Application Relevant Evaluation of Trapping Effects in AlGaN/GaN HEMTs With Fe-Doped Buffer

This paper investigates the impact of different iron (Fe) buffer doping profiles on trapping effects in microwave AlGaN/gallium nitride (GaN) high electron mobility transistors (HEMTs). We characterize not only the current collapse due to trapping in the buffer, but also the recovery process, which is important in the analysis of suitable linearization schemes for amplitude modulated signals. It is shown that the simple pulsed dc measurements of current transients can be used to investigate transient effects in the RF power. Specifically, it is revealed that the design of the Fe-doping profile in the buffer greatly influences the recovery time, with the samples with lower Fe concentration showing slower recovery. In contrast, traditional indicators, such as S-parameters and dc as well as pulsed I-V characteristics, show very small differences. An analysis of the recovery shows that this effect is due to the presence of two different detrapping processes with the same activation energy (0.6 eV) but different time constants. For highly doped buffers, the faster process dominates, whereas the slower process is enhanced for less doped buffers.