Variable temperature carrier dynamics in bulk (In)GaAsNSb materials grown by MOVPE for multi-junction solar cells

Abstract

III-V multi-junction solar cells are typically based on a triple-junction design that consists of an InGaP top junction, a GaAs middle junction, and a bottom junction that employs a 1 -1.25 eV material grown on GaAs substrates. The most promising 1 -1.25 eV material that is currently under extensive investigation is bulk dilute nitride such as (In)GaAsNSb lattice matched to GaAs substrates. The approach utilizing dilute nitrides has a great potential to achieve high performance triple-junction solar cells as recently demonstrated by Wiemer, et al., who achieved a record efficiency of 43.5% from multi-junction solar cells including MBE-grown dilute nitride materials [1]. Although MOVPE is a preferred technique over MBE for III-V multi-junction solar cell manufacturing, MOVPEgrown dilute nitride research is at its infancy compared to MBE-grown dilute nitride. In particular, carrier dynamics studies are indispensible in the optimization of MOVPE materials growth parameters to obtain improved solar cell performance. For the present study, we employed time-resolved photoluminescence (TR-PL) techniques to study carrier dynamics in MOVPE-grown bulk dilute nitride InGaAsN materials (E g = 1 -1.25 eV at RT) lattice matched to GaAs substrates. In contrast to our earlier samples that showed high background C doping densities, our current samples grown using different metalorganic precursors at higher growth temperatures showed a significantly reduced background doping density of ~ 10 17 /cm 3 . We studied carrier dynamics in (In)GaAsNSb double heterostructures (DH) with different N compositions at room temperature. Post-growth annealing yielded significant improvements in carrier lifetimes of (In)GaAsNSb double heterostructure (DH) samples. Carrier dynamics at various temperatures between 10 K and RT were also studied from (In)GaAsNSb DH samples including those samples grown on different orientation substrates.

Photoelectric Property Improvement of 1.0-eV GaInNAs and Applications in Lattice-Matched Five-Junction Solar Cells

“…[14,15] Meanwhile, high densities of background impurities make the material quality even worse. [16,17] As for the solar cell application, the peak EQE of the GaInNAs sub-cell grown in MOCVD by Wu et al was 35%. [18] By using TEGa as the Ga source, Dimroth et al reported a GaInNAs solar cell with a peak EQE of 70% at 600 nm and an average EQE of 46% in the expected working range (880-1200 nm).…”

“…The ECV test of the GaInNAs layers shows that the p-type doping concentration reduces from 1.2 × 10 17 cm −3 (H 2 ambient) to 7.4 × 10 16 cm −3 (N 2 ambient), indicating the concentration reduction of carbon, which is considered as the p dopant in GaInNAs. [16,17] This can be explained by the reduction of CH • 3 and CN • impurities in GaInNAs. The reduction of CH • 3 is a result of a lower DMHy flux, while the reduction of CN • impurities in GaIn-NAs may be caused by the relatively higher incorporation efficiency of NH • 2 compared to that of HCN.…”