In this paper we report on the effect of an lnxGal xN 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 InxGa1-xN 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.
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 exper- iment results show that the output powers of the LEDs with 22° undercut sidewalls are 34.8 rnW 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 tile 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.
Due to their low power consumption,long lifetime and high efficiency,nitrides based white lightemitting-diodes（LEDs） have long been considered to be a promising technology for next generation illumination.In this work,we provide a brief review of the development of GaN based LEDs.Some pioneering and significant experiment results of our group and the overview of the recent progress in this field are presented.We hope it can provide some meaningful information for the development of high efficiency GaN based LEDs and solid-statelighting.
Two kinds of short-period type II superlattices(SLs)InAs(6 monolayers(MLs))/GaSb(3 MLs)and InAs(8 MLs)/GaSb(8 MLs)which can serve for mid-infrared(MIR)detection have been grown by molecular beam epitaxy(MBE)on p-type GaSb(100)substrates.The cutoff wavelength for the two superlattices(SLs)was found to be around 4.8 lm at 300 K.The high resolution X-ray diffraction(HRXRD)measurements indicated that the InAs(8 MLs)/GaSb(8 MLs)SLs have better crystalline quality than that of the InAs(6 MLs)/GaSb(3 MLs)SLs.However,compared with infrared absorption in the 2.5–4.3 lm range,the optical absorption of InAs(6 MLs)/GaSb(3MLs)SLs was more excellent.This can be attributed to increase probability of the electron and hole wave function overlap in the thinner period thickness.
