Recombination activity of chromium-gallium pairs in silicon

Understanding metallic impurities in silicon is essential for the development of silicon-based devices such as solar cells. Transition metals such as iron and chromium have been recognised as harmful impurities in silicon, particularly in p-type silicon. As the photovoltaic industry shifted from boron to gallium doping in p-type silicon, understanding the recombination behaviour of chromium-gallium (CrGa) pairs becomes crucial. This study assesses the recombination parameters of CrGa pairs in silicon using both injection-dependent lifetime spectroscopy (IDLS) and deep-level transient spectroscopy (DLTS). Customised Czochralski (Cz) silicon ingots with known amounts of intentional Cr contamination during the ingot growth process were used, with wafer resistivities varying across the range of 0.2 Ωcm – 8 Ωcm. The presence of Cr in these silicon wafers was first confirmed by monitoring the CrGa pair association and dissociation processes through lifetime-based measurements, which also confirmed the fully paired state of CrGa pairs. The CrGa concentrations in wafers were confirmed by DLTS. Through IDLS and DLTS, the following CrGa defect parameters were extracted: defect energy level E_t = E_V + 0.47 eV, electron capture cross section σ_n = 5.1 × 10⁻¹⁵cm² and hole capture cross section σ_p = 1.1 × 10⁻¹⁵cm².