Photoluminescence and infrared spectroscopy for impurities identification in silicon for photovoltaic applications

Spectroscopic investigations of impurities and defects in silicon, in particular photoluminescence (PL) and infrared (IR) studies strongly contributed to the outstanding development of silicon based devices in the last 60 years. Oxygen, carbon (i.e. the main non-dopant impurities in electronic grade and solar grade silicon, respectively) and their aggregates have been extensively investigated both by PL and IR spectroscopies since the 60s of the last century. As well, dopants, point and extended defects both in monocrystalline silicon (mono-Si) and multicrystalline silicon (mc-Si) have been extensively studied by PL at low temperature. In particular, luminescence related to dislocations and oxygen agglomerates was the subject of thousands of papers. Apart from this specific application, PL and PL mapping strongly emerged as valuable characterization tools of silicon wafers and solar cells since luminescence from mc-Si was found to be spatially inhomogeneous and correlated to the diffusion length of minority carriers. Spectroscopic studies allowed a deeper understanding of such complex issues both in the past and very recently, allowing for the detection and identification of specific impurities and defects regardless of their very low concentration (up to 1011 defects/cm3 ) . Thanks to the huge amount of works published in the last sixty years on silicon for both microelectronics and photovoltaics, most of the impurities, defects and complexes are very well known and under control. However, in order to push Si solar cell efficiency as near as possible to the Schockley-Queisser limit an even deeper knowledge is needed. All that considering, aim of this seminar is to review both dated and most recent findings also at MIBSOLAR center on relevant defects in Si for PV applications detectable by PL and IR.