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.