1.65 eV p-AlGaAs/n-GaAs QW/n-AlGaAs Tunnel Junctions with Delta-Doping for Monolithic III–V/Si Tandem Solar Cells

Abstract

Thermally stable and optically transparent 1.65−1.72 eV III−V tunnel junctions (TJ) are necessary for interconnecting III−V/Si tandem cells. In this study, we systemically investigate the performance of p-Al 0.18 Ga 0.82 As/n-GaAs QW/n-Al 0.18 Ga 0.82 As TJs with cladding layers grown under various growth conditions before and after thermal annealing. TJs grown using Si dopant revealed poor tunneling current under all growth conditions studied, even prior to thermal load. We replaced Si with Te and achieved peak current densities of 1900 mA/cm 2 , which plummeted to 27 mA/cm 2 after extensive annealing at 600 °C for 90 min. By introducing two spikes of Te δ-doping with 8% surface coverage, along with optimizations in growth temperature, doping, and Al content in cladding layers, we achieved a further enhanced peak current density of 82 100 mA/cm 2 for as-grown devices which is 5 orders of magnitude higher compared to Si-doped TJs. After thermal annealing, the TJ demonstrated a peak current density of 464 mA/cm 2 , which significantly exceeds the requirements for III−V/Si tandem cells under 1 sun operation. As a proof of concept, we fabricated 1.65 eV AlGaAs solar cells grown with either Si or Te δ-doped TJ and show that Te δ-doping is a key approach for AlGaAs TJ devices. This result is useful not only for monolithically integrated III−V/Si tandem solar cells but also for high-performance light-emitting devices with low electrical resistance.