Deep defects in wide bandgap materials investigated using deep level transient spectroscopy.

摘要

Deep levels in GaAs, GaN, ScN and SiC, have been investigated using Deep Level Transient Spectroscopy (DLTS). Properties of deep levels, such as electronic behavior, activation energy, capture cross-section and concentration have been calculated.; In order to be able to perform DLTS measurements, Schottky or p-n junctions were fabricated from the material of interest. For this, contact formation and characterization has been studied. For each material, several types of contacts have been investigated. The contacts with the best properties in terms of leakage currents, band bending, and interface states density were used for DLTS measurements.; GaN materials have been synthesized using metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) and rf-sputtering, in an attempt to compare and correlate the existence of the B defect (activation energy of E_C-E_T = 0.59 eV) with the method of growth. Only material grown using MOCVD could be used for DLTS analysis.; ScN material grown using plasma assisted physical vapor deposition (PAPVD) and rf-sputtering, has been used with p-type Si to form p-n junctions. Depending upon the method of growth, different defects are found in the material. A defect with activation energy of 0.51 eV has been identified as an electron trap in the PAPVD material and one electron trap with activation energy of 0.91 eV in rf-sputtered material.; The influence of substrate annealing upon the deep levels in two SiC polytypes, 4H-n-type SiC and 6H-p-type SiC has been investigated. For each set of annealed samples, several new defects were found (activation energies of E_C-E_T = 0.41 eV, 0.50 eV for n-type 4H-SiC, E_C-E_T = 0.37 eV and 0.33 eV for p-type 6H-SiC), all of them being electron traps, with the exception of one hole trap on the 4H-SiC material (E_T-E_V = 0.14 eV). The activation energies range from (0.14–0.50) eV below the conduction band. The nature of five of the found defects is not clear. For all the other defects, their existence has been correlated with published studies.