Materials Science Forum Vols. 483-485

Abstract: In this paper, we extend the super junction concept to SiC high voltage devices and further expand the SiC theoretical limit. It is shown that the super-junction concept can reduce the theoretical specific on-resistance by several times to several orders of magnitude for both silicon and SiC. The unique merit of SiC super-junction devices is that the required P and N pillars have a much smaller aspect ratio and may be easier to form than their silicon counterparts. Furthermore, SiC super-junction devices are much less sensitive to charge imbalance issue than silicon SJ devices.

Abstract: 4H-SiC pin diodes fabricated on epitaxial films grown in-house on various substrates along with devices fabricated on commercial epi-material are presented. Defects have been observed using electroluminescence imaging and are correlated with device electrical performance. Most diodes fabricated with in-house epi-layers up to 25µm thick show relatively stable forward biased operation, although stacking fault propagation has been confirmed in all samples using electroluminescence imaging. Significant stacking fault propagation induced in the vicinity of testing probes has been observed and resulting design considerations are discussed.

Abstract: The path to commericializing a 4H-SiC power PiN diode has faced many difficult challenges. In this work, we report a 50 A, 10 kV 4H-SiC PiN diode technology where good crystalline quality and high carrier lifetime of the material has enabled a high yielding process with VF as low as 3.9 V @ 100 A/cm2. Furthermore, incorporation of two independent basal plane dislocation reduction processes (LBPD 1 and LBPD 2) have produced a large number of devices that exhibit a high degree of forward voltage stability with encouraging reverse blocking capability. This results in a total yield (forward, 10 kV blocking, and drift) of >20% for 8.7 mm x 8.7 mm power PiN diode chips—the largest SiC chip reported to date.

Abstract: The dependence of forward voltage degradation on crystal faces for 4H-SiC pin diodes has been investigated. The forward voltage degradation has been reduced by fabricating the diodes on the (000-1) C-face off-angled toward <11-20>. High-voltage 4H-SiC pin diodes on the (000-1) C-face with small forward voltage degradation have also been fabricated successfully. A high breakdown voltage of 4.6 kV and DVf of 0.04 V were achieved for a (000-1) C-face pin diode. A 8.3 kV blocking performance, which is the highest voltage in the use of (000-1) C-face, is also demonstrated in 4H-SiC pin diode.

Abstract: Forward current-voltage characteristics, reverse current recovery and post-injection voltage decay are measured for high voltage 4H-SiC p+non+-diodes. The effects of both minority carrier lifetime in diode no-base and injection coefficient of p+-emitter are investigated with respect to device performance at high injection levels.

Abstract: Large area 4H-SiC PIN diodes have been fabricated which exhibit a stable avalanche ranging between 4.5 and 5.5 kV. The avalanche occurs at an electrical field strength of 2.1 MV/cm at the pn junction. The temperature coefficient of the avalanche is positive (0.3 V/K). The avalanche is tested in DC mode. The device concept as well as the fabrication process is described in detail. Static and dynamic characteristics are shown.

Abstract: We fabricated a p+/n-/n+ 4H-SiC IMPATT diode with guard-ring termination. The p+ - layer and the guard-ring were formed by ion implantation. The diode showed abrupt avalanche breakdown characteristics and we obtained a peak output power of 1.8 W at 11.93 GHz, which is the highest peak output power ever for the SiC IMPATT diodes in X-band.

Abstract: This paper reports the first demonstration of the lifetime control of the minority carrier in 4H-SiC PiN diodes by He+ ion implantation. In this work, we fabricated 4H-SiC PiN diodes with the epitaxial junction and the blocking voltage of 2.6kV, precisely corresponding to the theoretical blocking voltage calculated from the doping concentration (4.0x1015/cm2) and the thickness of the drift layer (16.5 µm). He+ ion implantation was performed with the energy and the dose of 400kV and 1.0x1013-2.0x1014/cm2, respectively. We observed no different characteristics in the blocking voltage (2.6kV) and leakage current (<10µA@2.5kV) between the PiN diodes with/without He+ ion implantation. However, we confirmed the improvement of the current recovery characteristics in the diodes with He+ ion implantation.

Abstract: The degradation of diffused SiC PIN diodes during forward-biased operation was studied by first fabricating PIN diodes by diffusion of aluminum or boron into 4H-SiC substrates with n-type 10-15 µm thick epilayers doped by nitrogen up to 5x1015cm-3. The formed diodes were subjected to degradation testing under an applied current density of 200A/cm2 at room temperature. The majority of the Al diffused diodes demonstrated a voltage drift, ΔVf, of more than 2 V, while B-doped diodes showed no significant change in forward voltage. The EBIC mode of SEM was employed to monitor nucleation and expansion of stacking faults.

Abstract: The effect of gamma-ray and neutron irradiation on recombination current, injection electroluminescense and the value of the lifetime of nonequilibrium carriers for 4H-SiC pn structures was investigated. The irradiation was carried out with gamma-ray (dose 5x106 rad) and 1 MeV neutrons in the doses range from 1.2x1014 cm-2 to 6.24x1014 cm-2. Neutron irradiation with a dose 1.2x1014 cm-2 increased the recombination current, decreased the lifetime for deep-level recombination in the space charge region and decreased the intensity of the edge injection electroluminescense (hnmax » 3.16 eV) by 1.5-2 orders of magnitude; the neutron irradiation with high dose (6.24x1014 cm-2) resulted in increase of the recombination current up to 2 orders of magnitude and decrease of lifetime at least up to 2 orders of magnitude. Gamma-ray irradiation and annealing at temperatures in the range 350-650 K left the recombination current and lifetime practically unchanged.