Quantumdots are particles of semiconductor material with the size so small that the electron energies that can exist within them are limited. These energy levels, defined by the size of quantumdots, in turn define the bandgaps. The dots can be grown to any needed size, allowing them to be tuned across a wide variety of bandgaps without changing the underlying material or construction techniques
Free(wannier-mott)
Radius >> a(exciton Bohr radius)
Small binding energy :~ 0.01 eV
Delocalized states
Move freely through crystal
(semiconductors)
Tighthly-bound(Frenkel)
Radius ~ a(exciton Bohr radius)
large binding energy : 0.1 -1.0 eV
localized on one lattice site
Moving by hopping
(insulators and molecules)
Eadd = △E + Ec
Ec = e2/C
C = 2πεεod
(depend on geometr
Quantumdot
2.1 Quantumdot 정의
반도체 Quantumdot (QD)은 band gap이 서로 다른 두 물질 중 band gap이 좁은 물질을 band gap이 넓은 물질 내에 de Broglie 파장 정도의 크기가 되도록 성장 및 조작을 한 반도체 구조이다. 이렇게 형성 된 QD는 band gap이 반도체 내의 전자와 정공 모두의 움직임을 3차원적으로 제한하게
②White emission using mixtures of CdSe quantumdots and PMMA as a phosphor
This paper explain WLED that have mixture stucture (one single chip(emit blue light) and cdse/PMMA quantumdots). CdSe quantumdots are synthesized by the wet chemical method using CdO and Se powder as precursor. And they control the size of quantumdot and mix the phospors(PMMA).
These quantumdots have three differe
Potential bio-accumulation of nanoscale particles.
Accumulation of a substance within a species can occur due to lack of degradationor excretion
Many nanoparticles are not biodegradable.
If nanoparticles enter organisms low in the food web, they may be expected to accumulate in organisms higher in the food web.
Very little is understood about possible health
effects of nanoparti
optical and electrical properties
Quantum confinement effects
luminescence of semiconductor
CdSe nanoparticles of different sizes
광반도체 재료로서 우수한 특성을 가짐
(Quantum confinement effects)
양자 구속효과에 대란 상태밀도 a. 벌크(3D) b. 양자우물(2D) c. 양자점(0D)
Quantumdot LEDs, LED
기존의 LED와 Quantumdot LED
: two metal depositions followed by an oxidation and a further metal deposition from a different angle form an overlap of two stripes
Why GaAs quantumdot ?
Proper quantumdot size enough to be placed between source and drain by using templates-based technique
2) Band gap of GaAs (1.42eV~1.52eV) higher than basic thermal energy (0.0259eV)
3) GaAs quantumdot has Coulomb blockade
What is LED?
Light Emission Diode
Using P-N Junction
Wave length is defined
by Element’s Band Gap
Compound Red, Green, Blue
↓
Express Color!(white…)
Core : 2~10 nm
- Ⅱ-Ⅳ element (CdSe, CdTe, Cds)
Shell
- metallic molecular plating(ZnS, ZnSe)
Polymer Coating
- To disperse in the aqueous solution