<p>A detailed study is presented of power and spectral measurement methodology commonly used to characterize and optimize the fundamental continuous-wave properties of semiconductor lasers. These properties include: efficiency, optical loss, the temperature sensitivity of threshold, gain, and spectral linewidth. The techniques studied are found to often yield erroneous or misleading results. The conditions under which errors can occur are investigated and precautionary measures necessary to avoid these problems are outlined. The effect of well number, length, and temperature on efficiency and optical loss is investigated. A phenomenological model based on inter-valence band absorption (IVBA) for the description of the results is developed. The model provides evidence of the importance of IVBA in determining laser characteristics, including the failure to lase. The operating regime where IVBA dominates is found to be clearly identifiable. It is also found that, in the presence of IVBA, there exists a poptential for misleading measurements of the internal efficiency and the optical loss. Using the high temperature sensitivity of the gain coefficient, it is possible to obtain an indication as to whether IVBA is affecting the experimental results. In order to study the temperature dependence of the threshold current, a derivation of the empirical Tmax relation is given which provides meaning to the fitting parameters. The experimentally determined Tmax is shown to correlate with the Tmax predicted from data obtained by the IVBA model for a range of lengths and well numbers. The conditions under which the Tmax relation is valid are determined. The gain coefficient for lasers having five quantum wells is calculated theoretically and compared to the gain coefficient obtained experimentally both from the IVBA model for efficiency and from the length dependence of the threshold current density. The efficiency method agrees with theory to within experimental error. However, the threshold method yields a value which is approximately one-half of the theoretical value, a phenomenon which has been previously observed in the literature but for which no explanation has been found. Direct measurement of the below-threshold output spectrum of the lasers demonstrates that the cause of this discrepancy is an unexpected length dependence of the gain coefficient. Non-uniform carrier injection into the quantum wells is suggested as a possible physical mechanism. A potential for gross inaccuracies in the measurement of laser linewidth using the delayed self-homodyne (DSH) technique is discovered. It is found that the accuracy of the DSH technique depends on the amount of noise in the laser bias current source to a previously unappreciated degree. This is due to a combination of the high FM sensitivity of semiconductor lasers and the long optical delay lines required by the DSH technique. The errors behave in a manner usually associated with intrinsic 1/f noise, and can cause all of the associated properties of residual linewidth, floor, non-Lorentzian lineshape, and premature re-broadening of the laser line. Guidelines for proper filtering of the current source are given to ensure accurate measurements.</p> / Doctor of Philosophy (PhD)

<p>A miscibility gap exists in the InGaAsP/InP system of heterostructures such that a lateral composition modulation (LCM) occurs on the surface during growth resulting in the production of InAs-rich and GaP-rich regions within the layer. As a consequence, the important material properties relevant to optoelectronic device performance, such as the carrier mobility, luminescent properties and surface morphology, are less than optimum. Hence, this work investigates the influence of LCM on the structural and optical properties of InGaAsP quantum wells and thick layers grown by gas source molecular beam epitaxy on (100) InP substrates. Two novel growth techniques, argon plasma-assisted epitaxy and atomic hydrogen-assisted epitaxy, are developed to reduce the LCM. The reduction in LCM obtained with plasma-assisted epitaxy is explained in terms of the presence of atomic hydrogen within the argon plasma stream. A detailed atomistic model, including surface reconstruction effects based on reflection high energy electron diffraction observations, is developed to describe the surface-mediated processes that occur during growth in the presence of atomic hydrogen. A simple rate equation is used to understand the reduced LCM in terms of a decreased surface diffusion length of adatoms.</p> / Doctor of Philosophy (PhD)

<p>A multi-component defect model for degradation in semiconductor lasers is derived, discussed, and compared to experimental data and other existing degradation models for semiconductor lasers. The degradation model was designed to describe the change of threshold current as a function of aging time and is based on a population growth model in which only limited resources for the creation or growth of defects exist. Besides degradation, defect-annealing effect is incorporated into the multi-component model to examine high-power lasers that exhibit an annealing effect. A compatible lifetime estimation scheme is derived, discussed, and compared to the Hartman-Dixon method [Appl. Phys. Lett. 26, 239 (1975)] for lifetime estimation. Photoluminescence topography was utilized to probe the surface stability of semiconductor lasers during aging. A degradation of photoluminescence yield was observed at the active region. The degradation signifies an increase of surface recombination velocity. However, the reflectance of the surface is not modified by the aging-induced photoluminescence degradation.</p> / Doctor of Philosophy (PhD)

<p>An examination of the die bonding of semiconductor diode lasers is presented. The effects of changing a number of bonding parameters such as reflow time, reflow temperature, and cooling rate on InP-based diode laser chips are investigated. Lasers bonded with both preform solder and pre-deposited solder are explored. It is also observed that stress relaxation occus in die bonds of diode lasers after a time period of hundreds of hours. A finite element method model that iteratively fits to degree of polarization of photoluminescence data is presented. It is shown how this model is used to determine components of stress and strain owing to die bonding at the facet of diode lasers. The model is shown to be capable of helping to characterize die bonds. The effect of die bonding induced strain on the spectra of distributed feedback diode lasers is also investigated. Bonding strain effects the in situ grating in distributed feedback lasers which manifests as changes in the modes of the output spectrum and the stopband width. As well, it is observed that the lasting mode can flop from one side of the stopband to the other upon bonding and this effect is successfully modelled using a DFB laser model.</p> / Doctor of Philosophy (PhD)

<p>Cadmium processing of ZnGa₂O₄films provides a new fabrication route for phosphor powders and thin films. It relies on the enhanced diffusion due to the large vacancy concentration left by the sublimation of cadmium. Photoluminescent powders can be made with a single high temperature firing. Thin film devices can be processed at a significantly lower temperature, expanding the range of available substrates. Powders and thin films of ZnGa₂O₄: Mn were fabricated using starting materials in which between 0% and 50% of the ZnO was substituted by CdO. It was found that the emission spectra of the various compositions was unaffected by the change in composition, peaking at 504 nm, with the colour coordinates x=0.08 and y=0.69. The invariance of the emission spectrum is due to the spinel crystal structure exhibited by the compound. However, the maximum PL brightness was obtained from powders in which 10% of the ZnO had been substituted by CdO in the starting materials. The improved brightness is the result of better manganese incorporation which resulted from CdO sublimation during processing. This left a large vacancy concentration which enhanced the diffusion, and hence the manganese incorporation. In the case of thin films sputtered from cadmium processed targets, the composition of the films as deposited closely mirrored that of the target starting materials. The as deposited films were not luminescent and had to be annealed in vacuum in order to activate the manganese. EDX of these films showed that all of the cadmium had sublimed during the anneal. Very long anneal times also resulted in the loss of zinc. The decomposition products were amorphous or nanocrystalline. These films had an identical PL emission to the powders. The loss of cadmium correlated with the onset of bright 254 nm photoluminescence in the films, indicating that cadmium loss aided in the activation of the manganese. This was the result of the enhanced diffusion due to the large vacancy concentration left by the sublimed material, which aided the incorporation and activation of the manganese. The cadmium in the sputtering targets also impacted the crystal structure of the films. Films from cadmium free targets exhibited a strong (111) x-ray diffraction peak, while those from cadmium processed targets more closely resembled the powder structure. The optimum thin film electroluminescent performance was obtained for films sputtered from targets processed with between 5% and 15% cadmium substituted for zinc. This was the result of improved diffusion during the anneals, due to the sublimation of cadmium oxide and the resulting large vacancy concentration. The best performance was obtained for films annealed at between 875∘C and 900∘C for 6-12 hours. These films exhibited both the maximum luminance (55 cd/m² at 60Hz) and the lowest transferred charge (~20 μC/cm²). This combined for a peak efficiency of 0.5 Im/W at 60 Hz). Beyong 12 hours at 900∘C or temperatures higher than this, EL performance degraded due to the decomposition of thin film. It was concluded that the luminescent performance of this material is strongly influenced by the loss of cadmium during processing. The enhanced diffusion afforded by the cadmium sublimation results in improved EL performance at annealing temperature lower than that of pure zing gallate.</p> / Doctor of Philosophy (PhD)

<p>Distributed feedback (DFB) semiconductor lasers have a periodic modulation of refractive index, or Bragg grating, in the active region of the device. The Bragg grating causes a wavelength dependent distributed feedback of light. This thesis develops a below-threshold model for the spectra of DFB lasers. The model is shown to treat spontaneous emission in a manner that is quantum mechanically correct. Most other models in the literature do not treat spontaneous emission correctly, and are shown to yield spurious spectral predictions for truncated quantum-well DFB lasers. Techniques for fitting the model to spectral data are explained, and the model is demonstrated to be a useful diagnostic tool for understanding the performance and behaviour of DFB lasers. The effects of facet phase on DFB laser spectra are documented and explained. The model is then expanded to the above threshold regime, and is used to predict correctly spatial hole burning phenomena in DFB laser spectra.</p> / Doctor of Philosophy (PhD)

<p>This thesis documents the development of a new optoelectronic device capable of functioning as a high resolution wavelength monitor near 1.55 μm. The primary objective of this work was to devise a simple and potentially low cost approach to monitor wavelength shifts in wavelength division multiplexing (WDM) networks and fiber Bragg grating optical strain sensors. The presented technique utilizes in-line pairs of quantum well waveguide photodiodes fabricated in an InGaAsP /InP material system. The ratio of photocurrents produced between two consecutive waveguide detectors is taken as a sensitive measure of wavelength near the absorption band edge of the quantum wells. The device is shown to function over the conventional wavelength band with near pm wavelength sensitivity, while performing independently of the optical input power and signal polarization. The simultaneous monitoring of several incoming wavelengths is also demonstrated, where arrays of in-line detectors are utilized with a wavelength demultiplexer. In this thesis, several unique methods are presented to improve the performance of the devices, including the use of the quantum confined Stark effect to expand the wavelength operating range and to reduce the thermal sensitivity. Finally, as a practical demonstration, the in-line detectors are used to track the small wavelength shifts induced in various types of fiber Bragg grating optical strain sensors.</p> / Doctor of Philosophy (PhD)

<p>Wavelength tunable ultrashort pulses are generated with mode-locked InGaAs/GaAs semiconductor lasers mounted in an external cavity. A broad tuning range is achieved through the use of an asymmetric quantum well (AQW) structure in the active region of the devices. Furthermore, the incorporation of a bend in the waveguide of the devices results in a broadband, low modal reflectivity. This allows the lasers to be mode-locked in a compact, linear external cavity. Passive mode-locking of dual asymmetric quantum wen deviceshave produced pulses 2 to 5 ps in duration, tunable from 954 nm to 1015 nm. Compression of the pulses using a modified grating pair compressor has yielded optical pulses as short as 510 fs. Similar devices based on a triple asymmetric quantum well active region are capable of producing pulses 2 to 11 ps in duration under passive mode-locking, tunable from 942 nm to 1017 nm. Preliminary work with long wavelength InGaAs/GaAs lasers has resulted in pulses 2 to 5 ps in duration with average output powers ranging from 750 /-lW to 1.8 mW. Pulse compression yields pulses as short as 570 fs. The synchronization of a passively mode-locked semiconductor laser to a mode-locked Ti:Sapphire laser, using an all-optical synchronization method, is studied. The parameter space is explored in order to determine the operating conditions that yield optimal synchronization of the two lasers. Good qualitative agreement is obtained between a simple theoretical model of the synchronization process and the corresponding experimental measurements. It is also shown that the synchronization of the mode-locked semiconductor laser with a femtosecond laser provides an additional means by which the mode-locked semiconductor laser can be characterized.</p> / Doctor of Philosophy (PhD)

<p>This thesis details the results of femtosecond laser ablation and micromachining of indium phosphide (InP). The experimental results presented consist of six sets of investigations divided into two categories: I) single and multiple pulse ablation of stationary samples; 2) laser micromachining and analysis of grooves cut in InP. The first series of experiments dealt with the analysis of the final state of InP after single and multiple pulse irradiation. The experiments were perfonned with femtosecond pulses, 60 -175 fs in duration, centered around wavelengths of 400, 800, 660, 800, 1300 and 2100 nm. In the first set of investigations, single pulse laser ablation craters on InP and GaAs were studied via scanning and plan-view transmission electron microscopy. The final state of the material near the laser-ablated region following femtosecond ablation was characterized in detail for three selected laser fluences. In the second set of investigations, single pulse ablation threshold measurements were performed in the wavelength range from 400 - 2100 nm, covering the photon energy above and below the bandgap of InP. The ablation thresholds detennined from depth and volume measurements varied from 87 mJ/cm2 at 400 nm to 250 mJ/cm2 at 2050 nm. The measurements were performed with optical microscopy, atomic force and scanning electron microscopy. In addition, sharp onsets of the measured depths versus laser fluence were observed at the ablation thresholds. In the third set of investigations, laser induced periodic surface stnlctures were investigated on the surfaces of InP, GaP, GaAs, InAs, Si, Ge and sapphire after multiple pulse femtosecond laser irradiation in the wavelength range from 800 - 2100 nm. High spatial frequency periodic stnlctures were observed on surfaces of InP, GaP, GaAs and sapphire. The periods of the structures were 4.2 - 5.1 times smaller than the free space wavelength of the incident radiation. Conditions required for formation of these ripple stnlctures were identified. The second series of experiments dealt with the analysis of the final state of the material after the cutting of grooves in InP under conditions potentially encountered in practical applications. The experiments can be grouped into three sets of investigations. In the fourth set of investigations, the ablation rate for grooves micromachined with ~ 150 fs pulses centered around 800 nm was investigated as a function of pulse energy, feed rate, number of passes over the same groove, and the light polarization relative to the cutting direction. A logarithmic dependence of the groove depth on the laser Iluence was observed with two regimes characterized by different ablation rates and different thresholds. The groove depth was found to be inversely proportional to the feed rate or equivalently, linearly proportional to the effective number of pulses delivered. With multiple passes over the same groove the depth was found to increase linearly up to approximately 20 consecutive passes. Above 20 passes the ablation rate decreased until a depth limit was asymptotically approached. The best results in terms of groove geometry and depth limit were obtained for grooves cut with the polarization of the beam perpendicular to the cutting direction. In the fifth set of investigations, the residual strain fields resulting from laser micromachining of grooves in InP with femtosecond and nanosecond pulses centered around 800 nm were analyzed using a spatially resolved degree-of-polarization photoluminescence technique. Significant differences in the geometry of the strain patterns were observed in grooves machined in the two temporal domains. The experimental data were compared with results from a finite element model. In the sixth set of investigations, grooves micromachined in InP with femtosecond and nanosecond pulses were investigated by cross- ectional transmission electron microscopy. Substantial densities of defects, extending over a few microns in depth, were observed beneath the grooves machined with femtosecond pulses. The high peak power density and the stress confinement caused by irradiation with femtosecond pulses, along with incubation effects, were identified as the major factors leading to the observed plastic deformations.</p> / Doctor of Philosophy (PhD)

<p>This thesis involved the characterization of InP and InGaAsP grown by He-plasma-assisted gas source molecular beam epitaxy. Samples were typically grown under standard GSMBE conditions, in terms of growth rate and substrate temperature, except for the presence of a low energy helium plasma generated from an electron-cyclotron resonance source. These materials exhibit increased resistivity and faster optical response times with respect to standard materials grown without the plasma. The unusual properties are believed to be caused by the impact of the plasma particles during growth. Samples were characterized under various doping and anneal conditions using Hall effect measurements, temperature-dependent resistivity studies, positron annihilation spectroscopy, photoluminescence and SIMS analysis. Undoped He-InP was weakly n-type as-grown, with a carrier concentration much lower than that of standard InP, suggesting that electron traps were present. On anneal, the carrier concentration decreased further, implying that donor-like defects had been removed. The sample doped with 3 × 1017 cm-3 Be was also n-type; the Be was found to be compensated by donor-like defects. Positron annihilation measurements indicated the presence of single and divacancy defects, which enlarged upon anneal. The characterization of the quaternary constituted the core of the experimental work. He-InGaAsP exhibited the wane trends as the binary He-InP. The undoped and Si-doped samples exhibited low carrier concentrations, indicating the presence of electron traps. Annealing removed these electron traps. The samples doped with <2 × 1018 cm-3 Be were weakly n-type as-grown, but became p-type on anneal, suggesting the removal of donor-like compensating defects. Samples doped with >2 × 10 18 cm-3 Be were p-type as grown, but the hole concentration was lower than expected. As for the He-InP, positron annihilation spectroscopy indicated the presence of neutral or negatively-charged open volume defects that increased in size on anneal. None of the He-InGaAsP samples exhibited photoluminescence until annealed at temperatures of ∼600°C. To estimate the energy levels and concentrations of the defects responsible for the unusual properties of the quaternary, a Fermi-Dirac model was fitted to the Hall effect data. Two donor-like and two acceptor-like levels were identified.</p> / Doctor of Philosophy (PhD)