Extracting surface recombination parameters of germanium-dielectric interfaces by corona-lifetime experiments

The interest in germanium (Ge) is rising for use in field-effect transistors, (space) photovoltaics, and silicon photonics. Suppressing and understanding carrier recombination at the Ge surface are vital for the performance of Ge in these applications. In this work, we have investigated the surface recombination at various germanium-dielectric interfaces (Ge/Al2O3, Ge/SiNx, Ge/GeOx/Al2O3, and Ge/a-Si:H/Al2O3). For this purpose, we performed corona-lifetime experiments and extracted a set of recombination parameters by fitting the data with the theoretical Girisch model. To keep the model straightforward, the distributions of the capture cross sections and the interface defect density (D i t) were parameterized. The importance of each parameter in these distributions was examined so that a minimum number of parameters was distilled: the so-called fundamental recombination velocities (S p 0 and S n 0) and the magnitude of the D i t near the valence and conduction band edge (D it, VB and D it, CB). These parameters form together with the fixed charge density (Q f), the spatial distribution thereof (σ Q), and a minimum surface recombination velocity (S min), a set of parameters that can well describe our experimental data. Relevant insights were obtained from the experiments, with highlights including a Ge/GeOx/Al2O3 stack with virtually no fixed charge density, a highly passivating Ge/a-Si:H/Al2O3 stack, and a negatively charged Ge/SiNx stack. The findings in this study are valuable for applications where a more profound understanding of recombination at Ge surfaces is of concern, such as in photonics, photovoltaics, and nano-electronics.