Niobium nitride (NbN) is widely used in high-frequency superconducting electronics circuits because it has one of the highest superconducting transition temperatures (Tc ∼ 16.5 K) and largest gap among conventional superconductors. In its thin-film form, the Tc of NbN is very sensitive to growth conditions and it still remains a challenge to grow NbN thin film (below 50 nm) with high Tc. Here, we report on the superconducting properties of NbN thin films grown by high-temperature chemical vapor deposition (HTCVD). Transport measurements reveal significantly lower disorder than previously reported, characterized by a Ioffe-Regel (kF ℓ) parameter of ∼ 14. Accordingly we observe Tc ∼ 17.06 K (point of 50 % of normal state resistance), the highest value reported so far for films of thickness below 50 nm, indicating that HTCVD could be particularly useful for growing high quality NbN thin films.Niobium nitride (NbN)thin films -thanks to their high T c ∼ 16.5 K, superconducting energy gap ∆ ∼ 2.5 meV, and upper critical field B c2 ∼ 40 T -have been the subject of intense research for the last few decades, both on application and fundamental grounds. The combination of high T c and small coherence length (ξ(0) ∼ 5 nm) allows one to fabricate very thin NbN films with reasonably high T c , which is essential for, e.g, Superconducting Single Photon Detectors (see e.g. [1,2]). NbN thin films are used as hot electron bolometers and superconducting radio frequency cavities. NbN has higher kinetic inductance to other S-wave superconductors [3], which this helps fabricating superconducting micro wave resonators with high characteristic impedance and microwave kinetic inductance detectors. On the fundamental level, the effects of disorder on superconducting and normal state properties have been studied in NbN thin films [4][5][6]. Nano-wires, made from NbN thin films, have demonstrated thermal and quantum phase slips [7]a phenomenon of great interest in understanding onedimensional superconductivity. Further, the large superconducting energy gap of NbN can be explored in designing circuit Quantum Electrodynamics experiments in the THz frequency range.Thus, there has been a growing demand of high quality NbN thin films. Reactive DC magnetron sputtering from an Nb target in an argon and nitrogen atmosphere is most commonly used to deposit NbN on various substrates [8][9][10]. The main difficulty in this process, arises from the creation of atomic level nitrogen vacancies and from the formation of non-superconducting Nb 2 N and hexagonal phases. Besides, in the optimal parameter range, the high sputtering rate (typically ∼ 1-5 nm/sec) makes it difficult to control the thickness below 10 nm. Some other methods, where the superconducting properties of NbN thin films were probed, include Pulsed Laser Deposition (PLD) [11,12], Molecular Beam Epitaxy (MBE) [13] and Atomic Layer Deposition (ALD) [14]. In this regard, de-position of superconducting NbN films by high temperature chemical vapor deposition (HTCVD) is rather rare. HTCVD, comp...

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