Erbium in crystal silicon: optical activation, excitation, and concentration limits

The optical activation, excitation, and concentration limits of erbium in crystal Si are studied. Preamorphized surface layers of Czochralski-grown (Cz) Si(100), containing 1.7x10¹⁸ O/cm³, were implanted with 250 keV Er at fluences in the range 8x 10¹¹-8x10¹⁴ cm^-2. After thermal solid-phase epitaxy of the Er-doped amorphous layers at 600 °C, Er is trapped in the crystal at concentrations ranging from 3x10¹⁶ to 7x10¹⁹ Er/cm³, as measured by secondary-ion-mass spectrometry. Photoluminescence spectra taken at 77 K show the characteristic Er³⁺ intra-4ƒ luminescence at 1.54 µm. Photoluminescence excitation spectroscopy shows that Er is excited through a photocarrier-mediated process. Rapid thermal annealing at 1000 °C for 15 s increases the luminescence intensity, mainly due to an increase in minority-carrier lifetime, which enhances the excitation efficiency. Luminescent Er forms clusters with oxygen: the maximum Er concentration that can be optically activated is determined by the O content, and is (3±1)x10¹⁷ Er/cm³ in Cz-Si. The internal quantum efficiency for electrical excitation of Er in Cz-Si is larger than 3x10^-6.