Depth-resolved spectroscopy of interface defects in AlGaN/GaN heterostructure field effect transistors device structures

We report depth-resolved low energy electron excited nanometer spectroscopy from AlGaN/GaN heterostructure field effect transistors structures with Al GaN thicknesses as thin as 20 nm. By varying the voltage of a low energy el ectron beam in ultrahigh vacuum, we can determine whether defect induced lu minescence is being emitted from the GaN buffer layer, the interfacial regi on where the two-dimensional electron gas (2DEG) resides, and the AlGaN bar rier layer. By increasing the GaN buffer thickness, known to enhance the el ectron concentration of the 2DEG by reducing the dislocation density in the active region, we observed an enhancement in AlGaN luminescence, and a 20% reduction in the full width at half maximum of the near band edge peak. Wh en a similar structure with no 2DEG is measured, we find a factor of 8 incr ease in midgap yellow luminescence relative to the GaN buffer emission. Tak en together, these findings indicate that differences in buffer layer thick ness and electrical quality can affect not only dislocation density and poi nt defect densities, but also the optical properties of the AlGaN barrier l ayer and its 2DEG interface. (C) 2000 American Vacuum Society. [S0734-211X( 00)03504-6].