On the observation of electron-hole liquid luminescence under low excitation in Al2O3-passivated c-Si wafers

We report on low-temperature photoluminescence (PL) from aluminum oxide (Al2O3)-passivated c-Si wafers, which surprisingly exhibits clear signature of the formation of the so-called electron-hole liquid (EHL), despite the use of excitation powers for which the condensed phase is not usually observed in bulk Si. The elevated incident photon densities achieved with our micro-PL setup together with the relatively long exciton lifetimes associated with a good quality, indirect band-gap semiconductor such as our float-zone c-Si, are considered the key aspects promoting photogenerated carrier densities above threshold. Interestingly, we observe a good correlation between the intensity of the EHL feature in PL spectra and the passivation performance of the Al2O3 layer annealed at different temperatures. The change in the extension of the sub-surface space-charge region that results from the balance between the induced fixed charge in the Al2O3 and the defect states at the alumina/Si interface is at the origin of the observed correlation. ((c) 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)