Keywords

Nitride, InGaN, GaN, Thermodynamics, epitaxy

Abstract

Nitride semiconductor materials have been used in a variety of applications, such as LEDs, lasers, photovoltaic cells and medical applications. If incandescent bulbs could be replaced by white GaN LEDs, they would not only provide compactness and longer lifetime, but this would also result in huge energy savings. A renewed interest in InGaN emerged recently after it was discovered that the band gap for InN is 0.7eV, instead of the previously published value of 1.9eV. Thus InGaN solid solutions cover almost the whole visible spectrum, from a band gap of 3.34eV for GaN and 0.7eV for InN. Hence, InGaN can have excellent applications for photovoltaic cells. The objective of this work was to investigate and search for new ways of synthesis of nitrides. We studied the thermodynamics and evaluated chemical compatibilities for the growth of AlN, GaN, InN and their solid solutions from metallic solvents. The compatibility between potential substrate, crucible and solvent materials and various growth atmospheres was evaluated from Gibbs free energy calculations. Most of the nitride synthesis experiments performed by other groups were at higher temperatures (around 2,000C) and pressures up to 1GPa using different growth methods. Therefore, their results could not be extrapolated to our growth system, as their growth conditions were significantly different from ours Moreover, to the best of our knowledge; no-one has ever evaluated such compatibilities by thermodynamic calculations. We used those calculations to design our experiments for further studies on nitrides. Experimentally, we encountered fewer issues such as corrosion problems than others observed with their growth procedures, because near-atmospheric pressures and temperatures not exceeding 1,000C could be used. Preliminary experiments were performed to confirm the thermodynamic computations and test the behavior of the chosen system. A suitable configuration was found that allowed to nucleate films of InGaN on the templates. Nitride templates or 'Buffer layers' were used to saturate the solution and grow the films. A relatively simpler configuration, to create a temperature gradient in the solution was used. Two templates were placed in the crucible, one at the top and the other one at the bottom. The temperature was raised to 950C and they were soaked there for 15-20hrs. After the growth the surface morphology was analyzed using an optical microscope and it was found to be entirely different for both the templates. The atoms from the top template dissolved and attached at the bottom template. This can be explained by the thermal gradient between the two templates: one at the bottom was at lower temperature than the top template, so there was diffusion from the top substrate towards the bottom one. AFM studies were carried out on the film to study the surface morphology of the top and the bottom templates. Growth hillocks having step height typically between 15 and 50 nm were observed. Such hillocks were not present on the templates before the experiment.

Notes

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Graduation Date

2007

Semester

Summer

Advisor

Klemenz, Christine

Degree

Master of Science in Materials Science and Engineering (M.S.M.S.E.)

College

College of Engineering and Computer Science

Department

Mechanical, Materials and Aerospace Engineering;

Degree Program

Materials Science and Engineering

Format

application/pdf

Identifier

CFE0001806

URL

http://purl.fcla.edu/fcla/etd/CFE0001806

Language

English

Release Date

July 2008

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

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