Electronic band structure and optical properties of GaNxPyAs1-x-y with y≥0.6 studied by electro-modulation spectroscopy and photoluminescence

International audienc

Nitrogen-related intermediate band in P-rich GaNxPyAs1-x-y alloys.

The electronic band structure of phosphorus-rich GaNxPyAs1-x-y alloys (x ~ 0.025 and y ≥ 0.6) is studied experimentally using optical absorption, photomodulated transmission, contactless electroreflectance, and photoluminescence. It is shown that incorporation of a few percent of N atoms has a drastic effect on the electronic structure of the alloys. The change of the electronic band structure is very well described by the band anticrossing (BAC) model in which localized nitrogen states interact with the extended states of the conduction band of GaAsP host. The BAC interaction results in the formation of a narrow intermediate band (E- band in BAC model) with the minimum at the Γ point of the Brillouin zone resulting in a change of the nature of the fundamental band gap from indirect to direct. The splitting of the conduction band by the BAC interaction is further confirmed by a direct observation of the optical transitions to the E+ band using contactless electroreflectance spectroscopy

Nitrogen-related intermediate band in P-rich GaNxPyAs1−x−y alloys

Abstract The electronic band structure of phosphorus-rich GaNxPyAs1−x−y alloys (x ~ 0.025 and y ≥ 0.6) is studied experimentally using optical absorption, photomodulated transmission, contactless electroreflectance, and photoluminescence. It is shown that incorporation of a few percent of N atoms has a drastic effect on the electronic structure of the alloys. The change of the electronic band structure is very well described by the band anticrossing (BAC) model in which localized nitrogen states interact with the extended states of the conduction band of GaAsP host. The BAC interaction results in the formation of a narrow intermediate band (E− band in BAC model) with the minimum at the Γ point of the Brillouin zone resulting in a change of the nature of the fundamental band gap from indirect to direct. The splitting of the conduction band by the BAC interaction is further confirmed by a direct observation of the optical transitions to the E+ band using contactless electroreflectance spectroscopy

RTA effects on optical absorption and thermal conductivity of GaAsPN grown on GaP for tandem solar cell applications

International audienc

Optical absorption and thermal conductivity of GaAsPN absorbers grown on GaP in view of their use in multijunction solar cells

International audienceThe optical absorption and thermal conductivity of GaAsPN absorbers are investigated by means of optical absorption spectroscopy and photo-thermal deflection spectroscopy (PDS) for different 100 nm-thick GaAsNP/GaP samples under different growth conditions and various post-growth annealing temperatures. It is first shown that the As content strongly modifies the optical absorption spectrum of the GaAsPN: with a maximum absorption coefficient of 38,000 cm À 1 below the GaP bandgap energy. The optical absorption and thermal conductivities of the samples are then evaluated for various growth and annealing conditions using PDS: the results showing overall agreement with optical absorption spec-troscopy measurements. A significant improvement in optical absorption and thermal conductivity after annealing is demonstrated. The best thermal conductivity measured is equal to 4 W/m K. These results are promising for the development of absorbers in multijunction solar-cell architecture

GaAsPN Absorbers Grown on GaP for Multijunction Solar Cells: Optical Absorption and Thermal Conductivity Properties

International audienceOptical absorption and thermal conductivity of GaAsPN absorbers grown on GaP are investigated by optical absorption spectroscopy and photo‐thermal deflection spectroscopy (PDS). First, the strong dependence of optical absorption on As content is shown: with a maximum absorption coefficient of 38,000 cm‐1 below the GaP bandgap. Optical absorption and thermal conductivity of the samples are then evaluated for various growth and annealing conditions using PDS. The significantly positive impact of annealing on both properties is demonstrated. Thermal conductivity reached 4W/mK for the best sample. These results are promising for the development of absorbers in multijunction solar cells