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

More documents

Recommendations

Info

Experimental Growth and Characterization Techniques mode, and usually results in a fairly faithful topographical (hence the alternative name, height mode). During contact with the sample, the probe predominately experiences repulsive Van der Waals forces (contact mode). This leads to the tip deection described previously. As the tip moves further away from the surface attractive Van der Waals forces are dominant (non-contact mode) as illustrated in Fig. 4.5. Generally, the AFM operation modes can be classied to mainly three modes [? ]: • Contact mode: (repulsive VdW force regime), when the spring force of the cantilever is less than the surface repulsion force, the cantilever bends. The force on the tip is repulsive. By maintaining a constant cantilever deection (using the feedback loops) the force between the probe and the sample remains constant and an image of the surface is obtained. The probe-surface separation in this mode is less than 0.5 nm. • Intermediate contact or (tapping) mode: The imaging is similar to contact with probe-surface separation less than 2 nm. However, in this mode the cantilever is oscillated at its resonant frequency. The probe lightly taps on the sample surface during scanning, contacting the surface at the bottom of its swing. By maintaining a constant oscillation amplitude a constant tip-sample interaction is maintained and an image of the surface is obtained. • Non-contact mode: Non-contact mode belongs to a family of AC modes, which refers to the use of an oscillating cantilever. A sti cantilever is oscillated in the attractive regime, meaning that the tip is quite close to the sample, but not touching it (hence, non-contact). The forces between the tip and sample are quite low, on the order of pico Newton (pN) (10 −12 N). The detection scheme is based on measuring changes to the resonant frequency or amplitude of the cantilever with a probe-surface separation between 0.5 - 10 nm. However, most of the AFM measurements reported in this thesis, are conducted via the last mode (non-contact mode) using CP II AFM system, due to the advantages of very low force exerted on the sample (pN range) and the large 58
4.4 High Resolution Transmission Electron Microscopy probe-surface separation, this in turns will extend the probe lifetime for many scans using the same cantilever. 4.4 High Resolution Transmission Electron Microscopy Transmission electron microscopy is a valuable technique for the observation of dislocations, stacking faults, twin boundaries, and other crystal defects in heteroepitaxial layers. TEM characterization is applicable to most heteroepitaxial semiconductor samples, provided that they can be thinned to transmit electrons and that they are stable when exposed to a high-energy electron beam in an ultrahigh vacuum. Due to the very high atomic resolution (typically 0.1 nm) obtained by TEM, lattice constants can be accurately determined, which in turns open possibilities for strain calculations and mapping of the heteroepitaxial structures. However, conventional TEMs use electron energies of few hundreds keV. For observation in a conventional TEM, typical heteroepitaxial semiconductor samples must be thinned to less than 400 nm according to the corresponding applied voltage. This requirement may be relaxed somewhat if the sample is made up of light atoms with low atomic number (such as Si, SiC, or sapphire) or if high voltage electrons are used. The sample preparation is destructive, and in some cases, it can alter the defects that are to be observed [73]. There are four main components of a transmission electron microscope: an electron optical column, a vacuum system, the necessary electronics (lens supplies for focusing and deecting the beam and the high voltage generator for the electron source), and control software. A modern TEM typically comprises an operating console surmounted by a vertical column and containing the vacuum system, and control panels conveniently placed for the operator. The microscope may be fully enclosed to reduce interference from environmental sources. The operation of a TEM instrument is shown schematically in Fig. 4.6. The condenser electromagnetic lens system focuses the electron beam onto the specimen under investigation as much as necessary to suit the purpose. The objective lens produces an image 59
Page 1:
Molecular Beam Epitaxial Growth of
Page 4 and 5:
Gutachter (Supervisors): 1. Prof. D
Page 6 and 7:
patterns indicating a 2D smooth sur
Page 8 and 9:
(MEE = migration enhance epitaxy) u
Page 10 and 11:
viii
Page 12 and 13:
CONTENTS 3.4.4 Planar Defects Assoc
Page 14 and 15:
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
Page 118 and 119: MBE Growth of InAs and InGaAs Quant
Page 120 and 121: MBE Growth of InAs and InGaAs Quant
Page 122 and 123:
MBE Growth of InAs and InGaAs Quant
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Optimization of MEE and MBE growth
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Conclusions substrates, respectivel
Page 144 and 145:
REFERENCES [8] J. M. Gerard, O. Cab
Page 146 and 147:
REFERENCES [29] http://www.wmi.badw
Page 148 and 149:
REFERENCES [49] M. R. Brenner: GaP/
Page 150 and 151:
REFERENCES [66] Y. Ishida, T. Takah
Page 152 and 153:
REFERENCES [84] A. Garcia, C. M. Ma
Page 154 and 155:
REFERENCES [100] M. Felici, P. Gall
Page 156 and 157:
REFERENCES [116] H. Usui, H. Yasuda
Page 158 and 159:
REFERENCES [133] Grassman, T. J. Br
Page 160 and 161:
Conferences Contributions: Tariq Al
Page 162 and 163:
Nomenclature
Page 164 and 165:
REFERENCES symbol Descriptions γ f
Page 166 and 167:
like to thank all member of the Ins
Page 168:
REFERENCES Erklärung Hiermit versi
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?