T1.3 MOCVD Growth of All III-phosphide (AlInP-InGaP) Distributed Bragg Reflectors for Use in Multijunction Solar Cells*
David Rowell (Microlink Devices), Kamran
Forghani (Microlink Devices),
Rao Tatavarti (Microlink Devices)
We report on the MOCVD growth of all III-phosphide (AlInP-InGaP) Distributed Bragg Reflectors and their applications for multijunction (MJ) solar cell devices. DBR’s with peak reflectance of 0.89um GaAs bandgap energy were grown on top of inverted GaAs single junctions and are compatible with epitaxial lift off processing of solar cells. The DBR’s were grown on 150 mm (6”) substrates and exhibited smooth surfaces. Dual junction InGaP/GaAs solar cells with AlInP-GaInP DBR exhibited an increase of 3% in Jsc, and 44% increase in the EL integrated intensity of both GaAs and InGaP peaks.
At MicroLink Devices, we have been developing inverted metamorphic (IMM) based devices using epitaxial lift off (ELO) process for the past decade. In this work, we present the first ever growth and application of InAlP-InGaP DBR structure as a reflective stack for a GaAs subcell. This all-phosphide DBR has unique qualities suitable for IMM devices. These DBRs can be used as a wavelength-selective reflector with three major implications: (i) Photon recycling increases internal quantum efficiency (IQE). (ii) The back mirror also results in an increase of effective optical path thickness. Thus, the sub-cell can be thinned down while maintaining the photogenerated current. (iii) The reduced diffusion length for minority carriers reaching the tunnel junctions or contact layers results in the devices being more radiation hard, i.e. they have a higher EOL, as well as an overall improvement to the BOL performance.
The DBR did not reduced the Voc or FF, which can sometimes happen due to the introduction of defects or excess series resistance. Moreover, the DBR structure seems to be reducing the leakage current in the DIV tests. This work proves the feasibility of using phosphide-based DBRs for various MJ solar cells for various applications, including terrestrial (1-sun or concentrated: CPV) and space applications.
*Poster presentation available at the coffee break.
Event Timeslots (1)
SYMPOSIUM T1 – MATERIALS FOR OPTOELECTRONICS
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David Rowell
Location: Technological Institute LR4