| 摘要 |
PCT No. PCT/GB90/01365 Sec. 371 Date Feb. 26, 1992 Sec. 102(e) Date Feb. 26, 1992 PCT Filed Sep. 4, 1990 PCT Pub. No. WO91/03758 PCT Pub. Date Mar. 21, 1991.By forming quantum well (QW) structures with two different heterojunctions having different band offsets it is possible to form QWs having, when subjected to optical excitation, dipoles. The presence of a dipole in a narrow enough well results in QWs having absorption edges which, unlike those of conventional QWs can be shifted to the blue by application of an electric field of appropriate polarity.
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