Gallium-arsenide diode lasers

In a laser diode, population inversion of charge carriers in a semiconductor is achieved by a very high electric field across a pn junction in gallium arsenide. Most laser diodes operate at red and near-infrared wavelengths (680-1 550 nm). 

Fig. 12. Details of an aluminum gallium arsenide semiconductor diode laser.

Soft, silver white metal that melts in the hand (29.8 °C) and remains liquid up to 2204 °C (difference 2174 °C, suitable for special thermometers). Gallium is quite widespread, but always in small amounts in admixtures. Its "career" took off with the advent of semiconductors. Ga arsenide and Ga phosphide, which are preferential to silicon in some applications, have extensive uses in microchips, diodes, lasers, and microwaves. The element is found in every mobile phone and computer. Ga nitride (GaN) is used in UV LEDs (ultraviolet light-emitting diodes). In this manner, a curiosity was transformed into a high-tech speciality. 

Infrared diode lasers are used in compact disc players and laser printers, and in bar code readers (see Chapter 11). They are solid-state devices, typically constructed of gallium arsenide, and energy is pumped into them at a low potential... 

Gallium aluminum arsenide in solar cells Gallium arsenide phosphide in light-emitting diodes Gallium arsenide infrared detectors, lasers, and photocopiers... 

Heterostructures in the (In,Ga,Al)P/Ga(As,P) systans are being used increasingly in diode lasers, various types of transistors, as well as in LEDs [15-17]. The latter are now available in all the primary colours. Most widely used LEDs are red emitters based on gallium phosphide/arsenide combinations (Tables 12.59 and 12.60). 

The first semiconductor laser devices were made from chips of gallium arsenide (see Fig. 1). The gallium arsenide was grown such that a p-n junction, or diode, was formed inside the crystal. The chip had a metallic base with a wire contact attached to the top to allow the injection of the electrical current. Smooth end faces were formed on the diode, which acted as mirrors to provide the optical feedback necessary to attain laser oscillation, while the sidewalls of the laser chip were roughened to prevent laser oscillation in the direction perpendicular to... 

In recent years, semiconductor fabrication techniques have progressed to an extent that permits the construction of highly complex integrated devices such as the distributed Bragg-reflector (DBR) laser diode shown in Figure 7-9. This device contains a gallium arsenide /in-junction diode that produces infrared radiation at about 975 nm. In addition, a stripe of material... 

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