Fabrication and characterization of GaSb based thermophotovoltaic cells using Zn diffusion from a doped spin-on glass source

The GaInSb material system is attractive for application in thermophotovolt aic (TPV) cells since its band gap can be tuned to match the radiation of t he emitter. At present, most of the TPV cells are fabricated using epitaxia l layers and hence ase expensive. To reduce the cost, Zn diffusion using el emental vapors in a semiclosed diffusion system is being pursued by several laboratories. In this paper, we present studies carried out on Zn diffusio n into n-type (Te-doped) GaSb substrates in an open tube diffusion furnace. The dopant precursor was a 2000 Angstrom thick, zinc doped spin-on glass. The diffusion was carried out at temperatures ranging from 550 to 600 degre es C, for times from 1 to 10 h. The diffused layers were characterized by H all measurements using step-and-repeat etching by anodic oxidation, seconda ry ion mass spectrometry measurements, and TPV device fabrication. For diff usion carried out at 600 degrees C, the junction depth was 0.3 mu m, and th e hole concentration near the surface was 5 x 10(19)/cm(3). The external qu antum efficiency, measured without any anti-reflection coating of the TPV c ells fabricated using mesa-etching had a maximum value of 38%. Masked diffu sion was also carried out by opening windows in a Si3N4 coated, GaSb wafer. TPV cells fabricated on these structures had similar quantum efficiency, b ut lower dark current.