Al-implanted 4H-SiC Research Articles

Real Relationship between Acceptor Density and Hole Concentration in Al-Implanted 4H-SiC

Al-implanted p-type 4H-SiC layers with different conditions of implantation and annealing temperatures are formed, and the temperature dependence of the hole concentration ) (T p in the p layer is obtained from Hall-effect measurements. In order to determine the reliable acceptor density ( A N ) from ) (T p , it is found that the Fermi-Dirac distribution function is not appropriate and that a distribution function including the influence of the excited states of Al acceptors is required. This is because the Al acceptor level in SiC is deep (~180 meV) and because its first excited state level, which is calculated by the hydrogenic model, is still deep (~35 meV), which is close to the acceptor level of B in Si. It is demonstrated that the proposed distribution function is suitable for obtaining the actual relationship between A N and ) (T p .

Vacancy-Type Defect Distributions of <sup>11</sup>B-, <sup>14</sup>N- and <sup>27</sup>Al-Implanted 4H-SiC Studied by Positron Annihilation Spectroscopy

Vacancy-Type Defect Distributions of <sup>11</sup>B-, <sup>14</sup>N- and <sup>27</sup>Al-Implanted 4H-SiC Studied by Positron Annihilation Spectroscopy

Microstructural features of Al-implanted 4H–SiC

The microstructural features of highly damaged 4H–SiC implanted with Al22+ ions at 450 K were studied using transmission electron microscopy (TEM) and electron energy-loss spectroscopy. Conventional TEM images reveal that the crystalline SiC domains are highly strained/distorted when the relative disorder on the Si sublattice ranges between about 0.4 and 0.8, as determined by Rutherford backscattering spectrometry in channeling geometry. As the relative disorder approaches 1.0, the high strain contrast appears to be relieved, and localized amorphized domains are observed. Plasmon-loss energy shows a red shift following the implantation, and the magnitude of the red shift increases with increasing relative disorder. Based on the red shift, the estimated volume expansion is approximately 8% for highly damaged crystalline SiC and approximately 16% for the amorphous state. Energy-loss near-edge-structure of both the C and Si K edge reveals the existence of Si–Si and C–C bonding in the Al22+ implanted SiC.

Effects of implantation temperature and ion flux on damage accumulation in Al-implanted 4H-SiC

The effects of implantation temperature and ion flux on damage accumulation on both the Si and C sublattices in 4H-SiC have been investigated under 1.1-MeV Al22+ irradiation at temperatures from 150 to 450 K. The rate of damage accumulation decreases dramatically, and the damage profile sharpens due to significant dynamic recovery at temperatures close to the critical temperature for amorphization. At 450 K, the relative disorder and the density of planar defects increase rapidly with the increasing ion flux, exhibiting saturation at high ion fluxes. Planar defects are generated through the agglomeration of excess Si and C interstitials during irradiation and post-irradiation annealing at 450 K. A volume expansion of ∼8% is estimated for the peak damage region.

Damage evolution and recovery on both Si and C sublattices in Al-implanted 4H–SiC studied by Rutherford backscattering spectroscopy and nuclear reaction analysis

Damage evolution and subsequent recovery in 4H–SiC epitaxial layers irradiated with 1.1 MeV Al22+ molecular ions at 150 K to ion fluences from 1.5×1013 to 2.25×1014 Al cm−2 were studied by Rutherford backscattering spectroscopy (RBS) and C12(d,p)13C nuclear reaction analysis (NRA) using a 0.94 MeV deuterium (D+) beam in channeling geometry. Disorder on both the Si and C sublattices was measured simultaneously from the RBS scattering and NRA reaction yields. The relative disorder on both sublattices follows a nonlinear dependence on ion fluence that is consistent with a model based on simple defect accumulation and a direct-impact, defect-stimulated process for amorphization. At low ion fluences, the relative disorder on the C sublattice is higher than that on the Si sublattice. Isochronal annealing up to 870 K revealed the existence of three distinct recovery stages at ∼350, 520, and 650 K for low to intermediate damage levels. In highly damaged samples, where a buried amorphous layer is produced, the onset of a fourth recovery stage appears above 800 K. Similar recovery behaviors on both the Si and C sublattices suggests some coupling of recovery processes for Si and C defects.

Damage Evolution and Recovery in Al-Implanted 4H-SiC

Damage evolution in 4H-SiC epitaxial layers irradiated with 1.1 MeV Al molecular ions at 150 K to a range of ion fluences and subsequent isochronal recovery were studied by Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA). The relative disorder on both the Si and C sublattices follows a sigmoidal dependence on ion fluence, and a buried amorphous layer is formed when the local dose reaches a critical amorphization value (0.12 dpa). The buried amorphous thickness increases rapidly at {approx} 2.0 x 1014 Al/cm2 and eventually saturates at the highest fluence. Isochronal annealing studies up to 870 K reveals the existence of three distinct recovery stages at {approx} 335, 520 and 650 K for low to intermediate ion fluences, where the relative disorder has not yet reached the fully amorphous level. In high-dose samples, where a buried amorphous layer is produced, the onset of a fourth recovery stage appears above 800 K. Recrystallization occurs at the rear interface and in the surface region, and the relative amount of recovery decreases with increasing fluence for the same annealing temperatures. Defect-stimulated epitaxial growth rather than thermal-stimulated epitaxial growth dominates the recrystallization.

Characterization of Al-implanted 4H SiC High Voltage Diodes

The properties of 4H-SiC chemical vapor deposition epitaxial layers were studied by different methods. The effects of structural defects in 4H-SiC epitaxial layers on electrical and luminescence properties of Al high dose ion implanted p+-n junctions were studied. It has been shown that the structural imperfections of low-doped layers affect some electrical characteristics of the ion doped p+-n junctions created in these epitaxial layers.

High-dose Al-implanted 4H-SiC p+-n-n+ junctions

p + -n-n + junctions were fabricated by ion implantation with Al of low-doped epitaxial n layers of 4H-SiC grown by chemical vapor deposition on commercial 4H-SiC wafers both with and without reduction of micropipe densities. It was shown that, using high levels of Al ion doping (5×1016 cm−2) in combination with rapid thermal anneal, single-crystal p+-4H-SiC layers can be obtained. These layers do not form barriers at the contact metal–semiconductor interface and do not introduce additional resistance into structures with p+-n junctions. This significantly reduces the forward voltage drop across the structure in a wide range of current densities up to 104 A cm−2.