Hydride Vapour Phase Epitaxy (HVPE)

Oxford Instruments recently acquired Technologies and Devices Inc (TDI). Based at Silver Spring, Maryland, USA, TDI are a world leading company in the development of Hydride Vapour Phase Epitaxy (HVPE) processes and techniques 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.

Nitride-based Templates by TDI
The company produces a wide range of materials on different substrates, including the following:

Templates	Sizes	Applications
GaN on Sapphire	2" to 4"	Blue and White LED applications
AlN on Silicon Carbide	2" to 4"	Typically used for RF electronic devices such as HEMT
AlGaN on Sapphire	2" or 3"	Optoelectronic devices operating in UV spectral region
InN on Sapphire	Research grade available in 2"	For work on sensors and high frequency electronic devices
InGaN on Sapphire	2" for Green LED	Green LED and green laser Developments

The HVPE Process
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) (Refer to diagram below). The metal chlorides are generated by passing hot HCl gas over the hot Group III metals. All reactions are done in a temperature 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 with Argon as the carrier gas.
Advantages of HVPE
Developed in the 1960s, it was the first epitaxial method used for the fabrication of single GaN crystals. One of the key features of the technique is its high growth rate (at up to 100 µm per hour) which is almost two orders of magnitude faster than typical MOCVD and MBE processes.
The technique is able to produce crack-free, high quality GaN epitaxial layers (e.g., a typical dislocation density can be as low as 107/cm3 for a 10 µm thick GaN template on sapphire.) Figure 1 shows the X-ray diffraction of a 10 µm thick GaN template on sapphire. The narrow FWHM of 250 arcsec measured at w-scan (0002) peak demonstrates excellent material quality.
Another advantage of HVPE is its ability to grow thick, high quality of AlGaN and AlN for use in optoelectronic and RF electronic devices. The technique has been demonstrated by TDI to grow thicker high quality AlGaN-based active regions of shorter wavelength emitters, which have a high radiative recombination efficiency – an essential feature for high-efficiency UV LEDs. Unlike MOCVD, the HVPE process does not involve metalorganics, thus providing a 'carbon-free' environment for epitaxial growth. In addition, the use of gaseous hydrogen chloride also provides an impurity 'self-cleaning' effect, which results in epitaxial layers with low background impurities and more efficient doping level.
TDI has demonstrated the industry's first HVPE-grown, multilayer, submicron AlGaN/GaN heterostructures.