Mesa architecture and efficiency of InGaP/Ga(In)As/Ge solar cells

It has been shown that the mesa architecture and achieved quality of the mesa sidewall of concentrator multijunction solar cells ensured increasing their efficiency up to 36.7% at the sunlight concentration before 100 (AM0; 0.136W/cm$^2$). Creation of the mesa structure architecture with following separation of epitaxial plates of monolithic InGaP/GaAs/Ge nanoheterostructure into chips was carried out by single step chemical wet etching in the НВr:H$_{2}$O$_{2}$:H$_{2}$O (8:1:100) through a photoresist mask to the depth of 12–18$\mu$m. Conditions of single step etching, which ensure formation of a smooth and even side surface of the InGaP/Ga(In)As/Ge nanoheterostructure mesa containing different in composition and thickness layers have been determined. Determination of the activation energy has shown that etching occurs in the diffusion region of the heterogeneous process. In raising etchant temperature from 2 to 36$^\circ$C, a change of the tilt angle in the Ge substrate region from 4.5 to 25 angular degrees is observed, what allows optimizing the amount of concentrator solar cells and their quality at final mechanical separation of the epitaxial plate into chips.