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Title: Spectroscopic characterisation of semiconductor laser structures for in-line monitoring in the growth industry
Author: Constant, Stephanie Benedicte
ISNI:       0000 0001 3561 4553
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2003
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We investigate the results of different spectroscopic characterisation techniques on different semiconductor laser structure pre-fabrication wafers, in view of early stage in-line monitoring in the growth industry. We report non-contact, non-destructive angle- (Q) and temperature- (T-) dependent photo-modulated reflectance (PR) studies on visible resonant-cavity light-emitting diodes (RCLEDs). We use lineshape fitting of the PR spectra, the PR "modulus", the PR "amplitude resonance", the PR "symmetry", and the "virtual DeltaSigma2 plot" techniques, to determine the energies of several quantum well (QW) transitions and the relative position of the cavity mode (CM) and the QW ground state energies. We present results of front- and edge-EL performed on a series of different visible edge-emitting laser (EEL) and vertical-cavity surface-emitting laser (VCSEL) structures. We show the existence of a wavelength shift between the front- and TE polarised edge-EL peaks of the EELs and we demonstrate how to obtain the true absorption wavelength from the TE polarised edge-EL peaks of the VCSELs. We finally explain the potential of the edge- EL TM polarisation to determine the strain in a structure. We show that the theta-dependent reflectance (R) measurements performed on 850 nm infrared VCSELs give information about several QW transitions. Indeed, we believe that the changes in the CM dip area, its FWHM and depth are closely related to the QW dielectric function. This is corroborated by PR analyses and EL measurements. We report theta-dependent PR measurements performed on a 980 nm infrared VCSEL. We show that the "symmetry" theory must be used, rather than the "resonance" theory. We define the conditions necessary for the use of the symmetry theory and we demonstrate its potential for the characterisation of samples such as this one; it is possible to obtain the QW ground state transition energy from only two PR spectra measured at different theta. We report non-destructive electro-modulated reflectance (ER) measurements performed on 1450 nm EELs. A comprehensive analysis of the ER, including lineshape fitting, the ER "modulus" method and theoretical calculations, allows the determination of several QW transition energies and the bandgap energy of the barrier and the waveguide-core material, and the refinement of crucial parameters such as the composition of the barrier, waveguide-core and QW layers. These results are corroborated by PR and photo-luminescence measurements, as well as spontaneous emission measurements performed on corresponding devices. Finally, the strength of the built-in electric field in the structure is determined by the analysis of the Franz Keldysh Oscillations in the waveguide-core energy region and a theoretical calculation allows one to determine their origin. Finally, we investigate the effects of adding SiO2/TiO2 dielectric distributed Bragg reflectors (DBRs) on top of a partial AlGaAs-based DBR VCSEL structure, by performing normal incidence R measurements and simulations of prepared structures. Furthermore, the effect of increasing the thickness of the first SiO2 layer on the. CM wavelength is monitored with normal incidence R experiments and simulations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Optics & masers & lasers