a typical third generation materials of wide band gap semiconductors in
Material field. Compared with formal semiconductor materials, GaN owns several
advantages like higher frequency, higher power, and higher density for making
integrated electronics. What’s more, the strong radiation resistance ability
for GaN could also make great contributions in microwave power devices field.
Properties for GaN
GaN is very hard and stable chemical compound and it’s melting point is
about 2000K. Generally, the atomic structure for GaN is closed-packed hexagonal
structure and that results in relatively low symmetry of lattice and strong piezoelectricity
GaN is regard as wide band gap semiconductor. The band gap is 3.4 eV and
thermal conductivity is 1.3 W/cm*K. This two factors lead to the GaN has a high
working temperature and breakdown voltage and a strong ability of radiation
resistance. The bottom of conduction band of GaN is at ? position which makes a
huge energy difference with other with other valley to resist the scattering
between different valleys. As a result, GaN has a very high saturated drift
velocity of electrons.
Generally, wide-band gap semiconductors materials have band gaps in the
range of 2-4 eV, whereas typical semiconductors have band gaps in the range of
1-1.5 eV. Higher energy of band gap makes it suitable for working in a high
temperature. Wide band gap semiconductors are associated with a high voltage.
This is due to a large electric filed to generate carries through impact
However, GaN also has its
shortcomings. Because of it structure of energy bond, the electron mobility is
relatively low while the charge carriers have a high valuable mass.
Preparation for GaN
preparation of GaN includes four main steps: metalorganic chemical vapor
deposition, hydride vapor phase epitaxy, separation and second growth.
MOCVD step, ultra-pure gases are transferred into a reactor and finally result
in a deposition of a very thin layer of atoms onto a semiconductor wafer. For
instance, Pin can be grown in a heated substrate by trimethylindium and
molecular decomposition happens in the absence of oxygen. Two temperature
should be carefully noticed when we heat the substrate. One is around 823K and another is around 1273K. In the low temperature condition, there will
be a buffer layer growing firstly. However, in the high temperature, GaN will
grow directly. So the temperature should be controlled.
The HVPE makes the GaN grow continually. The hydrogen chloride is reacted
at a certain temperature while the group (III) metal producing gaseous metal
chlorides and then it will react with ammonia to produce group (III) metal nitride.
As to the separation part, the technique of laser lift-off is better than
natural separation which uses high power pulsed laser directly to the surface.
the typical application for GaN is power devices. Compared GaN with other materials, it has relatively small
volume and high efficiency to transport. Nowadays, as the popularization of 4G
cell site and wireless power, the potential market could be expected too.
from the strong ability for GaN to transport information, the high luminous
efficiency of GaN also could be applied to the LED. For instance, many
companies have put their eye on the research and exploitation on GaN materials,
like Samsung, Mitsubishi etc.
to the graph mentioned on the slides, it can easily show us the promising
future of GaN, the statistics also show that the total value in US in 2015 has
arrived at 298 million Dollars, and many of the cost is concentrated on