Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

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Experimental Growth and Characterization Techniques solid source material is held in an inert crucible. Typically, the eusion cells are made of pyrolytic boron nitride with tantalum heat shields. The source temperatures are maintained with an accuracy of ± 0.1 ◦ C to control the ux of evaporating atoms. The vapor pressure of each species is controlled by setting the temperature of the eusion cell and is monitored with a beam ux ion-gauge that is inserted from the back of the substrate manipulator, from which material growth rates can be determined. Tantalum shutters in front of each cell can be opened and closed to control the deposition of individual elements with monolayer accuracy. However, group-V material such as As and P are normally loaded in cracker cells or (valve controlled cells), in order to achieve V/III ratio control for dierent layers in shortest time and avoiding any growth interruptions during the growth. Therefore, the valve opening of the cell is changed accurately and more precisely in this type of cell. The III-V MBE substrates are heated by DC powered laments located behind the substrate, and the substrate temperature is measured by both infrared pyrometry on the front side and manipulator-mounted thermocouple on the back side. The III-V MBE system in the epitaxy laboratory located at the Institute of Nanostructure Technologies and Analytics (INA), University of Kassel, is a modied Varian Gen II MBE system. A new high temperature manipulator (HTM) from Veeco system was installed in order to achieve high substrate temperatures (T s > 1000 ◦ C) for silicon dioxide (SiO 2 ) desorption. Another modication was the installation of a new electron beam evaporation system (Careera system) for silicon homoepitaxy, which was designed to t to the MBE Varian Gen II geometry. 4.2.1 Reection High Energy Electron Diraction Real time monitoring of MBE growth as well as the surface preparation eciency prior to the epitaxial growth are conducted via in-situ reective high energy electron diraction. RHEED, in fact, is a critical in-situ diagnostic tool for MBE growth. It allows the verication of a smooth, contaminant-free surface prior to growth, as is necessary for the epitaxy of high-quality material. It can also be used to determine the growth rate, composition, and growth mode in-situ. The Gen II 52
4.2 Molecular Beam Epitaxy Technique Figure 4.2: (a) 3D sketch shows the directions of the elastically scattered electrons in real space. These scattered electron beams hit a uorescent RHEED screen in certain RHEED spots, lying on so-called Laue circles which are numbered starting from zero. (b) Streaks RHEED pattern indicates a 2D surface for Ewald sphere larger than the separation of the reciprocal lattice rods [33, 29]. MBE system used for the work presented here has a RHEED system consisting of a high energy electron gun capable of 35 kV beam energy and a phosphor coated screen with recording camera on the opposite side of the chamber to record the RHEED patterns, as shown in Fig. 4.1. In a typical RHEED experiment, a high energy beam of electrons is incident on the sample surface at a shallow angle of 1 to 2 ◦ (reection condition). Diraction of the electrons is governed by the Bragg law, as with x-ray diraction. However, there are two important dierences between RHEED and the x-ray case. First, the electrons do not penetrate signicantly into the sample, so diraction is essentially from the two-dimensional lattice on the surface. Second, for the high energy electrons used in RHEED, the Ewald sphere is large in diameter, so many reections are excited at once. RHEED is a surface sensitive technique that provides a real time prole of the atomic surface periodicity during MBE growth. The reection from the substrate is directed toward a phosphor screen, displaying a pseudo-1D diraction pattern during growth or prior to the growth in preparation stage [33]. The intensity of the reected RHEED spots/streaks is sensitive to the atomic arrangement of atoms on the substrate surface. Because the diraction occurs 53
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Molecular Beam Epitaxial Growth of
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Gutachter (Supervisors): 1. Prof. D
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patterns indicating a 2D smooth sur
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(MEE = migration enhance epitaxy) u
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viii
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CONTENTS 3.4.4 Planar Defects Assoc
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CONTENTS xii
Page 16 and 17: Introduction thesis a detailed stud
Page 18 and 19: Introduction 1.1.2 Thesis Approach
Page 20 and 21: Introduction 1.2 Thesis Outline The
Page 22 and 23: Theoretical Background of Semicondu
Page 36 and 37: Heteroepitaxial Growth of III-V Sem
Page 64 and 65: Experimental Growth and Characteriz
Page 78 and 79: MBE Growth of Self-Assembled InAs a
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MBE Growth of Self-Assembled InAs a
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MBE Growth of InAs and InGaAs Quant
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Optimization of MEE and MBE growth
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Conclusions substrates, respectivel
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REFERENCES [8] J. M. Gerard, O. Cab
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REFERENCES [29] http://www.wmi.badw
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REFERENCES [49] M. R. Brenner: GaP/
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REFERENCES [66] Y. Ishida, T. Takah
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REFERENCES [84] A. Garcia, C. M. Ma
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REFERENCES [100] M. Felici, P. Gall
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REFERENCES [116] H. Usui, H. Yasuda
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REFERENCES [133] Grassman, T. J. Br
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Conferences Contributions: Tariq Al
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Nomenclature
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REFERENCES symbol Descriptions γ f
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like to thank all member of the Ins
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REFERENCES Erklärung Hiermit versi
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Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

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