What is a characteristic feature of a semiconductor laser?

A semiconductor laser, often referred to as a laser diode, is characterized primarily by its construction from semiconductor materials such as gallium arsenide or indium phosphide. This distinct material allows it to efficiently convert electrical energy into light, enabling it to be electrically pumped. This feature is crucial because it allows for compact and efficient designs that can be integrated into various electronic systems, making semiconductor lasers widely used in applications ranging from communication to consumer electronics.

Being electrically pumped means that when an electrical current passes through the semiconductor material, it generates a population inversion necessary for lasing. This is unlike other types of lasers, which may use different mechanisms for achieving energy conversion and population inversion, such as gas or solid-state lasers.

Other characteristics, such as emitting a continuous wave or being made from glass, are not defining features of semiconductor lasers. While some semiconductor lasers can emit continuous waves, they are also capable of pulsed operation, showcasing their versatility. Further, the notion that they can only operate with gas is incorrect, as their primary operation relies on the properties of solid-state semiconductor physics. Thus, the unique construction and operational mechanism using semiconductor materials and electrical pumping are what distinctly define a semiconductor laser.