BETAVOLTAIC CELLS AND ARRAYS BASED ON AlGaAs/GaAs HETEROSTRUCTURES

摘要

The paper describing the betavoltaic cells base-d on AlGaAs/GaAs heterostructures is presented. Theoretical maximum for the direct conversion of betas to electricity is about 22-25% for semiconductors with E_g = 1.9-2.2 eV. Theoretical limit of tritium betas conversion reduces to about 12-15% for these semiconductors owing to low photocurrent density (10~(-7) - 10~(-6) A/cm~2) in the betacells under tritium beta particles. The developed AlGaAs/GaAs heterostructures consist of n-GaAs substrate, p-Al_xGa_(1-x)As based layer, p-Al_xGa_(1-x)As (x = 0.15-0.35) and p-Al_(0.85)Ga_(0.15)As front passivating layer. Betacells based on these heterostructures ensure the efficient conversion of tritium betas to electricity as well as photovoltaic conversion of light from tritium-fueled radioluminescent lamps. Since the front wide bandgap layer is thin (0.02-0.05 μm) the separation of carriers generated by the low-energy betas from tritium mainly near the cell surface is highly efficient. Low value of leakage current i = 10~(-12) A/cm~2 was measured in these cells. Generated current of about 10~(-6) A/cm~2, V_(OC) = 0.65-0.93, FF = 0.8-0.85, maximum output specific power of 550 nW/cm~2 and the maximum conversion efficiency of 5.8% were received in the AlGaAs betacells situated in tritium gas. Efficiency of 5.6% was received in betacells under T_2-Ti source of betas. Optical efficiency of 12%, V_(OC) = 0.8, and I_(SC) - 150 nA/cm~2 were achieved in the PV cell based on Al_(0.35)Ga_(0.65)As under green tritium lamp. The batteries with output voltage of 1.5-3.5 V and output power up to 340 nW were fabricated on the PV arrays and tritium lamps.