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 carried out thermodynamics studies of the Mg-B system with the calculation of phase diagrams (CALPHAD) modeling technique and found that the superconductor MgB 2 phase is thermodynamically stable only under fairly high Mg pressures at elevated temperatures. This has lead us to the investigation of chemical vapor deposition in which the pressure during the film deposition can be high. Although the initial effort on metal-organic chemical vapor deposition (MOCVD) was not successful due to carbon contamination, a unique hybrid physical-chemical vapor deposition (HPCVD) technique has successfully produced high quality in situ MgB 2 films. The epitaxially-grown MgB 2 films show high transition temperature and low resistivity comparable to the best bulk samples, and their surfaces are smooth. In this paper, the details of the technique and the results of the HPCVD films are presented.

A three-layer Pd/Ru/Au electrolessly deposited ohmic contact to p-InGaAs, suitable for use in a self-aligned process, is presented. Cross-sectional transmission electron microscopy shows that the electrolessly plated metal layers are dense with a thin uniform reaction between the Pd and InGaAs. This contact metallization remains shallow and electrically stable even after aging for 4 h at 250°C. An average specific contact resistance of ͑1.6 Ϯ 0.6͒ ϫ 10 −6 ⍀ cm 2 was obtained for as-deposited contacts with an HCl surface treatment. When a UV ozone and NH 4 OH surface treatment was used, specific contact resistances as low as ͑2.1 Ϯ 0.9͒ ϫ 10 −7 ⍀ cm 2 were obtained.

Pt contacts to the wide band gap icosahedral boride semiconductor B 12 As 2 have been studied. All Pd and Pt contacts exhibited nonlinear I-V characteristics, while Cr/ Pt contacts were Ohmic. The specific contact resistance was reduced from 6 ⍀ cm 2 as-deposited to 3 ϫ 10 −4 ⍀ cm 2 after the Cr/ Pt contacts were annealed at 750°C for 30 s in Ar. Annealing at 600°C or higher drastically reduced the semiconductor sheet resistance, whether annealing was performed before or after metallization. This apparent activation of the semiconductor is a likely cause for the improvement in the Ohmic contacts with annealing.