Static hot carrier populations as a function of optical excitation energy detected through energy selective contacts by optically assisted IV



We investigated the behavior of carrier populations generated at the interface of an n-Si wafer to an Si quantum dot (QD) array embedded in SiO2 with a photon flux ranging from 1.24 to 2.48 eV (1000 to 500 nm). The optically assisted IV method was used with the Si wafer as hot carrier (HC) absorber and the Si QD array as energy selective contact (ESC). Charge carriers obtain excess energy from photons with energies significantly exceeding the band gap, resulting in an HC population. This reduces the bias field required to provide kinetic energy by field emission. The ESC can collect HCs at lower bias voltages. Tunneling resonances show the energy selective behavior under illumination at 80 K and room temperature (295 K). The data at 80 K can arguably be interpreted as an HC population in Si within the range of the ballistic mean free path from the QD array. We discovered a correlation between the energetic shift of the average hot hole temperature near the valence band edge and the energy of the photons impinging on the mesa structures. The optically assisted IV technique delivers a proof of principle for operation of an Si QD array as an ESC at room temperature, and furthermore for an HC solar cell with one ESC at 80 K. Copyright © 2013 John Wiley & Sons, Ltd.