| Popis: |
We use depth-resolved cathodoluminescence spectroscopy (DRCLS), Kelvin probe force microscopy (KPFM), and surface photovoltage spectroscopy (SPS) on a nanometer scale to map the temperature, stress, and defects inside GaN high electron mobility transistors (HEMTs). DRCLS maps temperature at localized depths, in particular within the two-dimensional electron gas (2DEG) region during device operation. KPFM maps surface electric potential across the device, revealing lower potential patches that decrease rapidly with increasing off-state stress. CL spectra acquired at these patches exhibit defect emissions that increase with both on- and off-state stress and that increase with decreasing surface potential. SPS also reveals features of deep level gap states generated after device operation that reduce near band edge (NBE) emission and increase surface band bending. These techniques also reveals that electronic defects form in AlGaN layer due to field-induced stress accompanied with the decrease of the surface potential and the increase of the gate leakage current. The splitting of the AlGaN emission and the enhancement of yellow and blue band luminescence indicate crystal quality deterioration caused by stress. Our nanoscale measurements are consistent with defect mainly generation by inverse piezoelectric field-induced stress at the gate edge on the drain side at high voltage.Our DRCLS, SPS, time-resolved SPS (t-SPS), current-voltage-temperature (I-V-T) shows that fast and thermal neutron preferentially affect device properties. Fast neutron will induce defects in GaN by recoil and displacement damage whereas thermal neutron tends to enhance the interaction between metal/semiconductor interfaces due to heat. Time-resolved surface photovoltage spectroscopy (t-SPS) results reveal a defect evolution of GaN under fast neutron irradiation that indicates low fast neutron dosage will enhance GaN properties a result which is confirmed by DRCLS results. XPS results show that Ti and Ni are more resistant than other metal but will interact with GaN at higher thermal neutron fluence. Our results show that fast and thermal neutrons are both detrimental electronic devices without proper protection. |
