Semiconductor materials are essential for modern electronics. Many semiconductor based devices (such as computers and mobile phones) have become an inseparable part of everyday life. The best known and most widely used semiconductor material is silicon but many others have important applications as well. Wide-band-gap semiconductors are needed for light emitting devices operating in the blue or ultraviolet spectral regions, such as white light emitting diodes (LEDs) and blue lasers (for example, for high-density optical data storage in discs similar to DVDs) which can already be found in many homes.