Revisiting radiative deep-level transitions in CuGaSe{sub 2} by photoluminescence
- Laboratory for Photovoltaics, Physics and Material Science Research Unit, University of Luxembourg, Rue du Brill 41, L-4422 Belvaux (Luxembourg)
Recent defect calculations suggest that the open circuit voltage of CuGaSe{sub 2} solar cells can be limited by deep intrinsic electron traps by Ga{sub Cu} antisites and their complexes with Cu-vacancies. To gain experimental evidence, two radiative defect transitions at 1.10 eV and 1.24 eV are characterized by steady-state photoluminescence on epitaxial-grown CuGaSe{sub 2} thin films. Cu-rich samples are studied, since they show highest crystal quality, exciton luminescence, and no potential fluctuations. Variations of the laser intensity and temperature dependent measurements suggest that emission occurs from two deep donor-like levels into the same shallow acceptor. At 10 K, power-law exponents of 1 (low excitation regime) and 1/2 (high excitation regime) are observed identically for both transitions. The theory and a fitting function for the double power law is derived. It is concluded that the acceptor becomes saturated by excess carriers which changes the exponent of all transitions. Activation energies determined from the temperature quenching depend on the excitation level and show unexpected values of 600 meV and higher. The thermal activation of non-radiative processes can explain the distortion of the ionization energies. Both the deep levels play a major role as radiative and non-radiative recombination centers for electrons and can be detrimental for photovoltaic applications.
- OSTI ID:
- 22594420
- Journal Information:
- Applied Physics Letters, Vol. 109, Issue 3; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACTIVATION ENERGY
COPPER SELENIDE SOLAR CELLS
DEFECTS
ELECTRIC POTENTIAL
ELECTRONS
EPITAXY
EXCITATION
FLUCTUATIONS
IONIZATION
MEV RANGE 100-1000
PHOTOLUMINESCENCE
PHOTOVOLTAIC EFFECT
QUENCHING
STEADY-STATE CONDITIONS
TEMPERATURE DEPENDENCE
THIN FILMS
VACANCIES