Laser diodes?
This section was contributed by Kathy Meehan, meehan@srvr.third-wave.com. The first semiconductor lasers were fabricated in 1962 independently by three different groups (GE, IBM and ???, none of which currently makes semiconductor lasers). They are utilized in a number of different applications, most notably the compact disc players. The commercially available wavelengths cover a spectral range (with a few holes) from the visible to the mid-infrared, with a blue GaN laser on one horizon and HgCdTe lasers on the other. A laser can be described as a gain medium in an optical cavity. In the case of a semiconductor laser, the gain medium is a specific layer, usually sandwiched by a p-type and n-type layer – the reason why they are frequency refered to as laser diodes. The gain medium, generally called the active region, is a direct bandgap semiconductor. The population inversion is created by forward biasing the p-n junction, injecting electrons and holes into the gain medium. These electr
