Papers by Author: Masahiro Nagano

Abstract: This paper describes 3D imaging of extended defects in 4H-SiC using optical second-harmonic generation (SHG) and two-photon-exited photoluminescence (2PPL). SHG selectively yields the 3D images of 3C-inclusions in a 4H-SiC epilayer, while 2PPL provides 3D images of 3C-inclusions, 8H stacking faults and single Shockley stacking faults. 2PPL band-edge emission visualizes dislocation lines of threading screw dislocations and threading edge dislocations, the tilt angles of which are evaluated.

Abstract: This paper demonstrates high-resolution photoluminescence (PL) imaging and discrimination of threading dislocations in 4H-SiC epilayers. Threading screw dislocations (TSDs) and TEDs are distinguished by differences in PL spot size and spectrum. We found that TEDs are further discriminated into six types according to their Burgers vector directions by the appearance of PL imaging. Cross-sectional PL imaging reveals inclination angles of threading dislocations across a thick epilayer.

Abstract: Basal plane dislocations (BPDs) converting to threading edge dislocations (TEDs) has been observed in 4H-SiC epilayers after thermal annealing at high temperatures. Grazing incidence reflection synchrotron X-ray topography was used to investigate the dislocation behaviors. It is argued that the conversion is achieved by constricted BPD segments cross-slipping to the prismatic plane and TED glide on its slip plane. Higher conversion ratio and better surface morphology were achieved by performing ion implantation and annealing before epitaxial growth.

Abstract: The benefits of a new method used to incorporate nitrogen at the dielectric/semiconductor interface of 4H-SiC oxide-based devices are presented. High temperature exposure of the SiC surface to hydrogen and nitrogen, prior to oxide deposition, greatly reduces the amount of electrically active defects to a density at least as low as the one of thermally formed interfaces. These results demonstrate the potential of increasing minority carrier mobility with a low gate dielectric forming thermal budget, with deposited dielectrics, and with limited health hazards.

Abstract: Morphologies of BPDs in 4H-SiC epilayers with different nitrogen doping concentrations are explained in detail. While BPDs in low-doped epilayers have the typical morphology of gliding dislocations responding to stress, BPDs in highly doped ([N]≥1.0×10¹⁸ cm^-3) epilayers are straight and tilt away from [11-20]. Structures of BPDs are further studied by weak-beam TEM.

Abstract: Interfacial dislocations are frequently observed to form during 4H-SiC epitaxy and thermal annealing. This report attempts to establish the correlation between the distribution of interfacial dislocations and the thermal stress induced by a radial temperature gradient. In addition, it is argued that they are misfit dislocations formed by the interaction between thermal strain and misfit strain.

Abstract: Condition dependences of defect formation in 4H-SiC epilayer induced by the implantation/annealing process were investigated using synchrotron reflection X-ray topography and transmission electron microscopy. Nitrogen, phosphorus or aluminum ions were implanted in the 4H-SiC epilayers and then activation annealing was performed. To compare the implantation/annealing process, a sample receiving only the annealing treatment without the implantation was also performed. Two different crucibles (conventional and improved) were used in the annealing process. The formation of single layer Shockley-type stacking faults near the surface was found to have no ion-implantation condition or crucible dependence. The formation of BPD half-loops and the glide of pre-existing BPDs showed clear dependence on the crucibles.

Abstract: Burgers vector directions of threading edge dislocations (TEDs) in 4H-SiC epitaxial layer are distinguished by grazing incidence high resolution topography. Based on comparison between appearance of KOH etch pits and direction of TED Burgers vector, the size difference of the TED etch pits is found to be dependent on their Burgers vector directions. Examining TEDs in the epilayer by topography, the Burgers vector direction of basal plane dislocations (BPDs) in the substrate is identified. Correspondence between the topography contrast and the sense of a BPD is also investigated.

Abstract: Fast and thick 4H-SiC epitaxial growth is demonstrated in a vertical-type reactor under a low system pressure within the range 13-40 mbar. A very fast growth rate of up to 250 m/h is obtained. The material quality of the epilayers grown in the reactor is evaluated by low-temperature photoluminescence, deep level transient spectroscopy, microwave photoconductive decay, synchrotron topography and room temperature PL imaging. The carrier lifetime of thick epilayers with or without the application of the C+-implantation/annealing method and extended defects in the epilayers grown on 8º and 4º off substrates are discussed.

Abstract: Defect formation during the ion implantation/annealing process in 4H-SiC epilayers is investigated by synchrotron reflection X-ray topography. The 4H-SiC epilayers are subjected to an activation annealing process after Aluminum ions being implanted in the epilayers. The formation modes of extended defects induced by the implantation/annealing process are classified into the migration of preexisting dislocations and the generation of new dislocations/stacking faults. The migration of preexisting basal plane dislocations (BPDs) takes place corresponding to the ion implantation interface or the epilayer/substrate interface. The generation of new dislocations/stacking faults is confirmed as the formation of Shockley faults near the surface of the epilayer and BPD half-loops in the epilayer.