Structural and compositional characterization of widebandgap semiconductor heterostructure by ion beam analysis

• Autores: Andrés Redondo Cubero
• Directores de la Tesis: Elías Muñoz Merino (dir. tes.), Raúl Gago Fernández (tut. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2010
• Idioma: español
• Tribunal Calificador de la Tesis: Carlos Palacio Orcajo (presid.), Rafael Pérez Casero (secret.), Mykola Vinnickenko (voc.), Gastón García López (voc.), Adrián Hierro Cano (voc.), Katharina Lorenz (voc.), Olga Caballero Calero (voc.)
• Materias:
  • Física
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • his thesis addresses the application of ion beam analysis (IBA) to the study of several wide bangdap semiconductor heterostructures. The studies carried out along this thesis were motivated by the need of improving the epitaxial growth of the active and base layers composing high electron mobility transistors (HEMTs) and high-power optoelectronic devices. At the same time, this thesis explores the advantages and limits of ion beam techniques for the structural and compositional characterization of such heterostructures, as an alternative and complement to X-ray diffraction methods.

    Next, the main aspects considered within this work are specified.

    Concerning the growth of base layers on sapphire, the effect of the nucleation layers and the temperature was investigated for GaN and ZnO, respectively. The results obtained in this research were used to determine the optimum conditions for the growth of GaN and ZnO layers, especially regarding the crystal quality and the adequate incorporation of the different elements to the wurtzite lattice.

    As an important point for the development of HEMTs, the presence of Al gradients affecting the AlGaN/GaN interface was studied by different IBA techniques. Such compositional Al profiles were examined together with the induced strain relaxation.

    The application of IBA in very thin AlGaN layers is also tackled for two different base layers. In relation with this study, high-resolution depth profiles of hydrogen were developed in samples prepared by different growth methods. The relevant role of the indiffusion mechanisms for the introduction of hydrogen in the two-dimensional electron gas of HEMTs is explored.

    This memory also deals with the difficult growth of high-quality ternary InGaN layers associated to the low miscibility of In inside the GaN matrix. This phenomenon is investigated for a series of samples covering the whole compositional range and grown with different substrate temperatures. The deterioration of the crystal quality of InGaN layers for intermediate contents of In is verified and evaluated as a function of the progressive relaxation of the lattice parameters. The critical effect of the temperature in this sense is emphasized. The obtained results helped to establish a growth diagram of InGaN on the basis of the effective composition.

    The bandgap engineering in MgZnO films is investigated in terms of the Mg content to determine the dependence of the electrical properties on the stoichiometry. These layers are also used for N doping by means of ion implantation. The optimization of the thermal annealing processes after the implantation to recover the crystal quality and the dopant activation is carried out and checked with additional photoluminiscence studies.

    Finally, the studies showed in this thesis about lattice-matched AlInN and AlGaInN heterostructures revealed the synergy of the III/V ratio and the substrate temperature on the growth of epitaxial layers, affecting the crystal quality and the composition. The strain state of the films was analyzed by ion channeling and X-ray diffraction, evidencing the presence of anomalous channeling behaviors. Monte Carlo simulations explained these phenomena, linked to the steering effects of the projectiles at the interface. These simulations were also used to establish the role of the tetragonal distortion, thickness, and beam energy on this effect. The breakdown of the anomalous channeling is demonstrated theoretically and experimentally in specific lattice-matched heterostructures, allowing the accurate determination of the strain state.