p-GaSb/n-GaAs heterojunction diodes for TPV and solar cell applications

A series of samples has been grown to investigate the effect of doping and GaSb epilayer thickness on dark and photo I-V curves, and on spectral respo nse. The optimum GaSb thickness is a trade-off between the diffusion length and the thickness required to maximise light absorption. The highest open circuit voltage, V-oc, similar to 0.33V, to date has been obtained from a t hin (0.3 mu m) GaSb layer doped at 6 x 10(19) cm(-1), under illumination by a focused tungsten-halogen lamp (similar to 1 W cm(-2)). The short circuit current, I-sc, was similar to 13 mA/cm(2) with a corresponding fill factor of 0.63, and an external quantum efficiency of similar to 10%. The devices were not anti-reflection coated and some parameters important for solar ce lls, such as contact form and series resistance, have not been optimised. T he shape of the spectral response is strongly dependent on GaSb thickness. Increasing the thickness of the epilayer increases the external quantum eff iciency above 870 nm (i.e. above the GaAs band edge) while the external qua ntum efficiency in the short wavelength range (below 870 nm) reduces.