Graphite/h-BN van der Waals heterostructure as a gate stack for HgTe quantum wells

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Two-dimensional topological insulators are crucial for spintronics and quantum computing.
• Tuning the Fermi level into the bulk band gap with electric fields is essential for observing exotic phenomena.
• Hexagonal boron nitride (h-BN) offers a flat, charge-free surface ideal for gate dielectrics.

Purpose of the Study:

• To investigate a h-BN/graphite van der Waals heterostructure as a top gate for HgTe heterostructure-based Hall bar devices.
• To compare the performance of h-BN/graphite gates with conventional h-BN/Ti/Au and HfO2/Ti/Au gates.
• To address the issue of significant carrier density shifts in gated HgTe heterostructures.

Main Methods:

• Fabrication of HgTe heterostructure-based Hall bar devices.
• Integration of h-BN/graphite van der Waals heterostructures as top gates.
• Comparison with devices using h-BN/Ti/Au and HfO2/Ti/Au gates.
• Analysis of charge carrier density and electron mobility.

Main Results:

• Devices with h-BN/graphite gates exhibited no charge carrier density shift.
• HfO2/Ti/Au gated devices showed a significant n-type carrier density increase.
• Electron mobility was slightly higher in h-BN gated devices compared to HfO2-based devices.
• The work function of HgTe and graphite was identified as a key factor for the observed stability.

Conclusions:

• h-BN/graphite van der Waals heterostructures are effective top gates for HgTe devices, preventing undesirable carrier density shifts.
• The compatibility of layered material transfer with wet-etched structures is demonstrated.
• This approach offers a viable strategy for precise control of carrier density in gated topological insulator devices.