Phys. Rev. Appl. 5, 024005 (2016)

An all-optical, contactless scheme for measuring the Seebeck coefficient in a semiconductor advantageously offers high spatial resolution and avoids material or electrical artefacts that can be encountered in other measurement schemes. The Seebeck effect, whereby an electrical voltage is generated due to a temperature gradient in a material, is employed to construct thermopiles and thermoelectric generators. The strength of the effect is material dependent and determined by a material's Seebeck coefficient. François Gibelli and co-workers have now developed an optical measurement scheme and successfully applied it to a multi-quantum-well semiconductor structure with wells made from In0.78Ga0.22As0.81P0.19 and barriers from In0.8Ga0.2As0.44P0.56. The sample is excited with 980-nm light from a continuous-wave single-mode laser and photoluminescence images captured across the 600 to 1,700 nm wavelength band. Analysis of these spectral images can be used to determine the sample's electrochemical potential and temperature gradient and thus the Seebeck coefficient.