COMPOSITE SEMICONDUCTORS - SELECTIVE ABSORBERS OF SOLAR-ENERGY

We have produced composite semiconductors by cosputtering CaF2 with either Ge or Si and measured their optical constants. Their optical behavior can be used described as being similar to that of the parent semiconductor, with the same energy gap but with a reduced, concentration dependent index of refraction. The normal specular reflectance of films sputtered on mirrored surfaces was measured. These data were used to compute the solar absorptance αs and thermal emittance εth. It was found that αs ≈ 0.7 and εth ≈ 0.06 with a weak dependence on composition, thickness and operating temperatures. Thus at T = 500°C conversion efficiencies of 50% are currently possible at solar concentration ratios C of 7-8 and about 70% for C ≈ 40 and improved performance can be expected with continuing research. © 1979.