Due to its unique properties GaN is a material useful for a variety of applications but obtaining good quality films is still a challenge. MOCVD is the main method for epitaxial growth of GaN for mass production and the early stages of growth are decisive for the quality of the film. While extensive work has been devoted to GaN in the last decade, the in-situ analysis of MOCVD films has not received the same amount of attention due to experimental difficulties.; Ion beam analysis is a very powerful technique both for bulk and surface analysis that we have used in conjunction with other complementary techniques to look at the early stages of growth of GaN films grown on sapphire substrate. A new MOCVD reactor has been designed built and integrated with the W. M. Keck Thin Film Analysis Facility such that the characterization is performed in-situ without taking the sample out of the ultra high vacuum environment. We have extensively characterized the sapphire substrate after the preliminary preparation that consisted of cleaning and nitridation. After optimizing the growth parameters we have been able to grow wurtzite GaN films in a wide temperature range (450--1050°C) with un-reconstructed surface and of good quality. We have observed the crystalline quality, surface morphology and the growth mode of the films as a function of growth temperature and the film thickness.; Using Ion Channeling we have determined the thickness and temperature range for which the films are either epitaxial single-crystal, polycrystalline with a preferred orientation or polycrystalline randomly oriented. Even though thin films grown at various temperatures have comparable defect densities we observe that when the substrate temperature is higher the rate of defect annihilation as the film grow is high such that we obtain good films within a thickness of approx. 300 nm.; By comparing the channeling and LEED results we observed that samples for which we observe diffraction patterns can in fact be very poor crystals. This is indicative of the fact that surface ordering can be achieved for polycrystalline films and that surface diffraction alone cannot be used as an indication of crystallinity.; The epitaxial films are oriented with the c-axis of the film paralleled with the c-axis of the substrate and the planes rotated by 30° with respect to the substrate. The defects density calculated for these films are similar to the ones obtained by other researchers for much thicker films.
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机译：由于其独特的性能，GaN是可用于多种应用的材料，但是获得高质量的薄膜仍然是一个挑战。 MOCVD是用于外延生长用于大规模生产的GaN的主要方法，生长的早期阶段对薄膜的质量起决定性作用。在过去的十年中，尽管对GaN进行了大量工作，但由于实验困难，MOCVD膜的原位分析并未引起同样的关注。离子束分析是一种用于体积和表面分析的非常强大的技术，我们已将其与其他互补技术结合使用，以研究在蓝宝石衬底上生长的GaN膜的早期生长阶段。设计了一种新型MOCVD反应器，并将其与W. M. Keck薄膜分析设备集成在一起，从而可以在原位进行表征，而无需将样品从超高真空环境中取出。在初步准备工作之后，我们对蓝宝石衬底进行了广泛的表征，包括清洁和氮化。优化生长参数后，我们已经能够在宽广的温度范围（450--1050°C）中生长纤锌矿GaN膜，该膜的表面未经重建且质量良好。我们已经观察到薄膜的晶体质量，表面形态和生长方式随生长温度和薄膜厚度的变化而变化。使用离子通道，我们已经确定了薄膜是外延单晶，具有优选取向的多晶或随机取向的多晶的厚度和温度范围。即使在不同温度下生长的薄膜具有可比的缺陷密度，我们也会观察到，当基板温度较高时，随着薄膜生长，缺陷an灭的速度会很高，从而我们可以得到厚度约为5％的优质薄膜。 300纳米通过比较通道效应和LEED结果，我们观察到观察到衍射图样的样品实际上可能是非常差的晶体。这表明以下事实：可以对多晶膜实现表面有序化，并且不能仅将表面衍射用作结晶度的指示。外延膜的取向是使膜的c轴与基板的c轴平行，并且平面相对于基板旋转30°。这些薄膜的缺陷密度与其他研究人员针对较厚的薄膜得出的缺陷密度相似。
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