Electrical characteristics of thin-base semiconductor diodes

The influence of device parameters, circuit parameters (where applicable) and operating conditions on the current/voltage characteristics and switching behaviour of thin-base diodes (i.e. diodes for which the p-n junction and ohmic contact are separated by a thin uniform base layer) is examined. An expression is derived for the saturation current in terms of the base width and surface recombination velocity of the ohmic contact. The relationship between reverse current and voltage accounts for the non-saturation of reverse current resulting from the decrease in the effective base width with increase in voltage. Current and voltage measurements to test the validity of the theory are given. The rate of decay of minority-carrier storage charge when the diode is switched from forward to reverse conduction is treated theoretically, taking into account for the first time the finite surface recombination velocity of the ohmic contact. An expression is also obtained for the independent rate of discharge of the depletion layer. Finally, switching from reverse to forward conduction is discussed.