|
Plasma Technology | |
On the 9th April Oxford Instruments PLC acquired Technologies
and Devices Inc (TDI) who are based at Silver Spring, Maryland, USA.
TDI are a world leading company in the development of Hydride
Vapour Phase Epitaxy (HVPE) processes and techniques which are
used for the production of novel compound semiconductors such as
GaN, AlN, AlGaN, InN, InGaN. These materials are used in a variety
of applications the primary ones being solid state lighting, short
wavelength optoelectronics and RF power electronics.
HVPE is a well established process and is essentially based on
flowing HCl gas over a nitride metal melt such as Gallium into a
reactor where it meets Ammonia (NH3) and forms GaN on a substrate
such as sapphire. Dopants such as Magnesium and Zinc can be added
during the process using Argon as a carrier gas. The reaction takes
place at ~1,000 deg C and does not require any vacuum with growth
rates of 1 to 10um per minute being achieved.
TDI was founded in 1997 by Vladimir Dmitriev who sadly passed away
in January of this year, however the team he set up is now led by
Dr Alexander Usikov who worked closely with Vladimir over a number
of years. The company produces a wide range of materials on different
substrates, these are briefly:
GaN on Sapphire Sizes from 2 to 4
---Ideal for Blue and White LED applications
AlN on Silicon Carbide Sizes from 2 to 4
--- Typically used for HEMT devices
AlGaN on Sapphire in 2 or 3 format
--- Used in optoelectronic devices operating in UV spectral region
InN on Sapphire Available in 2 for work on
--- sensors and high frequency electronic devices
InGaN on Sapphire Available in 2 for Green
--- LED and green laser developments
Customers can specify different thickness levels, doping requirements
and of course the substrate they need.
In addition to the above templates TDI conducts specific research and
development programmes for a wide range of organizations. It has been
awarded US dept of Defence and Energy contracts and is proud to be part
of the DARPA VIGIL programme which is developing a green laser. They
also do leading edge research and development for a number of private
companies helping them to speed up delivering their end product to market.
The team at Silver Spring is proud to have joined Oxford Instruments
and look forward to continuing support from their existing customers
as well as discussing nitride requirements with a range of new customers.
In the HVPE process, Group III nitrides (e.g., GaN, AlN) are formed by
reacting hot gaseous metal chlorides (e.g., GaCl or AlCl) with ammonia
gas (NH3). The metal chlorides are generated by passing hot HCl gas over
the hot Group III metals. All reactions are done in a termperature
controlled quartz furnace.
e.g.,
Hot HCl (g) + Ga (l) ------> GaCl (g)
GaCl (g) + NH3 (g) -------> GaN (s) + HCl (g) + H2 (g)
The GaN or AlN templates have been grown on substrates such as SiC or
sapphire. p-type GaN or AlN can be achieved by using Mg during the
process and n-type by silane gas.
Growth rate of the HVPE process can be up to several microns per minutes,
resulting in high quality, cracker free GaN or AlN templates. Figure 1 shows
the X-ray diffraction of a XXX thick GaN template on sapphire. The narrow
FWHM of XX arc demonstrates excellent material quality. (I need to get an
x-ray scan from these folks this week.)
The team at Silver Spring is proud to have joined Oxford Instruments and
look forward to continuing support from their existing customers as well
as discussing nitride requirements with a range of new customers.
The XRD data for undoped 6.3 µm HVPE GaN layer grown on 2-inch c-plane
sapphire substrate. The XRD was measured at the center of the substrate
in double-crystal monochromator geometry.
The full width at half maximum (FWHM) of XRD omega-scan (rocking curve)
for symmetrical (0002) reflection is 281 arcsec.