InGaN/GaN多量子阱的组分确定和晶格常数计算

采用金属有机化学气相沉积(MOCVD)技术以蓝宝石为衬底在n型GaN单晶层上生长了InGaN/GaN多量子阱结构外延薄膜，利用高分辨X射线衍射(HRXRD)，卢瑟福背散射/沟道(RBS/channeling)，以及光致发光(PL)技术对InGaN/GaN多量子阱结构薄膜分别进行了平均晶格常数计算、In原子替位率计算和In组分的定量分析.研究表明：InGaN/GaN多量子阱的水平和垂直方向平均晶格常数分别为a_epi=0.3195nm，c_epi=0.5198nm，In原子的替位率为99.3%，利用HRXRD和RBS/channeling两种分析技术计算In的组分分别是0.023和0.026，并与样品生长时设定的预期目标相符合，验证了两种实验方法的准确性；而用室温条件下的光致发光谱(PL)来计算InGaN/GaN多量子阱中In的组分是与HRXRD和RBS/channeling的实验结果相差很大，说明用PL测试In组分的方法是不适宜的. 关键词： InGaN/GaN多量子阱 高分辨X射线衍射 卢瑟福背散射/沟道 光致发光     

全息技术制作二维光子晶体蓝宝石衬底提高发光二极管外量子效率

为了提高GaN基发光二极管(LED)的外量子效率,在蓝宝石衬底制作了二维光子晶体.衬底上的二维光子晶体结构采用激光全息技术和感应耦合等离子体(ICP)干法刻蚀技术制作,然后采用金属氧化物化学气相沉积(MOCVD)技术在图形蓝宝石衬底(PSS)上生长2μm厚的n型GaN层,4层量子阱和200nm厚的p型GaN层,形成LED结构.衬底上制作的二维光子晶体为六角晶格结构,晶格常数为3.8μm,刻蚀深度为800nm.LED器件光强输出测试结果显示,在PSS上制作的LED(PSS-LED)的发光强度普遍高于蓝宝石平 关键词： 全息 发光二极管 图形蓝宝石衬底 外量子效率     

Gain mechanisms in field‐free InGaN layers grown on sapphire and bulk GaN substrate

The gain mechanisms and recombination dynamics of InGaN layers strongly depend on the structural properties of the substrate material. The 4.5 nm and 9.5 nm thick layers were grown by metal organic chemical vapor deposition on two different substrates (sapphire and GaN) with different dislocation densities. Time‐resolved photoluminescence spectroscopy at high excitation densities identifies the saturation of nonradiative recombination centers through excited carriers as a major gain mechanism. The prime argument is an unusual nonexponential luminescence decay. This was confirmed by a lower threshold of the optical gain for the structures grown on GaN with lower dislocation densities. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural, electrical and optical characterization of InGaN layers grown by MOVPE

We present a study on n-type ternary InGaN layers grown by atmospheric pressure metalorganic vapour phase epitaxy(MOVPE) on GaN template/(0001) sapphire substrate.An investigation of the different growth conditions on n-type InxGa1 xN(x = 0.06 0.135) alloys was done for a series of five samples.The structural,electrical and optical properties were characterized by high resolution x-ray diffraction(HRXRD),Hall effect and photoluminescence(PL).Experimental results showed that different growth conditions,namely substrate rotation(SR) and change of total H2 flow(THF),strongly affect the properties of InGaN layers.This case can be clearly observed from the analytical results.When the SR speed decreased,the HRXRD scan peak of the samples shifted along a higher angle.Therefore,increasing the SR speed changed important structural properties of InGaN alloys such as peak broadening,values of strain,lattice parameters and defects including tilt,twist and dislocation density.From PL results it is observed that the growth conditions can be changed to control the emission wavelength and it is possible to shift the emission wavelength towards the green.Hall effect measurement has shown that the resistivity of the samples changes dramatically when THF changes.     

Strain Effect on Photoluminescences from InGaN MQWs with Different Barriers Grown by MOCVD

InGaN/GaN MQWs, InGaN/AlGaN MQWs and InGaN/AlInGaN MQWs are grown on （0001） sapphire substrates by MOCVD. Membrane samples are fabricated by laser lift-off technology. The photoluminescence spec-ra of membranes show a blue shift of peak positions in InGaN/GaN MQWs, a red shift of peak positions in InGaN/AlGaN MQWs and no shift of peak positions in InGaN/AIlnGaN MQWs from those of samples with substrates. Different changes in Raman scattering spectra and HR-XRD （0002） profile of InGaN/AlInGaN MQWs, from those of InGaN/GaN MQWs and InGaN/AlGaN MQWs, are observed. The fact that the strain changes differently among InGaN MQWs with different barriers is confirmed. The AIlnGaN barrier could adjust the residual stress for the least strain-induced electric field in InGaN/AIlnGaN quantum wells.     

Near-field optical characterization of GaN and InxGa1−xN/GaN heterostructures grown on freestanding GaN substrates

Using near-field scanning optical microscopy (NSOM), we report the spatial distribution of photoluminescence (PL) intensity in III-nitride-based semiconductor layers grown on GaN substrates. Undoped GaN, In_0.11Ga_0.89N, and In_0.13Ga_0.87N/GaN multi-quantum wells (MQWs) were grown by metal organic chemical vapor deposition (MOCVD) on freestanding GaN substrates. Micro-Raman spectroscopy has been used to evaluate the crystalline properties of the GaN homoepitaxial layers. The variation of the PL intensity from the NSOM imaging indicates that the external PL efficiency fluctuates from 20% to 40% in the 200 nm InGaN single layer on freestanding GaN, whereas it fluctuates from 20% to 60% in InGaN/GaN MQWs. In the NSOM-PL images, bright island-like features are observed. After deconvolution with the spatial resolution of the NSOM, the size of these features is estimated to be in the range of 150–250 nm.     

A Comparison of GaN Epilayers with Multiple Buffer Layers and with a Single Buffer Layer Grown on Si（111） Studied by HRXRD and RBS/Channeling

Two hexagonal GaN epilayers （samples A and B） with multiple buffer layers and single buffer layer are grown on Si （111） by metal-organic vapour phase epitaxy （MOVPE）. From the results of Rutherford backscattering （RBS）/channeling and high resolution x-ray diffraction （HRXRD）, we obtain the lattice constant （a and c） of two GaN epilayers （aA = 0.3190 nm, cA = 0.5184 nm and aB = 0.3192 nm, CB = 0.5179 nm）, the crystal quality of two GaN epilayers （ ХminA=4.87%, ХminB =7.35% along 〈1-↑213〉 axis） and the tetragonal distortion eT of the two samples along depth （sample A is nearly fully relaxed, sample B is not relaxed enough）. Comparing the results with the two samples, it is indicated that sample A with multiple buffer layers have better crystal quality than sample B with a single buffer layer, and it is a good way to grow GaN epilayer on Si （111） substrates using multiple buffer layers to improve crystal quality and to reduce lattice mismatch.     

Strain relaxation and optical properties of etched In_0.19Ga_0.81 N nanorod arrays on the GaN template

InGaN/GaN epilayers,which are grown on sapphire substrates by the metal-organic chemical-vapour deposition(MOCVD) method,are formed into nanorod arrays using inductively coupled plasma etching via self-assembled Ni nanomasks.The formation of nanorod arrays eliminates the tilt of the InGaN(0002) crystallographic plane with respect to its GaN bulk layer.Photoluminescence results show an apparent S-shaped dependence on temperature.The light extraction efficiency and intensity of photoluminescence emission at low temperature of less than 30 K for the nanorod arrays are enhanced by the large surface area,which increases the quenching effect because of the high density of surface states for the temperature above 30 K.Additionally,a red-shift for the InGaN/GaN nanorod arrays is observed due to the strain relaxation,which is confirmed by reciprocal space mapping measurements.     

Strain relaxation and optical properties of etched In0.19Ga0.81N nanorod arrays on the GaN template

InGaN/GaN epilayers,which are grown on sapphire substrates by the metal-organic chemical-vapour deposition(MOCVD) method,are formed into nanorod arrays using inductively coupled plasma etching via self-assembled Ni nanomasks.The formation of nanorod arrays eliminates the tilt of the InGaN(0002) crystallographic plane with respect to its GaN bulk layer.Photoluminescence results show an apparent S-shaped dependence on temperature.The light extraction efficiency and intensity of photoluminescence emission at low temperature of less than 30 K for the nanorod arrays are enhanced by the large surface area,which increases the quenching effect because of the high density of surface states for the temperature above 30 K.Additionally,a red-shift for the InGaN/GaN nanorod arrays is observed due to the strain relaxation,which is confirmed by reciprocal space mapping measurements.     

用X射线衍射法测定氮化镓马赛克结构中的面内扭转角

Ⅲ-Ⅴ族氮化物半导体材料在发光二极管、激光器和探测器方面有着广泛的应用,采用高分辨X射线衍射来测定用金属有机化学气相沉淀法在蓝宝石衬底上生长的氮化镓外延层马赛克结构的扭转角,分别研究了(0002)、(1013)、(1012)、(1011)、(2021)五个面的X射线摇摆曲线,并且用Pseudo-Voigt方程拟合每一个面的摇摆曲线,我们利用外推法很方便地测得氮化镓外延薄膜的面内扭转角。另外我们采用同步辐射X射线掠入射衍射对样品进行(1100)面反射φ扫描直接测得面内扭转角,对第一种方法进行验证,两种方法测量结果相同。从而提供一种简单、方便的GaN外延层的面内扭转角的测试方法,为深入研究GaN材料奠定良好基础。     

Microstructures of grain boundaries in (001)-oriented strontium bismuth tantalate thin films grown by pulsed laser deposition

(001)-oriented strontium bismuth tantalate thin films have been grown on Pt/TiO₂/SiO₂/Si (100) substrates by pulsed laser deposition. The room-temperature current–electric field dependence of the films has been investigated, which revealed a space-charge-limited conduction mechanism. The microstructures of grain boundaries and structural defects in these films were also examined by transmission electron microscopy and high-resolution transmission electron microscopy, respectively. The grains of the films deposited at 550 °C exhibited polyhedral morphologies, and the average grain size was about 50 nm in length and 35 nm in width. At a small misorientation angle (8.2°) tilt boundary, a regular array of edge dislocations with about 3-nm periodic distance was observed, and localized strain contrast near the dislocation cores was also observed. The Burgers vector b of the edge dislocation was determined to be [110]. At a high misorientation angle (39.0°) tilt grain boundary lattice strain contrast associated with the distortion of lattice planes was observed, and the mismatching lattice images occurred at about 2 nm along the boundary. The relationship between microstructural defects at grain boundaries and leakage currents of these films is also discussed. Received: 8 September 2000 / Accepted: 18 December 2000 / Published online: 28 February 2001     

An evaluation of the growth of nitrides on semipolar substrates using two indicators

We evaluate the properties of nitride heterostructures on semipolar substrates using two indicators: the cancellation of the Quantum Confined Stark Effect and the volume density of elastic energy stored in the strained layers of GaN–GaInN heterostructures lattice‐matched to (hkl)‐oriented GaN semipolar substrates. These two parameters indicate that the growth on specific orientations is a plus when compared to growth on (0001) polar substrates. We will show that, unfortunately, one cannot simultaneously minimize the stored elastic energy and cancel the Quantum Confined Stark Effect, but it is possible to significantly reduce both of them. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of GaN layers grown on silicon-on-insulator substrates

In this study, we report growth and characterization of GaN layers on (1 0 0)- and (1 1 1)-oriented silicon-on-insulator (SOI) substrates. Using metalorganic chemical vapor deposition (MOCVD) technique, GaN layers are grown on KOH treated Si (1 0 0) overlayers of thin SIMOX SOI substrates. Growth of GaN on such surface with an AlN buffer leads to c-axis orientated textured GaN. This is evident from high-resolution X-ray diffraction (HRXRD) measurement, which shows a much broader rocking curve linewidth. Significantly enhanced photoluminescence (PL) intensity and partial stress relaxation is observed in GaN layers grown on these SOI substrates. Furthermore, GaN grown on (1 1 1)-oriented bonded SOI substrates shows good surface morphology and improved optical quality. Micro-Raman, micro-PL, and HRXRD measurements reveal single crystalline hexagonal GaN oriented along (0 0 0 1) direction. We also report growth and characterization of InGaN/GaN multi-quantum well structures on (1 1 1)-oriented bonded SOI. Such an approach to realize nitride epilayers would be useful to fabricate GaN-based micro-opto-electromechanical systems (MOEMS) and sensors.     

X-ray diffraction micro-imaging of strain in laterally overgrown GaAs layers. Part I: analysis of a single GaAs stripe

Spatially resolved X-ray diffraction (SRXRD) is used for micro-imaging of strain in GaAs:Si layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO₂-masked GaAs substrates. We show that laterally overgrown parts of the layers (wings) are tilted towards the underlying mask. By SRXRD mapping local wing tilt is easily distinguished from macroscopic sample curvature. The direction of the tilt and distribution of tilt magnitude across the width of each layer can also be readily determined. This allows measuring of the shape of the lattice planes in individual ELO stripes. Downward wing tilt disappears completely when the mask is removed by selective etching. Then residual strain in ELO layers is exposed. In particular, upward tilt is found in free-standing ELO wings. Numerical simulations show that this phenomenon is caused by different concentrations of silicon dopant in vertically and laterally grown parts of the layer. PACS 61.05.cp; 61.72.Ff; 68.55.ag     

InGaN/GaN p-i-n Photodiodes Fabricated with Mg-Doped p-InGaN Layer

Mg-doped p-InGaN layers with In composition of about 10% are grown by metalorganic chemical vapor deposition (MOCVD). The effect of the annealing temperature on the p-type behavior of Mg-doped InGaN is studied. It is found that the hole concentration in p-InGaN increases with a rising annealing temperature in the range of 600-850°C, while the hole mobility remains nearly unchanged until the annealing temperature increases up to 750°C, after which it decreases. On the basis of conductive p-type InGaN growth, the p-In_0.1Ga_0.9N/i-In_0.1Ga_0.9N/n-GaN junction structure is grown and fabricated into photodiodes. The spectral responsivity of the InGaN/GaN p-i-n photodiodes shows that the peak responsivity at zero bias is in the wavelength range 350-400nm.     

Optical characterization of InxGa1−xN alloys

InGaN layers were grown by molecular beam epitaxy (MBE) either directly on (0 0 0 1) sapphire substrates or on GaN-template layers deposited by metal-organic vapor-phase epitaxy (MOVPE). We combined spectroscopic ellipsometry (SE), Raman spectroscopy (RS), photoluminescence (PL) and atomic force microscopy (AFM) measurements to investigate optical properties, microstructure, vibrational and mechanical properties of the InGaN/GaN/sapphire layers.The analysis of SE data was done using a parametric dielectric function model, established by in situ and ex situ measurements. A dielectric function database, optical band gap, the microstructure and the alloy composition of the layers were derived. The variation of the InGaN band gap with the In content (x) in the 0 < x ≤ 0.14 range was found to follow the linear law E_g = 3.44-4.5x.The purity and the stability of the GaN and InGaN crystalline phase were investigated by RS.     

Comparison of InGaN/GaN light emitting diodes grown on m ‐plane and a ‐plane bulk GaN substrates

InGaN/GaN‐based light emitting diodes (LEDs) grown on m ‐plane, a ‐plane and off‐axis between m ‐ and a ‐plane GaN bulk substrates were investigated. A smooth surface was obtained when a ‐plane substrate was applied; however, large amounts of defects were observed. Photoluminescence measurements of the LEDs with a well thickness of 2.5 nm revealed that all the LEDs showed the peak emission wavelength at 389 nm. The PL intensity of the a ‐plane LED is one order of magnitude lower than that of the m ‐plane LED. The a ‐plane LEDs showed significant lower electroluminescence output powers than m ‐plane LEDs, suggesting that excitons are trapped by the defects, which act as non‐radiative recombination centers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

GaAs(001)衬底上分子束外延生长立方和六方GaN薄膜

采用分子束外延方法在GaAs(001)衬底上生长出了03微米厚的GaN薄膜,X射线双晶衍射和室温光荧光测试结果表明,采用GaAs氮化表面作为成核层可获得高纯度立方GaN薄膜而采用AlAs氮化表面作为成核层可获得高纯度六方GaN薄膜.这一研究结果表明在GaAs衬底上生长GaN薄膜的相结构可以通过选择不同的成核层来控制. 关键词：     

Influence of growth parameters on the properties of InGaN/GaN multiple quantum well grown by metalorganic chemical vapor deposition

The effects of growth parameters such as barrier growth time, growth pressure and indium flow rate on the properties of InGaN/GaN multiple quantum wells (MQWs) were investigated by using photoluminescence (PL), high resolution X-ray diffraction (HRXRD), and atomic force microscope (AFM). The InGaN/GaN MQW structures were grown on c-plane sapphire substrate by using metalorganic chemical vapor deposition. With increasing barrier growth time, the PL peak energy is blue-shifted by 18 nm. For InGaN/GaN MQW structures grown at different growth pressures, the PL intensity is maximized in the 300 Torr – grown structure, which could be attributed to the improved structural quality confirmed by HRXRD and AFM results. Also, the optical properties of InGaN/GaN MQW are strongly affected by the indium flow rate.     

垒掺In提高InGaN/GaN多量子阱发光特性

利用金属有机物化学气相淀积技术在蓝宝石衬底上生长InGaN/GaN多量子阱结构.对多量子阱垒层掺In和非掺In进行了比较研究，结果表明，垒掺In 的样品界面质量变差，但明显增加了光致发光谱的峰值强度和积分强度，带边峰与黄光峰强度之比增大，降低了表面粗糙度.利用这两种结构制备了相应的发光二极管(LED)样品.通过电荧光测量可知，垒掺In的LED比非掺In的LED有较高的发光强度和相对均匀的波长，这主要是由于垒掺In后降低了阱与垒之间晶格失配的应力，从而降低了极化电场，提高了辐射复合效率. 关键词： InGaN/GaN多量子阱 X射线双晶衍射 原子力显微镜 光致发光