Multiquantum well structures

Quantum well semiconductor lasers with both single and multiple active layers have been fabricated. Quantum well lasers with one active are called single-quantum-well (SQW) lasers and lasers with multiple quantum well active regions are called multiquantum-well (MQW) lasers. The layers separating the active layers in a multiquantum well structure are called barrier layers. Typical examples of the energy band diagram of both SQW and MQW are schematically represented in Fig. 18. 

Agrawal. N, C. M. Weinert, H.4. Ehrke, G. G. Mekonnen, D. Franke, C. Bornholdt, and R. Langenhorst (1995) "Fast 2x2 Mach-Zehnder optical space switches using InGaAsP-InP multiquantum- well structures" IEEE Photonics technology letters, Vol. 7, No. 6, page no. 644-645, June 1995. 

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

CL(oo,oo n) is realized by superlattice structures such as Si and Ge multiquantum wells, in which n values correspond to the silicon layer thickness. 

New kinds of dilute-nitride type-II InAsN/GaSb laser diodes on InAs substrate with "W" or "M" design are theoretically investigated. For these laser diodes, designed to qjerate at 3.3 im at room temperature, the total threshold current densities are calculated. Under the hypothesis of a total loss coefficient a = 50 cm", these multiquantum well laser structures present a calculated threshold current density J lower than 1.1 kA/cm. ... 

At this stage, it is too early to compare the optical properties of polar and nonpolar lasers. However, our results on homoepitaxial multiquantum wells and optically pumped lasers prove that it is possible to grow high-quality nitride structures along with nonpolar directions. It goes without saying that further research is necessary. 

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