Giovanni Alfieri

Detection and depth analyses of deep levels generated by ion implantation in n- and p-type 4H-SiC

The authors investigated deep levels in the whole energy range of bandgap of 4H-SiC, which are generated by low-dose N+, P+, and Al+ implantation, by deep level transient spectroscopy (DLTS). Ne+-implanted samples have been also prepared to investigate the pure implantation damage. In the n-type as-grown material, the Z1∕2 (EC−0.63eV) and EH6∕7 (EC−1.6eV) centers are dominant deep levels. At least, seven peaks (IN1, IN3–IN6, IN8, and IN9) have emerged by implantation and annealing at 1000°C in the DLTS spectra from all n-type samples, irrespective of the implanted species. After high-temperature annealing at 1700°C, however, most DLTS peaks disappeared, and two peaks, IN3 and IN9, which may be assigned to Z1∕2 and EH6∕7, respectively, survive with a high concentration over the implanted atom concentration. In the p-type as-grown material, the D (EV+0.40eV) and HK4 (EV+1.4eV) centers are dominant. Two peaks (IP1 and IP3) have emerged by implantation and annealing at 1000°C, and four traps IP2 (EV+0.39eV), ...

Engineering the band gap of SiC nanotubes with a transverse electric field

The effects of a transverse electric field, of intensities ranging from 0 to 0.20 V/A, on the band gap width of SiC nanotubes (SiCNTs) are investigated by means of density functional theory. A decrease in the band gap width, as a function of the electric field, is observed and the mechanism for such reduction, as well as its dependence on the nanotube diameter, is analyzed. An empirical model to describe the field dependence of the band gap is also proposed.

Major deep levels with the same microstructures observed in n-type 4H-SiC and 6H-SiC

Major deep levels observed in as-grown and irradiated n-type 4H–SiC and 6H–SiC epilayers have been investigated. After low-energy electron irradiation, by which only carbon atoms are displaced, five traps, EH1 (EC−0.36 eV), Z1/Z2 (EC−0.65 eV), EH3 (EC−0.79 eV), EH5 (EC−1.0 eV), and EH6/7 (EC−1.48 eV), were detected in 4H–SiC and four traps, E1/E2 (EC−0.45 eV), RD5 (EC−0.57 eV), ES (EC−0.80 eV), and R (EC−1.25 eV), were detected in 6H–SiC. The Z1/Z2, EH6/7 centers in 4H–SiC and the E1/E2, R centers in 6H–SiC exhibit common features as follows: their generation rates by the e−-irradiation were almost the same each other, their concentrations were not changed by heat treatments up to 1500 °C, and they showed very similar annealing behaviors at elevated temperatures. Furthermore, these defect centers were almost eliminated by thermal oxidation. Taking account of the observed results and the energy positions, the authors suggest that the Z1/Z2 center in 4H–SiC corresponds to the E1/E2 center in 6H–SiC, and the...

Deep level transient spectroscopy study of defects in hydrogen implanted p-type 4H‐SiC

p-type 4H‐SiC epitaxial layers grown by chemical vapor deposition have been implanted with 200 and 100keV protons at five different implantation temperatures. An isochronal annealing series was performed from 100to1800°C, and Al-doped epitaxial layers have been characterized by means of deep level transient spectroscopy (DLTS) after each annealing step. DLTS measurements were carried out in the 150–670K temperature range and revealed the presence of eight hole traps located in the 0.18–1.8eV range above the valence band (EV). Heat treatments for temperatures above 700°C showed the progressive reactivation of the Al doping in the implanted region, which is completed after a 1500°C annealing treatment. Two traps located at EV+0.44eV and EV+1.8eV are persistent even after annealing at 1800°C, while the other traps anneal out after heat treatments at ⩽1700°C. An activation energy for dissociation of 6.2eV is estimated for the hole trap at EV+0.79eV, and the nature of this defect is discussed on the basis of p...

Capacitance Spectroscopy Study of Midgap Levels in n-Type SiC Polytypes

As-grown and 116 keV electron-irradiated n-type 3C and 4H-SiC epilayers were electrically characterized by means of Fourier-transform deep level transient spectroscopy (FT-DLTS). A total of four deep levels, in the 0.20-0.73 eV range, below the conduction band, have been detected. By considering the band gap offset between 4H and 3C polytypes, we found that the deepest level in 3C-SiC labeled K3 (Ec-0.73 eV) has an energy position close to the EH6/7 level in 4H-SiC. An electron-dose dependence study of K3 and EH6/7, reveals that these two centers display a similar dose dependence behavior, suggesting that they may be related to the same defect.

Ab initio study of isolated chlorine defects in cubic SiC

The electronic properties and formation energy of isolated Cl defects in SiC were investigated by first-principles calculations. Chlorine was studied in a substitutional position, in either a carbon (Cl(C)) or a silicon site (Cl(Si)), and in two interstitial positions (Cl(i)), either tetrahedral or octahedral configurations. Our calculations revealed that Cl(C) is energetically favored and it is a likely candidate to explain the nature of the experimentally observed Cl incorporation reported in SiC epilayers grown by chloride-based chemical vapor deposition.

Structural stability and electronic properties of SiC nanocones: First-principles calculations and symmetry considerations

The structural and electronic properties of SiC nanocones (SiCNCs), as a function of the disclination angle and electric field intensity and orientation, are investigated by means of ab initio calculations. Phonon analysis revealed that SiCNCs with only three disclination angles are allowed and, among these, the band gap of only one SiCNC is affected by a transverse electric field. An interpretation of these findings, from a group theoretical point of view, is also given.

Thermal Stability of Defect Centers in n- and p-Type 4H-SiC Epilayers Generated by Irradiation with High-Energy Electrons

This paper comprises a systematic study of the thermal stability of defect centers observed in n- and p-type 4H-SiC by deep level transient spectroscopy (DLTS); the defects are generated by irradiation with high-energy electrons of 170 keV or 1 MeV.

Deep Levels Observed in High-Purity Semi-Insulating 4H-SiC

We report on the electrical characterization of high-purity semi-insulating 4H-SiC after annealing at temperatures between room temperature and 1700 oC by current-mode deep level transient spectroscopy (I-DLTS). I-V and Hall-effect measurements revealed that the investigated substrates possess p-type conductivity. Four deep levels were detected by I-DLTS with activation energies in the 0.15-1.29 eV range. We studied their thermal stability as well as their stability with respect to light illumination.

Thermal stability of deep levels between room temperature and 1500 °C in as-grown 3C-SiC

We report on the thermal stability of deep levels detected in as-grown bulk 3C-SiC. The investigation was performed by Fourier-transform deep level transient spectroscopy and an isochronal annealing series was carried out in the 100–1500 °C temperature range. We found three traps located between 0.14–0.50 eV below the conduction band edge minimum (EC). The shallower trap anneals out at temperatures below 1200 °C while the others display a high thermal stability up to at least 1500 °C. The nature of the former trap is discussed in detail on the basis of its annealing behavior and previous theoretical data found in the literature.