Solid state refers to electronic components, devices, and systems that are based entirely on semiconductor materials, such as silicon, germanium, or gallium arsenide. These solid-state systems utilize diodes and transistors, which are two common types of solid-state devices. Diodes are electronic components that allow current to flow in one direction while blocking it from the other direction. They can also serve as rectifiers, converting alternating current (AC) to direct current (DC). Examples of diodes include laser diodes, P-N junction diodes, and light-emitting diodes (LEDs).