Complementary Metal Oxide Semiconductor (CMOS) transistor structures are essential in many modern electronic devices. CMOS chips include microprocessor, microcontroller, static RAM, and other digital logic circuits. A primary advantage of CMOS logic is that it only uses significant power when its transistors are switched between the on and off states. As a result, CMOS devices use little power and produce little heat.
CMOS structures are “complementary” in that a single CMOS device requires one PMOS transistor and one NMOS transistor, only one of which is switched on at a time. Traditionally, the PMOS transistor and the NMOS transistor in a CMOS device are both made of the same material, but are doped differently to provide the desired characteristics. High hole mobility is desirable for PMOS devices, and high electron mobility is desirable for NMOS devices. When the same material is used for both the NMOS and PMOS devices, often a tradeoff is made between high hole mobility and high electron mobility. For example, silicon, the most prevalently used semiconductor material, has a high electron mobility of 1400 cm2/Vs, but only a moderate hole mobility of 450 cm2/Vs.