1：Experimental Design and Method Selection:

The study involves depositing ultrathin NbTiN films on various III-nitride substrates using reactive magnetron co-sputtering at room temperature to investigate the impact of substrate lattice mismatch on superconducting properties. Structural and electrical characterizations are performed using techniques like X-ray reflectivity, X-ray diffraction, high-resolution transmission electron microscopy, and atomic force microscopy. Superconducting nanowire single photon detectors are fabricated and tested to assess application suitability.

2：Sample Selection and Data Sources:

Substrates include AlN-on-sapphire, GaN/AlN heterostructure on sapphire, and GaN substrates (both conductive and semi-insulating). Samples are listed in Table 1 of the paper with specific details on substrate type and properties.

3：List of Experimental Equipment and Materials:

Equipment includes an ultra-high vacuum chamber for sputtering, X-ray diffractometer (Panalytical Empyrean with cobalt anode), transmission electron microscope (FEI-Tecnai operated at 200kV), atomic force microscope (Dimension 3100 system), and facilities for e-beam lithography and plasma etching. Materials include Nb and Ti targets, Ar and N2 gases, and various III-nitride substrates.

4：Experimental Procedures and Operational Workflow:

Substrates are cleaned and treated with Ar plasma before deposition. NbTiN films are deposited with specific power settings and gas mixtures. Post-deposition, samples undergo X-ray reflectivity, XRD, HRTEM, and AFM analyses. SNSPDs are fabricated using e-beam lithography and plasma etching, then tested in liquid helium with laser excitation.

5：Data Analysis Methods:

Data analysis includes fitting X-ray reflectivity with GenX software, calculating lattice parameters from XRD, measuring roughness from AFM, and simulating absorption efficiencies using finite-difference time-domain calculations with RSoft FullWave software.