gate voltage enhances conductance quantization and increases the subband energy spacing, reaching 5.4&#xa0;meV for an 80&#xa0;nm side-gate gap. Systematic measurements for side-gate gaps from 40 to 80&#xa0;nm, together with electrostatic calculations based on the Davies model, reveal the existence of an optimal side-gate gap that maximizes the subband energy spacing. Extending the analysis to different 2DEG depths shows that the optimal gap scales with the 2DEG depth, while the maximum subband energy spacing decreases for deeper 2DEGs. These results indicate that both the gate geometry and the 2DEG depth critically determine the subband energy spacing, and that shallower 2DEG wafers with optimized gate gaps provide a promising route toward QPCs with larger subband energy gaps.</p>

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Toward larger subband energy spacing in quantum point contacts via trench-gate engineering

  • 期刊论文

  • 发表日期：

    2026年2月27日

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  • Gyutae Park,
  • Jihong Ju,
  • Hyeon Seonwoo,
  • Yunchul Chung

摘要

We investigate a trench-gated quantum point contact (QPC) formed in a GaAs/AlGaAs two-dimensional electron gas (2DEG), where the trench-gate is positioned above the side gates and electrically insulated by an HfO₂ layer. This geometry enables enhanced electrostatic confinement and reduced side-gate gaps. Low-temperature transport measurements at 50 mK show that increasing the positive trench-gate voltage enhances conductance quantization and increases the subband energy spacing, reaching 5.4 meV for an 80 nm side-gate gap. Systematic measurements for side-gate gaps from 40 to 80 nm, together with electrostatic calculations based on the Davies model, reveal the existence of an optimal side-gate gap that maximizes the subband energy spacing. Extending the analysis to different 2DEG depths shows that the optimal gap scales with the 2DEG depth, while the maximum subband energy spacing decreases for deeper 2DEGs. These results indicate that both the gate geometry and the 2DEG depth critically determine the subband energy spacing, and that shallower 2DEG wafers with optimized gate gaps provide a promising route toward QPCs with larger subband energy gaps.