Selective area grown AlInGaN nanowire arrays with core-shell structures for photovoltaics on silicon

To pave the way for InGaN-on-Si integrated photovoltaics, uniform and close-packed n-GaN/(Al)InGaN/p-GaN nanowire (NW) arrays with a similar to 0.29 mu m thick absorption segment of similar to 2.35 eV energy bandgap were fabricated on a Si substrate using Ti-mask selective area growth (SAG) in a molecular beam epitaxy (MBE) chamber. Instead of using thick and insulting buffer layers, this SAG process was realized by employing a 3 nm AlN/GaN: Ge buffer layer to facilitate electrical and thermal conduction between NWs and Si. Scanning transmission electron microscopy and high-resolution electron energy loss spectroscopy mapping revealed the discontinuities of AlN and the embedments of GaN:Ge which contribute to a negligible resistance of the NWs-on-Si interface. AlInGaN active segment exhibits core-shell structures, which suppress nonradiative surface recombination at NW surfaces. Working of AlInGaN core-shell NW solar cells was demonstrated with improved open-circuit voltage (V-oc) and higher energy conversion efficiency (eta) than those reported for InGaN NW solar cells. Stable output characteristics including the V-oc of 1.41 V and eta of 2.46% were obtained under 30-Sun illuminations. Such NWs-on-Si devices use Si substrate as the bottom electrode. With a low series resistance of similar to 1 omega, this work paves the way to monolithically integrate MBE-SAG III-nitride devices and Si-based electronics, such as Si solar cells and CMOS devices.

Automated summary

This study presents a method for fabricating InGaN solar cells on a Si substrate with improved open-circuit voltage and energy conversion efficiency, using Ti-mask selective area growth to form nanowire arrays for enhanced electrical and thermal conduction. The core-shell structure of the AlInGaN active segment suppresses nonradiative surface recombination and stable output characteristics were achieved under 30-Sun illuminations.