Low-Temperature Ohmic Contacts to n-ZnSe for all-Electrical Quantum Devices

The II/VI semiconductor ZnSe is an ideal host for novel devices for quantum computation and communication as it can be made nuclear-spin free to obtain long electron spin coherence times, exhibits no electron valley-degeneracy, and allows optical access. A prerequisite to electrical quantum devices is low-resistive Ohmic contacts operating at temperatures below 10 K, which have not been achieved in ZnSe yet. Here, we present a comprehensive study on the realization of Ohmic contacts to ZnSe by three different technological approaches, ion implantation of halogen donors, epitaxial doping with in situ contact processing, and finally, a unique ZnSe regrowth technique. The latter allows fabrication of Ohmic contacts with local doping that can be used to connect to a buried conducting channel such as those used in unipolar devices. DC measurements revealed high contact resistivity for Ohmic contacts to ZnSe doped via halogene ion implantation, while in situ aluminum (Al) contacts on epitaxially chlorine-doped ZnSe yield record low contact resistivities in the order of 10–5 Ω cm2 even at cryogenic temperatures. Finally, making use of the regrowth technique, local Ohmic contacts to ZnSe are demonstrated, which still feature low contact resistivities of (1.4 ± 0.4) × 10–3 Ω cm2 at 4 K. These findings pave the way for new electrical devices in the ZnSe material system such as field-effect transistors, electrostatically defined qubits, or quantum repeaters operating at cryogenic temperatures.