Structure and transformation of the metastable boron- and oxygen-related defect center in crystalline silicon

Abstract

We analyze the core structure of the carrier-lifetime-reducing boron- and oxygen-related metastable defect center in crystalline silicon by measuring the correlation of the defect concentration with the boron and the oxygen contents on a large number of different silicon materials. The experimental results indicate that the defect is composed of one substitutional boron and two interstitial oxygen atoms. Formation and annihilation of the metastable boron-oxygen complex are found to be thermally activated processes, characterized by two strongly differing activation energies. Measurements of the defect generation rate as a function of light intensity show that the defect generation rate increases proportionally with light intensity below 1 ${\mathrm{m}\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ and saturates at higher intensities. All experimental results can be consistently explained using a defect reaction model based on fast-diffusing oxygen dimers $\left({\mathrm{O}}_{2\mathrm{i}}\right),$ which are captured by substitutional boron $\left({\mathrm{B}}_{\mathrm{s}}\right)$ to form a metastable ${\mathrm{B}}_{\mathrm{s}}-{\mathrm{O}}_{2\mathrm{i}}$ complex. Based on this model, new strategies for an effective reduction of the light degradation of solar cells made on oxygen-rich silicon materials are derived. The model also explains why no lifetime degradation is observed in aluminum-, gallium-, and indium-doped oxygen-rich silicon.