Room temperature characterisation of InGaAlAs quantum well laser structures using electro-modulated reflectance and surface photovoltage spectroscopy



In this study, two tri-metal quaternary InGaAlAs quantum well (QW) laser structures grown on InP are compared to a conventional InGaAsP QW structure, also grown on InP, all designed to lase at 1.55 μm. Several spectroscopic methods are used to study the samples including surface photo-voltage (SPV) and electro-modulated reflectance (ER). In the tri-metal samples the ground- and two excited-state QW transitions are detectable in both types of spectroscopy. The SPV and ER give results in agreement to within a few meV of each other. By comparing the position of the measured QW transitions with those predicted theoretically, the conduction band offsets of the tri-metal samples can be determined and compared to that in the InGaAsP sample. It is found that the tri-metal samples have a much larger conduction band offset of ∼66% compared to the ∼40% in the InGaAsP sample. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)