GaN HEMT/MIS-HEMT technology and device reliability activities at TU Vienna

Orateur : Dionyz POGANY (Institute for Solid State Electronics, Vienna University of Technology)

Due to wide energy band gap, heterostructure tunability and excellent transportproperties, III-nitride semiconductors are promising for opto-electronic, RF, power switching and digital applications. Since 2003, our institute participated in four EU projects related to technology and characterization of GaN-based HEMTs. In the first part I will review our activitiesin development of InAlN/GaN, AlGaN/GaN and AlN/GaN HEMTs and MIS-HEMTs going toward the normally-off operation which is demanded for power applications. Even if the dielectric insulation decreases the gate leakage current, the positive fixed charge at the dielectric/III-N barrier interface, which is of the order of the polarization charge, prevents from the achievement of higher positive threshold voltage. Physics of threshold voltage scaling with thedielectric layer thickness will be discussed. Furthermore examples of studies of lateral and vertical (i.e. across the GaN buffer) breakdown, self-heating effects and low frequency noise analysis of degraded devices will be presented. Finally some results of investigations of the threshold voltage instabilities in MIS-HEMTs subjected to forward bias stress will be presented. The stress-recovery characteristics of the threshold voltage drift show logarithmic dependence on time indicating a broad distribution of relaxation time constants. The role of traps at the dielectric/III-N barrier interface and of the III-N barrier in this dynamics will be discussed.

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