Abstract
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.
Highlights
Wide bandgap semiconductor materials such as silicon carbide, gallium nitride (GaN), aluminum nitride, or diamond are gaining fast growing interest for the power and optoelectronic device market
Auto-doping means doping by adjusting growth conditions such as temperature, pressure, or V/III-ratio in order to promote incorporation of C from background C-impurities.1,6. Such a doping process scitation.org/journal/adv needs no additional supply of C, but it is difficult to control precisely and the material is often overcompensated. This results in high C-concentrations, which are detrimental for the dynamic properties of GaN high electron mobility transistors (HEMTs)
We investigate the influence of extrinsic C-doping by ethene and by auto-doping on crystalline quality, total density of threading dislocations (TDs), and density of threading screw dislocations (TSDs)
Summary
Wide bandgap semiconductor materials such as silicon carbide, gallium nitride (GaN), aluminum nitride, or diamond are gaining fast growing interest for the power and optoelectronic device market. Scitation.org/journal/adv needs no additional supply of C, but it is difficult to control precisely and the material is often overcompensated This results in high C-concentrations, which are detrimental for the dynamic properties of GaN HEMTs. Current collapse and hysteresis phenomena are mainly related to trapping effects due to C.7. Extrinsic doping means doping with an external source of C This allows us to maintain ideal GaN growth conditions and to grow sharper and more precisely controlled doping profiles.. An understanding of C-doping in terms of resulting crystalline quality and material properties is essential, as device performance and reliability might be impaired by defects forming either due to non-ideal growth conditions or due to the incorporation of C itself. The resulting electrical performance in terms of vertical breakdown and observed leakage current paths is related to the materials’ microstructure
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