共查询到20条相似文献,搜索用时 15 毫秒
1.
《Current Applied Physics》2002,2(4):305-310
Until recently, molecular beam epitaxy (MBE) has been behind metalorganic chemical vapor deposition (MOCVD) as a growth technique for III-nitride thin films, due to the lack of nitrogen source powerful enough for the growth in vacuum and the understanding of growth mechanism. We have clarified that the quality of GaN epilayers on sapphire substrates grown by N2 plasma-assisted MBE can be much improved by realizing Ga-polarity growth mode, which enables us to fabricate HFETs using the MBE-grown AIGaN/GaN 2DEG structures. The Ga-polarity growth mode was found to be achieved by Al high temperature buffer process, In flux exposure etc., and directly confirmed by coaxial impact collision ion scattering spectroscopy (CAICISS) technique. The relation between the surface reconstruction structure of GaN epilayers and the lattice polarity of the epilayers is also shown. 相似文献
2.
Miasojedovas S Butkus M Jursenas S Lucznik B Grzegory I Suski T 《Micron (Oxford, England : 1993)》2009,40(1):118-121
Luminescence properties of 100-mum thick GaN epilayers grown by hydride vapor phase epitaxy (HVPE) over three different substrates: high-pressure grown n-type bulk GaN (HP-n-GaN), high-pressure bulk GaN doped with magnesium (HP-GaN:Mg), and free-standing HVPE lifted-off from sapphire (FS-HVPE-GaN), were compared by means of one-photon and two-photon excitations. The contribution of carrier capture to nonradiative traps was estimated by the analysis of luminescence transients with carrier diffusion taken into account. The estimated values of carrier lifetime of about 3ns and diffusion coefficient of 1cm(2)/s indicate the highest quality of GaN epilayers on FS-HVPE-GaN substrates. 相似文献
3.
GaN外延层中的缺陷对光学性质的影响 总被引:1,自引:1,他引:0
用金属有机化合物气相外延(MOVEP)方法生长具有不同表面形貌的非掺杂GaN,并对部分样品的外延层表面进行镜面加工.用阴极射线发光、光散射和拉曼散射方法观察GaN中深能级发光、缺陷散射光分布和拉曼散射光频移.结果表明,缺陷不但影响GaN的发光和光散射,而且影响拉曼频移 相似文献
4.
Weijun Luo Xiaoliang Wang Lunchun Guo Hongling Xiao Cuimei Wang Junxue Ran Jianping Li Jinmin Li 《Superlattices and Microstructures》2008,44(2):153-159
Low temperature (LT) AlN interlayers were used to effectively reduce the tension stress and micro-cracks on the surface of the GaN epilayer grown on Si (111) substrate. Optical Microscopy (OM), Atomic Force Microscopy (AFM), Surface Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were employed to characterize these samples grown by metal-organic chemical vapor deposition (MOCVD). In addition, wet etching method was used to evaluate the defect of the GaN epilayer. The results demonstrate that the morphology and crystalline properties of the GaN epilayer strongly depend on the thickness, interlayer number and growth temperature of the LT AlN interlayer. With the optimized LT AlN interlayer structures, high quality GaN epilayers with a low crack density can be obtained. 相似文献
5.
6.
This paper reports on N-, mixed-, and Ga-polarity buffer layers are
grown by molecular beam epitaxy (MBE) on sapphire (0001) substrates,
with the GaN thicker films grown on the buffer layer with different
polarity by hydride vapour epitaxy technique (HVPE). The surface
morphology, structural and optical properties of these HVPE-GaN
epilayers are characterized by wet chemical etching, scanning
electron microscope, x-ray diffraction, and photoluminescence
spectrum respectively. It finds that the N-polarity film is unstable
against the higher growth temperature and wet chemical etching, while
that of GaN polarity one is stable. The results indicate that the
crystalline quality of HVPE-GaN epilayers depends on the polarity of
buffer layers. 相似文献
7.
Undoped GaN epilayers were grown on c-plane sapphire substrates under different growth temperatures by metalorganic chemical
vapour deposition (MOCVD). The optical and structural characteristics of these grown samples were studied and compared. It
was found that the crystalline quality of GaN film deposited at 1050°C was better that of other samples. Photoluminescence
spectra showed that the intensities of yellow luminescence band of the samples decreased as the growth temperature increased.
All above test results demonstrate that high temperature deposition can serve as a good method for high-quality GaN epilayer
growth and there exists an optimal growth temperature. 相似文献
8.
《Current Applied Physics》2003,3(4):385-388
Double crystal rocking curve (DCRC), atomic force microscopy (AFM), scanning electron microscopy (SEM), and photoluminescence (PL) measurements on GaN epilayers grown with various thicknesses (3.4, 8.5, 17, 34, and 51 nm) of the AlN buffer layer were carried out to investigate the surface, the structural, and the optical properties of the GaN epilayers. The results of the DCRC, AFM, SEM, and PL measurements showed that the GaN epilayer grown on a 3.4 nm AlN buffer layer had the best quality. These results indicate that GaN active layers grown on 3.4 nm AlN buffer layers hold promise for potential applications in optoelectronic devices. 相似文献
9.
Effect of Reactor Pressure on Qualities of GaN Layers Grown by Hydride Vapour Phase Epitaxy 下载免费PDF全文
The influence of reactor pressure on GaN layers grown by hydride vapour phase epitaxy (HVPE) is investigated. By decreasing the reactor pressure from0. 7 to 0.5 mm, the GaN layer growth mode changes from the island-like one to the step flow. The improvements in structural and optical properties and surface morphology of GaN layers are observed in the step flow growth mode. The results clearly indicate that the reactor pressure, similarly to the growth temperature, is One of the important parameters to influence the qualities of GaN epilayers grown by HVPE, due to the change of growth mode. 相似文献
10.
A. Guillén-Cervantes Z. Rivera-ÁlvarezM. López-López A. Ponce-PedrazaC. Guarneros V.M. Sánchez-Reséndiz 《Applied Surface Science》2011,258(3):1267-1271
GaN thin films grown by MOCVD on (0 0 0 1) Al2O3 substrates at different growth pressures were characterized by field-emission scanning electron microscopy, atomic force microscopy, micro-Raman, and photoluminescence at room temperature. It was found that there is an optimum pressure of 76 Torr at which the structural and optical properties of the GaN samples are superior. On the other hand samples grown at higher pressure exhibited hexagonal surface pits and surface spirals. The results showed that the growth pressure strongly influences the morphology, and significantly affects the structural and optical properties of the GaN epilayers. 相似文献
11.
Comparative study of different properties of GaN films grown on(0001) sapphire using high and low temperature AlN interlayers 下载免费PDF全文
Comparative study of high and low temperature AlN
interlayers and their roles in the properties of GaN epilayers
prepared by means of metal organic chemical vapour deposition on
(0001) plane sapphire substrates is carried out by high resolution
x-ray diffraction, photoluminescence and Raman spectroscopy. It is
found that the crystalline quality of GaN epilayers is improved
significantly by using the high temperature AlN interlayers, which
prevent the threading dislocations from extending, especially for
the edge type dislocation. The analysis results based on
photoluminescence and Raman measurements demonstrate that there
exist more compressive stress in GaN epilayers with high temperature
AlN interlayers. The band edge emission energy increases from
3.423~eV to 3.438~eV and the frequency of Raman shift of $E_{2
}$(TO) moves from 571.3~cm$^{ - 1}$ to 572.9~cm$^{ - 1}$ when the
temperature of AlN interlayers increases from 700~$^{\circ}$C to
1050~$^{\circ}$C. It is believed that the temperature of AlN
interlayers effectively determines the size, the density and the
coalescence rate of the islands, and the high temperature AlN
interlayers provide large size and low density islands for GaN
epilayer growth and the threading dislocations are bent and
interactive easily. Due to the threading dislocation reduction in
GaN epilayers with high temperature AlN interlayers, the approaches
of strain relaxation reduce drastically, and thus the compressive
stress in GaN epilayers with high temperature AlN interlayers is
high compared with that in GaN epilayers with low temperature AlN
interlayers. 相似文献
12.
M.M. Bülbül S.R.P. Smith B. Obradovic T.S. Cheng C.T. Foxon 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):423-429
We report on Raman scattering measurements of all Raman-active phonons in wurtzite and zinc blende structure GaN epilayers
grown on GaAs (001), GaAs (111)A, and GaAs (111)B oriented substrates by means of molecular beam epitaxy (MBE). Raman spectra
are taken from these epilayers at room temperature and 77 K in backscattering geometry. The measured values of the phonon
frequencies are in agreement with other studies and with lattice dynamic calculations of phonon modes in GaN zinc blende and
wurtzite structures. We show that crystal quality is much better in samples grown on GaAs (111) substrates than in samples
grown on GaAs (001) substrates. The observation of disorder-activated modes gives information about sample quality. Comparison
of the spectra from different thickness epilayers shows that the GaN is more highly disordered close to the substrate, particularly
for the (001) substrates.
Received 16 July 1999 相似文献
13.
P. Chen R. Zhang X.F. Xu Y.G. Zhou Z.Z. Chen S.Y. Xie W.P. Li Y.D. Zheng 《Applied Physics A: Materials Science & Processing》2000,71(2):191-194
The oxidation of GaN epilayers in dry oxygen has been investigated. The GaN epilayers, about 1 7m thick, were grown on (0001) sapphire substrates by rapid thermal process/low pressure metalorganic chemical vapor deposition. Bulk /-2/ X-ray diffraction (XRD) data showed that the slight oxidation of GaN began to occur at 800 °C for 6 h. The oxide was identified as the monoclinic #-Ga2O3. The GaN epilayers were completely oxidized at 1050 °C for 4 h or at 1100 °C for 1 h. For all samples, the strongest oxide's peak is (11-3), and (30-6) followed. There is a rapid oxidation process in the initial stage of oxidation, and a relatively slow process followed when the temperature was over 1000 °C. The oxidation of two stages was limited by the rate of an interfacial reaction mechanism and by the diffusion mechanism, respectively. When the temperature reaches 1100 °C, the oxidation rate is very fast, which is considered as the results of the GaN decomposition at high temperature under atmosphere. The oxide layers were also observed by a scanning electron microscope, which shows a rough oxide surface and an expansion of the volume of 40%. The photoluminescence (PL) seriously influenced by the oxidation is also discussed. 相似文献
14.
S. Yu. Karpov R. A. Talalaev Yu. N. Makarov N. Grandjean J. Massies B. Damilano 《Surface science》2000,450(3):191-203
The kinetics of surface processes during the growth of GaN by molecular-beam epitaxy (MBE) with ammonia as the source of reactive nitrogen is studied theoretically and experimentally. A model of surface processes is developed taking into account specific effects of the blocking of NH3 adsorption sites by Group III and Group V surface species. Parameters of the model (respective kinetic rate constants) are determined from comparison with experimental data. It is shown that the evaporation rate of GaN in ammonia atmosphere is much lower than that in vacuum. Kinetics of GaN growth under gallium-rich and nitrogen-rich conditions are compared. Under nitrogen-rich conditions the GaN surface is predicted to be enriched by NHx surface radicals, in contrast to the case of growth under gallium-rich conditions or of free evaporation in vacuum. It is shown that use of the nitrogen-rich conditions allows one to increase the growth temperature by 80–90°C compared with the case of gallium-rich conditions or plasma-activated MBE. The increased growth temperature is favorable in improving the optical and electrical properties of the material grown. 相似文献
15.
利用高分辨X射线衍射(HRXRD)与拉曼散射光谱(Raman scattering spectra)研究了氮化处理与低温AlN缓冲层对低压金属有机化学气相沉积(LP-MOCVD)在r面蓝宝石衬底上外延的a面GaN薄膜中的残余应变的影响。实验结果表明:与氮化处理后生长的a-GaN相比,使用低温AlN缓冲层后生长的a-GaN具有较小的摇摆曲线的半高宽和较低的残余应变,而且其结构各向异性和残余应变各向异性也均有一定程度的降低。因此,与氮化处理相比,低温AlN缓冲层更有利于a-GaN的生长。 相似文献
16.
Daqing Xu Yimen Zhang Yuming Zhang Peixian Li Chao Wang 《Journal of magnetism and magnetic materials》2009,321(16):2442-2445
Manganese ions were implanted into unintentionally doped GaN epilayers grown by metal organic chemical vapor deposition (MOCVD). The (Ga,Mn)N and GaxMny phases were formed after Mn-implanted undoped GaN epilayers annealed at 700 and 800 °C. The samples showed ferromagnetic behavior at room temperature with the highest magnetization obtained in the sample annealed at 800 °C. Ferromagnetic signal reduces as annealing temperature increased above 900 °C. It is believed that the room-temperature ferromagnetic property of Mn-implanted undoped GaN epilayers are mainly from (Ga,Mn)N. The GaxMny phases play a critical role in providing holes and also contribute to increasing the ferromagnetic property. 相似文献
17.
Thermal characterization of GaN heteroepitaxies using ultraviolet transient thermoreflectance 下载免费PDF全文
《中国物理 B》2019,(6)
Thermal transport properties of GaN heteroepitaxial structures are of critical importance for the thermal management of high-power GaN electronic and optoelectronic devices. Ultraviolet(UV) lasers are employed to directly heat and sense the GaN epilayers in the transient thermoreflectance(TTR) measurement, obtaining important thermal transport properties in different GaN heterostructures, which include a diamond thin film heat spreader grown on GaN. The UV TTR technique enables rapid and non-contact thermal characterization for GaN wafers. 相似文献
18.
Optical and structural investigation of a-plane GaN layers on r-plane sapphire with nucleation layer optimization 下载免费PDF全文
Nonpolar a-plane GaN epilayers are grown on several r-plane sapphire substrates by metal organic chemical vapour deposition using different nucleation layers:(A) a GaN nucleation layer deposited at low temperature(LT);(B) an AlN nucleation layer deposited at high temperature;or(C) an LT thin AlN nucleation layer with an AlN layer and an AlN/AlGaN superlattice both subsequently deposited at high temperature.The samples have been characterized by Xray diffraction(XRD),atomic force microscopy and photoluminescence.The GaN layers grown using nucleation layers B and C show narrower XRD rocking curves than that using nucleation layer A,indicating a reduction in crystal defect density.Furthermore,the GaN layer grown using nucleation layer C exhibits a surface morphology with triangular defect pits eliminated completely.The improved optical property,corresponding to the enhanced crystal quality,is also confirmed by temperature-dependent and excitation power-dependent photoluminescence measurements. 相似文献
19.
20.
《Current Applied Physics》2001,1(2-3):191-195
After the undoped GaN epilayers were grown on (0 0 0 1) sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE), the photoconductivity (PC) and thermally stimulated current (TSC) measurements have been carried out so as to investigate the hydrogenation and annealing effect of the deep levels. These results indicate that the values of concentrations of the deep levels in the GaN epilayers decrease by the passivation of hydrogenation in both PC and TSC measurements. After hydrogenation, the PC intensity for the hydrogenated GaN epilayer decreased remarkably in comparison with that for the as-grown sample and the TSC peak near 150 K drastically decreased.In the case of PC measurement, the PC intensity for the hydrogenated and annealed GaN epilayer was approximately half that for the hydrogenated only GaN epilayer when the hydrogenated epilayer was annealed at 700°C. This result reveals that the passivation of the deep levels due to the hydrogenation is still effective at the annealing temperature of 700°C. In the case of TSC measurement, the deep levels changed slightly in comparison with that of hydrogenated GaN epilayer when the hydrogenated GaN epilayer was annealed at 600°C for 30 s. This result also shows that the passivation of deep levels due to the hydrogenation is still effective at the annealing temperature of 600°C for 30 s. In considering the above circumstances, these TSC results are in reasonable agreement with the PC results. 相似文献