[en] We study the effect of substrate orientation on defect formation in 4H-SiC. Both (1 1 2-bar 0) and (0 0 0 1) n-type 4H-SiC substrates were implanted with 400 keV P. The various samples, both as-implanted samples and annealed, were studied by Rutherford backscattering and channeling and transmission electron microscopy in an attempt to understand the damage evolution and defect structures resulting from different crystal orientations. Secondary ion mass spectrometry (SIMS) was performed for P elemental profiling before and after annealing. We observe a significantly different damage accumulation in the two directions with a broader amorphous layer formed in the c-cut crystal compared to the a-cut crystal. The annealing of the damage results in a range of different defects including dislocation loops and voids in both a-cut and c-cut crystals. The SIMS profiles show in some cases distinct differences between the two crystal directions

[en] Epitaxial layers of low doped 4H-SiC are implanted with 20 keV ²H⁺ ions to a dose of 1 x 10¹⁵ cm^-2. The samples are subsequently annealed at temperatures ranging from 1040 to 1135 C. Secondary ion mass spectrometry is used to obtain the concentration versus depth profiles of the atomic deuterium in the samples. It is found that the concentration of implanted deuterium decreases rapidly in the samples as a function of anneal time. The experimental data are explained by a model where the deuterium migrates rapidly and becomes trapped and de-trapped at implantation-induced defects which exhibit a slightly shallower depth distribution than the implanted deuterium ions. Computer simulations using this model, in which the damage profile is taken from Monte Carlo simulations and the surface is treated as a perfect sink for the diffusing deuterium atoms, are performed with good results compared to the experimental data. The complexes are tentatively identified as carbon-deuterium at a Si-vacancy and a dissociation energy (E_D) of approximately 4.9 eV is extracted for the deuterium-vacancy complexes

[en] Epitaxial 4H-SiC structures with heavily boron or aluminium doped layers have been prepared by vapour phase epitaxy. The samples have been annealed in Ar atmosphere in an RF-heated furnace between 1700 and 2000 deg. C for 45 min to 64 h. Secondary ion mass spectrometry has been employed to obtain depth distributions as well as lateral distributions (ion imaging) for boron and aluminium. Transmission electron microscopy has been used to study the crystallinity and determine phase composition. Solubility limits of ∼1x10²⁰ Al/cm³ (1700 deg. C) and <1x10²⁰ B/cm³ (1900 deg. C) have been deduced

[en] The mean projected range R_p for a large number of ¹H, ²H, ⁷Li, ¹¹B, ¹⁴N, ¹⁶O, ²⁷Al, and ³¹P implantations into SiC with ion energies ranging from 0.5 keV to 4 MeV are investigated. From the R_p data the electronic stopping cross sections S_e are extracted. A plot of the extracted S_e at a fixed velocity--below the Fermi velocity of the target valence electrons--versus the ion atomic number Z₁ reveals a local maximum around Z₁=7. Furthermore, in this velocity regime a slower than velocity-proportional energy dependence, S_e∝E^0.30-E^0.45, is found for ions with 1≤Z₁≤8, while ²⁷Al and ³¹P exhibit an energy dependence just above velocity-proportionality: S_e∝E^0.52, for both ions. These finding are in good qualitative agreement with the low-velocity electronic stopping behavior previously reported for carbon targets

[en] Deep level transient spectroscopy (DLTS) was employed to investigate the annealing behaviour and thermal stability of radiation induced defects in nitrogen doped 4H-SiC epitaxial layers, grown by chemical vapor deposition (CVD). The epilayers have been irradiated with 15 MeV electrons and an isochronal annealing series has been carried out. The measurements have been performed after each annealing step and six electron traps located in the energy band gap range of 0.42-1.6 eV below the conduction band edge (E_c) have been detected. (orig.)

[en] Ion implantation is an important technique for a successful implementation of commercial SiC devices. Much effort has also been devoted to optimising implantation and annealing parameters to improve the electrical device characteristics. However, there is a severe lack of understanding of the fundamental implantation process and the generation and annealing kinetics of point defects and defect complexes. Only very few of the most elementary intrinsic point defects have been unambiguously identified so far. To reach a deeper understanding of the basic mechanisms SiC samples have been implanted with a broad range of ions, energies, doses, etc., and the resulting defects and damage produced in the lattice have been studied with a multitude of characterisation techniques. In this contribution we will review some of the results generated recently and also try to indicate where more research is needed. In particular, deep level transient spectroscopy (DLTS) has been used to investigate point defects at very low doses and transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS) are used for studying the damage build-up at high doses

[en] The annealing behavior of irradiation-induced defects in 4H-SiC epitaxial layers grown by chemical-vapor deposition has been systematically studied by means of deep level transient spectroscopy (DLTS). The nitrogen-doped epitaxial layers have been irradiated with 15-MeV electrons at room temperature and an isochronal annealing series from 100 to 2000 deg. C has been performed. The DLTS measurements, which have been carried out in the temperature range from 120 to 630 K after each annealing step, revealed the presence of six electron traps located in the energy range of 0.45-1.6 eV below the conduction-band edge (E_c). The most prominent and stable ones occur at E_c-0.70 eV (labeled Z_1/2) and E_c-1.60 eV(EH_6/7). After exhibiting a multistage annealing process over a wide temperature range, presumably caused by reactions with migrating defects, a significant fraction of both Z_1/2 and EH_6/7 (25%) still persists at 2000 deg. C and activation energies for dissociation in excess of 8 and ∼7.5 eV are estimated for Z_1/2 and EH_6/7, respectively. On the basis of these results, the identity of Z_1/2 and EH_6/7 is discussed and related to previous assignments in the literature

[en] Structural disorder and relocation of implanted Mn in semi-insulating 4H–SiC has been studied. Subsequent heat treatment of Mn implanted samples has been performed in the temperature range 1400–2000 °C. The depth distribution of manganese is recorded by secondary ion mass spectrometry. Rutherford backscattering spectrometry has been employed for characterization of crystal disorder. Ocular inspection of color changes of heat-treated samples indicates that a large portion of the damage has been annealed. However, Rutherford backscattering shows that after heat treatment, most disorder from the implantation remains. Less disorder is observed in the [0 0 0 1] channel direction compared to [112^¯3] channel direction. A substantial rearrangement of manganese is observed in the implanted region. No pronounced manganese diffusion deeper into the sample is recorded.

[en] Ion implantation induced defects and their consequent electrical impact have been investigated. Unintentionally doped n-type gallium nitride was implanted with 100 keV Si⁺ and 300 keV Ar⁺ ions in a fluence range of 10¹⁴-10¹⁵ ions/cm². The samples were characterized with Rutherford backscattering/Channeling method for damage buildup. Time of flight elastic recoil detection analysis was implied on the Si implanted samples to see the ion depth distribution. Ar implanted GaN samples were studied electrically with scanning spreading resistance microscopy. Our results show that an Ar fluence of 5 x 10¹⁴ cm^-2 increases the resistance by five orders of magnitude to a maximum value. For the highest fluence, 6 x 10¹⁵ cm^-2, the resistivity decreases by two orders of magnitude.

[en] Self-diffusion of carbon (¹²C and ¹³C) in low-doped (intrinsic) 4H-SiC has been studied using secondary ion mass spectrometry. A two layer ¹³C enriched structure with ¹³C/¹²C ratios of 0.01 and 0.1, respectively, have been prepared by vapor phase epitaxy. Subsequent anneals have been carried out in Ar atmosphere in a rf heated furnace between 2100 and 2350 deg. C for 15 min-40 h. The ¹³C depth profiles reveal a strict √(t) evolution for the diffusion, and the extracted carbon self-diffusion coefficients closely follow an Arrhenius temperature dependence: D^*=8.4x10² exp(-8.50 eV/kT) cm²/s. The extracted D^* are found to be 5 orders of magnitude lower than previously reported for the same temperatures in ¹⁴C radio-tracer experiments