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INDUSTRY MOCVD


low doping concentrations is not easy, requiring control of the very diluted SiH4


gas supply and a low level of carbon


impurities, so that it is possible to produce low compensation n-type GaN.


Realising GaN fi lms with these attributes requires a suitable reactor design and a good growth process. As previously stated, the growth rate of GaN in a conventional reactor leads to device deposition times that can be 10 hours or more. But with our system, because it is possible to cut carbon concentration via atmospheric pressure growth, n-type GaN growth rates can be very high, leading to runs of just several hours for epiwafers production.


The carrier concentration in n-type GaN grown on 6-inch sapphire depends on the ratio of SiH4


Figure 4). Uniform doping at 5×1015 cm-3


to tri-methyl-gallium (see is possible under


growth rates as high as 3.6 μm/h, indicating that our reactor is very suitable for growth of nitride-based vertical diodes.


Ultraviolet LED structures


Essential ingredients for the ultraviolet LED – which can be used for curing, money checking, and air purifi cation – are the growth of AlN and high aluminium composition AlGaN. These layers are normally deposited on sapphire, and when conventional equipment is used, within-wafer uniformity and crystal quality are hampered by an excessive gas phase reaction. This impacts productivity and yield.


Figure 4. The carrier concentration in n-type GaN depends on the ratio of SiH4


and tri-methyl-gallium and the V/III ratios. The inset reveals the uniformity of doping across a 6-inch epiwafer


Figure 5. A high level of uniformity of peak emission wavelength indicates the potential of the Taiyo Nippon Sanso reactor for ultraviolet LED production.


Figure 3. Increasing the growth pressure leads to faster growth rates with a low carbon concentration


However, if engineers use our tool, the parasitic reaction is controlled and high-quality, uniform AlN and AlGaN fi lms can be grown at high growth rates. For example, it is possible to deposit AlGaN with an aluminium content of about


60 percent on 4-inch sapphire at 6.4 μm/h. Photoluminescence measurements of an InAlGaN multi-quantum well structure produce intense emission at 330 nm, and a high level of uniformity in the peak emission wavelength across the wafer (see Figure 5). These results demonstrate that our reactors have the capability to increase productivity for manufacturers of ultraviolet LEDs, just like they can do for the makers of electronic devices based on nitride materials.


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Further reading K. Matsumoto et. al. Proc. SPIE. 8262 826202 (2012) H. Tokunaga et. al. Phys. Stat. Sol. 5 3017-3019 (2008) Y. Yano et. al. Jpn. J. Appl. Phys. 52 08JB06 (2013) Y. Yano et. al. Taiyo Nippon Sanso Technical Report 32 27-28 (2013) (in Japanese). S. Kato et. al. J. Cryst. Growth 298 831 (2007) J. Selvaraj et. al. Jpn. J. Appl. Phys. 48 121002 (2009) A. Fujioka et. al. Appl. Phys. Express 3 041001 (2010)


March 2014 www.compoundsemiconductor.net 43


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