We invistegated the characteristic of GaN grown on LiAlO2 substrate by molecular epitaxy beam. We observed the c-plane GaN crystalls assembled at the step-edge of M-plane GaN terraces, with 200 nm ~ 600 nm diameter and 300 nm height. Furthermore, we also observed that there are two kinds of formations for c-palne GaN: one is grown from the hexagonal plane of LAO, the other is transformed from the defeat of M-plane GaN. In addition, we changed the growth ratio and concluded some relation between the quality of thin film and roughness of surface. We expect to improve the quality of M-plane GaN and the size and density of c-plane GaN single-crystals by changing growth conditions.

The dominant research subjects are focused on the growth of high quality stoichiometric undoped CuInSe2 epitaxial films by molecular beam epitaxial growth. For MBE growth, it is possible to obtain the high quality epitaxial films and to get the reproducibility and stability of the composition and properties of epilayers by controlling the growth parameters carefully. Under the conditions of fixed Cu molecular beam flux and excess Se molecular beam flux, we can control the In/Cu compositon ratio by changing In molecular beam flux to get stoichiometric and In-rich or Cu-rich epitaxial films. We hope it can be used in the manufacture of solar cell and get high conversion efficiency.

The objective of this proposed study is to develop the new material CuInSe2 for large area, low cost and high efficiency commercial CuInSe2 based solar cell for the solar resource in Taiwan. The compositions of CuInSe2 films are modulated precisely to obtain an ideal electrical and optical characteristics resulting in high conversion efficiency for commercial solar cell applications. Numerous experimental investigations have shown the electrical properties of undoped CuInSe2 are dominated by various types of electrically active intrinsic defects caused by the deviations from the ideal stoichiometry. Without any intentional doping CuInSe2 can be made n-type and p-type conducting with carrier concentrations varying over many orders of magnitude either by slightly changing the composition of the material during growth or by appropriate post-growth annealing procedures. Several attempts have been made successfully by the crucial construction and application of intrinsic defect chemistry model to investigate the trend in the conductivity of CuInSe2, however, there investigation still remain no clear evidence to directly correlate composition and electrical properties reported by several authors, and the results of experimental data shows in contradiction to the intrinsic defect model. According to the point defect model, that samples with DX¡Õ0 and larger values of |DY| are always n-type conducting, and sample with DX>0 and DY>0 are always p-type conducting. In addition, as DX<0 and DY<0, the dominant defect pair calculated from the point defect model is VCu and InCu, their concentrations varies as a function of DY. Once DY is relatively more negative, [VCu] increase and that forms [VCu]¡Ö[InCu]. Therefore, the electrical conductivity of CuInSe2 changed from n-type to p-type. The Growth model of MBE is considered to investigate the reactive mechanism of epitaxial growth. At 500¢J, the BEP of In and Cu molecular beam fluxes supplied were 5¡Ñ10-8~5¡Ñ10-7 torr for the MBE growth of CuInSe2 films. The change of Se molecular beam flux not only affect the composition of CuInSe2 films, but also the deviation from molecularity DX and the deviation from valence stoichiometry. As Se molecular beam flux increase to 10-6 torr, the concentrations of dominant defects show to decrease about three orders. Thus, the increase of Se BEP results in increasing the mobility as well as the conductivity. On the whole, this study is based on the simulation to investigate the mechanism of MBE. It could be used to control precisely the composition of CuInSe2 films leading to obtain the electrical characteristics for solar cell design.

InN thin films were grown on £^-LiAlO2 (100) by plasma-assisted molecular-beam epitaxy (PAMBE). Structural properties were investigated by reflective high-energy electron diffraction (RHEED), x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). XRD measurements showed that the crystal orientation of InN films was non-polar m-plane (11 ¡Â00). In addition, from SEM images, a striped morphology was observed along [112 ¡Â0]. Optical properties were characterized by photoluminescence (PL) spectroscopy, cathodoluminescence (CL) spectroscopy and micro-Raman scattering. Both CL/PL results revealed that InN films have a luminescence-emission peak-energy of about 0.65 eV. Carrier concentration had been determined by Hall measurements.

In this thesis , we study the surface morphology of InN thin film grown on O-polar ZnO substrate by Macular Beam Epitaxy with varied N/In flow ratio. In addition, we also observe the difference to surface of InN between the substrate have been thermal annealed or not. We analysis the samples¡¦ surface morphology and lattice structures with many different ways, such as atomic force microscope, scanning electron microscope, reflection high energy electron diffraction,transmission electron microscope, X-ray diffraction analysis and transmission spectrum measurement. From the results of SEM and AFM,while the N/In ratio increased for the process of epitaxy, InN thin film¡¦s surface would become much smooth but accompany some pin holes on the surface which indicates that there exist the interaction between substrate and InN thin film. In the X-ray diffraction analysis, the greatest value of Full Width at Half Maximum (FWHM) we get is 94.44 (arcsec) to the (0002) surface of InN that confirm pretty high quality of InN thin film grown on O-polar ZnO substrate have been made. Furthermore, the band gap measured by transmission spectrum is wider for the N/In ratio increasing either which may be caused by the formation of InxNyOz.

The group III nitride semiconductor grown on c-plane sapphire by radio frequency plasma assisted molecular beam epitaxy has been studied. To archive good quality GaN thin film, nitridation and low temperature AlN buffer layer were applied to overcome the issue of lattice mismatch. Low temperature and long period nitridation process shows better improved of optical properties and crystal quality of GaN film. Buffer layer grown with slightly Ga-rich, substrate temperature at 600¢J, for 20 minutes leads to better GaN thin film. High substrate temperature and sufficient nitrogen to gallium ratio are two important factors to control the growth of the good quality GaN epilayer. We have grown M-plane GaN films with self-assembled c-plane GaN nanopillars on a £^-LiAlO2 substrate by plasma-assisted molecular-beam epitaxy. The diameters of the basal plane of the nanopillars are about 200 to 900 nm and the height is up to 600 nm. The formation of self-assembled c-plane GaN nanopillars is through nucleation on hexagonal anionic bases of £^- LiAlO2. Dislocation defects were observed and analyzed by transmission electron microscopy. From the experimental results, we developed a mechanism underlying the simultaneous growth of three-dimensional c-plane nanopillars and two dimensional M-plane films on a £^-LiAlO2 substrate.

Im Mittelpunkt der vorliegenden Arbeit steht die Herstellung ultradünner epitaktischer Galliumnitrid-Schichten auf einem Siliziumkarbid-Substrat mit dem Verfahren der ionenstrahlgestützten Molekularstrahlepitaxie. Für die Analyse der Oberflächentopographie der Galliumnitrid-Schichten direkt nach der Abscheidung – ohne Unterbrechung der Ultrahochvakuum-Bedingungen – wurde ein Rastersondenmikroskop in die Anlage integriert. Als weitere Hauptanalysenmethode wurde die Reflexionsbeugung hochenergetischer Elektronen zur Bestimmung der Oberflächenstrukturen in situ während der Schichtabscheidung eingesetzt. Weiterhin wurden die Galliumnitrid-Schichten hinsichtlich ihrer strukturellen Eigenschaften mittels Röntgenstrahl-Diffraktometrie, Röntgen-Photoelektronenspektroskopie und Transmissionselektronenmikroskopie ex situ charakterisiert. Wesentliches Ziel dieser Arbeit war die Herausstellung des Einflusses maßgeblicher Abscheidungsparameter (vor allem Substrattemperatur und Gallium-Depositionsrate) auf die Schichteigenschaften sowie die Optimierung dieser Wachstumsparameter. Besonderes Augenmerk lag auf der Untersuchung der Auswirkungen des Stickstoffion-zu-Galliumatom-Verhältnisses und des Einflusses der niederenergetischen Ionenbestrahlung auf das Galliumnitrid-Schichtwachstum im Frühstadium. Dies betrifft hauptsächlich den Wachstumsmodus (zwei- oder dreidimensional) und die Bildung der hexagonalen oder der kubischen Phase.

Im Mittelpunkt der vorliegenden Arbeit steht die Herstellung ultradünner epitaktischer Galliumnitrid-Schichten auf einem Siliziumkarbid-Substrat mit dem Verfahren der ionenstrahlgestützten Molekularstrahlepitaxie. Für die Analyse der Oberflächentopographie der Galliumnitrid-Schichten direkt nach der Abscheidung – ohne Unterbrechung der Ultrahochvakuum-Bedingungen – wurde ein Rastersondenmikroskop in die Anlage integriert. Als weitere Hauptanalysenmethode wurde die Reflexionsbeugung hochenergetischer Elektronen zur Bestimmung der Oberflächenstrukturen in situ während der Schichtabscheidung eingesetzt. Weiterhin wurden die Galliumnitrid-Schichten hinsichtlich ihrer strukturellen Eigenschaften mittels Röntgenstrahl-Diffraktometrie, Röntgen-Photoelektronenspektroskopie und Transmissionselektronenmikroskopie ex situ charakterisiert. Wesentliches Ziel dieser Arbeit war die Herausstellung des Einflusses maßgeblicher Abscheidungsparameter (vor allem Substrattemperatur und Gallium-Depositionsrate) auf die Schichteigenschaften sowie die Optimierung dieser Wachstumsparameter. Besonderes Augenmerk lag auf der Untersuchung der Auswirkungen des Stickstoffion-zu-Galliumatom-Verhältnisses und des Einflusses der niederenergetischen Ionenbestrahlung auf das Galliumnitrid-Schichtwachstum im Frühstadium. Dies betrifft hauptsächlich den Wachstumsmodus (zwei- oder dreidimensional) und die Bildung der hexagonalen oder der kubischen Phase.:Kapitel 1 1 Einführung 1 Kapitel 2 5 Grundlagen 5 2.1 Kristallstruktur und Eigenschaften von Galliumnitrid 5 2.2 Wechselwirkung niederenergetischer Ionen mit der Oberfläche 8 2.2.1 Energiefenster für die optimale ionenstrahlgestützte Epitaxie 9 2.3 Einfluss der Teilchenenergie auf die Oberflächenmobilität 11 2.3.1 Strukturzonenmodelle 11 2.3.2 Thermisch induzierte Oberflächenmobilität 13 2.3.3 Ballistisch induzierte Oberflächenmobilität 14 2.4 Herstellungsverfahren 15 2.4.1 Metallorganische Gasphasenepitaxie 15 2.4.2 Molekularstrahlepitaxie 16 2.4.3 Ionenstrahlgestützte Molekularstrahlepitaxie 17 2.5. Schichtwachstum 18 2.5.1 Frühstadium des Wachstums 18 2.5.2 Wachstumsmodi 20 2.5.3 Wachstum an Stufen 21 2.5.4 Ionenstrahlgestütztes GaN-Wachstum 23 2.6 Modellsystem GaN auf 6H-SiC 25 2.6.1 Epitaxiebeziehungen von GaN-Schicht und 6H-SiC(0001)-Substrat 25 2.6.2 Schichtspannungen 28 Kapitel 3 32 Experimentelle Bedingungen 32 3.1 Experimenteller Aufbau 32 3.1.1 UHV-Anlage zur ionenstrahlgestützten Abscheidung 32 3.1.2 Gallium-Effusionszelle 33 3.1.3 Stickstoff-Hohlanoden-Ionenquelle 34 3.1.4 RHEED-System 35 3.1.5 UHV-STM 37 3.2 Probenherstellung 40 3.2.1 Vorbehandlung 40 3.2.2 Abscheide- und Ionenstrahlparameter 41 3.3 Charakterisierung 43 3.3.1 Kristallographische Struktur 44 Reflexionsbeugung hochenergetischer Elektronen 44 Röntgenstrahl-Diffraktometrie 49 Röntgenstrahl-Reflektometrie 52 Transmissionselektronenmikroskopie 53 3.3.2 Oberflächentopographie 54 Rastertunnelmikroskopie 54 Rasterelektronenmikroskopie 56 3.3.3 Chemische Zusammensetzung 57 Röntgen-Photoelektronenspektroskopie 57 Kapitel 4 59 Ergebnisse und Diskussion 59 4.1 GaN-Wachstum auf 6H-SiC(0001) bei Variation des Ion/Atom-Verhältnisses 59 4.1.1 Oberflächenstruktur und Oberflächentopographie 59 4.1.2 Kristallographische Struktur und chemische Zusammensetzung 63 4.1.3 Diskussion: Einfluss des I/A-Verhältnisses 70 4.2 Inselwachstum: Oberflächenstruktur und Oberflächentopographie 74 4.2.1 Einfluss des I/A-Verhältnisses 75 4.2.2 Einfluss der Substrattemperatur 75 4.2.3 Einfluss der Depositionsdauer 78 4.2.4 Diskussion: Einfluss von I/A-Verhältnis, Depositionsdauer und Substrattemperatur auf die Oberflächentopographie der 3D-GaN-Schichten 82 4.3 Inselwachstum: Kristallographische Struktur und Morphologie 84 4.3.1 Morphologie der inselförmigen GaN-Schichten 84 4.3.2 Gitteranpassung und mechanische Spannungen 86 4.3.3 Diskussion: Kubisches GaN und Spannungsaufbau 88 4.4 Zweidimensionales Schichtwachstum: Oberflächenstruktur und Oberflächentopographie 90 4.4.1 Einfluss des I/A-Verhältnisses 90 4.4.2 Oberflächentopographie ultradünner 2D-Schichten 93 4.4.3 Einfluss der Depositionsdauer 96 4.4.4 Einfluss der Substrattemperatur 99 4.4.5 Diskussion: Einfluss von I/A-Verhältnis, Depositionsdauer und Substrattemperatur auf die Oberflächentopographie der 2D-GaN-Schichten 102 4.5 Zweidimensionales Schichtwachstum: Kristallographie und Morphologie 106 4.5.1 Einfluss des I/A-Verhältnisses 106 4.5.2 Einfluss der Depositionsdauer 107 4.5.3 Einfluss der Substrattemperatur 109 4.5.4 Morphologie und Gitterfehlanpassung 112 4.5.5 Koaleszenz von Inseln im Anfangswachstum 116 4.5.6 Diskussion: Einfluss von I/A-Verhältnis, Depositionsdauer und Substrattemperatur auf Struktur und Morphologie der 2D-GaN-Schichten 119 4.6 Moduswechsel von 3D- zu 2D-Wachstum bei sequenzieller Abscheidung unter Verringerung des I/A-Verhältnisses 124 Kapitel 5 128 Zusammenfassung und Ausblick 129 Anhang A 134 Anhang B 136 Literaturverzeichnis 137 Danksagung 145 Veröffentlichungen 146 Lebenslauf des Autors 147 Selbständigkeitserklärung 148

Neste trabalho, estudamos o crescimento epitaxial por feixe molecular assim como as propriedades ópticas e estruturais de camadas de InGaAs depositadas sobre substratos de GaAs(001) com diferentes ângulos e direções de corte. Um ênfase foi dada à investigação da segregação dos átomos de Índio que modifica consideravelmente o perfil de potencial das heteroestruturas e influencia as características dos dispositivos contendo este tipo de camadas. Um novo método experimental baseado em medidas de difração de elétrons de alta energia (RHEED) possibilitou a determinação in situ e em tempo real do coeficiente de segregação dos átomos de Índio e, conseqüentemente, do perfil de composição das camadas de InGaAs. Medidas de raios X e de fotoluminescência em baixa temperatura foram realizadas em amostras de poços quânticos de InGaAs e confirmaram, a posteriori, os resultados obtidos pela técnica RHEED. Foi também demonstrado que o uso de substratos desorientados podia reduzir levemente o efeito de segregação e melhorar as propriedades ópticas das camadas em baixa temperatura. / In this work, we investigated the molecular-beam-epitaxy growth as well as the optical and structural properties of InGaAs layers deposited on top of GaAs (001) substrates with different miscut angles and directions. We emphasized the investigation of the segregation of In atoms that considerably modifies the potential profile of the heterostructures and influences the characteristics of the devices based on this type of layers. A new experimental method involving the diffraction of high-energy electrons (RHEED) allowed the in-situ and real-time determination of the segregation coefficient of the In atoms and, consequently, of the compositional profile of the InGaAs layers. X-rays and low-temperature photoluminescence measurements were carried out InGaAs quantum wells and confirmed, a posterior, the results obtained by the RHEED method. It was also demonstrated that the use of vicinal substrates slight reduces the segregation effect and improves the optical properties of the layers at low temperature.

Neste trabalho, estudamos o crescimento epitaxial por feixe molecular assim como as propriedades ópticas e estruturais de camadas de InGaAs depositadas sobre substratos de GaAs(001) com diferentes ângulos e direções de corte. Um ênfase foi dada à investigação da segregação dos átomos de Índio que modifica consideravelmente o perfil de potencial das heteroestruturas e influencia as características dos dispositivos contendo este tipo de camadas. Um novo método experimental baseado em medidas de difração de elétrons de alta energia (RHEED) possibilitou a determinação in situ e em tempo real do coeficiente de segregação dos átomos de Índio e, conseqüentemente, do perfil de composição das camadas de InGaAs. Medidas de raios X e de fotoluminescência em baixa temperatura foram realizadas em amostras de poços quânticos de InGaAs e confirmaram, a posteriori, os resultados obtidos pela técnica RHEED. Foi também demonstrado que o uso de substratos desorientados podia reduzir levemente o efeito de segregação e melhorar as propriedades ópticas das camadas em baixa temperatura. / In this work, we investigated the molecular-beam-epitaxy growth as well as the optical and structural properties of InGaAs layers deposited on top of GaAs (001) substrates with different miscut angles and directions. We emphasized the investigation of the segregation of In atoms that considerably modifies the potential profile of the heterostructures and influences the characteristics of the devices based on this type of layers. A new experimental method involving the diffraction of high-energy electrons (RHEED) allowed the in-situ and real-time determination of the segregation coefficient of the In atoms and, consequently, of the compositional profile of the InGaAs layers. X-rays and low-temperature photoluminescence measurements were carried out InGaAs quantum wells and confirmed, a posterior, the results obtained by the RHEED method. It was also demonstrated that the use of vicinal substrates slight reduces the segregation effect and improves the optical properties of the layers at low temperature.