Impact of Gd Doping on Morphology and Superconductivity of NbN Sputtered Thin Films

Abstract

We report the effect of Gd inclusion in the NbN superconductor thin films. The films are deposited on single crystalline Silicon (100) by DC reactive sputtering technique, i.e., deposition of Nb and Gd in presence of reactive N2 gas. The fabricated relatively thick films (400 nm) are crystallized in cubic structure. These films are characterized for their morphology, elemental analysis, and roughness by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDAX), and Atomic Force Microscopy (AFM) respectively. The optimized film (maximum T c ) is achieved with gas ratio of Ar:N2 (80:20) for both pristine and Gd-doped films. The optimized NbN film possesses T c (R=0) in zero and 140 kOe fields are at 14.8 K and 8.8 K, respectively. The Gd-doped NbN film showed T c (R=0) in zero and 130 kOe fields at 11.2 K and 6.8 K, respectively. The upper critical field H c2(0) of the studied superconducting films is calculated from the magneto-transport [R(T)H] measurements using GL equations. It is found that Gd doping deteriorated the superconducting performance of NbN.