Interplay between C-doping, threading dislocations, breakdown, and leakage in GaN on Si HEMT structures

• Published in: AIP advances 2020-04, Vol.10 (4), p.045028-045028-6
• Main Authors: Besendörfer, S., Meissner, E., Zweipfennig, T., Yacoub, H., Fahle, D., Behmenburg, H., Kalisch, H., Vescan, A., Friedrich, J., Erlbacher, T.
• Format: Article
• Language: English
• Subjects: Aluminum gallium nitrides; Atomic force microscopy; Breakdown; Current carriers; Degradation; Dislocation density; Doping; Electron mobility; Gallium nitrides; Leakage current; Material properties; Screw dislocations; Self compensation; Statistical methods; Threading dislocations; Transistors
• ISSN: 2158-3226; 2158-3226
• DOI: 10.1063/1.5141905

This work describes electrical characteristics and the correlation to material properties of high electron mobility transistor structures with a C-doped GaN current blocking layer, grown either by an extrinsic or auto-doping process with different doping levels. Increasing degradation of crystalline quality in terms of threading dislocation density for increasing C-doping levels was observed for all samples. Different growth conditions used for the auto-doped samples played no role for overall degradation, but a higher fraction of threading screw dislocations was observed. Independent of the doping process, 90% of all TSDs were noted to act as strong leakage current paths through the AlGaN barrier. This was found statistically and was directly verified by conductive atomic force microscopy in direct correlation with defect selective etching. Vertical breakdown was observed to increase with increasing C-concentration and saturated for C-concentrations above around 1019 cm−3. This was attributed to an increasing compensation of free charge carriers until self-compensation takes place. A progressive influence of TDs for high C-concentrations might also play a role but could not be explicitly revealed for our material.