Materials aspects of multijunction solar cells

Atomic layer epitaxy (ALE) was used to grow several components of the cascade solar cell structure in the AlGaAs/GaAs system. An ALE reactor was constructed for multiwafer growth with a growth rate of 0.6 μm h⁻¹. Device quality GaAs and $\text{As}{}_{\mathrm{x}}\text{Ga}{}_{\mathrm{1-x}}\text{As}$ films were grown with p-type background carbon doping in the ranges 10¹⁵–10¹⁹ cm⁻³ and 10¹⁶–10²⁰ cm⁻³ respectively. N-type films were achieved by SiH₄ doping, producing carrier concentrations in the range 10¹⁶–10¹⁸ cm⁻³. In addition, the potential applications of the ALE technique in the photovoltaic field are discussed.