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.
Benefits: 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. Potential NASA applications would be in systems using high power electronic devices, communication devices, ultraviolet (UV) laser and light emitting diodes, and, UV photodetectors. The physical vapor deposition (PVD) reactor proposed will find numerous applications for In-Space manufacturing of high temperature materials using vapor phase process. Serving as the foundation for epitaxial growth, bulk AlN wafers enable customer creation of specialized optoelectronics and power semiconductor devices leveraging AlN’s unique physical properties. These are: Ultraviolet Lasers: Materials processing applications across semiconductors, electronics and medical device manufacturing utilize deep UV light for precision ablation and forming of polymers/composites. AlN substrates enable improved power-conversion efficiencies. Enhanced Radar and Communication Systems: The project’s outcomes and the unique material properties of AlN will directly benefit the defense industry by significantly improving radar and communication systems in applications such as onboard guidance & optical sensors in hypersonic weapons. Advanced High-Voltage Switches: The high voltage, high switching frequency, and ultra-low loss characteristics of AlN-based high-voltage switches would enable the US to explore High Voltage Direct Current (HVDC) transmission that minimizes loss and expands grid capacity. Other applications include: Ultraviolet (Germicidal) LEDs, Ultraviolet Detectors, Directed Energy Weapons (DEW), Non-Line-of-Sight (NLOS) Communications, Solar blind UV communication and .Ultra-High Temperature Electronics.