Abstract
The progress of nitride technology is widely limited and hindered by the lack of high-quality gallium nitride (GaN) wafers. Therefore, a large number of GaN epitaxial devices are grown on heterogeneous substrates. Although various additional treatments of substrate have been used to promote crystal quality, there is still plenty of room for its improvement, in terms of direct and continuous growth based on the hydride vapor phase epitaxy (HVPE) technique. Here, we report a three-step process that can be used to enhance the quality of GaN crystal by tuning V/III rate during successive HVPE process. In the growth, a metal-organic chemical vapor deposition (MOCVD) grown GaN on sapphire (MOCVD-GaN/Al2O3) was employed as substrate, and a high-quality GaN polyporous interlayer, with successful acquisition, without any additional substrate treatment, caused the growth stress to decrease to 0.06 GPa. Meanwhile the quality of GaN improved, and the freestanding GaN was directly obtained during the growth process.
Highlights
Gallium nitride (GaN), a III-V compound semiconductor, has a very wide range of applications in optoelectronic devices, including light-emitting diodes (LEDs) [1,2], laser diodes (LDs) [3,4], high-power and high-temperature electronic devices [5,6], and visible-blind photodetectors [7], thanks to its wide bandgaps
Lack of homoepitaxial substrate becomes the main reason that major GaN crystals are grown on foreign substrates, such as sapphire (Al2 O3 ) [14], gallium arsenide (GaAs) [15], and silicon (Si) [16]
Heteroepitaxial growth will generate high dislocation density, about 108 cm−2 caused by lattice mismatch, which is bad for the manufacturing of GaN-based devices with reliability and long lifetime [17]
Summary
Gallium nitride (GaN), a III-V compound semiconductor, has a very wide range of applications in optoelectronic devices, including light-emitting diodes (LEDs) [1,2], laser diodes (LDs) [3,4], high-power and high-temperature electronic devices [5,6], and visible-blind photodetectors [7], thanks to its wide bandgaps. Several growth techniques have been developed to grow GaN crystal, such as the hydride vapor phase epitaxy (HVPE) technique, the ammonothermal method, the high-pressure solution growth method, and the Na flux method [8,9,10,11,12]. HVPE is generally accepted as the most promising growth technique, due to the simple equipment and the flexibility of high growth rates [13]. Lack of homoepitaxial substrate becomes the main reason that major GaN crystals are grown on foreign substrates, such as sapphire (Al2 O3 ) [14], gallium arsenide (GaAs) [15], and silicon (Si) [16]. Heteroepitaxial growth will generate high dislocation density, about 108 cm−2 caused by lattice mismatch, which is bad for the manufacturing of GaN-based devices with reliability and long lifetime [17]. Greater efforts for the improvement of GaN crystal quality need to be done
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