S. Ortolland

Low temperature annealing of 4H–SiC Schottky diode edge terminations formed by 30 keV Ar+ implantation

Edge termination of Schottky barrier diodes has been achieved using 30 keV Ar+ ions implanted at a dose of 1×1015 cm−2. The reverse-bias leakage current is reduced by 2 orders of magnitude following postimplant annealing at a temperature of 600 °C. The thermal evolution of the implantation induced defects was monitored using positron annihilation spectroscopy and deep-level transient spectroscopy. Two distinct defect regions are observed using the positron technique. The depth of the first is consistent with the range of the implanted Ar+ ions and consists of clustered vacancies. The second extends to ∼250 nm, well beyond the range of the incident ions, and is dominated by point defects, similar in structure to Si–C divacancies. An implant damage related deep level, well defined at Ec−Et=0.9 eV, is observed for both the as-implanted and the 600 °C annealed sample. The effect of annealing is a reduction in the concentration of active carrier trapping centers.

Enhanced nitrogen diffusion in 4H-SiC

Experimental evidence is given for boron (B) enhanced diffusion of nitrogen (N) in ion-implanted 4H silicon carbide (4H-SiC), when a nitrogen implant is co-doped within an existing boron p-type well. The co-implanted nitrogen is shown to diffuse continuously with time when samples are annealed at 1600 °C—with little movement of the boron p-well implant profile. An effective nitrogen in boron diffusivity at 1600 °C is determined to be at least 60 times larger than that of a mono-doped nitrogen implant.

Surface effects on current mechanisms in 6H-SiC n+pp+ structures passivated with a deposited oxide

Bipolar n+pp+ diodes fabricated by nitrogen implantation and passivated with a deposited oxide have been characterized. Current–voltage measurements in a large temperature range have been analyzed. We also used the optical beam induced current method to represent the depleted zone at the surface around a reverse-biased device. We show that phenomena as the diameter-dependent current for low reverse and forward biases, the specific value for the energy activation of current under low bias equal to 0.65 eV, the reverse current–voltage characteristics evolution with time, or the anomalous spread of the depleted layer around a reverse-biased diode can be correlated with the presence of the deposited oxide as a passivation layer. A study of the current–time characteristic, obtained for a set reverse bias, is used to prove the presence of charges in the oxide and interface states responsible for an eventual inversion channel along the mesa.

Optimisation of a power 4H-SiC SIT device for RF heating applications

Abstract In this paper, the optimisation procedure for a static induction transistor (SIT) in silicon carbide is described and its application in a typical RF heating circuit is presented. A field plate edge termination is optimised for a 10 μm thick epitaxial layer with doping in the range 10 15 cm −3 to 10 16 cm −3 . Results show a breakdown voltage of 1280 V, corresponding to 68% of the theoretical value. For the chosen application an epitaxial layer doping level of 5×10 15 cm −3 is revealed to offer the best compromise. This allows pinch off of drain voltages exceeding 600 V from a 20 V gate drive whilst achieving a current density of 250 A cm −2 at an on-state voltage of less than 1 V. Transient simulations are performed for a series load resonant converter with a switching frequency of 27.12 MHz. The results emphasise the suitability of the device for RF heating applications.