Judith L. McFall
Description
AlGaN and GaN have gained attention in the last few years for their applications in the blue and ultraviolet (Uv) wavelength range. However, the major
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ity of the attention has been directed to studying GaN rather than AlGaN. AlGaN is however of great interest militarily since it has a wide, direct band gap, which makes it suitable for various applications in the military such as plume detection and threat warning systems. Cathodoluminescence (CL), photoluminescence (PL), and optical absorption were used to characterize AlGaN samples grown by molecular beam epitaxy (MBE). These samples utilized an AIN buffer layer to match the AlGaN epilayer to the sapphire substrate. CL was run at four different beam energies (2, 5, 10, and 15 keV) with four different beam currents (1, 10, 50, and 90 or 100 microA) on a GaN standard, the AlGaN samples, and the MN buffer layer. PL was performed in an attempt to distinguish DAP transitions that were not observed in CL. PL was done on the GaN standard and the ALGaN samples (x =0.10,0.20, and 0.30). Optical absorption measurements were performed to get an estimate of the band gap energies for comparison to those obtained in CL and PL. CL and PL were performed at liquid helium temperatures and optical absorption was performed at room temperature. AlGaN with different mole fractions of aluminum (x =0.10,0.20,0.30,0.40, and 0.50) was studied. Each sample was doped with approximately 10 to the 18th power/cu cm silicon atoms. The major finding of this study was that MBE is a good method for growing ALGaN with mole fraction of aluminum less than x = 0.30. Above this mole fraction, either a different growth technique or modifications to the MBE growth cycle are necessary to obtain quality material for semiconductor devices.
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