Analysis and Optimal Design of a Novel SiGe/Si Power Diode for Fast and Soft Recovery

We propose a novel p⁺ (Si_1-xGe_x-n^--n⁺ hetero-junction power diode with three-step gradual changing doping concentration in the base region, and the structure mechanism is analysed. The fast and soft reverse recovery characteristics have been obtained and the optimal design of the changing doping concentration gradient and the percentage of Ge is carried out. Compared to the conventional structure of p⁺ (Si_1-xGe_x-n^--n⁺ with a constant doping concentration, the softness factor S increases nearly two times, the reverse recovery time and the peak reverse current are reduced over 15% for the device with the optimized concentration gradient, while the forward drop is almost unchanged. Taking into account of the improvement of the whole characteristics of the novel device, we obtain the optimal percentage of Ge to be 20%.