Thin GaAs photovoltaic heterostructures are grown by MOCVD with various p-GaAs
base thicknesses. The total n/p absorbing thickness is varied systematically.
Output voltages up to ∼1.155V were obtained for individual n/p
junctions at an average illumination intensity of ∼8W/cm2.
Novel phototransducer devices are then achieved with a vertical epitaxial
heterostructure architecture, monolithically integrating 5 or more such thin n/p
junctions. Around the design wavelength, the stacked heterostructure design is
yielding an optimal external quantum efficiency approaching unity divided by the
number of junctions. The modeled and measured conversion efficiencies are
exceeding 60%. The photocarrier extraction properties are simulated for
different junction thicknesses using a model based on a 3-dimensional (3D)
radially-symmetric TCAD implementation of the heterostructures. The study
clearly demonstrates that for such thin n/p junctions the photocarrier
extraction can still be efficient due to the operation at reduced current
densities and higher voltages in heterostructures enhancing electrical power
extraction. With the supplementary add-on of a window layer with a reduced sheet
resistance for the stacked structure, we demonstrate the possible efficient
operation of phototransducers for optical inputs exceeding 150 W/cm2,
even for the case of devices designed without gridlines.