Preparation of Large Freestanding GaN Substrates by Hydride Vapor Phase Epitaxy Using GaAs as a Starting Substrate

Abstract

A freestanding GaN substrate over 2 inches in size was successfully prepared for the first time by hydride vapor phase epitaxy (HVPE) using GaAs as a starting substrate. In the experiment, a GaAs (111)A substrate with a SiO 2 mask pattern on its surface was used. A thick GaN layer was grown on the GaAs substrate at 1030 • C through the openings in the SiO 2 mask. By dissolving the GaAs substrate in aqua regia, a freestanding GaN substrate about 500 µm thick was obtained. The fullwidth at half maximum (FWHM) in the ω-mode X-ray diffraction (XRD) profile of GaN (0002) plane was 106 arcsec. The dislocation density of the GaN substrate obtained was determined to be as low as 2 × 10 5 cm −2 by plan-view transmission electron microscopy (TEM). Hall measurements revealed the n-type conductivity of the GaN substrate with typical carrier concentration and carrier mobility of 5 × 10 18 cm −3 and 170 cm 2 ·V −1 ·s −1 , respectively.

LEDs on HVPE grown GaN substrates: Influence of macroscopic surface features

“…With GaN bulk crystal growth still in its infancy, most of the bulk substrates are based on thick GaN layers grown by hydride vapor phase epitaxy (HVPE) separated from foreign substrates. [6][7][8] These free-standing GaN layers grown by HVPE offer an excellent crystal quality and low threading dislocation densities 9,10 with low AFM roughness. However, the fast HVPE growth of thick layers, even with homogeneously high crystal quality, on MOVPE templates introduces defects and pits which lead to a macroscopically rough surface.…”

Influence of Temperature Ramping Rate on Thick GaN Growth on GaAs (111)A Surfaces

“…The present authors recently reported that a GaAs substrate covered with a 50 nm thick low-temperature (LT)-GaN buffer layer grown by metalorganic hydrogen chloride vapor phase epitaxy (MOHVPE) at 550 C did not deteriorate even after subsequent heating at up to 1000 C using a GaAs (111)A substrate [4,5]. Based on this finding, the high-temperature growth of GaN layers on GaAs (111)A substrates [6] and preparation of a freestanding GaN substrate [3] were attempted. Although these attempts were successful, the effect of temperature ramping rate of LT-GaN buffer layer on the crystalline quality of subsequent high-temperature grown GaN layers has yet to be clarified.…”

“…Recently, large freestanding GaN substrates have been prepared by separating thick HVPE GaN layers from sapphire [1,2] or GaAs [3] substrates. However, separation of a GaN layer is very difficult when a sapphire is used as a substrate because sapphire is very hard and it has no known practical etchant.…”

“…Trimethylgallium (TMG) and ammonia (NH 3 were used as Ga and N sources. TMG transported with the hydrogen (H 2 ) carrier gas was mixed with hydrogen chloride (HCl) in the upstream region of the reactor maintained at 750 C to form gaseous GaCl.…”

Local current conduction due to edge dislocations in deformed GaN studied by scanning spreading resistance microscopy

“…Details of the growth technique and structural characterization of the crystals have been described elsewhere [15]. For compression tests, rectangular specimens with dimensions 1.0 × 1.0 × 3.6 mm 3 were cut out from single crystals.…”