Non-Micropipe Dislocations in 4H-SiC Devices: Electrical Properties and Device Technology Implications

Abstract

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vectors > 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = lc with no hollow core) in densities on the order of thousands per cm 2, nearly 100-fold micropipe densities. While not nearly as detrimental to SiC device performance as micropipes, it has been previously shown that diodes containing elementary screw dislocations exhibit a 5% to 35% reduction in breakdown voltage, higher pre-breakdown reverse leakage current, softer reverse breakdown I-V knee, and concentrated microplasmic breakdown current filaments when measured under DC testing conditions. This paper details the impact of elementary screw dislocations on the experimentally observed reverse-breakdown pulse-failure characteristics of low-voltage (< 250 V) small-area (< 5 × 10-4 cm2) 4H-SiC p+n diodes. The presence of elementary screw dislocations did not significantly affect the failure properties of these diodes when subjected to non-adiabatic breakdown-bias pulsewidths ranging from 0.1 μs to 20 μs in duration. Diodes with and without elementary screw dislocations exhibited positive temperature coefficient of breakdown voltage and high junction failure power densities well above the failure power densities exhibited by highly reliable silicon power rectifiers. This preliminary result, based on measurements from one wafer of SiC diodes, suggests that highly reliable low-voltage SiC rectifiers may be attainable despite the presence of elementary screw dislocations.

4,308V, 20.9 mΩ-cm² 4H-SiC MPS Diodes Based on a 30μm Drift Layer

“…Some SiC MPS diodes have been tested up to 1A/cm 2 avalanche current density at 4.3kV without failure, representin g an excellent failure power density of SiC larger than 4.3kW/cm 2 measured by a quasi-DC pulse width of 1 second, which is higher than the fitting value reported by P.G. Neudeck et al [4] for a quasi-DC measurement pulse width of 1ms. Fig.…”

High temperature CVD growth of SiC

“…Typical leakage current densities in DC mode were as low as 2·10 − 7 -10 − 6 A cm − 2 at 1 kV, with a rather high specific on-resistance of 28-30 mV cm − 2 , partly due to a non-optimised backside ohmic contact (V ON 1.6 V). A large number of diodes could block voltages ranging from 1 up to 1.8 kV (destructive breakdown in AC mode), with increasing yield for smaller diameter (from 0.5 to 0.1 mm) diodes, which may be correlated to substrate induced defects [15]. Although further optimisations will be required in order to fully assess the potential of the high temperature CVD chimney process for device applications above 2 kV, the present results favourably demonstrate the potential of the growth technique.…”

High-performance 4H-SiC single photon avalanche diode operating at solar blind wavelength

“…4H-SiC also has very different ionization coefficients for holes and electrons [7] which can lead to a less noisy avalanche process than SPADs based on GaN, another promising wide bandgap semiconductor. Other benefits from SiC include high thermal conductivity (2~4× higher than Si and GaN [8]), high power failure density (10× and 5× higher than Si and GaN [9]) and an availability of a native oxide (in comparison to GaN). These benefits potentially make SiC SPADs more robust and more reliable for avalanche based operations, especially when the voltage is high, device size is small, and the total power density is not negligible.…”