A thin film technology compatible with multilayer device fabrication is critical for exploring the potential of the 39-K superconductor magnesium diboride for superconducting electronics. Using a Hybrid Physical-Chemical Vapor Deposition (HPCVD) process, it is shown that the high Mg vapor pressure necessary to keep the MgB 2 phase thermodynamically stable can be achieved for the in situ growth of MgB 2 thin films. The films grow epitaxially on (0001) sapphire and (0001) 4H-SiC substrates and show a bulk-like T c of 39 K, a J c (4.2K) of 1.2 × 10 7 A/cm 2 in zero field, and a H c2 (0) of 29.2 T in parallel magnetic field. The surface is smooth with a root-mean-square roughness of 2.5 nm for MgB 2 films on SiC. This deposition method opens tremendous opportunities for superconducting electronics using MgB 2 .

We have studied the effect of deposition rate and layer thickness on the properties of epitaxial MgB 2 thin films grown by hybrid physical-chemical vapor deposition on 4H-SiC substrates. The MgB 2 film deposition rate depends linearly on the concentration of B 2 H 6 in the inlet gas mixture. We found that the superconducting and normal-state properties of the MgB 2 films are determined by the film thickness, not by the deposition rate. When the film thickness was increased, the transition temperature, T c , increased and the residual resistivity, ρ 0 , decreased. Above 300 nm, a T c of 41.8 K, a ρ 0 of 0.28 µΩ·cm, and a residual resistance ratio RRR of over 30 were obtained. These values represent the best MgB 2 properties reported thus far.

We have used two polytypes of silicon carbide single crystals, 4H-SiC and 6H-SiC, as the substrates for MgB 2 thin films grown by hybrid physical-chemical vapor deposition ͑HPCVD͒. The c-cut surface of both polytypes has a hexagonal lattice that matches closely with that of MgB 2. Thermodynamic calculations indicate that SiC is chemically stable under the in situ deposition conditions for MgB 2 using HPCVD. The MgB 2 films on both polytypes show high-quality epitaxy with a Rutherford backscattering channeling yield of 12%. They have T c above 40 K, low resistivities, high residual resistivity ratios, and high critical current densities. The results demonstrate that SiC is an ideal substrate for MgB 2 thin films.