7 research outputs found
Photovoltaic characterisation of GaAsBi/GaAs multiple quantum well devices
A series of strained GaAsBi/GaAs multiple quantum well diodes are characterised to assess the potential of GaAsBi for photovoltaic applications. The devices are compared with strained and strain-balanced InGaAs based devices.
The dark currents of the GaAsBi based devices are around 20 times higher than those of the InGaAs based devices. The GaAsBi devices that have undergone significant strain relaxation have dark currents that are a further 10–20 times higher.
Quantum efficiency measurements show the GaAsBi devices have a lower energy absorption edge and stronger absorption than the strained InGaAs devices. These measurements also indicate incomplete carrier extraction from the GaAsBi based devices at short circuit, despite the devices having a relatively low background doping. This is attributed to hole trapping within the quantum wells, due to the large valence band offset of GaAsBi
Photoluminescence upconversion at interfaces driven by a sequential two-photon absorption mechanism
This paper reports on the results of an investigation into the nature of photoluminescence upconversion at
GaAs/InGaP2 interfaces. Using a dual-beam excitation experiment, we demonstrate that the upconversion in our
sample proceeds via a sequential two-photon optical absorption mechanism. Measurements of photoluminescence
and upconversion photoluminescence revealed evidence of the spatial localization of carriers in the InGaP2
material, arising from partial ordering of the InGaP2. We also observed the excitation of a two-dimensional electron
gas at the GaAs/InGaP2 heterojunction that manifests as a high-energy shoulder in the GaAs photoluminescence
spectrum. Furthermore, the results of upconversion photoluminescence excitation spectroscopy demonstrate that
the photon energy onset of upconversion luminescence coincides with the energy of the two-dimensional electron
gas at the GaAs/InGaP2 interface, suggesting that charge accumulation at the interface can play a crucial role in
the upconversion process
GaAsBi: An Alternative to InGaAs Based Multiple Quantum Well Photovoltaics
A series of GaAsBi/GaAs multiple quantum well
p-i-n diodes are characterized using IV, photocurrent and
illuminated IV measurements. The results are compared to an
InGaAs/GaAsP multiple quantum well control device of a design
that has demonstrated excellent performance in triple junction
photovoltaics. The extended absorption of the GaAsBi/GaAs
devices, compared to that of the InGaAs/GaAsP device, suggests
that GaAsBi/GaAs could present a viable alternative to
InGaAs/GaAsP for quad junction photovoltaics
Nanoparticle scattering for multijunction solar cells
We investigate the integration of Al nanoparticle arrays into the anti-reflection coatings (ARCs) of commercial triple-junction GaInP/ In0.01GaAs /Ge space solar cells, and study their effect on the radiation-hardness. It is postulated that the presence of nanoparticle arrays can improve the radiation-hardness of space solar cells by scattering incident photons obliquely into the device, causing charger carriers to be photogenerated closer to the junction, and hence improving the carrier collection efficiency in the irradiation-damaged subcells. The Al nanoparticle arrays were successfully embedded in the ARCs, over large areas, using nanoimprint lithography: a replication technique with the potential for high throughput and low cost. Irradiation testing showed that the presence of the nanoparticles did not improve the radiation-hardness of the solar cells, so the investigated structure has proven not to be ideal in this context. Nonetheless, this paper reports on the details and results of the nanofabrication to inform about future integration of alternative light-scattering structures into multi-junction solar cells or other optoelectronic devices