Thickness measurement of semiconductor thin films by energy dispersive X-ray fluorescence benchtop instrumentation: Application to GaN epilayers grown by molecular beam epitaxy (original) (raw)
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Spectrochimica Acta Part B: Atomic …, 2010
The importance of thin films in modern high technology products, such as semiconductors, requires fast and non-destructive analysis. A methodology to determine the thickness of single layers with benchtop energy dispersive X-ray fluorescence (EDXRF) instrumentation is described and tested following analytical validation criteria. The experimental work was carried out on gallium nitride thin films epitaxially grown on sapphire substrate. The results of samples with layers in the range from 400 to 1000 nm exhibit a good correlation with the layer thickness determined by optical reflectance. Spectral data obtained using thin layered samples indicate the possibility to precisely evaluate layer thickness from 5 nm, with a low relative standard deviation (RSD b 2%) of the results. In view of the limits of optical reflectance for very thin layer determination, EDXRF analysis offers the potential for the thickness determination of such kind of samples.
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Optics & Laser Technology, 2009
A method has been proposed for determining the optical properties of a thin film layer on absorbing substrates. The film optical parameters such as thickness, refractive index, absorption coefficient, extinction coefficient and the optical energy gap of an absorbing film are retrieved from the interference fringes of the reflection spectrum at normal incidence. The envelopes of the maxima of the spectrum E M and of the minima E m are introduced in analytical forms to find the reflectance amplitudes at the interfaces and approximate values of the thin film refractive index. Then, the interference orders and film thickness are calculated to get accurate values of the needed optical parameters. There are no complex fitting procedures or assumed theoretical refractive index dispersion relations. The method is applied to calculate the optical properties of an epitaxial gallium nitride thin film on a silicon substrate. Good agreement between our results and the published data are obtained.
X-ray absorption spectroscopy in the analysis of GaN thin films
Surface and Interface Analysis, 2003
Stoichiometric amorphous GaN thin films have been grown by an ion-assisted deposition method and examined by x-ray photoelectron spectroscopy and x-ray absorption near-edge spectroscopy (XANES). The crucial question is the nature of the local structure around the N and Ga in the x-ray amorphous films. The N K edge XANES has been used to determine coordination around the N centre and reveals substantial differences to crystalline GaN. Although the transitions observed mirror those of the crystalline material and are consistent with density of states calculations, the low-energy peak at ∼402 eV is dominant in all films less than ∼150 nm in thickness. This peak, initially attributed to an sp 2 environment, is associated with the presence of molecular nitrogen. For thicker films, a duplex-type structure is observed with a surface layer much closer to the structure of the crystalline material.
Current Applied Physics, 2009
In the present paper, the effects of nitridation on the quality of GaN epitaxial films grown on Si(1 1 1) substrates by metal-organic chemical vapor phase deposition (MOCVD) are discussed. A series of GaN layers were grown on Si(1 1 1) under various conditions and characterized by Nomarski microscopy (NM), atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD), and room temperature (RT) photoluminescence (PL) measurements. Firstly, we optimized LT-AlN/HT-AlN/Si(1 1 1) templates and graded AlGaN intermediate layers thicknesses. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.2 lm. Secondly, the effect of in situ substrate nitridation and the insertion of an Si x N y intermediate layer on the GaN crystalline quality was investigated. Our measurements show that the nitridation position greatly influences the surface morphology and PL and XRD spectra of GaN grown atop the Si x N y layer. The X-ray diffraction and PL measurements results confirmed that the single-crystalline wurtzite GaN was successfully grown in samples A (without Si x N y layer) and B (with Si x N y layer on ). The resulting GaN film surfaces were flat, mirror-like, and crack-free. The full-width-at-half maximum (FWHM) of the X-ray rocking curve for (0 0 0 2) diffraction from the GaN epilayer of the sample B in x-scan was 492 arcsec. The PL spectrum at room temperature showed that the GaN epilayer had a light emission at a wavelength of 365 nm with a FWHM of 6.6 nm (33.2 meV). In sample B, the insertion of a Si x N y intermediate layer significantly improved the optical and structural properties. In sample C (with Si x N y layer on Al 0.11 Ga 0.89 N interlayer). The in situ depositing of the, however, we did not obtain any improvements in the optical or structural properties.
Effect of thickness on the structural and optical properties of GaN films grown on Si(111)
Journal of Materials Science: Materials in Electronics, 2011
GaN films with different thicknesses were grown on Si(111) substrates by Plasma-Assisted Molecular Beam Epitaxy (PA-MBE). The optical properties of the films were investigated using spectrophotometric measurements of the reflectance in the wavelength range 200-3,300 nm. With increasing film thickness, the refractive index (n) increased slightly, while the optical energy gap (E g) changed with no specific trend. The structural properties of the grown films were studied at (002) reflections using two types of rocking curve measurements; normal rocking curve (x-scan) and triple axis rocking curve (x/2h-scan). The Full Width at Half Maximum (FWHM) of rocking curve decreased with increasing film thickness. Hall effect measurements showed that all the samples were n-type with carrier concentrations decreasing from 8.025 9 10 18 to 5.65 9 10 17 cm-3 , and mobility increasing from 14 to 110 cm 2 V-1 s-1 as increasing the film thickness from 590 to 1,420 nm, respectively. Photoluminescence (PL) spectra for the grown GaN films with different thicknesses were measured at room temperature. PL spectra for all the samples exhibited band edge (BE) emissions at peak energies of 3.24 eV, with peak intensities increased with increasing the film thickness. 2 Experimental methods GaN films were grown in Riber 32P molecular beam epitaxy (MBE) machine equipped with a 2,200 L/s turbo-molecular
Chinese Physics B, 2010
Microstructure and strain analysis of GaN epitaxial films using in-plane grazing incidence x-ray diffraction * Guo Xi(郭 希) a) † , Wang Yu-Tian(王玉田) a) , Zhao De-Gang(赵德刚) a) , Jiang De-Sheng(江德生) a) , Zhu Jian-Jun(朱建军) a) , Liu Zong-Shun(刘宗顺) a) , Wang Hui(王 辉) a) , Zhang Shu-Ming(张书明) a) , Qiu Yong-Xin(邱永鑫) b) , Xu Ke(徐 科) b) , and Yang Hui(杨 辉) a)b)
MRS Proceedings, 1996
We report a structural analysis of GaN layers with thicknesses ranging from 10 μm to 250 μm which have been grown on sapphire substrates by halide vapor phase epitaxy (HVPE). The effect of growth rate during HVPE growth has also been examined. The growth was performed using GaCl and ammonia as reactants; growth rates in excess of 90 μm/hr have been achieved. The structural characteristics of these layers have been performed wit'i high resolution x-ray diffractometry. Longitudinal scans parallel to the GaN [0002] direction, transverse scans perpendicular to the [0002], and reciprocal space maps of the total diffracted intensity have been obtained from a variety of GaN layers. The transverse scans typically show broad rocking curves with peak breadths of several hundreds of arcseconds. In contrast, the longitudinal scans (or “θ/2θ scans”) which are sensitive only to strains in the GaN layers (and not their mosaic distributions) showed peak widths that were at least an order of mag...
GaN Films under Different Growth Mechanisms Studied by Synchrotron X-ray Absorption Spectroscopy
Proceedings of the 2nd Annual International Conference on Advanced Material Engineering (AME 2016), 2016
Synchrotron radiation X-ray absorptionmeasurements wereperformed to study the structure of Si-doped n-type GaN layers grown on sapphire by metalorganic chemical vapor deposition (MOCVD) and undoped GaN epitaxial layers grown on Si by molecular beam epitaxy (MBE).It was found that the anisotropic characteristic of p-orbital from GaN/sapphire grown by MOCVD is somehow larger than GaN/Si grown by MBE.In addition, values of the lattice constant of different GaN films were deduced from the interatomic distances in the second coordination shell around Ga byextended X-ray absorption fine structure (EXAFS) analysis and the residual strain of the films was then deduced. The calculation results shows that the strain type is different in the two sets of samples which is due to the different substrate and AlN buffer layer.
N K -edge x-ray-absorption study of heteroepitaxial GaN films
Physical Review B, 1997
The microstructure of GaN films grown by electron cyclotron resonance ͑ECR͒ molecular-beam epitaxy ͑MBE͒ and hydride vapor-phase epitaxy ͑HVPE͒ is studied using x-ray-absorption measurements at the N K edge. The local microstructure around the N atom is found to be distorted. The nearest neighbors of the N atom are four Ga atoms, N 1 of which are located at a distance R 1 ϭ1.95 Å, which is expected, and N 2 at a distance R 2 ϭR 1 ϩ0.25 Å. This distortion is more pronounced in the cubic ECR-MBE and the HVPE hexagonal samples where the ratio N 2 /N 1 is equal to 1. In the rest of the samples the distortion is smaller and the ratio N 2 /N 1 takes the value 0.33. Nitrogen deficiency is not detected in the second nearest-neighbor shell and the N atoms are found at the expected distance of 3.11 Å.
Polarity determination of a GaN thin film on sapphire (0001) with x-ray standing waves
Journal of Applied Physics, 1998
The x-ray standing wave technique was used to determine the polarity of a 1 μm thick GaN film grown by molecular beam epitaxy on an α-Al2O3(0001) single crystal. The standing wave was generated by x-ray diffraction from the GaN film. The Ga Kα fluorescence yield was recorded as a function of incidence angle within the range of the GaN(0002) reflection. Analysis of the data reveals that the film has grown with N polarity, i.e., the nitrogen atoms occupy the top half of the wurtzite (0001) bilayers.