A novel intersubband laser based on the inverted-effective- mass feature of valence light-hole subband is investigated. Such inversion is a result of the interactions between subbands, which is much stronger in valence band of most diamond and zinc-blend semiconductors. Unlike the conventional conduction-band intersubband lasers, the proposed laser does not require elaborate and delicate engineering of quantum wells (QWs). We consider GaAs/AlGaAs QW structures which give rise to several confined subbands including ground state heavy-hole subband (HH1) and light- hole subband (LH1). The inverted-effective-mass feature in subband LH1 emerges only in wide QW structures which produce closely spaced subbands in energy that are strongly coupled. The energy separation between subbands LH1 and HH1 is typically below the optical phonon energy in the THz range. Laser wavelength determined by this energy separation is 62 microns for a well width of 7 nm. The laser structure is designed to facilitate electrical pumping with a quantum cascade scheme consisting of multiple GaAs QWs isolated by AlGaAs barriers. Our calculation shows that with only a small fraction of the carrier population in the upper subband (LH1), it is still possible to achieve population inversion between the two subbands locally in k-space where the light-hole effective mass is inverted. Our result indicates that optical gain in excess of 150/cm can be achieved with a relatively small pumping current density on the order of 100A/cm$+2$/.
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