Space charge induced variation in silicon double drift IMPATT diode parameters

The effect of space charge on the space charge region (SCR) width, diode voltage and the maximum field in Si double drift IMPATT diode is studied under the operating conditions for various current and doping densities. The rate of increase in SCR width and diode voltage with current density depends appreciably on majority carriers´ space charge. The simple analytical expression for the variation of these parameters with current density is presented. The author´s analytical expression for the variation of SCR width and diode voltage with current density is found to be the best fit throughout the range, while Kuno´s approximate estimation (1979) for the increase of SCR width is valid only at low current densities where the carriers´ space charge is insignificant. The analytical expression and the data are thus useful for the design of practical IMPATT diodes at microwave and millimetre wave frequencies