(Invited) High Brightness, Large Scale GaN Based Light-Emitting Diode Grown on 8-Inch Si Substrate

GaN based light-emitting diodes(LEDs) grown on a Si substrate is one of promising future technologies in LED industry due to its scalability and costeffectiveness compare to the conventional sapphire based LEDs.One of major technical issues in GaN/Si LED is the severemismatch oflattice and thermal expansion coefficientsbetween GaNand Si, which induces significant tensile strain in the GaNepilayer that often leads to wafer cracking. Optical loss by the absorbing Si substrate is another barrier to overcome for realizing high-brightness LEDs competitive to those on sapphire or SiC substrates.

In this study, we demonstrated blue LEDs grown on  8-inch diameter Si substrate and fabricated high brightness devicesutilizing vertical chip process Thecrack-free InGaN/GaN LED waferswith strain-engineered buffer structure were grown on 8-inch diameter Si(111) substrates by metalorganic chemical vapor deposition (MOCVD) system (Veeco TurboDisk k465i).The optimized growth conditions of AlN buffer layer improved the crystalline quality of GaNepilayers. The FWHM of (002) and (102) ω-scan is 280 and 420 arcsec, respectively. These values are comparable to the best reported so far for GaN on silicon. The surface morphology of GaN layer investigated using atomic force microscopy (AFM) exhibits very smooth surface and clear atomic step flow patterns. The root-mean-square (RMS) roughness is 0.15 nm in a 5x5 μm² scan area.For LED on 8-inch Si, MQW PL wavelength uniformity of ~0.5% (2.4 nm) has been achieved using the proper strain/curvature engineering with optimized wafer carrier designs. These are among the lowest values reported to date.

After the epitaxial growth with silicon substrate, a 1mm × 1mm sized vertical type LED(VLED) was fabricated using both wafer bonding process and Si removing process. While the GaN on sapphire employs a laser lift-off technique to remove the substrate, we developed the wet etching process in order to remove the silicon substrate without any damageon the surface of LED structure. The electro-optical characteristics of the fabricated VLED in this work shows good efficiency(almost 1W light power at 1A inject current) with operating voltage of 4.0V.