Materials Science Forum Vols. 527-529

Abstract: Deep-ultraviolet (DUV) micro-Raman spectroscopy was applied to study the micro structures of surface defects in a 4H-SiC homoepitaxially grown film. From DUV Raman spectrum, inclusions of 3C-SiC was found in comet defects. The shape of 3C-structure in comets was investigated and it was found that 3C inclusions in comets can be classified into two types. In addition, spectrum broadening due to the coupling of nonfolded longitudinal optical phonon mode and the photo-excited carriers was also found. The formation mechanisms of 3C inclusion in comets were discussed.

Abstract: Visible and deep UV Raman measurements have been applied to investigate the structural and electrical properties of stacking disordered 3C-SiC crystals. It is found that free-carrier density shows the significant dependence on the density of stacking faults in 3C-SiC. The density of stacking faults has been estimated from the comparison between experimentally obtained Raman spectra and Raman intensity profiles simulated using one-dimensional lattice models considering the disorder in bond polarizability arrangement.

Abstract: Bulk n+-4H-SiC wafers (n=1-2×1019 cm-3) containing annealing-induced stacking faults were examined by Raman scattering. The coupled plasmon-LO mode was observed to shift in a manner consistent with 1018 cm-3 doping in the 4H-SiC. Numerical simulations were performed using a self-consistent Poisson-Schrödinger solver and agree well with the experimental observations of carrier transfer from the 4H-SiC into the 3C-SiC stacking faults. The Raman data also shows that the 3C stacking faults induce a tensile strain on the surrounding 4H-SiC regions.

Abstract: The electronic driving force for growth of stacking faults (SF) in n-type 4H SiC under annealing and in operating devices is discussed. This involves two separate aspects: an overall thermodynamic driving force due to the capture of electrons in interface states and the barriers that need to be overcome to create dislocation kinks which advance the motion of partial dislocations and hence expansion of SF. The second problem studied in this paper is whether 3C SiC quantum wells in 4H SiC can have band gaps lower than 3C SiC. First-principles band structure calculations show that this is not the case due to the intrinsic screening of the spontaneous polarization fields.

Abstract: Optoelectronic devices with 1D modulation of the potential through hetero-structure or doping superlattices have so far been the privilege of III-V semiconductors. Based on the fact that SiC can be grown monolayer by monolayer, and that Si–Si and C–C double layers have been observed in it, we suggest the possibility of a stress-free polarization superlattice, consisting of the periodic variation of Si-face and C-face domains along the hexagonal axis of 4H-SiC. Such a structure could, in principle, be grown by molecular source atomic layer epitaxy. Investigating such superlattices by density functional theory, using a hybrid functional, we show that Si–Si and C–C double layers at the antiphase boundaries confine electrons within ~0.5 nm, and the periodic polarization field causes zig-zag shaped band edges which gives rise to tunable absorption, to spatial separation of free electrons and holes, as well as to optical nonlinearity. These properties could allow the application of SiC also in optoelectronics and photonics.

Abstract: First-principles calculations are used to investigate the partial dislocations in 4H-SiC. We show that the stability of the dislocation cores and the Peierls barriers of the first kind are chargestate dependent. In intrinsic bulk the partials are stable in the neutral asymmetric reconstructions. These reconstructions have no deep states and are characterized by high Peierls barriers. In strongly doped regime the symmetric reconstructions can become more stable. These reconstructions are always electrically active with a half filled band across the band gap. In particular the symmetric reconstructions of the 30° partial have a lower Peierls barriers than the respective asymmetric ones and could be the cause of the 1.8 eV electroluminescence peak observed under carrier injection conditions.

Abstract: Formation of I1 Shockley stacking faults by recombination-enhanced defect glide in 4HSiC p-i-n diodes subject to high forward current stress is studied in diodes on both c-oriented and aoriented substrates. The forward voltage increases during stressing for both orientations, accompanied by nucleation and expansion of faults visible in electroluminescence (EL) imaging. Low temperature photoluminescence (PL) measurements on degraded diodes of both orientations reveal the same set of exciton peaks, confirming that the electronic structure of the faults is the same in both cases. The spectroscopic data are compared to self-consistent solutions of the Schrödinger and Poisson equations including polarization charge. Dislocations nucleating the faults are bright in EL images but dark in electron beam-induced current (EBIC) imaging, confirming that they are sites of enhanced radiative recombination.

Abstract: In this paper the electrical activity of stacking faults and that of their bounding partial dislocations in degraded PiN diodes has been investigated by the technique of electron beam induced current (EBIC). The recombination behavior of C- and Si-core dislocations is discussed. It is proposed that nonradiative recombination significantly exceeds radiative recombination on both the C- and Si-core partial dislocations. At the same time, predominantly radiative recombination takes place in the faulted planes that presumably act as quantum wells.

Abstract: The nucleation sites of stacking faults (SFs) during forward current stress operation of 4H-SiC PiN diodes were investigated by the electron beam induced current (EBIC) mode of scanning electron microscopy (SEM), and the primary SF nucleation sites were found to be basal plane dislocations (BPDs). Damage created on the diode surface also acts as SF nucleation sites. By using a novel BPD-free SiC epilayer, and avoiding surface damage, PiN diodes were fabricated which did not exhibit SF formation under current stressing at 200A/cm2 for 3 hours.

Abstract: We provide evidence of shrinking of Shockley-type stacking faults (SSFs) in the SiC epitaxial layer by high temperature annealing. Photoluminescence (PL) mapping in combination with high-power laser irradiation makes it possible to investigate the formation of SSFs, which lie between a pair of partial dislocations formed by dissociation of a basal plane dislocation (BPD), without fabrication of pin diodes. Using this technique, we investigated the annealing effect on SSFs. Comparing before and after annealing at 600°C for 10 min, it became obvious that high-temperature annealing results in shrinking of the faulted area of the SSFs. The SSFs form into the same features as those before annealing when high-power laser irradiation is performed again on the same area. This result shows that the faulted area of SSFs shrinks by 600°C annealing but the nuclei of SSFs (BPDs) do not disappear.