Research On The Growth Of GaN With Bonding-thinned Template And Its Defects

Because of big direct bandgap, high carrier mobility, high breakdown voltage and inertness, GaN-based materials have promising application for light-emitting diodes, laser diodes, detectors and power devices. However, due to the lack of native GaN substrate, most of GaN-based materials and devices are epitaxial grown on foreign substrate, such as sapphire, SiC and Si. A hindrance to take full advantage of GaN is the high threading dislocations (TDs) density which originates from the lattice mismatch and the difference of thermal expansion coefficient between GaN and the substrates. The best solution is epitaxial growing GaN-based materials and devices on native free-standing GaN substrate. Because of low cost and relatively simple structure as well as high growth rate (dozens of micron to hundreds of micron per hour), HVPE is considered one of the most promising method to produce high quality bulk GaN crystal. In this paper, GaN crystal was successful grown by HVPE. The specific research contents are as follows:1. Gases distribution in HVPE reactor was simulated by Fluent software. The effect of different Ⅴ/Ⅲ and source gases to the uniformity of gas distribution in HVPE reactor was studied. The optimal Ⅴ/Ⅲ to the homogeneity of gas distribution was obtained. Then, on the basis of the optimal Ⅴ/Ⅲ, appropriate parameters for GaN of excellent homogeneity and high rate were gained. According to the simulation results, the growth parameters were adjusted and high quality GaN crystal was obtained. Also, the experiment cycle was shortened.2. On the basis of successfully grown GaN on sapphire, the stress in GaN was analyzed. Theory model was established to calculate the mismatch stress in GaN. According to this model, we concluded the method to reduce the stress and improve quality of GaN, then bonding-thinned template was designed and fabricated. By adapting parameters, GaN was successfully grown on the novel template. The characterization, such as HRXRD, Raman and PL, confirmed that the stress in GaN was greatly reduced and the quality of GaN was improved to a great extent.3. Molten eutectic of alkali was used to study the threading dislocations and positron annihilation technique was employed to analyze the native vacancies in GaN. The research results showed the connection between threading dislocations and native vacancies as well as dependence of the two defects on Ⅴ/Ⅲ.In conclusion, gas distribution in HVPE reactor, mismatch stress and defects in GaN were studied. Some important and novel experiment results were obtained.