Masaki Miyazato

Growth of Shockley type stacking faults upon forward degradation in 4H-SiC p-i-n diodes

The growth of Shockley type stacking faults in p-i-n diodes fabricated on the C-face of 4H-SiC during forward current operation was investigated using Berg-Barrett X-ray topography and photoluminescence imaging. After forward current experiment, Shockley type stacking faults were generated from very short portions of basal plane dislocations lower than the conversion points to threading edge dislocations in the epitaxial layer. The growth behavior of Shockley type stacking faults was discussed. Growth of stacking faults in the substrates was not observed.

Short minority carrier lifetimes in highly nitrogen-doped 4H-SiC epilayers for suppression of the stacking fault formation in PiN diodes

We investigated the dependency of minority carrier lifetimes on the nitrogen concentration, temperature, and the injected carrier concentration for highly nitrogen-doped 4H-SiC epilayers. The minority carrier lifetimes greatly shortened when the nitrogen concentration exceeded 1018 cm−3 through enhancing direct band-to-band and Auger recombination and showed a slight variation in the temperature range from room temperature (RT) to 250 °C. The epilayer with a nitrogen concentration of 9.3 × 1018 cm−3 exhibited a very short minority carrier lifetime of 38 ns at RT and 43 ns at 250 °C. The short minority carrier lifetimes of the highly nitrogen-doped epilayer were confirmed to maintain the values even after the subsequent annealing of 1700 °C. 4H-SiC PiN diodes were fabricated by depositing a highly nitrogen-doped epilayer as a “recombination enhancing layer” between an n− drift layer free from basal plane dislocations and the substrate. The PiN diodes showed no formation of stacking faults and no increase i...

Improvement of Channel Mobility in 4H-SiC C-Face MOSFETs by H2 Rich Wet Re-Oxidation

4H-SiC(000-1) C-face was oxidized in H2O and H2 mixture gas (H2 rich wet ambient) for the first time. H2 rich wet ambient was formed by the catalytic water vapor generator (WVG) system, where the catalytic action instantaneously enhances the reactivity between H2 and O2 to produce H2O. The dependence of SiC oxidation rate on the H2O partial pressure was investigated. We fabricated 4H-SiC C-face MOS capacitor and MOSFET by the H2 rich wet re-oxidation following the dry O2 oxidation. The density of interface traps was reduced and the channel mobility was improved in comparison with the conventional O2 rich wet oxidation.

Injected carrier concentration dependence of the expansion of single Shockley-type stacking faults in 4H-SiC PiN diodes

We investigated the relationship between the dislocation velocity and the injected carrier concentration on the expansion of single Shockley-type stacking faults by monitoring the electroluminescence from 4H-SiC PiN diodes with various anode Al concentrations. The injected carrier concentration was calculated using a device simulation that took into account the measured accumulated charge in the drift layer during diode turn-off. The dislocation velocity was strongly dependent on the injected hole concentration, which represents the excess carrier concentration. The activation energy of the dislocation velocity was quite small (below 0.001 eV between 310 and 386 K) over a fixed range of hole concentrations. The average threshold hole concentration required for the expansion of bar-shaped single Shockley-type stacking faults at the interface between the buffer layer and the substrate was determined to be 1.6–2.5 × 1016 cm−3 for diodes with a p-type epitaxial anode with various Al concentrations.

Origin analysis of expanded stacking faults by applying forward current to 4H-SiC p?i?n diodes

Stacking faults expanded by the application of forward current to 4H-SiC p–i–n diodes were observed using a transmission electron microscope to investigate the expansion origin. It was experimentally confirmed that long-zonal-shaped stacking faults expanded from basal-plane dislocations converted into threading edge dislocations. In addition, stacking fault expansion clearly penetrated into the substrate to a greater depth than the dislocation conversion point. This downward expansion of stacking faults strongly depends on the degree of high-density minority carrier injection.

Configuration of Hydrogen in Sp3-Rich Amorphous Hydrogenated Carbon Films Prepared by RF Magnetron Sputtering of Graphite

Sp3-rich amorphous hydrogenated carbon (a-C:H) films were fabricated by reactive rf magnetron sputtering in argon and hydrogen gas mixture. To clarify the bonding configuration of hydrogen (i.e., CH, CH2 and CH3) in the film, the deconvolutions of the 2900 cm-1 IR absorption spectrum for the films were examined. As a result, the relationship between the bonding hydrogen and the physical properties of the film suggests that not only the bonding hydrogen concentration but also the relative ratio between the three configurations of hydrogen must be taken into account.

Suppression of the forward degradation in 4H-SiC PiN diodes by employing a recombination-enhanced buffer layer

Application of highly N-doped buffer layers or a (N+B)-doped buffer layer to PiN diodes to suppress the expansion of Shockley stacking faults (SSFs) from the epilayer/substrate interface was studied. These buffer layers showed very short minority carrier lifetimes of 30–200 ns at 250°C. The PiN diodes were fabricated with buffer layers of various thicknesses and were then tested under high current injection conditions of 600A/cm2. The thicker buffer layers with shorter minority carrier lifetimes demonstrated the suppression of SSFs expansion and thus that of diode degradation.

Extension of stacking faults in 4H-SiC pn diodes under a high current pulse stress

We investigated the expansion of stacking faults (SFs) under a high current pulse stress in detail. In situ observations showed bar-shaped SFs and two types of triangle SFs with different nucleation sites. The calculated partial dislocation velocity of the bar-shaped SFs was four times faster than that of the triangle SFs. The temperature dependence of the partial dislocation velocity was used to estimate activation energies of 0.23±0.02 eV for bar-shaped SFs and 0.27±0.05 eV for triangle SFs. We also compared the electrical characteristics before and after the stress. The forward voltage drop slightly increased by 0.05 V, and the leakage current did not increase.