Epitaxial growth of GaInAsSb for thermophotovoltaic devices

The growth and characterisation of GaInAsSb alloys, lattice-matched to GaSb substrates, are reported, with a particular focus on these alloys for thermophotovoltaic (TPV) devices. Using a unique combination of organometallic precursors, high-quality metastable GaInAsSb epitaxial layers with energy gaps as low as 0.5 eV have been grown by organometallic vapour-phase epitaxy. The GaInAsSb material quality is significantly improved for growth at a lower growth temperature of 525°C compared with 575°C, and at a higher growth rate of 5 μm/h compared with 1.2 μm/h. 4 K photoluminescence full width at half maximum values are as low as 4.3 meV for 0.59 eV GaInAsSb and 9.5 meV for 0.5 eV GaInAsSb. The importance of the surface step structure and growth kinetics on these metastable alloys is discussed. Uncoated TPV devices incorporating metastable GaInAsSb, with energy gaps in the range 0.495-0.549 eV, and a GaSb window layer exhibit an external quantum efficiency (QE) of nearly 60%, which corresponds to an internal QE of 90%. The open-circuit voltage is 313 mV for the 0.549 eV device, and decreases to 239 mV for the 0.495 eV device