Abstract

Single-junction InGaNAs solar cells were grown by MBE with active layers based on a GaAsN/InAs superlattice. Dependence of defect formation on thickness of InGaNAs was explored in the study. Thickness increase from 900 nm to 1200 nm leads to defect formation with two activation energies of 0.20 eV and 0.50 eV but the value of quantum efficiency stays almost the same. Further thickness increase up to 1600 nm leads to the increase of defect concentration in the InGaNAs active layer. These defects are non-radiative recombination centres because a significant decrease of solar cell quantum efficiency was observed. The existence of a critical thickness for defect-free growth of InGaNAs based on GaAsN/InAs superlattice is proposed.

Highlights

  • In 2015 multi-junction solar cells (MJ SC) based on III-V compounds with a record efficiency of 46% were fabricated [1]

  • The step position in C(f, T) curves does not depend on applied bias voltage indicating that the response originates from bulk defects rather than from the InGaNAs/GaAs interface

  • In our previous study [8] we showed the dependence of external quantum efficiency on thickness for these samples (Figure 4)

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Summary

Introduction

In 2015 multi-junction solar cells (MJ SC) based on III-V compounds with a record efficiency of 46% were fabricated [1]. Ga1-xInxNyAs1-y with a small content of nitrogen is one of the most promising alloys to reach this goal Such III-V-N alloys (GaPNAs, InGaNAs etc.) with nitrogen content less than 5% are called dilute nitrides. It has been shown that the small addition of nitrogen leads to large bowing parameters for the bandgap in quaternary Ga1-xInxNyAs1-y alloys: already few percent of nitrogen reduces the bandgap by hundreds of meV [4] and a value of 1 eV can be achieved. These layers can be epitaxially grown on Ge and GaAs wafers when y=0.35x.

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