Comparison Of Gallium Arsenide And Silicon PIN Diodes For High Speed Microwave Switches

By M/A-COM Technology Solutions, Inc.

Introduction

Silicon PIN diodes have been the most important semiconductor component used for the control of microwave signals for many years. Their major utilization has been for switching or variable attenuation elements to control RF power at frequencies from H.F. through millimeter frequency.

As systems requirements have placed increasing emphasis on extremely rapid switching, the ambipolar mobility of the Silicon material has placed limitations on switching speeds for Silicon PIN diodes. These limitations are presently in the range of a "few" nanoseconds for present "fast" Silicon PIN diodes. The major limitation for PIN switching speed is the removal of the charge or carriers used to produce a low impedance in forward bias. The charge removal is limited by the carrier mobility and the thickness of the I-layer necessary to support a moderate breakdown voltage (i.e., 30-100 volts).

Gallium Arsenide has several advantages over Silicon when making fast PIN diodes of similar dimensions. GaAs also has a few major disadvantages which limit the type of devices that can be produced. This paper will discuss these characteristics as they effect the type of GaAs PIN diode that can be built and the usage of GaAs PIN diodes in fast, moderate power switches.