Double Heterojunction Lasers

Schematic of the energy bands of a double heterojunction laser. The Fermi level is above the conduction band edge in the n-AlGaAs and below the valence band in the p-GaAs. Forward biasing the junction (below) causes the electrons to spill over into the active p-GaAs region where they are confined by the higher bandgap AlGaAs. The confined inverted population in the active region promotes stimulated emission.

Because there are two changes ia material composition near the active region, this represents a double heterojunction. Also shown ia Figure 12 is a stripe geometry that confines the current ia the direction parallel to the length of the junction. This further reduces the power threshold and makes the diffraction-limited spreading of the beam more symmetric. The stripe is often defined by implantation of protons, which reduces the electrical conductivity ia the implanted regions. Many different stmctures for semiconductor diode lasers have been developed. 

Eig. 10. Schematic of various LED and laser diode stmctures where S signifies material of a lower energy band gap (a) homojunction, (b) double-heterojunction (DH), and (c) multiquantum well (MQW) stmctures. 

Semiconductor laser diodes are widely used in CD players, DVDs, printers, telecommunication or laser pointers. In the structure, they are similar to LEDs but they have a resonant cavity where laser amplification takes place. A Fabry-Perot cavity is established by polishing the end facets of the junction diode (so that they act as mirrors) and also by roughening the side edges to prevent leakage of light from the sides of the device. This structure is known as a homojunction laser and is a very basic one. Contemporary laser diodes are manufactured as double heterojunction structures. 

Double helixes, self-recognition in the self- assembly of, 16 803 Double-heterojunction (DH) structures, for LEDs, 22 173, 174, 175 Double heterostructure (DH), 14 844 Double heterostructure laser diodes, 14 700 Double hetero structure OLEDs, 22 216 Double-immunodiffusion technique, 9 753-754... 

General Motors Research Laboratories (GMR). Molecular beam epitaxial (MBE) growth of Pbi xEuxSeyTei y lattice-matched to PbTe substrates has been used to fabricate double heterojunction diode lasers, including quantum well, large optical cavity (LOG) devices, the first such TDL structures reported for a lead-salt compound. These Mesa stripe... 

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