A fast avalanche Si diode with a 517 μ m low-doped region

Abstract

A silicon-avalanche shaper/sharpener is a fast-closing semiconductor switch. For positive voltages, it is activated by a high-voltage pulse at its cathode, and, when turned on, the current through the device rises rapidly. Using Synopsys TCAD software, a p+−n−n+ diode is numerically studied. It was shown that for the case of a high-doped active n region, 1014 cm−3, the breakdown process exhibits a fast electric field propagation, as expected. For a low doped active n region, <1011 cm−3, the electric field spreads uniformly along the structure. For this case, we show that the rise time, of the order of 100 ps, is not limited by the active region thickness, allowing the use of a thicker substrate in order to increase the operating voltage. A p+−n−n+ diode was fabricated on a thick, 525 μm, float-zone n-type Si (100) substrate, with a resistivity of 104 Ω cm. The active region, n<1012 cm−3, was 517 μm. When a stack of five, 8 mm2, diodes was driven by an ∼100 kV, 2.26 ns rise time pulse, the output voltage was 46 kV with the rise time and rise rate per diode of 215 ps and 38.4 kV/ns, respectively. When a single, 4 mm2, diode was driven by a 14 kV, 1 ns rise time pulse, the output on a 50 Ω load was around 8 kV, 100 ps, with a rise rate of 57 kV/ns. These results exceed the present state-of-the-art diodes. Furthermore, the thick active region eliminates current fabrication process difficulties such as deep diffusion or thick epitaxial layers.