The term III-N nanowire (NW) will refer throughout this work to the free-standing
nanowires made of group-III-nitrides semiconductors, namely InN, GaN and AlN.
These nanostructures have a large length/diameter ratio, of the order of 100 (sev-
eral micrometers versus tenths of nanometers). The term free-standing highlights
the fact that the NWs are not embedded in another material. The improvement of
the epitaxial techniques, and in particular, those based on III-N semiconductors,
has lead an important part of the Solid State Physics community to concentrate
the attention in the last years towards a better understanding of the physical
properties of those NWs.
Nanowires present several di erences with respect to the still widely investi-
gated two-dimensional layers and the zero-dimensional nanostructures (quantum
dots). We would like to highlight the following: (i) Nanowires grow strain-free
(except maybe at their base), and thus with a minimal presence of dislocations or
defects along the main structure. This fact opens the possibility of growing high-
quality materials with an important lattice mismatch with the substrate, contrary
to the situation found in quantum dots or superlattices. (ii) Depending on the NW
lateral dimensions, two types of NWs can be distinguished. When the diameter is
larger than 20 nm, the electronic properties of the NWs can be considered as
that of a bulk material, thus making them a suitable platform to study the bulk
optical and transport properties, which can be hardly investigated in bulk samples
(thin lms), that grow with a high density of defects, when there is a high lattice
mismatch with the substrate. (iii) For NWs of smaller diameters (. 20 nm), on
the other hand, the e ects of quantum con nement can lead to important changes
in the optical and transport properties, which can open the possibility of tuning
the NW properties by controlling their size.
One can roughly classify the investigations on nanowires into three main re-
search lines. The rst one concerns the fabrication, being the molecular beam
epitaxy or/and the metal organic chemical vapor deposition (MOCVD) the two
techniques that allow the growth of higher quality NWs. This research area is in
2
constant development, and is not limited only to the growth of pure compound
NWs, but also alloy-based NWs, which extend the possibilities of allowing beyond
those possible in standard bulk growth, or axially and radially structured NWs.
New physical phenomena arise which must be tacked by the physical community,
in particular the e ect of the surface in the optical and transport properties of
the NWs. Another focus of research is based on applications to optoelectronics
devices and photovoltaic cells. In particular, III-N NWs, as InN, GaN and AlN,
have attracted a special interest of the scienti c community, due to the band gap
engineering. InN has a band gap of 0.67 eV (1852 nm), in the infrared, whereas
GaN and AlN have a band gap of 3.5 eV (355 nm) and 6.2 eV (200 nm), respec-
tively, in the ultraviolet. This opens the possibility of covering the whole solar
spectrum by an appropriate alloying.
In this context, the theory and numerical simulations play a crucial role in
the explanation of NWs properties and a better understanding of the observed
phenomena. The predictions o ered by the theory can also drive the fabrication
of new heterostructures and the design of devices. In this work, we have studied
theoretically by using several models, the fundamental aspects of the electronic
structure and optical properties of the III-N bulk semiconductors in the rst place,
and have applied afterwards such models to the investigation of the III-N nanowires
physical properties. / En esta tesis hemos estudiado las propiedades electrónicas y ópticas de los
nanohilos de semiconductores III-V, es decir, de InN, GaN y AlN, referidos comúnmente
en la literatura como nanohilos III-N o nanohilos de nitruros del grupo III.
Estas estructuras se caracterizan por un longitud mucho más larga (en el orden de
micrómetros) que su sección (en el orden de nanómetros). La alta calidad cristalina
de estos nanohilos, alcanzada gracias al desarrollo de las técnicas de crecimiento
como la epitaxia de haces moleculares, ha dado lugar a un interés creciente en la
investigación de sus propiedades físicas, debido a su potencial uso en aplicaciones
de optoelectrónica, como los diodos de emisión de luz (LED), diodos láser (LD),
células solares, y el diseño de nuevos transistores. En concreto, los nanohilos de
materiales InN, GaN y AlN revisten especial interés por sus variados gaps, del
infrarrojo lejano (0.67 eV para el InN), pasando por el ultavioleta cercano (3.5 eV
para el GaN), hasta el ultravioleta lejano (6.2 eV para el AlN), que combinados
aproapiadamente pueden, por ejemplo, cubrir totalmente el espectro de energía
del sol.
En este contexto, el desarrollo de modelos teóricos que permitan la realización
de simulaciones de las propiedades de nanohilos y que expliquen las propiedades
físicas de dichas nanoestructuras, está más que justi cada. En este trabajo hemos
empleado diferentes modelos teóricos con el n de estudiar las propiedades electr
ónicas y ópticas de los nanohilos III-N, estudiando detalladamente los efectos del
con namiento cuántico en sus propiedades, cuando las dimensiones de los nanohilos
varían.
| Identifer | oai:union.ndltd.org:TDX_UV/oai:www.tdx.cat:10803/58722 |
| Date | 18 January 2011 |
| Creators | Molina Sánchez, Alejandro |
| Contributors | García Cristóbal, Alberto, Cantarero Sáez, Andrés, Universitat de València. Departament de Física Aplicada |
| Publisher | Universitat de València |
| Source Sets | Universitat de València |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | 216 p., application/pdf |
| Source | TDX (Tesis Doctorals en Xarxa) |
| Rights | info:eu-repo/semantics/openAccess, ADVERTIMENT. L'accés als continguts d'aquesta tesi doctoral i la seva utilització ha de respectar els drets de la persona autora. Pot ser utilitzada per a consulta o estudi personal, així com en activitats o materials d'investigació i docència en els termes establerts a l'art. 32 del Text Refós de la Llei de Propietat Intel·lectual (RDL 1/1996). Per altres utilitzacions es requereix l'autorització prèvia i expressa de la persona autora. En qualsevol cas, en la utilització dels seus continguts caldrà indicar de forma clara el nom i cognoms de la persona autora i el títol de la tesi doctoral. No s'autoritza la seva reproducció o altres formes d'explotació efectuades amb finalitats de lucre ni la seva comunicació pública des d'un lloc aliè al servei TDX. Tampoc s'autoritza la presentació del seu contingut en una finestra o marc aliè a TDX (framing). Aquesta reserva de drets afecta tant als continguts de la tesi com als seus resums i índexs. |
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