Abstract

The long wavelength of quantum cascade (QC) lasers mediates against good confinement of the optical mode to the waveguide core and so a thick, 'plasma-enhanced' waveguide¹ is normally used. However, one disadvantage of this waveguide is that mesa-etching usually needs to be used in order to achieved good electrical confinement; otherwise, the high doping level leads to extensive current spreading. Mesa-etching removes the material adjacent to the waveguide so that the lateral heat extraction from the core is much reduced. This is undesirable as heat dissipation is of prime importance in QC lasers, owing to the high electrical power required for operation and the dependence of performance on the non-equilibrium phonon population. We report a fabrication technique which provides electrical and optical confinement by conversion (rather than removal) of the Al_0.48In_0.52As upper cladding to a native oxide (see Figure 1). In this technique, planar (vertical) selective thermal wet oxidalion (PSWOX), the oxidation reaction begins at the AlInAs surface and proceeds downwards through the semiconductor using H₂O to convert the AlInAs into an oxide mainly composed of amorphous matrix (AlO_x, As), with crystallised In2O₃² This results in a planar device geometery with improved thermal properties. Here, the technique was applied to a QC laser design similar to Faist et al..¹ The initial results arc presented which show that the technique produces QC lasers with high output power, high slope efficiency and a reduced temperature dependence of the threshold current (larger T₀) compared to their mesa-etched counterparts.

© 2000 IEEE