Influence of Processing Temperature on Minority Carrier Diffusion Length of Lower Purity Silicon
V. Schlosser
Institut für Festkörperphysik Universität Wien
Ludwig Boltzmann Institut für Festkörperphysik
A-1060 Vienna, Austria
Samples of p-silicon -resistivity range 0.03 Ωcm-0.30 Ωcm-grown from metallurgical meltstock have been subjected to a series of heat treatments. Temperature ranges from 600 deg.Centigrade to 1020 deg.Centigrade and was kept constant for 30 min or 75 min. MIS structures with semitransparent metal contacts at the frontside and mesa diodes from planar pn-junctions have been prepared. The minority carrier diffusion length was determined from steady state monochromatic light photoresponse measurements at room temperature by varying the incident photon energy and at two fixed wavelengths (912 nm and 939 nm) in the temperature range between 77 K and 300 K. In addition to samples that have passed a heat treatment, MIS-structures have been prepared by evaporating silicon monoxide as an insulator. In our experiments a heat treatment of more than 730 deg.Centigrade was leading to a harmful decrease in minority carrier diffusion length whereas an increase has been observed for a heat treatment at 600 deg.Centigrade. Evaluation of the temperature dependence of the capture cross section from Ln(T) measurements indicate that there is more than one electrically active center responsible for the limitation of electron diffusion length.