Intersubband lasers based on the subband dispersion of inverted mass

We propose a novel intersubband laser based on transitions between subbands in the k-space region where the light-hole effective mass is inverted. We consider GaAs/AlGaAs quantum well (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 QWs which produce closely spaced subbands in energy that are strongly coupled. Laser wavelength determined by this energy separation is typically in the THz range. The laser structure is designed to facilitate electrical pumping with a quantum cascade scheme consisting of isolated single GaAs/AlGaAs QWs. 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 locally in k-space between the two subbands 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 pump current density on the order of 100A/cm(2) .