Generation-Recombination Defects In AlGaN/GaN HEMT On SiC Substrate, Evidenced By Low Frequency Noise Measurements And SIMS Characterization
Résumé
Wide bandgap devices such as AlGaN/GaN High Electron Mobility Transistors (HEMT) grown on silicon carbide (SiC) substrate are investigated. Low frequency noise (LFN) measurements have been carried out to evaluate the structural perfection of dual gated HEMT devices featuring 0.25x2x75µm² gate area: generation-recombination (GR) processes are evidenced. Two sets of GR-bulges related respectively to AlGaN/GaN interface and quantum well are identified. Each GR-bulge is composed of two GR centers. The devices are then characterized in a temperature controlled oven, and these GR centers are extracted from LFN spectra versus temperature. Activation energies of the defects located at the AlGaN/GaN interface are measured at 0.38±0.05eV and 0.21±0.05eV using Arrhenius plots under saturated biasing conditions. Equivalent activation energies are extracted under ohmic biasing conditions. These results are compared with SIMS measurements, using the deuterium in diffusion condition as a probe to integrally explore the presence of defects throughout the AlGaN-GaN HEMT structure. Large concentrations of deuterium (more than 10^20 D concentration per cm^3) are measured at the AlGaN/GaN interface and in the 2DEG layer, thus proving the presence of numerous vacations at the AlGaN/GaN interface as well as in the 2DEG. From the confrontation with previously published results, the defects might be assigned to the nitrogen vacancy and to Mg Ga-V N complexes.
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