Back-Side Illuminated Solar Blind AlxGa1-xN Ultraviolet Photodiodes by Lateral Epitaxial Overgrowth

The objective of this Phase II program is to achieve a prototype back-side illuminated solar blind AlGaN based p-i-n ultraviolet photodetector exhibiting a high solar blindness, quantum efficiency and a low dark current. The technical challenges in thisproject find their roots in the improvement of the AlxGa1-xN material overall quality for the very high Al concentrations needed in this program (x>0.49). This entails, in particular, the reduction of the defect density and the enhancement of the materialn-type and p-type conductivity. Lateral epitaxial overgrowth (LEO) will be used to obtain higher quality materials and novel doping schemes will be investigated. The technical work will involve developing the MOCVD growth and the LEO processes,conducting the material characterization, as well as modeling, designing, fabricating and measuring the performance of back-side illuminated solar blind AlGaN p-i-n photodiodes. Anti-reflective and high reflectivity coatings will also be developed and theuniformity of photodiode performance over a two inch diameter wafer will be improved for focal plane array applications. The technology developed here will constitute the fundamental basis for achieving high performance back-side illuminated solar blindultraviolet photodiodes based on AlxGa1-xN materials. It is anticipated that these results will provide the means necessary to advance towards the realization of solar blind ultraviolet focal plane arrays and meet the demands of BMDO systems such as theTMD and NMD. The technology is expected to result in low defective AlxGa1-xN materials, conductive n-type and p-type doped AlxGa1-xN films for large concentrations of Al. These will in turn be the cornerstone for a range of III-Nitride based commercialand defense applications, including compact solid state ultraviolet light sources and high power microwave electronics.