Impact of Surface Effects on RF Switching PIN Diodes

This paper presents a study of the impact of surface conditions on PIN diode resistance and carrier lifetime. The discussion shows that large radius PIN diodes exhibit less impact from surface conditions than do smaller radius devices. Knowledge of this feature is important for microwave and RF design engineers working in both high and low power applications. PIN diodes used in high power applications often need to be of wider radius to handle the larger current densities associated with the high-power operation, and so see a reduction of influence from the surface. PIN diodes in receive applications, where small cross section devices are often used, will see an associated greater influence of the surface on their operation. The advantage of the smaller radius device is that the capacitance of the device will be lower, impacting the upper frequency limit that these devices may be used. The discussion is verified with a series of measurements on carrier lifetime and resistance of PIN diodes of various geometries.