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.
Despite achievements of extremely high external quantum efficiency (EQE), 99.5%, the net cooling of GaInP|GaAs double heterostructures (DHS) has never been realized. This is due to an unknown source of parasitic absorption. Prior studies have ruled out the possibility of the bulk absorption from the GaAs layer. Thus it is thought to be either at the air- GaInP interface, through the presence of dangling bonds, or in bulk GaInP through impurities. Using two-color thermallens calorimetry (based on the Z-scan technique), this study indicates that that the parasitic absorption likely originates from the GaInP bulk layers.
Laser cooling in InGaP|GaAs double heterostructures (DHS) has been a sought after goal. Even though very high external quantum efficiency (EQE) has been achieved, background absorption has remained a bottleneck in achieving net cooling. The purpose of this study is to gain more insight into the source of the background absorption for InGaP|GaAs DHS as well as GaAs|AlGaAs DBRs by employing an excite-probe thermal Z-scan measurement.