Alphavoltaic Performance of 4H-SiC Schottky Barrier Diodes

The 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}^{241} {\text {Am}}$ </tex-math></inline-formula> alpha source of 1.414-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>Ci/cm2 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(V_{\text {OC}}) $ </tex-math></inline-formula> of 0.4 V, a short-circuit current density <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(J_{\text {SC}})$ </tex-math></inline-formula> of nearly <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${175~\text {pA}} / {\text {cm}}^{2}$ </tex-math></inline-formula>, 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {OC}}$ </tex-math></inline-formula> of 0.15 V, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$J_{\text {SC}} $ </tex-math></inline-formula> of 2.15 pA/cm2, and a conversion efficiency of 0.0005% though the Ti/4H-SiC SBD upon annealing at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400~^{\circ }$ </tex-math></inline-formula>C in nitrogen ambient exhibited better electrical characteristics compared to the Ni/4H-SiC SBDs. The analysis of the electrical characteristics of both the Schottky diodes reveals the higher surface state densities (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{\text {SS}}$ </tex-math></inline-formula>) for Ti/4H-SiC SBD compared to Ni/4H-SiC SBD. Significant degradation in the battery performance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {OC}}$ </tex-math></inline-formula> degraded to 18% and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$J_{\text {SC}} $ </tex-math></inline-formula> reduced to 30% of their initial values) is noticed upon long-term alpha exposure of the Ni/SiC SBDs beyond 30 h. 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, a significant increase in the density of surface states <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(N_{\text {ss}})$ </tex-math></inline-formula> 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.