Alphavoltaic Performance of 4H-SiC Schottky Barrier Diodes

Abstract-Alpha voltaic effect in 4H-SiC Schottky barrier diodes (SBDs) with Nickel (Ni) and Titanium (Ti) as Schottky contacts is demonstrated using 5.5 MeV energetic
²⁴¹
Am alpha source of 1.414 μCi/cm
²
activity. The as-developed SBDs for high resolution alpha spectroscopy are used here with no further optimization for alpha voltaic response. The fabricated Ni/4H-SiC Schottky diodes exhibited an open circuit voltage (V
_OC
) of 0.4
V
, a short-circuit current density (J
_SC
) of nearly 175 pA/cm
²
, and an energy conversion efficiency of 0.28% upon continuous alpha exposure. Whereas, relatively inferior performance is observed for Ti/4H-SiC Schottky diodes with V
_OC
of 0.15
V
, J
_SC
of 2.15 pA/cm
²
, and a conversion efficiency of 0.0005% though the Ti/4H-SiC SBD upon annealing at 400°C in Nitrogen ambient exhibited better electrical characteristics compared to the Ni/4H-SiC SBDs. Analysis of the electrical characteristics of both the Schottky diodes reveal the higher surface state densities (N
_SS
) for Ti/4H-SiC SBD compared to Ni/4H-SiC SBD. Significant degradation in the battery performance (V
_OC
degraded to 18% and J
_SC
reduced to 30% of their initial values) is noticed upon long-term alpha exposure of the Ni/SiC SBDs beyond 30 hrs. Meanwhile, no major changes are observed in Ti/4H-SiC SBD alpha voltaic cell performance with irradiation. Free-carrier-depth profiles extracted from C-V measurements of the irradiated devices reveal a considerable carrier removal possibly due to bulk damage. In addition, significant increase in the density of surface states (
N_ss
) is noted upon prolonged alpha exposure leading to inferior performance of the SBDs. Hence, further improvements in the alphavoltaic performance of the Ni/SiC SBD may be obtained by passivating the surface.