Impact of in-situ annealing on dilute-bismide materials and its application to photovoltaics

GaAs1−xBix/GaAs multiple quantum well heterostructures were grown by organo-metallic vapor phase epitaxy (OMVPE) at low temperatures and were subsequently in-situ annealed under an arsine (AsH3) overpressure in the OMVPE reactor. Photoluminescence (PL) measurements were performed to establish the optimized annealing condition for the highest luminescence intensity, as well as high resolution X-ray diffraction (XRD) measurements to detect any structural changes after annealing. In addition, the complex compositional profile and the interfacial abruptness were deduced from the combined XRD analysis with the transmission electron microscopy. A 5-fold increase in the PL intensity at room temperature was observed after annealing under the optimized conditions. Using the optimized annealing conditions, single junction solar cells (SJSC) incorporating 5-period GaAs0.964Bi0.036/GaAs (32 nm/20 nm) heterostructures for the device base region were fabricated and characterized. The spectral dependence of the external quantum efficiency of the SJSC exhibited improved spectral response as a result of the optimized in-situ annealing, with extended absorption edge up to 1.07 eV.