High-temperature, High-bandgap (InGaN) Energy Conversion:
IMS is pursuing the use of InGaN semiconductor technology for developing Photovoltaic (PV) solar cells (devices/systems) for energy conversion both for space and terrestrial applications. The key advantages of using this platform are the following:
With bandgaps from UV (GaN) to IR (InN), III-Nitrides can be alloyed together to give access to almost the entire solar spectrum.
InGaN has been found to be more radiation tolerant than multijunction III-V cell technologies.
III-Nitrides compounds have inherent superior thermal ruggedness properties compared to Si and III-Vs.
Growing high quality single-phase materials across a full range of binary and ternary group III nitrides on c-plane, a-plane, and m-plane sapphire and (111) silicon (Si) substrates is accomplished by exploiting advanced synthesis techniques, such as Molecular Beam Epitaxy (MBE). For all R&D exploratory activities, our (RF-MBE) chamber (reactor) is utilized for depositing precise thin crystalline films. MBE allows simple integration of molecular sources for the growth process. Spectrally-tailored materials can be synthesized with different microstructures and stacking configurations on the same substrate. This capability provides a more powerful design tool to implement a set of targeted material properties that can define more versatile devices. Recent results from InxGa1-xN growth have demonstrated films with bandgap energies tuned from 3.3 eV to 1.8 eV, which spectrally covers a range of (375-690) nm. IMS is currently investigating the fundamental materials properties of the InGaN alloy, determining how to optimize the quality of InGaN films given the substrate and lattice-matching limitations, and working to apply this knowledge to the development of high efficiency InGaN single and multijunction solar cells. The top portion of the figure below shows a schematic for the Solar Radiation (left axis) and indium (In) concentration (right axis) as a function of Energy Bandgap (Eg) and wavelength over the spectral range, where the InGaN solar cells operate. Three different energy bandgap classifications are identified as; high, medium, and low. These classifications aid in defining the roadmap outlining potential applications, advantages, and challenges associated with this group of materials, as shown in the following schematic: