1. Deposition Techniques
Thermal CVD
Laser-assisted CVD
Plasma enhanced CVD
Chemical beam epitaxy
Vapor phase epitaxy
Molecular beam epitaxy (MBE)
Laser ablation method

2. MoS2 film on SiO2 substrate (Few inches wafer scale)
1. Thermal CVD
Substrate
Source
■ Principle & Process
Heat energy is supplied to activate required source and gas-solid phase reaction.
■ Usages & Applications
- Thin films (Metal oxide, metal sulfide, silicon, various semiconductors, etc.)
■ Characteristics
Advantages
High quality product
Simple reactor
Large-scale synthesis
Drawbacks
Large quantity carrier gas in need
High crystallinity
MoS2 film on SiO2 substrate
(Few inches wafer scale)

3. Millimeter-sized boron helix
2. Laser-assisted CVD
Millimeter-sized boron helix
■ Principle & Process
Chemical reaction of source gas takes place at the spot on the substrate under laser irradiation.
■ Usages & Applications
- Thin rod and fibers. (Si, C, B, Al, etc.)
■ Characteristics
Advantages
Access to control directionality
Drawbacks
Limitation of mass-production (only suitable for academic research purpose)

4. Vertically aligned Carbon nanotube
3. Plasma enhanced CVD
■ Principle & Process
Discharge electrode excites the reactant gas into a plasma (ionized gas), which induces a chemical reaction and results in the reaction product being deposited on the substrate.
■ Usages & Applications
Silicon complex thin film (SiOx, SiNx, amorphous silicon, dopant)
Nanowire
■ Characteristics
Advantages:
Lower temperature( °C) processes compared to conventional CVD
(Less damages to sample, good when temperature is restricted)
Fast deposition
High step coverage (High quality: not as good as thermal CVD)
Drawbacks
Toxic byproduct gas
High cost
Chemical contamination
Vertically aligned Carbon nanotube
Silica film

5. 4. Chemical beam epitaxy ■ Principle & Process
Reactants are molecular beam of reactive gases, typically as hydride or metalorganic.
Molecular beam (alkyl beam) carries metal atoms. Decomposition happens on the substrate for metal to compose layered structure on the substrate.
■ Usages & Applications
Semiconductor films (GaAs, InP, Si1-xGex, etc.)
Heterostructures (GaAs/InGaAs films)
Carbon doped semiconductors (p-type GaAs)
■ Characteristics
Advantages
Low growth temperature
Uniform film coverage
Access to control chemical doping
Drawbacks
Requires ultra high vacuum (10-10~10-11) >> not good for mass production
High carbon contamination
Thin films

6. 5. Vapor phase epitaxy ■ Principle & Process
Solid metal source is thermally evaporated into vapor, and it deposits on the substrate.
■ Usages & Applications
Wide variety of thin films (semiconductors, metals, solar cells, etc.)
Metal film is much easier to make.
■ Characteristics
Advantages
Deposits almost any materials
Low contamination
Drawbacks
Undesired polycrystalline layers
Difficult to evaporate materials with low vapor pressure or high melting point.
SiC film

7. Thickness-controlled heterostructure layers
6. Molecular beam epitaxy (MBE)
Thickness-controlled heterostructure layers
■ Principle & Process
Sublimated gaseous elements (atoms) condense on crystal substrate.
Gas molecules (atoms) never collide each other before condensing on the substrate moving in the same direction. (Atomic beam, jet)
Substrate is slightly heated.
■ Usages & Applications
Thin film, especially semiconductors (GaAs, InP, Si1-xGex, etc.)
Heterostructures (GaAs/InGaAs films)
■ Characteristics
Advantages
Very pure and uniform material
Easy control of stoichiometry
Drawbacks
Very slow deposition rate(1µm/hr)
Requires ultra high vacuum (10-10~10-11)
>>>Not adequate for mass production (expensive and inefficient)

8. 7. Laser ablation method ■ Principle & Process
Al2O3 film
■ Principle & Process
High-power laser beam strikes a target, and then vaporized target (ablation plume) deposits onto substrate as thin film (Sputtering)
■ Usages & Applications
Thin film of complex compounds with complicated stoichiometry (YBCO, ceramics, etc.)
■ Characteristics
Advantages
Stoichiometry of a target can be reproduced on substrate (deposits almost any materials)
Drawbacks Requires ultra high vacuum
Possibility of incorporating impurities
Uneven coverage (Line-of-sight).