Growth of GaN on sapphire with MSE grown buffer layer

Details Growth of GaN on sapphire with MSE grown buffer layer Growth of GaN on sapphire with MSE grown buffer layer

1999-10-05

2001-09-18

Christianson, Keith (Department: 2813)

Semiconductor device manufacturing: process

Formation of semiconductive active region on any substrate

On insulating substrate or layer

Reexamination Certificate

active

06291318

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the growth of gallium nitride and like materials on a sapphire substrate.
BACKGROUND OF THE INVENTION
In recent years there has been tremendous interest in GaN based III-N materials. A dramatic improvement in the material quality has led to the development of high brightness light emitting diodes, and more recently “blue” laser diodes. There has also been a dramatic improvement in the performance of high power microwave metal-semiconductor field-effect transistors and modulation doped field-effect transistors based on these materials.
Crucial to all these applications is the growth of material with high crystalline quality and of high purity. Various techniques have been used to grow GaN including metalorganic vapor phase epitaxy (MOVPE), plasma molecular beam epitaxy (plasma MBE), ammonia molecular beam epitaxy (ammonia-MBE), also referred to as reactive molecular beam epitaxy, and magnetron sputter epitaxy (MSE). Typically GaN epilayers are grown on sapphire substrates, which are highly lattice mismatched, necessitating the predeposition of a thin (~500 Å) buffer
ucleation layer of either GaN or AlN. The observed electrical and optical properties of the resulting GaN layers is strongly dependent on the dislocation density and of the overall impurity content.
Using these growth techniques, room temperature electron mobilities for MOVPE-grown silicon doped GaN layers are typically reported in the range of 350-600 cm
2
/V s. The highest room temperature mobility ever reported for GaN was 900 cm
2
/V s deposited by MOVPE for a 4 &mgr;m thick layer. In contrast, the highest room temperature mobility for plasma-MBE grown GaN is around 300 cm
2
/V s and for ammonia-MBE is 350 cm
2
/V s.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of fabricating a gallium nitride or like epilayer on sapphire, comprising the steps of providing a sapphire substrate, growing a nucleation buffer layer on said sapphire substrate by magnetron sputter epitaxy (MSE) and subsequently forming said gallium nitride epilayer on said buffer layer.
Using this method, silicon doped GaN epilayers having room temperature electron mobilities>550 cm
2
/V s can be grown on grown on (0001 )sapphire. Unlike other growth techniques, the initial buffer
ucleation layer, preferably of AlN (aluminum nitride), is grown by MSE.
The deposition of the GaN layers may be performed in a dual mode MBE/MSE system. The MSE technique differs from conventional MBE in that an ultrahigh vacuum dc magnetron sputter cathode is used as the group III source and deposition of the layers occurs in the pressure range of 1-5 mTorr.
Typically, the MSE technique is employed only for the growth of the buffer
ucleation layer. The GaN layer is deposited by ammonia MBE where a conventional dual filament K cell is used for the gallium source, and high purity ammonia is used as the source of nitrogen.
Preferably, the deposition system is equipped with a substrate holder capable of heating the 2 in. sapphire(0001) wafers to temperatures in excess of 1000° C. Typical growth temperatures for the GaN layers were in the range of 860-920° C. as measured by an optical pyrometer (emissivity set to 0.3).


REFERENCES:
Singh, P. et al., “Growth and characterization of GaN thin films by magnetron sputter epitaxy”, J. Vac. Sci. Technol. A 16(2), pp. 786-789, May 1998.

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