Spectroscopic analysis of external stresses in semiconductor quantum-well materials
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Spectroscopic analysis of external stresses in semiconductor quantum-well materials Jens W. Tomm,1 Mark L. Biermann,2 B. S. Passmore,3 M. O. Manasreh,3 A. Gerhardt,1 and Tran Q. Tien1 1 Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, 12489 Berlin, Germany 2 Department of Physics and Astronomy, Moore 351, Eastern Kentucky University, Richmond, KY 40475, U.S.A. 3 Department of Electrical Engineering, Bell Engineering Center, University of Arkansas, Fayetteville, AR 72701, U.S.A. ABSTRACT We present an approach for spectroscopic strain analysis in semiconductor quantum-well devices. This approach is applicable to all types of semiconductor materials, and to spectroscopic techniques which employ the electronic band-structure of the material, such as photoluminescence, photoreflection, photocurrent, and transmittance. The approach is based on two components, namely the theoretical calculation of the strain-sensitivity of the spectral positions of the relevant quantum-confined optical transitions within a particular quantum-well, and the spatially resolved measurement of a substantial part of the optical transition sequence within the quantum-well. The primary experimental technique applied in our approach is photocurrent spectroscopy. InAlGaAs/GaAlAs/GaAs, high-power lasers serve as the model species.
INTRODUCTION Semiconductor structures such as quantum-wells (QW) are frequently designed as strained systems. This kind of strain, called intrinsic or built-in strain, is created during epitaxial growth and is caused by the lattice mismatch between the different semiconductor materials. During fabrication (processing, packaging) and operation, a quantum-well device such as a semiconductor laser might experience additional stresses of known or arbitrary symmetry. We refer to these as external stresses, which result in an additional strain contribution. We present an approach for analyzing quantum wells experiencing built-in strain that allows for the quantification of external stresses of known symmetry, and of the externally-induced strains that arise due to these stresses. For special cases, the approach also provides results regarding the symmetry of the additional stresses and induced strains. The approach is based on two main components. The first is the theoretical calculation of the strain-sensitivity of the spectral positions of the relevant quantum-confined optical transitions within a particular QW. These results are published separately [1] and are, in part, reproduced in the theory-section. Secondly, spectroscopic experiments are conducted, and the results are presented here. These experiments can be classified into two groups: those which are designed to check the theory, and those which employ the theory in order to translate spectroscopic data into quantitative information about strain in packaged, commercial high-power diode laser arrays, so-called cm-bars.
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There are several experimental techniques suitable for spectroscopic strain analysis, such as Ram
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