Physical vapor deposition reactor design and validation for in-space manufacturing of aluminum nitride single crystals

Aluminum nitride (AlN) has been identified as the wide bandgap semiconductor with superior material properties, that could enable revolutionary improvements in power electronics and optoelectronics devices beyond silicon carbide (SiC) and gallium nitride (GaN) device performance limits. AlN has made great advancements in the last 20 years towards becoming commercially viable, however there are significant challenges with the substrate material. AlN with dislocation densities below 10,000 per cm2 and between 1-2 inches in diameter can currently be produced terrestrially. For the commercial requirement of large area high power electronic devices, there are three technological gaps that needs to be solved: (i) a 10 - 100 x reduction in dislocations, (ii) increasing the diameter of wafers by a factor of 3, (iii) reduction in point defects by two to three orders of magnitude to mid-1015 per cm3. All three of these issues could be mitigated by growing crystals in the microgravity environment. Leveraging the space environment will (a) promote uniform mass flux at the crystal growth front, (b) control thermal gradients while scaling size of crystal, and (c) will allow for growth closer to the ideal growth rate for AlN. AlN is grown using physical vapor deposition (PVD) at temperature around 2100 oC. Currently there is no infrastructure for crystal growth of high temperature materials such as AlN in space. This is primarily limited by the electrical power level in the range of 500-1000 watts available for operating crystal growth furnaces at the International Space Station (ISS). In this proposal, a novel energy efficient PVD reactor will be designed for AlN bulk crystal growth at 2100 oC operating at power levels level in the 400-1000 watts for crystal diameters in the range of 1 - 6 inches. The fabricated PVD reactor will be designed per the space design constraints and tested for AlN bulk growth in terrestrial conditions.