AlGaSb-Based Solar Cells Grown on GaAs: Structural Investigation and Device Performance

GaSb and alloys based on the 6.1 Å family can be grown metamorphically on substrates such as GaAs allowing for the realization of several multijunction solar cell designs. This paper investigates the molecular beam epitaxy growth, crystal quality, and device performance of Al _x Ga _1-x Sb-based single-junction solar cells grown on GaAs substrates. The focus is on the optimization of the growth of Al _x Ga _1-x Sb on GaAs (001) substrates in order to minimize the threading dislocation density resulting from the large lattice mismatch between GaSb and GaAs. Utilizing optimum growth conditions, solar cells with absorbing layers of different Al _x Ga _1-x Sb compositions are studied and compared to control cells grown on lattice-matched GaSb substrates. GaSb, Al _0.15 Ga _0.85 Sb, and Al _0.5 Ga _0.5 Sb solar cells grown on GaAs substrates show open-circuit voltages of 0.16, 0.17, and 0.35 V, respectively. Furthermore, the lattice-mismatched cells demonstrate promising carrier collection with comparable spectral response to lattice-matched control cells grown on GaSb.