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1.
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, In0.11Ga0.89N, and In0.13Ga0.87N/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.  相似文献   

2.
GaN layers and Al1−xInxN/AlN/GaN heterostructures have been studied by scanning probe microscopy methods. Threading dislocations (TDs), originating from the GaN (0 0 0 1) layer grown on sapphire, have been investigated. Using Current-Atomic Force Microscopy (C-AFM) TDs have been found to be highly conductive in both GaN and AlInN, while using semi-contact AFM (phase-imaging mode) indium segregation has been traced at TDs in AlInN/AlN/GaN heterostructures. It has been assessed that In segregation is responsible for high conductivity at dislocations in the examined heterostructures.  相似文献   

3.
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aepi=0.3195nm,cepi=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  相似文献   

4.
利用金属有机气相外延方法研究了非故意掺杂GaN薄膜的方块电阻与高温GaN体材料生长时载气中N2比例的关系.研究发现,随着载气中N2比例的增加,GaN薄膜方块电阻急剧增加.当载气中N2比例为50%时,GaN薄膜方块电阻达1.1×108Ω/□,且GaN表面平整,均方根粗糙度为0.233nm.二次离子质谱分析发现,载气中N2比例不同的样品中碳、氧杂质含量无明显差别.随着载气中N2关键词: 半绝缘GaN薄膜 载气 金属有机气相外延 位错  相似文献   

5.
We report the growth of GaN epilayers on the sapphire substrate etched by MOCVD. Sapphire substrate is etched by H3PO4 and NaOH. The Raman scattering spectroscopy and photoetching analyses show that the substrate etched can effectively decrease the residual stress and the dislocations density in these epilayers. The X-ray diffraction analysis shows the process can reduce the value of the FWHM. Therefore, the quality of GaN epilayers should be improved by substrate etched.  相似文献   

6.
The crystal structure and dielectric properties of 0.95K0.5Na0.5NbO3-0.05BaZrO3 (KNN-BZ) ceramic have been investigated by X-ray diffraction and dielectric measurement. A rhombohedral distortion was caused and the dielectric permittivity near Curie temperature was significantly enhanced by introducing BZ into KNN. The dielectric and conductivity properties of the sample were studied by using AC impedance spectroscopy and universal dielectric relaxation law in detail. The typical high-temperature dielectric relaxation process was confirmed to be related to the oxygen vacancies inside the ceramic. The effect of lattice distortion on the activation energy for oxygen vacancy migration in KNN-BZ was discussed by comparing with KNN and KNN-BaTiO3.  相似文献   

7.
The effects of a KOH treatment on the properties of n-type GaN surfaces and associated Au/n-GaN contacts have been investigated by X-ray photoelectron spectroscopy, atomic force microscopy, reflection high-energy-electron diffraction, current–voltage and electron-beam-induced current characterization. Ga-polar surfaces grown by molecular beam epitaxy and metal–organic chemical vapour deposition were compared. A decrease in electron barrier height and an increase in non-radiative recombination properties of Au/n-GaN contacts were found with KOH treatment, correlated with an increase of surface Ga vacancies, an increase in surface N–H2 content and a decrease in surface C contamination. A 0.3-eV shift in the Ga3d peak position towards the valence band and a reduction in the dislocation contrast were observed for the case of molecular-beam-epitaxy-grown GaN only, demonstrating that surface Ga vacancies and threading dislocations play only a limited role in defining the resultant metal/GaN contact properties. Accordingly, the surface atomic content and the resulting surface states, following KOH treatment, should be taken into consideration when appraising the electrical properties of n-GaN surfaces and the performance of associated metallic contacts.  相似文献   

8.
An approximate theory of dipolar relaxation by the soft modes of magnetic vacancies and dislocations gives 23 and 1 for the power-law exponents of T2, while proton T1 and EPR linewidth measurements yield 0.67 ± 0.04 and 1.0 ± 0.1.  相似文献   

9.
冯倩  郝跃  岳远征 《物理学报》2008,57(3):1886-1890
在研制AlGaN/GaN HEMT器件的基础上,采用ALD法制备了Al2O3 AlGaN/GaN MOSHEMT器件.通过X射线光电子能谱测试表明在AlGaN/GaN异质结材料上成功淀积了Al2O3薄膜.根据对HEMT和MOSHEMT器件肖特基电容、器件输出以及转移特性的测试进行分析发现:所制备的Al2O3薄膜与AlGaN外延层间界面态密度较小,因而MOSHEMT器件呈现出较 关键词: 2O3')" href="#">Al2O3 ALD GaN MOSHEMT  相似文献   

10.
AlN with different thicknesses were grown as interlayers (ILs) between GaN and p-type Al0.15Ga0.85N/GaN superlattices (SLs) by metal organic vapor phase epitaxy (MOVPE). It was found that the edge-type threading dislocation density (TDD) increased gradually from the minimum of 2.5×109?cm?2 without AlN IL to the maximum of 1×1010?cm?2 at an AlN thickness of 20 nm, while the screw-type TDD remained almost unchanged due to the interface-related TD suppression and regeneration mechanism. We obtained that the edge-type dislocations acted as acceptors in p-type Al x Ga1?x N/GaN SLs, through the comparison of the edge-type TDD and hole concentration with different thicknesses of AlN IL. The Mg activation energy was significantly decreased from 153 to 70?meV with a?10-nm AlN IL, which was attributed to the strain modulation between AlGaN barrier and GaN well. The large activation efficiency, together with the TDs, led to the enhanced hole concentration. The variation trend of Hall mobility was also observed, which originated from the scattering at TDs.  相似文献   

11.
《Current Applied Physics》2015,15(9):1027-1031
We report on the effect of oxygen annealing for GaN surface on the Schottky barrier configuration and leakage current in Ni-AlGaN/GaN Schottky barrier diodes. After oxygen annealing, their turn-on voltage and reverse-bias leakage current characteristics are significantly improved due to a reduction in the Schottky barrier height (SBH) and suppression in the surface states respectively. Interface state density extracted from the Terman method was reduced by 2 orders of magnitude. X-ray photoelectron spectroscopy measurements show that the oxygen annealing induces Ga2O3 on the GaN surface. The formation of Ga2O3 reduces the interface state density as well as lowers the SBH through the modification of hybridized metal induced gap states.  相似文献   

12.
In-doped Ga2O3 zigzag-shaped nanowires and undoped Ga2O3 nanowires have been synthesized on Si substrate by thermal evaporation of mixed powders of Ga, In2O3 and graphite at 1000 °C without using any catalyst via a vapor-solid growth mechanism. The morphologies and microstructures of the products were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence spectroscopy (PL). The nanowires range from 100 nm to several hundreds of nanometers in diameter and several tens of micrometers in length. A broad emission band from 400 to 700 nm is obtained in the PL spectrum of these nanowires at room temperature. There are two blue-emission peaks centering at 450 and 500 nm, which originate from the oxygen vacancies, gallium vacancies and gallium-oxygen vacancy pairs.  相似文献   

13.
Optical properties of GaN/AlN multiple quantum wells (MQW) have been investigated by Raman scattering, photoluminescence and photoluminescence excitation measurements. A careful examination of the Raman spectrum reveals the fact that the constituent layers of GaN/AlN MQWs are well strained. The experimental results of emission and absorption in MQWs were compared with the calculated solutions of the finite quantum well and the bound states involved in the optical transitions were identified. It is found that the interband transitions up to n=3 bound state can be observed in the strained GaN/AlN MQWs sample. The temperature dependence of the heavy-hole transitions shows an interesting phenomenon, in which the peak energy first increases with increasing temperature and then decreases with the temperature rapidly. The observation can be explained in a consistent way by the strain effects of lattice mismatch due to the interplay between the thermal expansion of GaN and AlN layers. Our results indicate that pseudomorphic GaN/AlN MQWs with good quality can be readily grown, and their applications in optoelectronics can be expected in the near future.  相似文献   

14.
Compositions of polycrystalline Mg-Zn mixed ferrites with the general formula Mg1−xZnxFe2O4 (0≤x≤1) were prepared by the standard double sintering ceramic method. The structural properties of these ferrites have been investigated using X-ray diffraction and infrared absorption spectroscopy. The lattice parameter, particle size, bonds length, force constants, density, porosity, shrinkage and cation distribution of these samples have been estimated and compared with those predicted theoretically. Most of these values were found to increase with increasing Zn content. The energy dispersive (EDS) analysis confirmed the proposed sample composition. The scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs showed aggregates of stacked crystallites of about 200-800 nm in diameter. Far infrared absorption spectra showed two significant absorption bands. The wave number of the first band, ν1, decreases with increasing Zn content, while the band, ν2 shifts linearly towards higher wave numbers with Zn contents, over the whole composition range. The room temperature electrical resistivity was found to decrease as Zn-content increases. Values of the vacancy model parameters showed that the packing factors Pa and Pb decrease, the fulfillment coefficient, α, remains almost constant and the vacancy parameter, β, strongly increases with increasing Zn content in the sample. The small values of Pa, Pb, α and the strong increase of the vacancy parameter, β, indicate the presence of cation or anion vacancies and the partial participation of the Zn2+ vacancies in the improvement of the electrical conductivity in the Mg-Zn ferrites.  相似文献   

15.
In this study, the effects of an (NH4)2Sx treatment on the surface work function (SWF) and roughness of indium-tin-oxide (ITO) have been investigated. From the observed X-ray photoelectron spectroscopy results, optical transmittance measurements, atomic force microscopy measurements and four-point probe measurements, it is suggested that the surface chemical changes and an increase in the sheet resistance had strong effects on the SWF of ITO. We find that the S occupation of oxygen vacancies near the ITO surface after (NH4)2Sx treatment may result in a marked increase in the SWF and a slight increase in the surface roughness.  相似文献   

16.
GaN nanowires have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga2O3/Cr thin films at 950 °C. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectrophotometer, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), and photoluminescence (PL) spectrum were carried out to characterize the microstructure, morphology, and optical properties of GaN samples. The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure and high-quality crystalline, have the size of 30-80 nm in diameter and several tens of microns in length with good emission properties. The growth direction of GaN nanowires is perpendicular to the fringe of (1 0 1) plane. The growth mechanism of GaN nanowires is also discussed in detail.  相似文献   

17.
PASSIVATION OF THE InP(100) SURFACE USING (NH4)2Sx   总被引:1,自引:0,他引:1       下载免费PDF全文
InP(100) surface treated with (NH4)2Sx has been investigated by using photolumines-cence(PL), Auger electron spectroscopy and X-ray photoelectron spectroscopy, It is found that PL intensity increased by a factor of 3.3 after (NH4)2Sx passivation and the sulfur remained on the surface only bonded to indium, not to phosphorus. This suggests that the sulfur atoms replace the phosphorus atoms on the surface and occupy the phosphorus vacancies.  相似文献   

18.
Electrochemical water splitting requires efficient water oxidation catalysts to accelerate the sluggish kinetics of water oxidation reaction. Here, we designed an efficient Co3O4 electrocatalyst using a pyrolysis strategy for oxygen evolution reaction (OER). Morphological characterization confirmed the ultra-thin structure of nanosheet. Further, the existence of oxygen vacancies was obviously evidenced by the X-ray photoelectron spectroscopy and electron spin resonance spectroscopy. The increased surface area of Co3O4 ensures more exposed sites, whereas generated oxygen vacancies on Co3O4 surface create more active defects. The two scenarios were beneficial for accelerating the OER across the interface between the anode and electrolyte. As expected, the optimized Co3O4 nanosheets can catalyze the OER efficiently with a low overpotential of 310 mV at current density of 10 mA/cm2 and remarkable long-term stability in 1.0 mol/L KOH.  相似文献   

19.
魏合林  张磊  刘祖黎  姚凯伦 《中国物理 B》2011,20(11):118102-118102
Uniformly distributed polycrystalline indium nanohillocks are synthesized on silicon substrates with Au catalyst by using the radio frequency magnetic sputtering technique. The results show that the Au catalyst plays a key role in the formation of indium nanohillocks. After thermally oxidizing the indium nanohillocks at 500 ℃ in air for 5 h, the indium nanohillocks totally transform into In2O3 nanohillocks. The energy-dispersive X-ray spectroscopy result indicates that many oxygen vacancies and oxygen-indium vacancy pairs exist in the In2O3 nanohillocks. Photoluminescence spectra under an Ne laser excitation at 280 nm show broad emissions at 420 nm and 470 nm with a shoulder at 450 nm related to oxygen vacancies and oxygen-indium vacancies at room temperature.  相似文献   

20.
Interface properties of BCN/GaN metal-insulator-semiconductor (MIS) structures are investigated by X-ray photoelectron spectroscopy (XPS) and capacitance versus voltage (C-V) characteristics measurements. The BCN/GaN samples are fabricated by in situ process consisting of plasma treatment and deposition of BCN film in the plasma-assisted chemical vapor deposition (PACVD) apparatus. XPS measurement shows that the oxide formation at the BCN/GaN interface is suppressed by nitrogen (N2) and hydrogen (H2) plasma treatment. The interface state density is estimated from C-V characteristics measured at 1 MHz using Terman method. The minimum interface state density appears from 0.2 to 0.7 eV below the conduction band edge of GaN. The minimum value of the interface state density is estimated to be 3.0 × 1010 eV−1 cm−2 for the BCN/GaN structure with mixed N2 and H2 plasma treatment for 25 min. Even after annealing at 430 °C for 10 min, the interface state density as low as 6.0 × 1010 eV−1 cm−2 is maintained.  相似文献   

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