Materials Science Forum Vols. 600-603

Abstract: High-voltage (900 V) 4H-SiC Schottky-barrier diodes (SBD) terminated with guard pnjunction were fabricated and investigated. The guard pn-junction was formed by room temperature boron implantation followed by high temperature annealing. Owing to the transient enhanced boron diffusion during anneal, the depth of guard pn-junction is about 1.7 μm, that is approximately 1 μm deeper than the expected average range of 11B ions in 4H-SiC. The maximum reverse voltage of 4H-SiC SBD produced has been found to be limited by the avalanche breakdown in cylindrical portion of planar pn-junction. The value of the breakdown voltage of 910 V is close to theoretical one calculated for the dopant density  = 2.5×1015 cm-3, n-base thickness d = 12.5 μm and junction curvature rj = 1.7 μm. Dynamic (pulse) reverse current-voltage characteristics were measured in the breakdown regime. It was found that dynamic breakdown voltage increases with shortening the pulse duration. Due to homogeneous avalanche breakdown at the edge of the quard pn-junction and high differential resistance in the breakdown regime, the diodes under test are able to withstand, with no degradation, pulse reverse voltage at least 1600 V.

Abstract: The effect of the doping concentration and space of both p-grid and FLR on the electrical performances of 4H-SiC JBS diode has been investigated. A 4H-SiC JBS diode with the p-grid space of 3um, the FLR space of 3um, and the doping concentration of 5E18cm-3 showed the highest blocking voltage of 1500V.

Abstract: Two types of structures related to in-grown SF having a different influence on reverse currents of 4H-SiC SBDs were investigated. One type contained only a single SF formed by 1c of 8H poly-type and showed low reverse currents. The other type was accompanied with short SFs which consisted of 3C poly-type in addition to two SFs formed by 1c of 8H poly-type and showed high reverse currents. SF formed by 1c of 8H poly-type was not the cause of the high reverse current, and we speculate that the barrier height lowering at the short SF attributed to the high reverse currents of SBDs.

Abstract: The effects of basal-plane defects on the performance of 4H-SiC Schottky diodes using a Ni electrode are demonstrated. Systematic characterization was performed using 4H-SiC epitaxial layers grown by sublimation epitaxy on substrates with various off-axis angles. As the off-axis angle increases, the ideality factor of the current-voltage characteristics increases, and the Schottky barrier height decreases, corresponding to an increase in the number of basal-plane defects. The reverse-bias current degrades for high off-axis samples. These results indicate that basal-plane defects degrade the device performance. Schottky diodes that possesses good characteristics were obtained for samples with low off-axis angles (2o- and 4o-off samples).

Abstract: Schottky barrier diode (SBD) was fabricated by MOCVD using bistrimethylsilylmethane (BTMSM, C7H20Si2) precursor. The 4H-SiC substrates which had different crystallographic characteristics were used for the comparison of the crystallinity effect on the electrical properties of the SBDs. From the measurement of the reverse I-V characteristics of the SBDs with micropipes, it is shown that the origin of the main leakage path and early breakdown (or ohmic behavior in reverse bias) in 4H-SiC SBDs is the grain boundaries caused by the inclusions or other defects. The best performance of SBD were shown in the epilayer grown at 1440 oC using high quality substrate, and the breakdown voltage and reverse leakage current were about 450 V and 10-9 A/cm2, respectively.

Abstract: We report that it seems to be necessary to select Bologna University mobility model for accurate transient phenomenon analysis of SiC-SBD under the condition of forward surge current because the maximum of the temperature inside SiC-SBD arises up to above 425 K. Other mobility models seem to be mostly inadequate because they are corresponding to the experimental condition under the temperature below 425 K.

Abstract: The forward current density-voltage (JF-VF) characteristics of SiC Schottky barrier diodes (SBDs) with an epilayer thickness between 9.6 and 10 μm and donor concentration (ND) ranging from 4.0x1015 to 5.7x1015 cm-3 was evaluated. It was found that the Schottky barrier height (Φb) can be stabilized by Ti sintering process and the forward current (IF) abruptly rises at the same knee voltage for all samples. On the other hand, the on-resistance (Ron) and VF were dispersed. The instability corresponds to the values calculated by the dispersion of ND, substrate resistivity and substrate thickness.

Abstract: This paper presents a comparison between SiC and diamond Schottky barrier diodes using the oxide ramp termination. The influences of the dielectric thickness and relative permittivity on the diode’s electrical performance are investigated. Typical commercial drift layer parameters are used for this study. The extension of the space charge area throughout the drift region and the current distribution at breakdown are shown. The efficiency of the termination is also evaluated for both SiC and diamond diodes.

Abstract: Silicon dioxide (SiO2), one of the commonly used dielectrics for field plate terminated 4H-SiC devices suffers from high electric field and premature breakdown due to its low dielectric constant (k). This problem can be addressed by using high-k dielectrics such as AlN that will reduce the field and improve the breakdown voltage (VB). Sputter deposited amorphous AlN films with a thickness (tAl) ranging from 0.05 μm to 1.3 μm have been deposited on 4H-SiC n-type samples with a 10 μm thick epilayer doped with nitrogen to a concentration of 1.7–3.5×1015/cm3 . The VB of the diodes was found to improve to as much as 1500 V at tAl = 0.8 μm, which is more than 2 times the VB of unterminated structures which have a premature breakdown between 600-700 V due to field enhancement at the diode periphery.

Abstract: An innovative process has been developed by Linköping University to prepare the 4HSiC substrate surface before epitaxial growth. The processed PiN diodes have been characterized in forward and reverse mode at different temperature. The larger diodes (2.56 mm2) have a very low leakage current around 20 nA @ 500V for temperatures up to 300°C. A performant yield (68%) was obtained on these larger diodes have a breakdown voltage superior to 500V. Electroluminescence characteristics have been done on these devices and they show that there is no generation of Stacking Faults during the bipolar conduction.