MgB₂, with a T_c of 39 K, is a promising material for superconducting electronics and high field magnet applications. The development of deposition processes for MgB₂ has been hampered by the unusually high Mg overpressure required for phase stability at elevated temperatures. Hybrid physical-chemical vapor deposition (HPCVD), a process developed at Penn State, combines thermal decomposition of B₂H₆ gas with an evaporative Mg flux to deposit MgB₂ and is able to provide sufficient Mg overpressure for high temperature MgB₂ growth. The HPCVD process does, however, have limitations arising from the original reactor configuration. The substrate and Mg supply are heated on the same inductively heated susceptor, which prevents independent temperature control and limits both the size of substrates and the amount of Mg available for growth. This in turn limits the usable range of deposition parameters such as substrate temperature and restricts the growth time which is problematic for thick films and coatings.

The goals of this study were to develop an improved understanding of the HPCVD deposition process and design a new HPCVD reactor that addresses and improves upon the limitations of the original configuration. A combination of computational fluid dynamics simulations and growth experiments were used to study the HPCVD process in the original reactor. A transport and chemistry model for the growth of boron films from B₂H₆ was developed and used to evaluate new reactor configurations. The simple chemistry model consists of the gas-phase decomposition of B₂H₆ to BH ₃, the adsorption of BH₃ onto an activated site to form a BH₂-Site complex and the transformation of the complex into a boron film and the growth rates from this model were in quantitative agreement with experimental data.

A vertical dual-heater reactor configuration which was interchangeable with the original configuration was then developed to provide independent temperature control of the substrate and Mg source and increased substrate size. MgB₂ film growths in this configuration were achieved, with comparable film properties from the original configuration; however the process had poor reproducibility and low growth rates. Boron film growth experiments and numerical modeling, incorporating the previously developed chemistry model showed that there is substantial B₂H₆ depletion upstream of the substrate and indicated that this configuration was not an optimal design.

An impinging jet reactor configuration was then designed to reduce parasitic deposition upstream of the substrate, yet maintain the independent temperature control of the substrate and Mg source. Numerical modeling was used to explore process parameters for boron thin film growth and provide a guide for growth experiments. Initial experiments showed that a balance needed to be established between the loss of B₂H₆ and the gas-phase nucleation of Mg particles from cold-finger effects induced by the inlet jet flow. Superconducting MgB₂ films were successfully grown in the impinging jet reactor that a T_c of 39.8 K and critical current density greater than 2x10⁶ A/cm² at zero magnetic field. The impinging jet configuration introduced a large degree of flexibility in MgB₂ deposition with thin axis oriented films deposited at low jet flow rates with improved uniformity and thick coatings with growth rates in excess of 100 μm/hr at higher jet flow rates.