The Study On Growth And Luminescence Of Semipolar Group-? Nitride

Since the wurtzite Group-III nitride materials are of polar crystal,the strong spontaneous and piezoelectric polarization fields(PFs)are built within the InGaN/GaN and A1GaN/GaN heterostructure grown on polar(0001)atomic plane,leading to significant reduction of carrier recombination rate.In addition,with the increase of indium content in InGaN,the InGaN alloy phenomena(e.g.,InN decomposition,indium aggregation,phase separation,etc.)and the related pit formation become severe,due to the large difference of interatomic spacing,equilibrium vapor pressure,and formation enthalpies between InN and GaN.Therefore,the growth of high-quality high indium content InGaN materials required for high-performance long-wavelength optoelectronic devices is a big challenge.Growth of group-? nitride semiconductor heterostructures on nonpolar or semipolar planes has been demonstrated to the elimination or reduction of the PFs inherently existing in polar ?-nitrides growing along the c-(0001)axis.Among these,the growth on naturally-occurring semipolar(1122)planes combines the merits of nearly free PFs,high indium incorporation efficiency,a wide growth window,and high optical gain.Due to the lack of large-sized and low-priced(1122)GaN bulk substrates,semipolar(1122)GaN films grown on heterosubstrates have high-density structural defects and rough surfaces,which have deleterious effects on the electrical and optical properties,reliability,and lifetime of the semipolar optoelectronic devices.In this paper we foucs on the growth and luminescence of semipolar(1122)GaN and InGaN materials by experimental growth,properties characterizations and theoretical simulations,with the aim to improve the crystalline quality and optical properties of the semipolar(1122)GaN and InGaN materials.The major works are listed below:1.An in situ asymmetric island sidewall growth(AISG)is developed to modify surface/interface properties and to improve the crystalline quality and optical properties of the semipolar(1122)GaN epilayers and high indium content InGaN/GaN quantum wells(QWs).Pure semipolar(1122)epilayers with reduced surface striation density,a low basal-plane stacking fault density of?5.0x103 cm-1,and a low threading dislocation density of?8.Ox107 cm-2 are obtained.The FWHM of the(1122)peaks with the incident beam aligned to the[1123]and[1100]directions are as small as 91 and 293 arcsec,respectively,which is one of best reported data.With AISG,the semipolar InGaN/GaN QWs on modified GaN epilayers exhibit the uniform indium distribution in the absence of threading defects,and significantly strong luminescence with a peak wavelength of 540 nm.No strong blue-shift is observed in the temperature-dependent cathodoluminescence spectra(Temperature incease from 80K to 120K)and excitation-power-dependent photoluminescence spectra,indicating that the PFs built within the InGaN/GaN heterostructure are of nearly free.2.An interface modification,called as in situ site-specific gallium filling and nanograin growth,is realized by high-temperature annealing of an inserted low-temperature GaN layer.The interface modification can enhances adatom diffusion and site-selectively blocks threading defects for the semipolar(1122)GaN epilayers.The FWHM of the(1122)peaks with the incident beam aligned to the[1123]and[1100]directions are as small as 100 and 580 arcsec for the interface-modified semipolar GaN epilayers,respectively.The luminescence properties of the InGaN/GaN QWs grown on the interface-modified semipolar GaN epilayers are significantly enhanced by the interface modification.Green-amber emission with double peaks at 520 and 600 nm is observed for the InGaN/GaN QWs grown on the interface-modified semipolar GaN epilayers.No blue-shift in the excitation-power-dependent photoluminescence spectra indicates the abence of PFs built within the InGaN/GaN heterostructure by interface modification.3.An in situ SiNx pretreatment of m-sapphire substrate surface is employed to improve the the crystalline quality and optical properties of semipolar(1122)GaN epilayers.The FWHM of the(1122)peaks with the incident beam aligned to the[1123]and[1100]directions are as small as 110 and 465 arcsec for the SiNx-pretreated semipolar GaN epilayers,respectively.Interface modification of high indium content InGaN/GaN quantum wells was carried out by Mg pretreatment of the GaN barrier surface.The indium in the Mg pretreated InGaN layer was homogeneously distributed,making the interfaces abrupt.The cathodoluminescence intensity of the Mg pretreated InGaN/GaN quantum wells was correspondingly much stronger than those of the InGaN/GaN quantum wells without Mg pretreatment.4.We have demonstrated high-brightness ultraviolet,violet,blue,and green InGaN and InN ultrathin layers on the semipolar(1122)GaN epilayers.The InGaN ultrathin layers show the uniform indium distribution,abrupt interfaces,and abence of InGaN alloy phenomena and threading defects.Perfect-monochrome high-brightness ultraviolet and violet emission at 370 and 420 nm is observed from these InGaN ultrathin layers samples.High-brightness violet,blue,and green emission at 430,445,505 and 530 nm is observed from these InN ultrathin monolayers samples.