Growth and characterization of quaternary (GaInAsP-GaAs) graded heterostructures

The growth conditions of Ga_xIn_1-xAsyP_1-y lattice-matched to GaAs using MOCVD on (001) oriented substrates are analyzed. The epitaxial layer composition is varied from GaAs to lattice-matched Ga_0.52In_0.48P via quaternary grade. The layer quality is more sensitive to experimental variables as the composition approaches the Ga_0.52In_0.48P side than when growing quaternaries. TEM images show promising results even though the top layer Ga_0.52In_0.48P needs to be further optimized. The fundamental objective of this work is to improve understanding over the growth of LMM alloys on GaAs with special emphasis on quaternary grades. We believe that incorporation of LMM quaternaries with ternaries in a single-junction device will provide flexibility in design which may ultimately lead to record PV conversion efficiencies.