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Homoepitaxial ZnO growth is demonstrated from conventional RF-sputtering at 400 °C on both Zn and O polar faces of hydrothermally grown ZnO substrates. A minimum yield for the Rutherford backscattering and channeling spectrum, vmin, equal to ~3% and ~12% and a full width at half maximum of the 00.2 diffraction peak rocking curve of (70±10) arc sec and (1400±100) arc sec have been found for samples grown on the Zn and O face, respectively. The structural characteristics of the film deposited on the Zn face are comparable with those of epilayers grown by more complex techniques like molecular beam epitaxy. In contrast, the film simultaneously deposited on the O-face exhibits an inferior crystalline structure ~0.7% strained in the c-direction and a higher atomic number contrast compared with the substrate, as revealed by high angle annular dark field imaging measurements. These differences between the Zn- and O-face films are discussed in detail and associated with the different growth mechanisms prevailing on the two surfaces. [ABSTRACT FROM AUTHOR]

A strong influence of ion implantation flux on the accumulation of radiation damage, the so-called dose rate effect, is observed and systematically studied in SiC. The results are discussed in terms of migration and annihilation of intrinsic type defects for both the Si- and C-sublattices.

Implant temperature effects on secondary defects caused by MeV SN implantation in silicon are examined.

A study of Fe contamination and precipitation of Fe at the Si-SiO2 interface during dry oxidation reveals information about the precipitation kinetics and the precipitating phase. Atomic force microscopy and transmission electron microscopy reveal that the precipitating phase is beta-FeSi2, and that density of precipitation is related to the surface Fe and the presence of sharp asperites at the interface. Results indicate that the presence of Fe mars the microstructure of Si-SO2 interface and causes breakdown of oxide integrity.

We studied the structural properties, defect formation, and thermal stability of H in hydrothermally grown ZnO single crystals implanted with H- dose ranging from 2.5×1016 to 1×1017 cm-2. H implantation is found to create deformed layers with a uniaxial strain of 0.5-2.4% along the c-axis in ZnO, for the low and high dose, respectively. About 0.2-0.4% of the original implanted H concentration can still be detected in the samples by secondary ion mass spectrometry after annealing at a temperature up to 800 °C. The thermally stable H is tentatively attributed to H related defect complexes involving the substitutional H that are bound to O vacancies and/or the highly mobile interstitial H that are bound to substitutional Li occupying Zn vacancies as the samples are cooled slowly from high temperature annealing. H implantation to a dose of 1×1017 cm-2 and followed by annealing at 800 °C, is found to result in the formation of vacancy clusters that evolved into faceted voids with diameter varying from 2 to 30 nm. The truncations around the voids form more favorably on the O-terminated surface than on the Zn-terminated surface, suggesting that O is a preferred surface polarity for the internal facets of the voids in the presence of H. [ABSTRACT FROM AUTHOR]

Implantation, annealing, and oxidation processes have been used to form Au nanoparticles with a narrow size and depth distribution in a SiO2 layer. Different approaches have been attempted: in particular, the gettering of Au to fill preformed nanocavities (obtained by H-implantation and annealing) and thus overcome the broad particle size distribution that is normally associated with nanoparticles formed by implantation and annealing. The results suggest that nanocavities cannot be directly formed in SiO2 by H-implantation and a subsequent annealing due partly to the high mobility of H atoms in SiO2. However, cavities formed in Si are useful in obtaining a narrow size and depth distribution of Au precipitates: the Si substrate can then be oxidized to form Au nanoparticles in SiO2. Sequential wet oxidations of Si samples containing Au nanoparticles have revealed several interesting phenomena, namely, segregation of Au particles at a growing oxide interface, Au-enhanced oxidation, dissolution and reprecipitation of Au precipitates during oxidation, and preferential wetting of Au on the oxide layer. In particular, the Au dissolution and reprecipitation processes are Si interstitial mediated. By completely oxidizing the top Si layer, an array of Au precipitates can be confined at a precise depth within a SiO2 layer corresponding to the front interface of a buried oxide layer. The size distribution of the resulting Au precipitates in SiO2 is smallest when Au is first gettered to cavities and vacancies are subsequently introduced into the Si layer prior to oxidation. [ABSTRACT FROM AUTHOR]

Defect centers generated in crystalline silicon by MeV Si implants have been investigated by a combination of photoluminescence, variable-energy positron annihilation measurements, depth profiling by etching, annealing studies, and the dependence on impurities. The broad 935 meV photoluminescence band occurs at intrinsic interstitial complexes, the 835 meV band at small vacancy clusters, and the 1062 meV line at a low concentration of vacancy clusters which are possibly formed by aggregation of the 835 meV centers. [ABSTRACT FROM AUTHOR]

The article offers a detailed transmission electron microscopy analysis of defects formed in capped InAs/GaAs quantum dot samples. The three primary types of defects were: V-shaped defects, stacking fault pyramids and single stacking faults. These defects formed under growth conditions that resulted into either very large, indium-enriched, or coalesced islands. All of these defects start at the buried quantum dot layer.

In this work, rapid thermal annealing was performed on InGaAs/GaAs quantum dot infrared photodetectors (QDIPs) at different temperatures. The photoluminescence showed a blueshifted spectrum in comparison with the as-grown sample when the annealing temperature was higher than 700 °C, as a result of thermal interdiffusion of the quantum dots (QDs). Correspondingly, the spectral response from the annealed QDIP exhibited a redshift. At the higher annealing temperature of 800 °C, in addition to the largely redshifted photoresponse peak of 7.4 μm (compared with the 6.1 μm of the as-grown QDIP), a high energy peak at 5.6 μm (220 meV) was also observed, leading to a broad spectrum linewidth of 40%. This is due to the large interdiffusion effect which could greatly vary the composition of the QDs and thus increase the relative optical absorption intensity at higher energy. The other important detector characteristics such as dark current, peak responsivity, and detectivity were also measured. It was found that the overall device performance was not affected by low annealing temperature, however, for high annealing temperature, some degradation in device detectivity (but not responsivity) was observed. This is a consequence of increased dark current due to defect formation and increased ground state energy. [ABSTRACT FROM AUTHOR]

The influence of various growth parameters such as coverage, the AsH3 flow (V/III ratio), and growth interrupts on the self-assembled growth of InAs/GaAs quantum dots (QDs) by metal organic chemical vapor deposition is reported. Of the various growth parameters, the AsH3 flow has a particularly strong influence. Higher AsH3 flows during deposition led to a faster nucleation process and larger islands, while the presence of AsH3 after nucleation led to continued island ripening. We suggest that this is the result of increased indium redistribution from the highly strained wetting layer to the islands, and possibly between the islands, at higher AsH3 flows. A large defect density was observed by plan-view transmission electron microscopy, whenever the growth parameters led to larger islands. Using our optimized growth conditions we are able to avoid such defect generation and still achieve a high QD density (3×1010 cm-2). [ABSTRACT FROM AUTHOR]

Vacancy-type defect production in Al- and Si-implanted 4H–SiC has been studied as a function of ion fluence, ion flux, and implantation temperature in the projected ion range region by positron annihilation spectroscopy and Rutherford backscattering techniques. Ion channeling measurements show that the concentration of displaced silicon atoms increases rapidly with increasing ion fluence. In the ion fluence interval of 1013–1014 cm-2 the positron annihilation parameters are roughly constant at a defect level tentatively associated with the divacancy VCVSi. Above the ion fluence of 1014 cm-2 larger vacancy clusters are formed. For implantations as a function of ion flux (cm-2 s-1), ion channeling and positron annihilation measurements behave similarly, i.e., indicating increasing damage in the projected range region with increasing ion flux. However, for samples implanted at different temperatures the positron annihilation parameter S shows a clear minimum at approximately 100 °C, whereas the normalized backscattering yield decrease continuously with increasing implantation temperature. This is explained by the formation of larger vacancy clusters when the implantation temperature is increased. [ABSTRACT FROM AUTHOR]

In this article the effect of rapid thermal annealing (RTA) on a 30 stacked InAs/GaAs, molecular beam epitaxially grown quantum dot infrared photodetector (QDIP) device is studied. Temperatures in the range of 600–800 °C for 60 s, typical of atomic interdiffusion methods are used. After rapid thermal annealing the devices exhibited large dark currents and no photoresponse could be measured. Double crystal x-ray diffraction and cross sectional transmission electron microscopy studies indicate that this could be the result of strain relaxation. V-shaped dislocations which extended across many quantum dot (QD) layers formed in the RTA samples. Smaller defect centers were observed throughout the as-grown sample and are also likely a strain relaxation mechanism. This supports the idea that strained structures containing dislocations are more likely to relax via the formation of dislocations and/or the propagation of existing dislocations, instead of creating atomic interdiffusion during RTA. Photoluminescence (PL) studies also found that Si related complexes developed in the Si doped GaAs contact layers with RTA. The PL from these Si related complexes overlaps and dominates the PL from our QD ground state. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

4H-SiC wafers of orientations (0001) and (1120) were implanted with 60 keV Al[sup -] in different major axial, planar, and low symmetry (“random”) directions to ascertain the degree of channeling and to determine the optimum tilt conditions for ion implantation. Significant channeling was observed for all axial directions with the [1120] channel exhibiting the deepest channeling with a maximum penetration depth 45 times greater than the projected range of the random implants. Significant channeling was observed for the {1120} and especially the {0001} planar channels while the implants in the {1010} planar channels did not differ from the corresponding random implants. To minimize channeling in (0001) crystals, our results show that beam alignment normal to the surface is advisable for off-axis (0001) wafers with the miscut toward <1120>, while tilting of the wafer is necessary when the miscut is toward <1010>. For the (1120) material, channeling can be minimized by a tilt of >=10° toward the [0001] direction. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An experimental method of studying shifts between concentration-versus-depth profiles of vacancyand interstitial-type defects in ion-implanted silicon is demonstrated. The concept is based on deep level transient spectroscopy measurements utilizing the filling pulse variation technique. The vacancy profile, represented by the vacancy-oxygen center, and the interstitial profile, represented by the interstitial carbon-substitutional carbon pair, are obtained at the same sample temperature by varying the duration of the filling pulse. The effect of the capture in the Debye tail has been extensively studied and taken into account. Thus, the two profiles can be recorded with a high relative depth resolution. Using low doses, point defects have been introduced in lightly doped float zone n-type silicon by implantation with 6.8 MeV boron ions and 680 keV and 1.3 MeV protons at room temperature. The effect of the angle of ion incidence has also been investigated. For all implantation conditions the peak of the interstitial profile is displaced towards larger depths compared to that of the vacancy profile. The amplitude of this displacement increases as the width of the initial point defect distribution increases. This behavior is explained by a simple model where the preferential forward momentum of recoiling silicon atoms and the highly efficient direct recombination of primary point defects are taken into account. [ABSTRACT FROM AUTHOR]

In this work, different dielectric caps were deposited on the GaAs/AlGaAs quantum well (QW) structures followed by rapid thermal annealing to generate different degrees of interdiffusion. Deposition of a layer of Ga[sub x]O[sub y] on top of these dielectric caps resulted in significant suppression of interdiffusion. In these samples, it was found that although the deposition of Ga[sub x]O[sub y] and subsequent annealing caused additional injection of Ga into the SiO[sub 2] layer, Ga atoms were still able to outdiffuse from the GaAs QW structure during annealing, to generate excess Ga vacancies. The suppression of interdiffusion with the presence of Ga vacancies was explained by the thermal stress effect which suppressed Ga vacancy diffusion during annealing. It suggests that Ga[sub x]O[sub y] may therefore be used as a mask material in conjunction with other dielectric capping layers in order to control and selectively achieve impurity-free vacancy disordering. [ABSTRACT FROM AUTHOR]

Implantation, annealing, and oxidation processes are utilized to fabricate Au nanoparticles with a narrow size and depth distribution in a Si[O.sub.2] layer. The size distribution of the resulting Au precipitates in Si[O.sub.2] is found to be smallest when Au is first gettered to cavities and vacancies are subsequently introduced into the Si layer prior to oxidation.