MBE-grown GaAs:Si/GaAs:Be tunnel diodes for multijunction solar cells

We present the results of optimization of the design and molecular beam epitaxy (MBE) growth technology of N-AlGaAs:Si/$n^+$-GaAs:Si/$p^+$-GaAs:Be/P-AlGaAs:Be heterostructures for tunnel diodes (TDs). The achieved maximum peak current density level ($J_p$ = 513 A/cm$^2$) allows these TDs to be used for cascade connections both in multijunction solar cells and in structures of tunnel-coupled laser diodes. The initial region of the $J$–$U$ curve of TDs exhibits nonlinearity that is explained by a residual potential barrier left in the $p^+$–$P$–p$^+$ isotype heterojunction (confining the active region of TD) as a result of non-optimum doping of Al$_{0.4}$Ga$_{0.6}$As alloy.