Modern day integrated circuits comprise millions or billions of transistors devices. Transistors devices operate as switches that allow charge carriers (e.g., electrons) to flow when turned on, and which prevent charge carriers from flowing when turned off. The performance of a transistor is influenced by a charge carrier mobility of a material from which the transistor is made. Charge carrier mobility is a measure of how quickly charge carriers move though a material in the presence of an electric field. Increased charge carrier mobility can provide for faster transistor switching speeds, at a fixed voltage, or lower voltage for the same switching speed.
In recent years, strain engineering has become a widely used method of improving the performance of transistor devices. Strain engineering induces a pressure onto either a channel region and/or onto source and drain regions of a transistor device. The pressure stretches the crystalline lattice of region(s) to increase the distance between atoms beyond their normal inter-atomic distance. By stretching the crystalline lattice, strain engineering increases charge carrier mobility and thereby improves device performance.