Investigation of III-Nitride Alloys for Ultraviolet Photodetectors and Blue-Green Lasers

This AASERT contract was intended to support one graduate and one undergraduate students for three years, with the objective of conducting research work on the growth and characterization of wide bandgap GaN based semiconductors for ultraviolet photodetectors and visible light emitters. The research was directed toward optimizing the metalorganic chemical vapor deposition (MOCVD) growth and characterization of undoped, n-type and p-type doped wide bandgap GaN and AlxGa1-xN semiconductors, for x ranging from 0 to 1, on sapphire substrates. The optical and electrical properties of GaN grown using two different organometallic precursors, TMGa and TEGa, have been compared. The fabrication and characterization of GaN and GaN:Mg MSM photodetectors, with high speed and visible rejection is reported. GaN p-i-n photodiodes with a UV-to- visible rejection ratio of 6 orders of magnitude were demonstrated. The responsivity of these devices was analytically modeled and allowed the extraction of the minority carrier diffusion length for electrons in the p-type GaN material. Highly efficient AlxGa1-xN based visible blind and solar blind p-i-n photodiodes have been demonstrated which cover the widest spectral range ever reported, form 225 to 362 nm. By varying the doping of the GaInN active layer in GaInN/GaN double heterostructures, blue (525 nm) and green (560 nm) light emitting diodes were demonstrated and characterized.