In this paper we report on the effect of an In x Ga1-x N continuously graded buffer layer on an InGaN epilayer grown on a GaN template.In our experiment,three types of buffer layers including constant composition,continuously graded composition,and the combination of constant and continuously graded composition are used.Surface morphologies,crystalline quality,indium incorporations,and relaxation degrees of InGaN epilayers with different buffer layers are investigated.It is found that the In x Ga1-x N continuously graded buffer layer is effective to improve the surface morphology,crystalline quality,and the indium incorporation of the InGaN epilayer.These superior characteristics of the continuously graded buffer layer can be attributed to the sufficient strain release and the reduction of dislocations.
Periodic triangle truncated pyramid arrays are successfully fabricated on the sapphire substrate by a low-cost and high-efficiency laser interference lithography(LIL)system.Through the combination of dry etching and wet etching techniques,the nano-scale patterned sapphire substrate(NPSS)with uniform size is prepared.The period of the patterns is 460 nm as designed to match the wavelength of blue light emitting diode(LED).By improving the stability of the LIL system and optimizing the process parameters,well-defined triangle truncated pyramid arrays can be achieved on the sapphire substrate with diameter of 50.8 mm.The deviation of the bottom width of the triangle truncated pyramid arrays is 6.8%,which is close to the industrial production level of 3%.
We use a simple and controllable method to fabricate GaN-based light-emitting diodes(LEDs) with 22?undercut sidewalls by the successful implementation of the inductively coupled plasma reactive ion etching(ICP-RIE).Our experiment results show that the output powers of the LEDs with 22?undercut sidewalls are 34.8 mW under a 20-mA current injection,6.75% higher than 32.6 mW,the output powers of the conventional LEDs under the same current injection.
Influences of the Si doping on the structural and optical properties of the InGaN epilayers are investigated in detail by means of high-resolution X-ray diffraction(HRXRD),photolumimescence(PL),scanning electron microscope(SEM),and atomic force microscopy(AFM).It is found that the Si doping may improve the surface morphology and crystal quality of the InGaN film and meanwhile it can also enhance the emission efficiency by increasing the electron concentration in the InGaN and suppressing the formation of V-defects,which act as nonradiative recombination centers in the InGaN,and it is proposed that the former plays a more important role in enhancing the emission efficiency in the InGaN.
