Understanding the origin of parasitic absorption in GaAs double heterostructures

Despite achievements of extremely high external quantum efficiency (EQE), 99.5%, the net cooling of GaAs|GaInP double heterostructures (DHS) has been elusive. This is primarily due to the parasitic absorption, which originates from the GaInP passivation layers at long wavelengths. In samples with thin GaInP passivation layers, we report an EQE of 99%, approaching theoretical requirement for being heat neutral. Additionally, we investigate the EQE of MBE-grown GaAs|AlGaAs DHS versus temperature; the results compare well with that of GaAs|GaInP at and below 150 K. Also, initial measurements of parasitic absorption at shorter wavelengths is presented.