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1.
《Journal of Crystal Growth》2003,247(3-4):261-268
GaN and AlN films were grown on (1 1 1) and (0 0 1) Si substrates by separate admittances of trimethylgallium (or trimethylaluminum) and ammonia (NH3) at 1000°C. A high temperature (HT) or low temperature (LT) grown AlN thin layer was employed as the buffer layer between HT GaN (or HT AlN) film and Si substrate. Experimental results show that HT AlN and HT GaN films grown on the HT AlN-coated Si substrates exhibit better crystalline quality than those deposited on the LT AlN-coated Si substrates. Transmission electron microscopy (TEM) of the HT GaN/HT AlN buffer layer/(1 1 1)Si samples shows a particular orientation relationship between the (0 0 0 1) planes of GaN film and the (1 1 1) planes of Si substrate. High quality HT GaN films were achieved on (1 1 1) Si substrates using a 200 Å thick HT AlN buffer layer. Room temperature photoluminescence spectra of the high quality HT GaN films show strong near band edge luminescence at 3.41 eV with an emission linewidth of ∼110 meV and weak yellow luminescence.  相似文献   

2.
We have studied the in-situ boron doping of high Ge content Si1?xGex layers (x=0.3, 0.4 and 0.5). These layers have been grown at low pressure (20 Torr) and low temperature (600–650 °C) with a heavily chlorinated chemistry on blanket Si(0 0 1) substrates. Such a chemistry yields a full selectivity versus SiO2 (isolation) and Si3N4 (sidewall spacers) on patterned wafers with gate stacks. We have quantified the impact of the diborane flow on the SiGe layer crystalline quality, its resistivity, the SiGe:B growth rate and the apparent Ge concentration. Resistivity values lower than 1  cm are easily achieved, all the more so for high Ge content layers. The SiGe growth rate increases and the apparent Ge concentration (from X-ray diffraction) decreases as the diborane flow increases. B atoms (much smaller than Si or Ge) indeed partially compensate the compressive strain in the SiGe:B layers. We have also probed the in-situ boron and phosphorus doping of Si at 750 °C, 20 Torr with a heavily chlorinated chemistry. The B ions concentration increases linearly with the diborane flow, then saturates at a value close to 4×1019 cm?3. By contrast, the P ions concentration increases sub-linearly with the phosphine flow, with a maximum value close to 9×1018 cm?3. Adding diborane (phosphine) to the gaseous mixture leads to a sharp increase (decrease) of the Si:B (the Si:P) growth rates, which has to be taken into account in device layers. All the know-how acquired will be most handy for the formation of in-situ doped recessed or raised sources and drains in metal-oxide semiconductor devices.  相似文献   

3.
In this work, refractive index and extinction coefficient spectra of germanium nanoclusters – rich SiO2 layers have been determined using variable angle spectroscopic ellipsometry (VASE) in the 250–1000 nm range. The samples were produced by Ge+ ion implantation into SiO2 layers on Si substrates and subsequent annealing at temperatures from 700 to 1100 °C. It is known from previous investigations of similar samples that the Ge nanoclusterization process starts already at 800 °C and spherical Ge nanocrystallites 5–8 nm in diameter are observed in the SiO2 layers after annealing for 1 h at even higher temperatures of 1000–1100 °C. Rutherford backscattering spectrometry (RBS) was employed to measure the Ge atom concentration depth profiles in the studied samples. The RBS results helped us choose realistic models for the VASE analysis which were necessary for a proper interpretation of the VASE data. It has been found that the refraction index value for the SiO2/Si layer increases after Ge implantation. This effect can be explained by a defect-dependent compaction of ion-bombarded layers. A band’s tail in the extinction coefficient spectra for all the samples is observed which originates from a strong ultraviolet absorption band at 6.8 eV due to a Germanium Oxygen-Deficiency Center (GeODC) and/or a Ge-E’center in SiO2. The annealing process results in the emergence of weaker extinction coefficient bands in the 400–600 nm region, associated with direct band-to-band transitions in Ge nanostructures. Transformation of these bands, including their blue-shift with the increasing annealing temperature could be explained via a quantum-confinement mechanism, by size and structural changes in Ge nanostructures.  相似文献   

4.
《Journal of Crystal Growth》2006,286(2):235-239
The characteristics of Si-doped and undoped GaN/Si(1 1 1) heteroepitaxy with composite buffer layer (CBL) and superlattice are compared and discussed. While as-grown Si-doped GaN/Si(1 1 1) heteroepitaxy shows lower quality compared to undoped GaN, crack-free n-type and undoped GaN with the thickness of 1200 nm were obtained by metalorganic chemical vapor deposition (MOCVD). In order to achieve the crack-free GaN on Si(1 1 1), we have introduced the scheme of multiple buffer layers; composite buffer layer of Al0.2Ga0.8N/AlN and superlattice of Al0.2Ga0.8N/GaN on 2-in. Si(1 1 1) substrate, simultaneously. The FWHM values of the double-crystal X-ray diffractometry (DCXRD) rocking curves were 823 arcsec and 745 arcsec for n-GaN and undoped GaN/Si(1 1 1) heteroepitaxy, respectively. The average dislocation density on GaN surface was measured as 3.85×109 and 1.32×109 cm−2 for n-GaN and undoped GaN epitaxy by 2-D images of atomic force microscopy (AFM). Point analysis of photoluminescence (PL) spectra was performed for evaluating the optical properties of the GaN epitaxy. We also implemented PL mapping, which showed the distribution of edge emission peaks onto the 2 inch whole Si(1 1 1) wafers. The average FWHMs of the band edge emission peak was 367.1 and 367.0 nm related with 3.377 and 3.378 eV, respectively, using 325 nm He-Cd laser as an excitation source under room temperature.  相似文献   

5.
Epitaxial lateral overgrowth is reported for semi-polar (Al,Ga)N(1 1 .2) layers. The mask pattern consisted of periodic stripes of SiO2 oriented parallel to either the GaN[1 1 .0] or the GaN[1 1 .1] direction. Lateral growth occurred either along GaN[1 1 .1] or along GaN[1 1 .0]. For growth along the [1 1 .0] direction, coalescence was achieved for layer thicknesses >4 μm. However, planarization was not observed yielding extremely corrugated surfaces. For growth in [1 1 .1] direction, coalescence was delayed by a diminishing lateral growth rate. Growth of AlGaN during ELOG resulted in coalescence. Improvement in crystal quality of such buffer layers for the growth of InGaN/GaN quantum wells was confirmed by X-ray diffraction and photoluminescence spectroscopy.  相似文献   

6.
About 1.2 mm thick GaN bulk crystals were obtained by combining a pulsed NH3-flow modulation (PFM) method and a self-separation method of short-shutting NH3 flow when using hydride vapor phase epitaxy (HVPE). High crystal quality of bulk GaN was evaluated by X-ray rocking curves (XRC) and the full width at half maximum (FWHM) values were 110, 72 and 83 arcsec for (002), (102) and (100) reflection planes, respectively. The PFM method is proved to be effective in reducing cracks and keeping the surface smooth. And the method of short-shutting NH3 flow can lead to GaN thick layer separate from sapphire substrate when cooling from the high growth temperature. Growth and separation mechanisms were investigated. Two states were found in PFM method. With PFM method modulating between high quality state and low stress state, 300 μm thick GaN layers without cracks were obtained. Study of spontaneous separation mechanism revealed that the separation attributed to formation of voids inside the GaN layer.  相似文献   

7.
《Journal of Non》2005,351(49-51):3716-3724
Li2S + GeS2 + GeO2 ternary glasses have been prepared and a wide glass-forming range was obtained. The glass transition temperatures increase with the GeO2 concentration in the glasses. The vibrational modes of both bridging (Ge–S–Ge) and non-bridging (Ge–S) sulfurs are observed in Raman and IR spectra of binary Li2S + GeS2 glasses. Additions of GeO2 to this binary glass increase the bridging oxygen band (Ge–O–Ge) at the expense of decreasing the bridging sulfur band (Ge–S–Ge), whereas the bands associated with the non-bridging sulfurs (Ge–S) remain constant in intensity up to high GeO2 concentrations. At higher concentrations of GeO2 (⩾60%), the non-bridging oxygen band, which is not observed at low and intermediate GeO2 concentrations, appears and grows stronger. From these observations, it is suggested that the added lithium ions favor the non-bridging sulfur sites over the oxygen sites to form non-bridging sulfurs, whereas the added oxygen prefers the higher field strength Ge4+ cation to form bridging Ge–O–Ge bonds. The structural groups in the Li2S + GeS2 + GeO2 glasses that are consistent with results of Raman and IR spectra are described and are used to develop a structural model of these glasses.  相似文献   

8.
We have studied the impact of temperature and pressure on the structural and electronic properties of Ge:P layers grown with GeH4+PH3 on thick Ge buffers, themselves on Si(0 0 1). The maximum phosphorous atomic concentration [P] exponentially decreased as the growth temperature increased, irrespective of pressure (20 Torr, 100 Torr or 250 Torr). The highest values were however achieved at 100 Torr (3.6×1020 cm?3 at 400 °C, 2.5×1019 cm?3 at 600 °C and 1019 cm?3 at 750 °C). P atomic depth profiles, “box-like” at 400 °C, became trapezoidal at 600 °C and 750 °C, most likely because of surface segregation. The increase at 100 Torr of [P] with the PH3 mass-flow, almost linear at 400 °C, saturated quite rapidly at much lower values at 600 °C and 750 °C. Adding PH3 had however almost no impact on the Ge growth rate (be it at 400 °C or 750 °C). A growth temperature of 400 °C yielded Ge:P layers tensily-strained on the Ge buffers underneath, with a very high concentration of substitutional P atoms (5.4×1020 cm?3). Such layers were however rough and of rather low crystalline quality in X-ray Diffraction. Ge:P layers grown at 600 °C and 750 °C had the same lattice parameter and smooth surface morphology as the Ge:B buffers underneath, most likely because of lower P atomic concentrations (2.5×1019 cm?3 and 1019 cm?3, respectively). Four point probe measurements showed that almost all P atoms were electrically active at 600 °C and 750 °C (1/4th at 400 °C). Finally, room temperature photoluminescence measurements confirmed that high temperature Ge:P layers were of high optical quality, with a direct bandgap peak either slightly less intense (750 °C) or more intense (600 °C) than similar thickness intrinsic Ge layers. In contrast, highly phosphorous-doped Ge layers grown at 400 °C were of poor optical quality, in line with structural and electrical results.  相似文献   

9.
《Journal of Non》2006,352(9-20):1255-1258
Microcrystalline silicon–germanium (μc-Si1−xGex:H) alloy films have been grown by 100-MHz glow-discharge of a SiH4/GeH4/H2 gas mixture. Alloys over a full range of compositions were prepared to gain a comprehensive understanding of their growth and material properties. With increasing GeH4 concentration in the gas-phase, we observed a preferential Ge incorporation behavior in the solid. Growth rate studies revealed that the Ge incorporation efficiency from source gas to solid is about five times greater than for Si at growth temperature of 200 °C, which accounts for the variation of alloy composition. With increasing Ge incorporation in the solid, on the other hand, we find a monotonic decrease in photoconductivity, followed by an electrical transition from weak n-type to strong p-type conduction at x > 0.7. At x  0.4, however, we obtained relatively high photoconductivity gains by a factor of 20 and strong infrared response in the solar cell structure. The Ge incorporation behavior and its effect on charge carrier transport are discussed.  相似文献   

10.
T. Matsui  K. Ogata  C.W. Chang  M. Isomura  M. Kondo 《Journal of Non》2008,354(19-25):2468-2471
We report on the carrier collection characteristics of hydrogenated microcrystalline silicon–germanium (μc-Si1?xGex:H) p–i–n junction solar cells fabricated by low-temperature (~200 °C) plasma-enhanced chemical vapor deposition. Spectral response measurements reveal that the Ge incorporation into absorber i-layer reduces the quantum efficiencies at short wavelengths. Furthermore, the illumination of the solar cells for x ? 0.35, particularly in the wavelength range of <650 nm, induces a strong injection-level-dependent p–i interface recombination and a weak collection enhancement in the bulk. These results indicate that space charges near the p–i interface are largely negative, which gives rise to an electric field distortion in the i-layer. We attribute the negative space charges to the presence of the acceptor-like states that are responsible for the strong p-type conduction observed in undoped μc-Si1?xGex:H films for large Ge contents.  相似文献   

11.
We have studied the epitaxial-like growth of germanium (Ge), due to solid phase crystallization (SPC) from amorphous Ge (a-Ge) deposited on single crystal silicon (Si) substrate. The crystalline growth of Ge following the orientation of Si substrates was successfully obtained by the SPC at 400 °C or higher. The preferential growth on Si (111) substrates continues up to 10,000 Å. Different orientations from the substrate orientation in XRD patterns are slightly observed in the growth on Si (100) substrates at 450 °C, but the preferential growth of (100) orientation continued in the whole film thickness in TEM images. The epitaxial-like growth of Ge may be more preferable on the Si (111) substrate than the (100) one.  相似文献   

12.
C.W. Chang  T. Matsui  M. Kondo 《Journal of Non》2008,354(19-25):2365-2368
Paramagnetic defects of undoped hydrogenated microcrystalline silicon–germanium alloys (μc-Si1?xGex:H) grown by low temperature (200 °C) plasma-enhanced chemical vapor desposition (PECVD) have been measured by electron spin resonance (ESR) and compared with those of hydrogenated amorphous silicon–germanium (a-Si1?xGex:H). The spin density of μc-Si1?xGex:H increases with Ge content and shows a broad maximum of ~1017 cm?3 at x  0.5, which reasonably accounts for the decreased photoconductivity. While the Ge dangling bond defects prevail in a-Si1?xGex:H for Ge-rich compositions, we detected no ESR signal in μc-Si1?xGex:H for x > 0.75 where an electrical change occurs from weak n- to strong p-type conduction. These results indicate that dangling bonds are charged in large densities due to the presence of the acceptor-like states in undoped μc-Si1?xGex:H.  相似文献   

13.
《Journal of Non》2006,352(23-25):2332-2334
In this work we report on the growth and characterization of high quality MOCVD GaN film grown on Al2O3 substrates by using a HT (>1150 °C)-AlN buffer layer. We have investigated the most favorable growth conditions in terms of temperature, thickness and growth rate of AlN buffer layer in order to optimize the high temperature GaN layer. The improved morphological and structural properties of GaN layer were verified by AFM and XRD measurements. The optimized GaN layer presents a smooth surface with a rms value of 1.4 Å. The full width at half maximum (FWHM) for 800 nm thick GaN films is 144″. Furthermore PL measurements and CV analysis confirm that in GaN layer grown on HT-AlN buffer layer defect density is drastically reduced.  相似文献   

14.
《Journal of Crystal Growth》2007,298(2):145-152
Vicinal surface effects on homoepitaxial growth and boron-doping processes have been studied in case of single-crystalline diamond (0 0 1) surfaces grown using the high-power microwave plasma chemical-vapor-deposition (MWPCVD) method. The off-angles inclined from the on-orientation (0 0 1) surfaces ranged to 5° along the [1 1 0] or [1 0 0] direction, while the concentration of doping B(CH3)3 gas was kept constant with a B/C ratio of 50 ppm. Although a number of square-like growth hillocks often appeared, depending substantially on the crystalline quality of the high-pressure/high-temperature-synthesized (HPHT) Ib diamond substrates employed, the number and shape of the hillocks changed significantly with the increasing off-angle. For the vicinal surfaces with off-angles of ≈3° inclined along the [1 1 0] direction, macroscopically flat surfaces were obtained, compared with the other off-angle cases examined. Furthermore, the growth rate and acceptor density of substitutional boron atoms in the homoepitaxial layers were found to substantially increase with the increasing off-angle. These indicate that the step density can play important roles not only in the homoepitaxial growth but also in the boron-incorporation process during the high-power MWPCVD growth.  相似文献   

15.
《Journal of Non》2007,353(32-40):3376-3379
Energy dispersive X-ray diffraction measurements have been carried out for liquid Ge1−xSix alloys (x = 0.0, 0.3, 0.5, 1.0) using synchrotron radiation at SPring-8. We measured the X-ray diffraction spectra of liquid Ge and Si up to a high temperature range, (liquid Ge from 1270 to1870 K and liquid Si from 1680 to 2020 K), liquid Ge0.7Si0.3 at 1620 K, and liquid Ge0.5Si0.5 at 1540, 1590, 1670 and 1720 K. The total structure factors of the liquid Ge–Si alloys have a characteristic shoulder on the high-wave-vector side of the first peak. We deduced a pair distribution function from the Fourier transform of the observed structure factor, which was weakly dependent on the temperature. The nearest-neighbor coordination number of liquid Ge–Si alloys is close to that of pure liquid Ge and Si. The first peak of the pair distribution function moved to a shorter distance with increasing Si concentration. These results may indicate that the atomic radii of the Si and Ge atoms in the pure liquid are preserved in the liquid alloys.  相似文献   

16.
《Journal of Non》2006,352(40-41):4346-4350
The present contribution presents X-ray absorption fine structure (XAFS) measurements and analysis of the Ge and Ga local structure in glass of Ca3Ga2Ge3O12 composition, doped with rare-earth metals (Ce, Eu, Ho, Er in the amount of 0.7 wt% and Nd in the amount of 1.0 wt%). The Ge and Ga ion neighborhoods in the considered glass samples have been compared with data obtained for undoped glass. The results have shown that introduction of rare-earth ions modifies the local structure around the Ga ions in the glass network, leaving the same occurrence ratio of the GaO4 and GaO6 structural units as in undoped Ca3Ga2Ge3O12 glass. At the same time, the GeO2 subsystem remains completely unaffected by the presence of rare-earth dopants.  相似文献   

17.
The short-range structures of stoichiometric and Se-deficient binary GexSe100 ?x glasses with 42  x  33.33 have been investigated using a combination of Raman and 77Se Car–Purcell–Meiboom–Gill (CPMG) spikelet nuclear magnetic resonance (NMR) spectroscopy. When taken together, these spectroscopic results allow for self-consistent assignment of average 77Se NMR isotropic chemical shifts to Se atoms in various coordination environments in GexSe100 ?x glasses. Analysis of the compositional variation of the relative concentrations of these Se environments indicates considerable violation of chemical order in the nearest-neighbor coordination environments of the constituent atoms in the stoichiometric Ge33.33Se66.67 glass. On the other hand, the presence of a random distribution of Ge―Ge bonds can be inferred in the Se-deficient glasses. Simulations of the previously published 77Se NMR line shapes of Se-excess glasses on the basis of the revised structural assignments of 77Se NMR chemical shifts obtained in this study conclusively indicate that the structure of these glasses is intermediate between a randomly connected and a fully clustered network of GeSe4 tetrahedra and Se chains.  相似文献   

18.
To investigate the deposition of Ge films without toxic gas such as germane, we have studied the Ge films prepared by the hot-wire technique, which utilize the reaction between a Ge target and hydrogen atoms generated by the hot-wire decomposition of H2 gas. The films deposited on Si substrate were microcrystalline Ge films and the mean crystallite size of the films increased from 13.3 to 24.8 nm with increasing the substrate temperature from 300 to 500 °C. Moreover, the deposition rate of Ge films deposited on Si substrate was higher than that of Ge films deposited on Corning 1737 substrate. It was found that the substrate temperature and the kind of substrate are key parameters for the preparation of microcrystalline Ge films by the hot-wire technique.  相似文献   

19.
Bulk Ge15Te85 ? xSnx and Ge17Te83 ? xSnx glasses, are found to exhibit memory type electrical switching. The switching voltages (Vt) and thermal stability of Ge15Te85 ? xSnx and Ge17Te83 ? xSnx glasses are found to decrease with Sn content. The composition dependence of Vt has been understood on the basis of the decrease in the OFF state resistance and thermal stability of these glasses with tin addition. X-ray diffraction studies reveal that no elemental Sn or Sn compounds with Te or Ge are present in thermally crystallized Ge–Te–Sn samples. This indicates that Sn atoms do not interact with the host matrix and form a phase separated network of its own, which remains in the parent glass matrix as an inclusion. Consequently, there is no enhancement of network connectivity and rigidity. The thickness dependence of switching voltages of Ge15Te85 ? xSnx and Ge17Te83 ? xSnx glasses is found to be linear, in agreement with the memory switching behavior shown by these glasses.  相似文献   

20.
X-ray photoelectron spectroscopy (XPS) has been used to examine the atomic content of implanted SiO2/Si layers. In particular, an XPS analysis permits to identify elemental Ge and Si, as well as GeO2 precipitations in SiO2 matrices. The XPS results reveal valuable information not only about the formation mechanism of Ge and Si nanoclusters but also on the annealing kinetics of SiO2 whose properties are known to be significantly altered during the process of ion implantation and subsequent annealing. The composition of ion beam-modified SiO2 layers strongly depends on the annealing temperature. With respect to germanium implanted samples a possibility of Ge nanocrystals formation appears at high (above 1000 °C) annealing temperatures. It has been shown that an intermediate step in the Ge oxide formation is necessary for the creation of Ge nanoclusters. Additionally, the presence of a subsurface zone GeOx (about 100 nm thick) predicted in kinetic three-dimensional lattice simulations has been confirmed. In the case of Si+ implanted samples substoichiometric silicon oxide lines in the XPS spectra of a SiO2 layer for all samples have been observed. No evidence of a line connected to the Si–Si bonding has been observed even at the highest annealing temperatures, at which only stoichiometric SiO2 has been detected.  相似文献   

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