Quantum-Cascade-Laser Active Regions on Metamorphic Buffer Layers

Strained-layer superlattice (SL) structures have been grown by metalorganic vapor phase epitaxy (MOVPE) on metamorphic buffer layers (MBLs) for application in intersubband-transition devices, such as quantum cascade lasers. Using the MBL as an adjustable lattice-parameter platform, we have designed relatively-low-strain quantum-cascade-laser structures that will emit in the 3.0-3.5 mu m wavelength range while suppressing carrier leakage from the upper laser level. Thick (10-12 mu m) compositionally-graded, hydride-vapor-phase-epitaxy (HVPE)-grown MBL structures are employed. To improve the planarity of the MBL surface, we employ chemical mechanical polishing (CMP) followed by wet chemical etching prior to the growth of the SL/device structures. We find that the wet-chemical etching step is crucial to remove residual damage introduced during CMP. 20-period InxGa1-xAs (wells)/AlyIn1-yAs (barriers) SLs grown on the MBLs are characterized by x-ray diffraction (XRD). Intersubband electroluminescence emission is observed in the 3.5 mu m wavelength range from devices employing such SL structures.