In 4H silicon carbide, aluminum implantation causes unusual high compensation ratios as obtained from Hall effect investigations by fitting the neutrality equation with a single acceptor. We show that this approach cannot fully describe the experimental data, in particular in case of moderate doping and at high measurement temperatures above 450 K. We develop two extended models by adding an additional acceptor- or donor-like defect to the equation. Both approaches describe the data well. However, it turns out that an additional aluminum-correlated acceptor is the more reasonable choice. In this case, the compensation ratio stays almost independent of the implantation dose between 30 % and 40 %. The deep acceptor is located at EV + (280–400) meV.

In this work, we analyze compensating defects which are formed after implantation of aluminum (Al) into n-type 4H-SiC epitaxial layers and subsequent thermal annealing. These defects reduce the expected free charge carrier density by 84% for a low doped layer with [Al]impl≈ 9ž·1016cm-3and by 27 % for a high doped layer with [Al]impl≈ 2·ž1019cm-3. Furthermore, an electrical activation ratio of implanted aluminum ions of 100 % is calculated. The ionization energy of implanted aluminum as measured by Hall effect and admittance spectroscopy ranges from 101 meV to 305 meV depending on the doping concentration.

Lifetime-engineering in 4H-SiC is important to obtain a low forward voltage drop in bipolar devices with high blocking voltages above 10 kV. It is known that the implantation of carbon and subsequent thermal annealing can be used to improve the minority carrier lifetime of as-grown epitaxial layers due to annihilation of carbon vacancies and, therefore, reduce the lifetime limiting defect Z1/2. In this paper, the ion implantation of other ions (N, Al, B, and As) besides carbon and their impact on minority carrier lifetime and point defect concentration are shown. Special attention is paid to the effect of ion implantation with subsequent electrical activation by high temperature annealing. A strong influence of the implantation dose and, therefore, corresponding resulting doping concentration was found. A lifetime enhancement could be found for some implanted species for higher implantation doses whereas the detrimental effect of high temperature annealing dominated at low implantation doses. The results reveal that the implantation dose and the occupied lattice sites are important parameters to achieve a lifetime enhancement. A model is presented which explains the different impacts of various implanted ions and a more detailed understanding of lifetime-engineering by ion implantation. With this knowledge, it was possible to reduce the detrimental Z1/2 defect in a large part of thick epitaxial layers with conventional shallow ion implantation and high temperature annealing. Consequently, the minority carrier lifetimes of the epitaxial layers could be enhanced.

In this work, a lateral 4H-SiC n-LDMOS transistor, based on the principle of a reduced surface field due to charge compensation, is investigated by numerical simulations, in order to find adequate fabrication parameters for a lightly doped p-type epitaxy in combination with a higher doped channel region. The purpose of this work is the integration into an existing technology for a 10 V 4H-SiC-CMOS process. The simulations predict in a blocking voltage of 1.3 kV in combination with an On-resistance of 17 mΩcm2 for a device with a RESURF structure with a total implanted Al concentration of 6∙1016 cm-3 and a depth of 1 μm, a field plate of 5 μm and a drift region of 20 μm. The threshold voltage varies from 5 V to 10 V, depending on the thickness of the gate oxide (50 nm to 100 nm).

The prediction of the compensation induced hole concentration reduction in implanted Al regions is a key parameter in developing high power SiC devices. Hall effect measurements are commonly used to determine the compensation ratio of Al implanted regions. Due to the fact that this measurement method is rather complex, an approximate method was developed by using transfer length method structure measurements in combination with a TCAD simulation model. The determined compensation ratios from this work’s simulation and from Hall effect measurements from literature show consistent compensation ratios. Based on this data a fit function was derived which allows for estimating the compensation ratio for a wide Al concentration range.