The quantum cascade laser is a semiconductor light source based on resonant tunnelling and optical transitions between quantised conduction band states. In these devices the principles of operation are not based on the physical properties of the constituent materials, but arise from the layer sequence forming the heterostructure. The quantum design and the control of the layer thickness, down to an atomic mono-layer, allows one to ascribe into a semiconductor crystal, artificial potentials with the desired electronic energy levels and wavefunctions. In recent years the performance of quantum cascade lasers has improved markedly and this semiconductor technology is now an attractive choice for the fabrication of mid-far infrared lasers in a very wide spectral range (3.5-160 μm). At present, the best performances are reached at wavelength between 5-10 μm, but recent results on new material systems with deeper quantum wells are indicating that this technology will be soon available also in the 3-5 μm spectral region.
We report GaInAsSb/GaSb multiple quantum well lasers with type-II band alignment operating at room temperature. Basic properties of GaInAsSb/GaSb system in presence of strains are presented. Room temperature lasing has been achieved at wavelengths up to 2.65 micrometer. For the first time, stimulated emission has been obtained from a type-III quantum well structure at room temperature at 1.98 micrometer and 2.32 micrometer for the structures with 6- and 12-angstrom-thick InAs quantum wells, respectively. Modification of the band structure near interfaces of the type-II quantum wells due to carrier injection is shown to be a decisive factor allowing to obtain low threshold lasing in quantum well structures with indirect radiative recombination.
Low threshold lasers based on GaInSbAs/GaSb type-II QW structures operating between 2 and 2.4 micrometers at room temperature have been fabricated. The RT threshold current density as low as 305 A/cm2 was obtained for a 900- micrometers -long laser emitting at 2.36 micrometers . High efficiency of indirect radiative recombination is explained by accumulation of holes in potential wells situated in barrier layers near the QW interfaces.
Using a grating coupler technique, we report on accurate determinations of bulk and mode refractive indexes in the 1.5 micrometers wavelength region. On the one hand, InP bulk refractive index is measured within a relative accuracy of 10-3 as a function of wavelength range, temperature, and for two doping levels. On the other hand, quantum effects are evidenced on index measurements using a GaInAs multiquantum well waveguide. As a result, it is shown that the guided mode birefringence is strongly enhanced as predicted from energy levels and selection rules of fundamental electronic transitions.
We present the liquid phase epitaxy growth (LPE) of GaInAsSb/( 1 00) GaSb and InAsSbP/( 1 00) InAs near their miscibility gap (MG) boundaries. The conditions f or growing latticematched layers of optoelectronic quality are given. The cut-off wavelength limitations due to the MG are : 2. 4 p. m for GaInAsSb and 2. 6 p. m for lnAsSbP. As an example of application results are presented on LPE grown photodiodes based on these quaternary alloys. 1 -
In the present work, we report the systematic observation of the optical blue shift induced by electric field in a
GaAs/GaAIAs double-well system as far as 18 meV at room temperature. To this end, a detailed electroreflectance study of
a GaAs-Alo.3 Gao.7 As double quantum well structure was carried out at room temperature. This effect occurs at moderate
values ofthe applied field. In addition, a computer modeling of the electric field dependent optical properties is presented,
which is based upon a variational calculation, in the frame of the effective mass approximation. The calculated spectra agree
with the expefimental results. The model was used to engineer a coupled QW structure, which optimises the achievable
modulation depth, due to application of an electric field.