Growth, surface structure and morphology of semiconductor nano-structures [Elektronische Ressource] / von Subhashis Gangopadhyay

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• Physik

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• Publié par: universitat_bremen
• Publié le: 01 janvier 2006
• Nombre de lectures: 17
• Langue: English
• Poids de l'ouvrage: 23 Mo

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Growth, Surface Structure
and Morphology of
Semiconductor Nano-Structures
by
Subhashis GangopadhyayGrowth, Surface Structure
and Morphology of
Semiconductor Nano-Structures
Vom Fachbereich fu¨r Physik und Elektrotechnik
der Universit¨at Bremen
zur Erlangung des akademischen Grades eines
Doktor der Naturwissenschaften (Dr. rer. nat.)
genehmigte Dissertation
von
M.Sc. Subhashis Gangopadhyay
aus Howrah, West Bengal, Indien
1. Gutachter: Prof. Dr. rer. nat. J. Falta
2. Gutachter: Prof. Dr. rer. nat. D. Hommel
Eingereicht am: 20.04.2006
Tag des Promotionskolloquiums: 29.05.2006The work described in this thesis has been performed in the Surface Science Group of
Prof. Dr. J.Faltaatthe Institute ofSolidStatePhysics, University ofBremen, Germany.Growth, Surface Structure
and Morphology of
Semiconductor Nano-Structures
A dissertation submitted to the
Department of Physics and Electrotechniques
of
University of Bremen
in partial fulfilment of the requirements for the degree
of
Doctor of Natural Science
(Dr. rer. nat.)
in
Solid State Physics
by
M. Sc. Subhashis Gangopadhyay
from Howrah, West Bengal, India
1. Examiner: Prof. Dr. rer. nat. J. Falta
2. Examiner: Prof. Dr. rer. nat. D. Hommel
Date of submission: 20.04.2006
Date of defense: 29.05.2006Dedicated to my fatherAbstract
Self-assembled growth of semiconductor quantum dots has perspective applications in
optoelectronic devices and a detailed understanding of their growth mechanisms is of
high practical importance. Within this thesis work, the controlled formation and struc-
tural characterization of self-organized semiconductor nano-structures are discussed with
special focus on their surface properties. Two types of semiconducting nano-structures
have been investigated namely as Si–Ge based as well as GaN based quantum dot struc-
tures. In addition, GaN growth on Si(111) for integration of nitride semiconductors into
Si technology has also been studied.
Self-organized nano-patterning of Ga/Si(111)surfaces after submonolayer Ga deposition
has been studied by STM, LEEM and XPEEM. The surface defects of the Si(111)-7×7
surface (steps and the domain boundaries) play an important role in the initial Ga nucle-
ation. Post-deposition annealing of Ga/Si(111)surface or elevated temperature Ga depo-
sitiononSi(111)leads toa2Dphaseseparationandsurfacenano-patterning. Varyingthe
amount of Ga coverages, structures of the Ga/Si(111) nano-patterns can be controlled.√ √
Subsequent Ge deposition on partially 3× 3-Ga covered nano-patterned substrate
leads to a selective nucleation of 3D Ge islands and thus to the formation of an array of
highly aligned Ge dots. The formation of the nano-patterns can be explained in terms of
surface stress and surface free energy.
The structure, morphology and stoichiometry of silicon nitride films prepared by plasma
assisted reactive growth on the Si(111) surface at elevated temperatures have been exam-
ined using LEED, STM and ESCA microscopy. Low temperature nitridation results in
smoothsilicon nitridefilms ofpoorcrystallinity, whereasnitridationathightemperatures
leads to the formation of crystalline Si N layers but with a rough surface morphology.3 4
To facilitate the wurtzite GaN growth on Si(111), various silicon nitride inter-layers have
been used as a buffer and a significant improvement of the subsequently grown GaN films
morphology is obtained for Si(111) nitridation at higher temperatures.
In-situ cleaningandsurfacedefectscharacterizationofMOVPEgrownGaN(0001)/sapphire
templates andsubsequent homo-epitaxialgrowth ofthin GaNlayer usingMBE have been
studied using XPS and STM and RHEED. A combination of initial plasma assisted ac-
tive nitrogen cleaning at low temperature followed by a short duration high temperature
cleaning leads to an efficient removal of surface oxide while maintaining a smooth surface
morphology. For a smooth template surface, a layer-by-layer growth morphology of GaN
has been achieved for Ga-rich growth condition.
IXMOVPE grown self-organized In Ga N nano-islands on GaN(0001) templates havex 1−x
been investigated using STM. The morphology and density of these In Ga N nano-x 1−x
islands can be controlled by the choice of proper MOVPE growth conditions such as tem-
perature, In Ga N deposit, growth rate and III-V flux ratio. With decreasing growthx 1−x
temperatures,theIn Ga NislandsizeisreducedandthehomogeneityoftheIn Ga Nx 1−x x 1−x
surfaceisimproved. HomogeneousnucleationofsmallIn Ga Nislandsofhighdensitiesx 1−x
12 2(10 /cm ), suitable for three-dimensional quantum confinement is found for growth at
◦600 CatalowInpartialpressure. However, these nano-islandsdonotshow quantum-dot
like emission after overgrowth. Instead, two-dimensional (2D) In Ga N islands grownx 1−x
◦at 700 C show a sharp photoluminescence (PL) emission lines, indicative of single dot
emission, after the GaN capping process.
X