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This thesis is concerned with a quantitative study of intermixing in GaAs/AlGaAs and ZnSe/ZnCdSe single quantum well semiconductor structures. In this study, a method of iterative isothermal anneals and photoluminescence used to characterize this phenomenon has enabled the evolution of the diffusion coefficients for the interdiffusion process with anneal time to be followed. The blue-shift emissions arising from this method are predicted by a model based on Fick's law of diffusion. This model is developed in an attempt to relate the energy shift that is observed experimentally to the diffusion length. The mixing is modelled using an error function expression to solve the diffusion equation so as to describe the variation in well shape which is attributed to compositional disordering induced during thermal processing. Using this approach, where evidence of intermixing was monitored, the emission would be expected to shift measurably. Data has been taken to cover a wide temperature range to establish values for the activation energy EA. From this data, it has been found that the diffusion coefficients at various temperatures are thermally activated with an energy of 3.6 +/- 0.2 eV in GaAs/AlGaAs. The data is compared with the available literature data taken under a wide range of experimental conditions. We show that despite the range of activation energies quoted in the literature all the data appears to be consistent with a single activation energy. Departures from the 'mean' value are ascribed to experimental uncertainties in determining the diffusion coefficients for example, to fluctuations in the composition of the material, to techniques used, or to a wide range of perturbations. Photoluminescence observations on ZnSe/ZnCdSe show that an improvement in the optical quality of these quantum well structures was found for anneals at temperatures (~500°C). A value of EA = 2.9 +/- 0.3 eV was derived from the experiments for the interdiffusion process over a 250 K temperature range and four decades of interdiffusion coefficient. The interdiffusion process of both these systems was inferred to be Fickian with no dependence on alloy composition or strain.

<p> This work presents theoretical calculations of some of the most important electrical characteristics of thin film, insulator-dominated semiconductor devices. Solutions of prespecified accuracy for an a.c. transmission line model of the semiconductor in such configurations as the MIS (Metal-Insulator-Semiconductor) structure and the SIS (Semiconductor-Insulator-Semiconductor) structure are given. Together with an accurate solution of the d.c. bias problem, exact C-V (Capacitance-Voltage) and G-V (Conductance-Voltage) characteristics can be found at any frequency. SRH (Shockley-Reed-Hall) impurity centres and surface states have been included in both the d.c. and a.c. solutions. In addition, accurate studies of the low temperature dopant impurity response can be made since the d.c. solution uses full Fermi integrals over arbitrary densities of states with the impurity dopant band treated like an SRH centre for the a.c. solution.</p> <p> In non-equilibrium situations, such as those which occur with the application of light or carrier injection by tunnelling, the a.c. solution requires active elements in the transmission line model but the transmission line can still be solved to a prespecified accuracy provided an accurate solution of the d.c. bias problem can be found. In this thesis the d.c. solution for the case of light-induced pair production is considered under the assumption of bulk controlled d.c. quasi Fermi level shifts. Thus the accuracy of the related a.c. conductance and capacitance solutions is dependent on the reliability of this assumption.</p> <p> The detailed treatment of the a.c. admittance of the MIS structure is justified by its technological importance and fundamental insight gained on impurity centre and surface state effects.</p> <p> The other work presented in this thesis is devoted to a study of a new thin film device structure, the SIS diode. First, the a.c. admittance characteristics for the thick insulator case are predicted to a prespecified accuracy. Then a simple treatment for part of the SIS d.c. tunnelling problem is done to qualitatively predict the effects of such parameters as doping density, temperature and insulator thickness on current-voltage characteristics. Finally, a simple generalization of the a.c. transmission line to include the effects of tunnelling is given which allows accurate solution for the a.c. admittance of tunnelling SIS diodes if the complete d.c. non-equilibrium problem can be accurately solved.</p> <p> Practical application of the thick-insulator SIS diode will undoubtedly stem from its wide range of interesting low and high frequency response characteristics. Among the most interesting of these characteristics is a bell-shaped high frequency C-V response previously unobserved in other two terminal devices.</p> <p> An interesting negative resistance feature, which partly resembles the negative resistance region of the p-n junction tunnel diode, is analyzed for the degenerate SIS p-i-n thin insulator structure. While the thick insulator SIS device has recently been fabricated and the bell-shaped high frequency response experimentally observed, experimental verification of the tunneling characteristics of the SIS diode has as yet not been fully realized.</p> / Thesis / Doctor of Philosophy (PhD)

[pt] A integração monolítica de um modulador com um guia de onda é de muito interesse para aplicação em comunicações ópticas pelo fato de que podemos diminuir as perdas por acoplamento óptico entre os dois dispositivos e usar moduladores curtos que operem em altas taxas de transmissão de dados. O crescimento epitaxial seletivo é uma das técnicas mais promissoras na atualidade para aplicação na integração monolítica de dispositivos semicondutores. Esta técnica permite controlar a espessura e a tensão das camadas crescidas seletivamente permitindo otimizar a integração e as características das estruturas dos dispositivos. A tese trata da implementação, do estudo e da aplicação do crescimento epitaxial seletivo por MOCVD de estruturas casadas e tensionadas de poços quânticos múltiplos de InGaAs/InAlAs para a fabricação de moduladores de amplitude baseados no efeito Stark e sua integração com guias de onda. O desempenho dos moduladores, baseados em estruturas de poços quânticos múltiplos de InGaAs/InAlAs que operam em 1,55 ym, é notavelmente melhorado quando é introduzida uma composição de 52% de Ga na liga e se tem um poço de ~100 A de espessura. Nesse caso, os moduladores possuem uma elevada figura de mérito e podem ser insensíveis à polarização. Nesse estudo foram crescidas várias amostras onde foi analisado o aumento na taxa de crescimento e a variação na composição das ligas de InGaAs e InAlAs em material bulk e em poços quânticos de InGaAs/InAlAs em função da geometria da máscara utilizada, i.e. diferentes larguras do dielétrico e largura da janela onde ocorre o crescimento fixo. Finalmente foram processados guias de onda cujas estruturas foram crescidas com a técnica de crescimento seletivo. Esses guias foram caracterizados por técnicas de campo próximo. / [en] The monolithic integration of a modulator with a waveguide is a lot of interest for application in optical communications for the fact in that can decrease the losses for optical joining between the two devices and to use short modulators that operate in high rates of transmission data. The selective growth is at the present time, one the more promising technique for application in the monolithic integration of semiconductors device. This technique allows to control the thickness and the stress of the grown layers allowing to improve the integration and the characteristics of the devices structures. These thesis is about the implementation, study and application of the selectuve growth by MOCVD of both match and tensile structures of multi quantum wells of inGaAs/InAlAs for the production of the amplitude modulators based on the Stark effect and its integration with waveguide. The performance of the modulators based on structures of multi quantum wells of InGaAs/InAlAs operating in 1,55 um, is notably improved whena Ga composition of 52% is used and the thickness of a quantum well is near to ~100 A. In that case, the modulators have a high figured of merit and they can be insensitive to the polarization. In this study, several samples was grown and the growing rate increase was analyzed and the variation of the composition in InGaAs and InAlAs in bulk alloys and in quantum wells of InGaAs/InAlAs in function of the window where the growth is spent. Finally, waveguides were processed whose structures were grown with the technique of selective growth. Those guides were characterized by the near field technique.

Tato dizertační práce se zabývá modelováním mikrovlnných polovodičových struktur. Stále vyšší pracovní kmitočty komunikačních systémů zvyšují nároky na aktivní prvky a přenosová vedení, realizované zpravidla v monolitické integrované podobě. Přenosová vedení s rozprostřeným zesílením představují perspektivní řešení nejen jako zesilovací prvky, ale také jako aktivní napáječe mikrovlnných antén. V součastné době neexistuje vhodný softwarový nástroj pro jejich efektivní simulaci a návrh. První část této práce je zaměřena na implementaci termodynamické formulace modelu driftu a difuze pro numerickou simulaci transportních procesů polovodičových struktur v komerčním programu COMSOL Multiphysics. Další část je věnována implementaci Gunnova jevu v makroskopické aproximaci a vypracování simulační procedury pro analýzu struktur využívajících tento jev. Poslední část je věnována návrhu a analýze aktivních přenosových vedení a zlepšení jejich vlastností.

The emperical pseudopotential method in the large basis approach was used to calculate the electronic bandstructures of bulk semiconductor materials and layered semiconductor heterostructures. The crucial continuous atomic form factor potentials needed to carry out such calculations were determined by using Levenberg-Marquardt optimization in order to obtain optimal cubic spline interpolations of the potentials. The optimized potentials were not constrained by any particular functional form (such as a linear combination of Gaussians) and had better convergence properties for the optimization. It was demonstrated that the results obtained in this work could potentially lead to better agreement between calculated and empirically determined band gaps via optimization / Physics / M. Sc. (Physics)

The emperical pseudopotential method in the large basis approach was used to calculate the electronic bandstructures of bulk semiconductor materials and layered semiconductor heterostructures. The crucial continuous atomic form factor potentials needed to carry out such calculations were determined by using Levenberg-Marquardt optimization in order to obtain optimal cubic spline interpolations of the potentials. The optimized potentials were not constrained by any particular functional form (such as a linear combination of Gaussians) and had better convergence properties for the optimization. It was demonstrated that the results obtained in this work could potentially lead to better agreement between calculated and empirically determined band gaps via optimization / Physics / M. Sc. (Physics)