Defect correlation studies on 4H-SiC crystals and epitaxial layers for radiation detector applications

Nuclear radiation detectors in the energy range of soft x-rays have been fabricated using bulk semi-insulating (SI) 4H-SiC crystals and SI and n-type 4H-SiC epitaxial layers grown by chemical vapor deposition (CVD) on highly doped (0001) 4H-SiC substrates. The devices have been characterized by optical microscopy, current-voltage (I-V) measurements, thermally stimulated current (TSC) spectroscopy (94K - 650 K), Hall effect, van der Pauw measurements, and electron beam induced current (EBIC) technique. Both epitaxial layers exhibited relatively shallow levels related to Al, B, L- and D- centers. Deep level centers in the n-type epitaxial layer peaked at ~ 400 K (E_a ~ 1.1 eV) and ~ 470 K were correlated with IL2 defect and 1.1 eV center in high purity bulk SI 4H-SiC. The SI epitaxial layer exhibited peak at ~ 290 K (E_a = 0.82 - 0.87 eV) that was attributed to IL₁ and HK2 centers, and at ~ 525 K that was related to intrinsic defects and their complexes with energy levels close to the middle of the band gap. Results of EBIC and optical microscopy characterization showed segregation of threading dislocations around comet tail defects in the n-type epitaxial layers. The I-V characteristics of the devices on SI epitaxial layers obtained in wide temperature range (94K - 650 K) exhibited steps at ~ 1 V and ~ 70 V corresponding to the ultimate trap filling of deep centers peaked at >; 500 K and at ~ 250 K (E_a ~ 0.57 eV), & ~ 300 K (E_a ~ 0.85 eV) respectively. The high temperature resistivity measurements of bulk SI 4H-SiC sample revealed resistivity hysteresis that was attributed to the filling of the deep level electron trap centers. The responsivity of the n-type epitaxial SiC sensors to low energy x-rays is reported for the first time.