42
4 Epitaxial of III-Nitride LED Materials
H + H → H 2
(4.6)
(5) Side reaction process:
Ga(CH 3 ) 3 + NH 3 → Ga(CH 3 ) 3 : NH 3 +
Ga(CH 3 ) 3
nNH 3
(4.7)
The above is the simplest reaction process of GaN thin films. The reaction
processes of AlGaN and InGaN are more complicated because the pre-reaction of
TMAl, TMIn and NH 3 is more complex. The products of these side reactions are
adsorbed on the wafer carrier or the ceiling, which is very difficult to clean. Baking
is typically carried out multiple times after the epitaxial growth of III–V nitride.
According to the principle of chemical reaction equilibrium, in order to enable
TMGa and NH 3 to proceed in the direction of positive reaction, we need a relatively
large N partial pressure, that is, a large V/III ratio. The product of the reaction is also
required to be able to discharge out of the reaction chamber in time.
4.3.3.2 Component of MOCVD Equipment
MOCVD is mainly composed of gas delivery system, reactor and heater system,
control system, exhaust and security system, and in-situ monitor system.
(1) Gas delivery system
The gas delivery system includes various reaction sources such as metal organic
sources, ammonia, pipes for delivery gases, valves, and various pressure gauges and
flow meters for controlling gas flow pressure and flow. The metal organic sources
are stored in the bubblers and dipped into the water bath with certain temperature.
The gas delivers various reaction gases to the reaction chamber in a certain order
and flow rate through carrier gases such as N 2 and H 2 . In order to avoid pre-reaction
between the Group III and Group V source gases, it is often necessary to transport
the organic source and hydride separately into the reaction chamber through separate
lines. In order to enable rapid switching of the reactant gases during the growth, a
valve is required to control the switching of the run-vent gas path.
The metal organic source used in the III–V nitride are mainly trimethylgallium
(TMGa), trimethylaluminum (TMAl), trimethylindium (TMIn), and ferrocenylmagnesium (Cp2Mg), etc. The group V gas is generally NH 3 , and the carrier gas used
is hydrogen and nitrogen (the epitaxial indium-containing nitride uses nitrogen as
a carrier gas). The organic source gas is typically stored in a sealed steel cylinder
and placed in a water bath at certain temperature to ensure a stable flow. Generally,
a pressure gauge is used at the outlet of the source bubbler to ensure the stability
of the vapor pressure of the organic source. The organic source gas in the bubbler
can ensure the flow stability at different stages. The stainless-steel pipe is used to
carry the source where a heating wire is generally wrapped around the pipe to ensure
stability during gas transport. In order to grow a quantum well with a sharp interface,
4 Epitaxial of III-Nitride LED Materials
H + H → H 2
(4.6)
(5) Side reaction process:
Ga(CH 3 ) 3 + NH 3 → Ga(CH 3 ) 3 : NH 3 +
Ga(CH 3 ) 3
nNH 3
(4.7)
The above is the simplest reaction process of GaN thin films. The reaction
processes of AlGaN and InGaN are more complicated because the pre-reaction of
TMAl, TMIn and NH 3 is more complex. The products of these side reactions are
adsorbed on the wafer carrier or the ceiling, which is very difficult to clean. Baking
is typically carried out multiple times after the epitaxial growth of III–V nitride.
According to the principle of chemical reaction equilibrium, in order to enable
TMGa and NH 3 to proceed in the direction of positive reaction, we need a relatively
large N partial pressure, that is, a large V/III ratio. The product of the reaction is also
required to be able to discharge out of the reaction chamber in time.
4.3.3.2 Component of MOCVD Equipment
MOCVD is mainly composed of gas delivery system, reactor and heater system,
control system, exhaust and security system, and in-situ monitor system.
(1) Gas delivery system
The gas delivery system includes various reaction sources such as metal organic
sources, ammonia, pipes for delivery gases, valves, and various pressure gauges and
flow meters for controlling gas flow pressure and flow. The metal organic sources
are stored in the bubblers and dipped into the water bath with certain temperature.
The gas delivers various reaction gases to the reaction chamber in a certain order
and flow rate through carrier gases such as N 2 and H 2 . In order to avoid pre-reaction
between the Group III and Group V source gases, it is often necessary to transport
the organic source and hydride separately into the reaction chamber through separate
lines. In order to enable rapid switching of the reactant gases during the growth, a
valve is required to control the switching of the run-vent gas path.
The metal organic source used in the III–V nitride are mainly trimethylgallium
(TMGa), trimethylaluminum (TMAl), trimethylindium (TMIn), and ferrocenylmagnesium (Cp2Mg), etc. The group V gas is generally NH 3 , and the carrier gas used
is hydrogen and nitrogen (the epitaxial indium-containing nitride uses nitrogen as
a carrier gas). The organic source gas is typically stored in a sealed steel cylinder
and placed in a water bath at certain temperature to ensure a stable flow. Generally,
a pressure gauge is used at the outlet of the source bubbler to ensure the stability
of the vapor pressure of the organic source. The organic source gas in the bubbler
can ensure the flow stability at different stages. The stainless-steel pipe is used to
carry the source where a heating wire is generally wrapped around the pipe to ensure
stability during gas transport. In order to grow a quantum well with a sharp interface,