研究目的
To investigate the epitaxial lateral overgrowth of GaN on nano-cavity patterned sapphire substrates (NCPSS) for improving the crystal quality, reducing threading dislocation density, and enhancing light extraction efficiency in GaN-based light-emitting diodes (LEDs).
研究成果
The use of NCPSS for GaN growth significantly reduces TDD and compressive stress while enhancing light extraction through effective light scattering by nano-cavities. This approach is promising for improving the efficiency of GaN-based LEDs.
研究不足
The study acknowledges imperfections in the nano-cavity pattern due to the spin coating process, which may affect the uniformity and performance of GaN growth. The correlation between diffuse reflectance enhancement and light extraction efficiency in LEDs is noted as difficult to directly quantify.
1：Experimental Design and Method Selection:
The study involved the fabrication of NCPSS using polystyrene sphere coating, reactive ion etching, alumina deposition, and thermal oxidation. GaN was grown on NCPSS using metal-organic chemical vapor deposition (MOCVD).
2：Sample Selection and Data Sources:
A 2-inch c-plane sapphire substrate was used for fabricating NCPSS. GaN layers were grown on both NCPSS and planar sapphire substrates for comparison.
3：List of Experimental Equipment and Materials:
Equipment included a Thomas Swan MOCVD reactor, FESEM (Hitachi S-4800), AFM, CL (Gatan MonoCL4), XRD (Phillips PANalytical X’pert Pro), TEM (JEOL JEM-2100F), FIB (NOVA 600 Nanolab), PL measurement setup, and micro-Raman spectroscopy (Horiba JY LabRAM HR Evolution). Materials included TMGa, NH3, TMAl, and H2O.
4：2O. Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The NCPSS was fabricated by spin coating PS spheres, O2 RIE, ALD of alumina, and thermal annealing. GaN was grown on NCPSS and planar substrates under controlled conditions.
5：Data Analysis Methods:
Structural and optical properties were analyzed using SEM, AFM, CL, XRD, TEM, PL, and Raman spectroscopy. TDD was calculated from CL images, and stress was evaluated from Raman shifts.
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TEM
JEM-2100F
JEOL
Investigation of threading dislocation behaviors in GaN layers
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FESEM
S-4800
Hitachi
Structural analysis of NCPSS and GaN layers
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AFM
Surface morphology analysis of GaN layers
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CL
MonoCL4
Gatan
Evaluation of crystal quality of GaN layers
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XRD
PANalytical X’pert Pro
Phillips
Evaluation of crystal quality of GaN layers
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FIB
NOVA 600 Nanolab
Preparation of TEM specimens
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PL measurement setup
Optical properties investigation of GaN layers
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micro-Raman spectroscopy
LabRAM HR Evolution
Horiba JY
Evaluation of residual stress in GaN layers
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spectrophotometer
Cary5000
Varian
Measurement of diffuse reflectance of GaN layers
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