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

Abstract

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 lowresistive 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 cm 2 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 cm 2 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.

In-situ grown single crystal aluminum as a non-alloyed ohmic contact to n-ZnSe by molecular beam epitaxy (MBE)

“…Since Ti has similar work (4.33 eV) function compared to Al, it seems contradict with the Schottky limit assumption. But a more recent work also showed that ex-situ deposited Ti on n-ZnSe with 2×10 19 cm −3 carrier concentration exhibited rectifying behavior, and researchers attributed this to the ZnSe surface oxide after being exposed to air 12 . Therefore, the in-situ deposited Al on ZnSe could still follow the Schottky model.…”

“…There has been past interest in ZnSe-GaAs heterojunction and quantum well systems for devices such as full-colored LED pixelated displays, high power heterojunction bipolar transistor (HBT) and field-effect transistor (FET) [5][6][7][8][9][10][11] . More recently, ZnSe is considered as candidate material for quantum computation and communication as it can be made nuclear-spin free to obtain long electron spin coherence times 12 . For all these applications, low-resistance ohmic contacts are essential for fabrication of high-performance devices.…”

“…Indium (In) has also been used as an ohmic contact, but this contact has high resistivity and low reliability due to In's low melting point and poor wetting 16 . Very recently, researchers also realized local ohmic contacts to a buried n-ZnSe layer through selective regrowth of heavily doped ZnSe layer, then deposited low work function metals such as aluminum (Al), magnesium (Mg) and titanium (Ti) 12 .…”

“…Schottky I-V characteristics for Al on lightly doped ZnSe samples suggests the Al-ZnSe could form a low barrier height Schottky contact, and there is no mid-gap fermi level pinning at n-ZnSe surface (both as-grown and air exposed), which is different from n-GaAs. In-situ grown Al on n-ZnSe could be a Schottky limit contact; (4) Comparison with recent work12 showed polycrystalline Al by evaporator and epitaxially single crystalline Al have different interface behaviors.…”

Orientation Dependent Mechanical Responses and Plastic Deformation Mechanisms of ZnSe Nano Films under Nanoindentation

“…Because of these excellent properties, ZnSe materials are widely used in nonlinear optical devices, flat panel displays, light emitting diodes (LEDs), lasers, logic gates, transistors, etc. [8][9][10][11][12][13][14]. In addition to thin films and macroscopic crystals, ZnSe has been obtained in a great variety of morphologies in the nanometric range, that make it suitable for applications such as field emitters, sensors, actuators, and many other optoelectronic devices [9,11,15,16].…”