Controlling voltage drops in silicon diodes by electron irradiation and thermal treatment

Abstract

High-frequency limiting rectifier diodes are used in power sources for rectifying alternating current, in protective elements of radio-electronic equipment, and in switching devices. They are the basis of energy-saving devices, meeting the high requirements for power limit and performance. The main task in the manufacturing process of high-frequency diodes is to ensure the low leakage current and the optimum value of the forward voltage drop which can be compared with the contact potential difference of the p–n junction.
This paper is devoted to studying the effect of radiation exposure and subsequent heat treatment on the current-voltage and capacitance characteristics of high-frequency silicon diodes. The authors studied p⁺–p–n–n⁺ diodes made of n-type KEF-4 (КЭФ-4) silicon wafers with an initial thickness of 235 μm. Radiation processing was performed using an ELU-6 (ЭЛУ-6) linear electron accelerator. The integral flux of "fast" electrons ranged from 1,0·10¹⁵ to 2,6·10¹⁷ cm^–2, energy was 1.5 MeV, density was 1,7·10¹¹ — 5,5·10¹³ cm^–2·s^–1. Heat treatment was performed for 5 hours at a temperature of 90°C in a special chamber.
The studies have shown that heat treatment lead to a shift of the forward current-voltage characteristic to a region of lower voltages (i.e., a given current can be reached at a lower voltage); at low current values, however, the voltage drop may increase after heat treatment. Reverse current decreased fivefold, resulting in a decrease in power output. At the same time, the temporal characteristics of the diode could also be improved by reducing the capacitance (to one order of magnitude).