Growth and characterization of epitaxial ultra-thin NbN films on 3C-SiC/Si substrate for terahertz applications

Abstract

We report on electrical properties and microstructure of epitaxial thin NbN films grown on 3C-SiC/Si substrates by means of reactive magnetron sputtering. A complete epitaxial growth at the NbN/3C-SiC interface has been confirmed by means of high-resolution transmission electron microscopy (HRTEM) along with x-ray diffractometry (XRD). Resistivity measurements of the films have shown that the superconducting transition onset temperature (T C) for the best specimen is 11.8 K. Using these epitaxial NbN films, we have fabricated submicron-size hot-electron bolometer (HEB) devices on 3C-SiC/Si substrate and performed their complete DC characterization. The observed critical temperature T C = 11.3 K and critical current density of about 2.5 MA/cm 2 at 4.2 K of the submicron-size bridges were uniform across the sample. This suggests that the deposited NbN films possess the necessary homogeneity to sustain reliable hot electron bolometer device fabrication for THz mixer applications.

A Technology Demonstrator for 1.6–2.0 THz Waveguide HEB Receiver with a Novel Mixer Layout

“…were wired for DC testing. The spread of the measured critical current at 4 K and normal-state resistance at 20 K are ±1.95 μA and ±2.7 Ω, respectively, in line with device uniformity data presented in [36]. This indicates suitability of the proposed process for fabrication of state-of-the-art HEB mixers for balanced and multipixel array receivers.…”

“…The NbN films were grown on the preheated (~700°C) substrates by means of reactive DC magnetron sputtering in a Ar/N 2 gas mixture using a 2″ Nb target, resulting in the NbN film deposition rate 75Å/min calibrated via the transmission electron microscopy (TEM) on satellite NbN/Si specimens. The critical temperature of the deposited film is 9.2 K. The bolometer was defined by the separation between its contact pads, ranging from 100 nm to 400 nm [36]. Definition of the NbN bridge between the contact pads was Fig.…”

Reduction of Phonon Escape Time for NbN Hot Electron Bolometers by Using GaN Buffer Layers

“…Despite advances in the reliable fabrication of NbN films with thicknesses ranging from 3.5 to 5 nm, approaching the coherence length of NbN unavoidably manifests in the suppression of its superconducting properties [10]. Thus, buffer-layers with similar crystal structure to NbN such as MgO [10] or 3C-SiC [11], [12] have been employed to promote the growth of single-crystal films with improved superconducting properties. Although, MgO is highly hydrophobic and complicates the fabrication of the delicate HEB device, it has yielded a larger (up to 3.7 GHz) gain bandwidth of the HEB when used on quartz substrates (2 GHz gain bandwidth) [13].…”

Highly oriented, free-standing, superconducting NbN films growth on chemical vapor deposited graphene

“…1 Much of the work on superconducting single photon detectors (SSPD) has been based on NbN thin films, [2][3][4] since NbN has a relatively high superconducting transition temperature, T C ∼16 K, and a short superconducting coherence length of a few nanometers and fast energy relaxation time. For increased detector efficiency by integrating SSPD with optical structures, NbN growth on non-conventional substrates like GaAs, 5,6 3C-SiC, 7 and Si 8 has been explored. Increased efficiency of terahertz detection is achieved by thermal isolation of HEBs by depositing NbN films on air bridges formed by thin membrane of Si 3 N 4 , 9 to improve the quality of these films alternative materials for buffer layer are being explored.…”