6 um thick AlnP55 Fe x-ray photovoltaic and 63Ni betavoltaic cells by Butera et al
Two 400 um diameter Al0.52In0.48P p+-i-n+ mesa photodiodes (6 um i layer) were fabricated from a wafer grown by metalorganic vapour phase epitaxy (MOVPE) and then studied at temperatures from 140 °C to -20 °C for the development of temperature tolerant 55Fe x-ray photovoltaic and 63Ni betavoltaic microbatteries. The Al0.52In0.48P epitaxial layers are the thickest so far reported for this emerging application. At each temperature, the performances of the Al0.52In0.48P detectors were analysed in dark conditions, as well as under the illumination of a 182 MBq 55Fe radioisotope x-ray source and a 185 MBq 63Ni radioisotope source. An open circuit voltage as high as 1.13 V was found for both the Al0.52In0.48P x-ray photovoltaic cells at -20 °C; whilst an open circuit voltage of 0.47 V was found for the best 63Ni betavoltaic cell, at the same temperature. Maximum output powers of 1.44 and 1.36 pW were obtained from the two x-ray photovoltaic cells at -20 °C; combining the output powers of these two Al0.52In0.48P x-ray photovoltaic cells, a total maximum output power as high as 2.8 pW could be obtained at -20 °C. Maximum output powers of 0.18 pW and 0.13 pW were instead extracted from the two betavoltaic cells at -20 °C, these could lead to a total maximum output power as high as 0.3 pW at -20 °C. Conversion efficiencies of 2.2% and 0.06% were found, respectively, for the best Al0.52In0.48P x-ray photovoltaic and betavoltaic cells at -20 °C. With respect to previously reported Al0.52In0.48P x-ray photovoltaic cells with thinner i layers, the 6 um Al0.52In0.48P x-ray photovoltaic cells had higher short circuit current, open circuit voltage, maximum output power, and conversion efficiency. The 6 um Al0.52In0.48P betavoltaic cells instead presented similar performances to previously analysed Al0.52In0.48P betavoltaic cells.
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