Quantum-cascade-laser active regions on metamorphic buffer layers

Abstract

ABSTRACT S trained -layer superlattice (SL) structures have been grown by metalorganic vapor phase epitaxy (MOVPE ) on m etamorphic 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 P m wavelength r ange while suppress ing carrier leakage from the upper las er level . Thick (10 -12 P m) compositionally -graded, hydride -vapor -phase -epitaxy (HVPE) -grown MBL structures are employed. To improve the planarity of the MBL surface, we e m ploy 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 In x Ga 1-x As (wells)/Al y In 1-y As (b arriers) SLs grown on the MBL s are characterized by x -ray diffraction (XRD). Intersubband electroluminescence emission is observed in the 3.5 P m wavelength range from devices employing such SL structures .