Single crystalline gallium nitride thick film having reduced bending deformation
View Patent ↗The present invention relates to a freestanding, thick, single crystalline gallium nitride (GaN) film having significantly reduced bending deformation. The inventive GaN film having a crystal tilt angle of C-axis to the <0001> direction per surface distance of 0.0022°/mm exhibits little bending deformation even at a thickness of 1 mm or more, and therefore, is beneficially used as a substrate for a luminescent device.
1. A method of preparing a freestanding, single crystalline gallium nitride (GaN) film comprising the steps of:
i) growing a heavily Si-doped GaN film on a substrate to a thickness of 20 to 50 μm using a hydride vapor phase epitaxy (HVPE) process, to induce the formation of cracks on the film;
ii) cooling the substrate/heavily Si-doped GaN laminate obtained in step i) to propagate the cracks to the bottom of the substrate;
iii) growing a GaN film on the crack-containing substrate/heavily Si-doped GaN laminate obtained in step ii) using an HVPE process; and
iv) removing the crack-containing substrate and heavily Si-doped GaN layer from the crack-containing substrate/Si-heavily doped GaN/GaN film composite obtained in step iii) to obtain the GaN film,
wherein the single crystalline gallium nitride film has a crystal tilt angle of C-axis to <0001> direction per surface crystal distance of 0.0022°/mm.
2. The method of claim 1 , wherein the substrate is sapphire.
3. The method of claim 1 , wherein in step i), the heavily Si-doped GaN film is grown by introducing HCl gas to a vessel containing a metallic Ga and maintained at an HVPE reaction temperature of 600 to 900° C. to generate gaseous GaCl, while separately introducing ammonia (NH 3 ) gas and a Si-precursor gas into the reactor, to allow the reactions between GaCl, the Si precursor, and the ammonia gas to occur on the surface of the substrate.
4. The method of claim 3 , wherein the HCl gas, the ammonia gas and the Si-precursor gas are employed in a volume ratio of 20:30:1 to 70:300:1.
5. The method of claim 1 , wherein the heavily Si-doped GaN film has a Si-doping concentration of 5×10 18 to 2×10 19 atoms/cm 3 .
6. The method of claim 1 , wherein the HVPE process in step i) or iii) is conducted at a GaN film growth temperature of 900 to 1100° C.
7. The method of claim 6 , wherein the HVPE process is conducted at a GaN film growth rate of 10 to 100 μm/h.
8. The method of claim 1 , wherein in step ii), the laminate is cooled to 200 to 400° C.