We propose a rare-earth/semiconductor combination so that the wavelengths of the dominant emission from the rare-earth Ion transitions are shorter than that of the band-edge emission of the host semiconductors as depicted in Figs. 1(a) and (b). In Fig. 1(a), a double-heterostructure laser with a built-in pn junction for carrier injection into the active layer is shown under a high injection level.1 As a result, the quasi-Fermi level for electrons EFc and holes EFV lie within the conduction band and valence band, respectively, as depicted in Fig. 1(b). Here it is also postulated that the upper level (excited state) of the rare-earth ion lies above the conduction-band edge of the host semiconductor, while the lower level (ground state) lies just above or below the valence-band edge. Although there exist no firm experimental data on the relative position on the energy scale of the rare-earth levels with respect to the band edges of the semiconductor, some speculations may be appropriate.

© 1987 Optical Society of America

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