Towards low-dimensional hole systems in Be-doped GaAs nanowires

Abstract

Abstract. GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying stronglyconfined 0D and 1D hole systems with strong spin-orbit effects, motivating our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowirebased quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top-gates produced using GaAs nanowires with three different Be-doping densities and various AuBe contact processing recipes. We show that contact annealing only brings small improvements for the moderately-doped devices under conditions of lower anneal temperature and short anneal time. We only obtain good transistor performance for moderate doping, with conduction freezing out at low temperature for lowlydoped nanowires and inability to reach a clear off-state under gating for the highlydoped nanowires. Our best devices give on-state conductivity 95 nS, off-state conductivity 2 pS, on-off ratio ∼ 10 4 , and sub-threshold slope 50 mV/dec at T = 4 K. Lastly, we made a device featuring a moderately-doped nanowire with annealed contacts and multiple top-gates. Top-gate sweeps show a plateau in the sub-threshold region that is reproducible in separate cool-downs and indicative of possible conductance quantization highlighting the potential for future quantum device studies in this material system.

Near-thermal limit gating in heavily doped III-V semiconductor nanowires using polymer electrolytes

“…The sub-threshold swing is comparable to the best obtained for n-InP (68 mV/dec) [5] and n-GaAs (70 mV/dec) [7] nanowire MOSFETs and within 25% of the room temperature thermal limit (60 mV/dec). We obtain on-current I on ∼ 0.25 µA at V sd = 100 mV corresponding to 400 kΩ channel resistance, with contact resistance R on ∼ 30 kΩ previously measured for this doping level [12]. Similar performance is obtained from separate nominallyidentical devices as demonstrated by the data in Fig.…”

“…This leads to a significant Schottky barrier for metal-GaAs interfaces. Ohmic contacts to GaAs typically use an annealed alloy of a noble metal and a diffusive dopant [27], e.g., AuGe for n-type [7] and AuBe for p-type [12]. The idea is that the diffusive dopant causes the semiconductor local to the metal contact to become very highly doped.…”

“…A Be-doped shell provides an ideal interface for AuBe contacts with narrow Schottky barrier and thereby p-type NWFETs with low resistance ohmic contacts. We recently showed that contact annealing is detrimental in this case likely because the Be diffusion rate within the nanowire exceeds the Be out-diffusion rate from the alloy, reducing the net doping level at the contact interface [12]. This provides a strong incentive to compensate by maximising shell doping density to ensure the Schottky barrier depletion width remains minimised.…”

“…There will possibly be some short wurtzite segments at the ends [26]; these will be buried under the contacts. We focus here on nanowires with shell acceptor density N A = 1.5 × 10 19 cm −3 ; the highest doping density from our earlier work on allinorganic p-GaAs NWFETs [12]. Nanowires were transferred to a pre-patterned HfO 2 /SiO 2 -coated n + -Si substrate for device fabrication with two architectures used: (a) a traditional metal-oxide Ω-gate structure ( Fig.…”

Influence of Boron Antisite Defects on the Electrical Properties of MBE‐Grown GaAs Nanowires

“…In addition, since B As acts as a doubly charged acceptor, incorporation of boron in planar GaAs layers was found to lead to high unintentional p‐doping . This offers an alternative route to p‐doping in MBE‐grown GaAs nanowires than those previously demonstrated, which include Be or Si . One interesting aspect of using B to dope GaAs nanowires is that since it is group III, it offers the possibility to tune the growth parameters between substitional incorporation or incorporation on defect sites.…”