Einfluss der Schichteigenschaften auf das elektrische und optoelektrische Verhalten von AlGaN-GaN-HEMT-Transistoren
The mismatch of the lattice constants and of the thermal expansion coefficients between gallium nitride (GaN) and its substrates like sapphire, silicon and silicon carbide is responsible for a high concentration of defects in AlGaN/GaN layers. The influence of these electrically active centres (traps) and their respective trapping effects are investigated using four different measurement methods. With photoionisation spectroscopy on layers grown on sapphire and silicon substrates two resp. three different traps responsible for the current collapse were found. Current collapse is assigned to traps in the GaN buffer layer. Using backgating current deep level transient spectroscopy the activation energies of a minority and a majority trap in the GaN buffer on silicon substrate were determined. For pulse measurements the drain current is measured at pulsed gate voltages. These measurements are used to investigate the influence of the "gate lag", i.e. trapping in surface states. This effect was suppressed largely by passivating the surface with a silicon nitride layer. Finally with admittance spectroscopy the activation energy of a GaN buffer anti-site, which is caused by sputtering during the processing of transistors, could be determined. Thus it was shown that surface states of AlGaN as well as defects in GaN, i.e. lattice defects and impurities, are responsible for trapping effects in AlGaN/GaN high electron mobility transistors. These traps could be confirmed in literature.
info:eu-repo/classification/ddc/530, HEMT, Heterostruktur-Bauelement, Aluminiumnitrid, Galliumnitrid, Epitaxieschicht, Gitterbaufehler, DLTS, Impedanzspektroskopie, Physik, GaN, AlGaN, Transistor, Defekte, Photoionisation, Admittanzspektroskopie, defects, admittance spectroscopy
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