A DLTS Study on Deep Trench Processing-Induced Trap States in Silicon Photodiodes

We present a Deep Level Transient Spectroscopy (DLTS) study on dedicated test samples to investigate the defect landscape of deep trench (DT) sidewalls. The DT is commonly used to prevent crosstalk between two neighboring optoelectronic devices or as a separator between different functional blocks on a monolithic semiconductor chip. However, in minority carrier-based optoelectronic devices, such as photodiodes, carriers might recombine at trap states located at the DT to silicon interface causing performance degradation. The extracted parameters of the DLTS study are further utilized to investigate this recombination in terms of TCAD simulations. The results suggest that carrier recombination at the DT sidewalls of DT-terminated photodiodes may lead to non-linear responsivities with respect to the optical radiant flux. Furthermore, on the example of silicon dangling bonds, we investigate the influence of structural relaxations at the defect sites which are incorporated in the nonradiative multiphonon (NMP) model. By a comparison between the NMP model to the conventional Shockley-Read-Hall (SRH) model we show, that a difference in the emission barrier of approx. 50 meV will arise, resulting in a strong shift of the corresponding DLTS transients.