Electronic properties of light-induced recombination centers in boron-doped Czochralski silicon

In order to study the electronic properties of the recombination centers responsible for the light-induced carrier lifetime degradation commonly observed in high-purity boron-doped Czochralski (Cz) silicon, injection-level dependent carrier lifetime measurements are performed on a large number of boron-doped p-type Cz silicon wafers of various resistivities (1-31 Ω cm) prior to and after light degradation. The measurement technique used is the contactless quasi-steady-state photoconductance method, allowing carrier lifetime measurements over a very broad injection range between 10¹² and 10¹⁷ cm^-3. To eliminate all recombination channels not related to the degradation effect, the difference of the inverse lifetimes measured after and before light degradation is evaluated. A detailed analysis of the injection level dependence of the carrier lifetime change using the Shockley-Read-Hall theory shows that the fundamental recombination center created during illumination has an energy level between E_v+0.35 and E_c-0.45 eV and an electron/hole capture time constant ratio between 0.1 and 0.2. This deep-level center is observed in all samples and is attributed to a new type of boron-oxygen complex. Besides this fundamental defect, in some samples an additional shallow-level recombination center at 0.15 eV below E_c or above E_v is found to be activated during light exposure. This second center dominates the light-degraded carrier lifetime only under high-injection conditions and is hence only of minor importance for low-injection operated devices.