Formation and magnetic properties of Fe16N2 films prepared by ion-beam-assisted deposition

Fe-N films containing the Fe16N2 phase were prepared in a high-vacuum system of ion-beam-assisted deposition (IBAD). The composition and structure of the films were analysed by Auger electron spectroscopy (AES) and X-ray diffraction (XRD), respectively. Magnetic properties of the films were measured by a vibrating sample magnetometer (VSM). The phase composition of Fe-N films depend sensitively on the N/Fe atomic arrival ratio and the deposition temperature. An Fe16N2 film was deposited successfully on a GaAs (1 0 0) substrate by IBAD at a N/Fe atomic arrival ratio of 0.12. The gram-saturation magnetic moment of the Fe16N2 film obtained is 237 emu/g at room temperature, the possible cause has been analysed and discussed. Hysteresis loops of Fe16N2 have been measured, the coercive force H-c is about 120 Oe, which is much larger than the value for Fe, this means the Fe16N2 sample exhibits a large uniaxial magnetocrystalline anisotropy. (C) 1998 Elsevier Science B.V. All rights reserved.

One-pot synthesis and self-assembly of colloidal copper(I) sulfide nanocrystals

A simple one-pot method is developed to prepare size-and shape-controlled copper(I) sulfide (Cu2S) nanocrystals by thermolysis of a mixed solution of copper acetylacetonate, dodecanethiol and oleylamine at a relatively high temperature. The crystal structure, chemical composition and morphology of the as-obtained products are characterized by powder x-ray diffraction (PXRD), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The morphology and size of the Cu2S nanocrystals can be easily controlled by adjusting the reaction parameters. The Cu2S nanocrystals evolve from spherical to disk-like with increasing reaction temperature. The spherical Cu2S nanocrystals have a high tendency to self-assemble into close-packed superlattice structures. The shape of the Cu2S nanodisks changes from cylinder to hexagonal prism with prolonged reaction time, accompanied by the diameter and thickness increasing. More interestingly, the nanodisks are inclined to self-assemble into face-to-face stacking chains with different lengths and orientations. This one-pot approach may extend to synthesis of other metal sulfide nanocrystals with different shapes and sizes.

INDIUM OHMIC CONTACTS TO N-ZNSE

The reaction between an indium over layer and high purity MBE grown n-ZnSe chlorine doped (2x 10(18) cm-3) epilayers has been investigated using X-ray diffraction, Rutherford backscattering spectroscopy, X-ray photoelectron and Auger electron spectroscopy, and by electrical function tests (I-V and C-V). Good ohmic contacts were formed after annealing at 250 or 300-degrees-C for a few minutes in forming gas. Annealing at lower or higher temperatures resulted in higher resistance or rectifying contacts. The data show that no compounds were formed at the interface; instead In appeared to diffuse into the ZnSe. High surface doping densities appear to allow an ohmic contact, but the electrical data suggest that compensation effects are also very significant in the formation of the contact. These effects must be considered for successful formation of the ohmic contact.

INTERFACIAL REACTIONS IN THE CO/SI/GAAS AND SI/CO/GAAS SYSTEMS

The interfacial reactions between thin films of cobalt and silicon and (100)-oriented GaAs substrates in two configurations, Co/Si/GaAs and Si/Co/GaAs, were studied using a variety of techniques including Auger electron spectroscopy, x-ray diffraction, and transmission electron microscopy. The annealing conditions were 200, 300, 400, 600-degrees-C for 30 min, and rapid thermal annealing for 15 s. It was found that Si layer in the Co/Si/GaAs system acts as a barrier at the interface between Co and GaAs when annealed up to 600-degrees-C. The interfacial reaction between Co and Si is faster than that between Co and GaAs in the system of Si/Co/GaAs. The sequence of compound formation for the two metallizations studied (Co/Si/GaAs and Si/Co/GaAs) depends strongly on the sample configuration as well as the layer thickness of Si and Co (Co/Si atomic ratio). From our results, it is promising to utilize Co/Si/GaAs multilayer film structure to make a CoSi2/GaAs contact, and this CoSi2 may offer an alternative to the commonly used W silicides as improved gate metallurgies in self-aligned metal-semiconductor field effect transistor (MESFET) technologies.

INTERFACIAL FORMATION PROCESS AND REACTIONS BETWEEN AU AND HYDROGENATED AMORPHOUS SI STUDIED BY XPS AND AES

Interfacial formation processes and reactions between Au and hydrogenated amorphous Si have been studied by photoemission spectroscopy and Auger electron spectroscopy. A three-dimensional growth of Au metal cluster occurs at initial formation of the Au/a-Si:H interface. When Au deposition exceeds a critical time, Au and Si begin interdiffusing and react to create an Au-Si alloy region. Annealing enhances interdiffusion and a Si-rich region exists on the topmost surface of Au films on a-Si:H.

CERIUM SILICIDE FORMATION IN THIN CE SI MULTILAYER FILMS

Alternating layers of Si(200 angstrom thick) and Ce(200 angstrom thick) up to 26 layers altogether were deposited by electron evaporation under ultrahigh vacuum conditions on Si(100) substrate held at 150-degrees-C. Isothermal, rapid thermal annealing has been used to react these Ce-Si multilayer films. A variety of analytical techniques has been used to study these multilayer films after annealing, and among these are Auger electron spectroscopy, Rutherford backscattering, X-ray diffraction, and high resolution transmission electron microscopy. Intermixing of these thin Ce-Si multilayer films has occurred at temperatures as low as 150-degrees-C for 2 h, when annealed. Increasing the annealing temperature from 150 to 400-degrees-C for 1 h, CeSi2 forms gradually and the completion of reaction occurs at approximately 300-400-degrees-C. During the formation of CeSi2 from 150-400-degrees-C, there is some evidence for small grains in the selected area diffraction patterns, indicating that CeSi2 crystallites were present in some regions. However, we have no conclusive evidence for the formation of epitaxial CeSi2 layers, only polycrystals were formed when reacted in the solid phase even after rapid thermal anneal at 900-degrees-C for 10 s. The formation mechanism has also been discussed in combining the results of the La-Si system.

INTERACTION OF CO WITH SI AND SIO2 DURING RAPID THERMAL ANNEALING

The interaction of Co with Si and SiO2 during rapid thermal annealing has been investigated. Phase sequence, layer morphology, and reaction kinetics were studied by sheet resistance, x-ray diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and scanning electron microscopy. With increasing annealing temperature, Co film on Si(100) is transformed sequentially into Co2Si, CoSi, and finally CoSi2 which corresponds to the minimum of sheet resistance. No evidence of silicide formation was observed for Co/SiO2 annealed even at the high temperature of 1050-degrees-C.

PHOTOEMISSION-STUDY OF THE INTERFACIAL FORMATION PROCESS AND REACTIONS BETWEEN AL AND HYDROGENATED AMORPHOUS SI

Using photoemission spectroscopy and Auger electron spectroscopy, the interfacial formation process and the reactions between Al and hydrogenated amorphous Si are probed, and annealing behaviors of the Al/a-Si:H system are investigated as well. It is found that a three-dimensional growth of Al metal clusters which includes reacted Al and non-reacted metal Al occurs at the initial Al deposition time, reacted Al and Si alloyed layers exist in the Al/a-Si:H interface, and non-reacted Al makes layer-by-layer growth forming a metal Al layer on the sample surface. The interfacial reactions and element interdiffusion of Al/a-Si:H are promoted under the vacuum annealing.

Optical and structural properties of anodized AlxGa1-xAs layers

The optical and structural properties of anodized AlxGa1-xAs films were investigated by using optical reflectance, X-ray photoemission and Auger electron spectroscopy (XPS and AES). II was found that the anodization process occurs progressively from the surface to the bulk of AlxGa1-xAs and the formed oxidation film comprises mainly oxides of Al and Ga together with a relatively small amount of As. The refractive indexes of the anodized Al0.8Ga0.2As film and Al0.8Ga0.2As film itself were deduced to be about 1.80 and 3.25, respectively, indicating that the anodization film is desirable for anti-reflection coating of the surface of AlxGa1-xAs/GaAs solar cells. (C) 1997 Elsevier Science S.A.

Microstructure studies of PdGe/Ge ohmic contacts to n-type GaAs formed by rapid thermal annealing

A low resistance and shallow ohmic contact to n-GaAs is performed by using Ge/Pd/GaAs trilayer structure and rapid thermal annealing process. The dependence of specific contact resistivity on the temperature of rapid thermal annealing is investigated. A good ohmic contact is formed after annealing at 400-500 degrees C for 60 s. The best specific contact resistivity is 1.4 x 10(-6) Omega cm(2). Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM) are used to analyze the interfacial microstructure. A strong correlation between the contact resistance and the film microstructure is observed.

Photoluminescence enhancement of (NH4)(2)S-x passivated InP surface by rapid thermal annealing

Photoluminescence enhancement of (NH4)(2)S-x passivated InP surface followed by rapid thermal annealing (RTA) has been investigated by using photoluminescence (PL), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), An increase in PL intensity of up to 10 times was observed after sulfur passivation and RTA treatment compared to unpassivated InP surface. XPS measurement results show that introduction of RTA process can enhance the sulfur remaining on the passivated surface to bond to indium but no evidence of S-P bond is noticeable. Passivation enhancement mechanism is discussed.

Diamond growth by carbon ion implantation of diamond

Medium energy (5-25 keV) C-13(+) ion implantation into diamond (100) to a fluence ranging from 10(16) cm(-2) to 10(18) cm(-2) was performed for the study of diamond growth via the approach of ion beam implantation. The samples were characterized with Rutherford backscattering/channelling spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and Auger electron spectroscopy. Extended defects are formed in the cascade collision volume during bombardment at high temperatures. Carbon incorporation indeed induces a volume growth but the diamond (100) samples receiving a fluence of 4 x 10(17) to 2 x 10(18) at. cm(-2) (with a dose rate of 5 x 10(15) at. cm(-2) s(-1) at 5 to 25 keV and 800 degrees C) showed no He-ion channelling. Common to these samples is that the top surface layer of a few nanometers has a substantial amount of graphite which can be removed by chemical etching. The rest of the grown layer is polycrystalline diamond with a very high density of extended defects.

PASSIVATION OF THE INP(100) SURFACE USING (NH4)(2)S-X

InP(100) surface treated with (NH4)(2)S-x has been investigated by using photoluminescence(PL), Auger electron spectroscopy and X-ray photoelectron spectroscopy. It is found that PL intensity increased by a factor of 3.3 after (NH4)(2)S-x 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.

CHARACTERISTICS OF OXIDES FORMED FROM A SI0.5GE0.5

X-ray photoelectron spectroscopy (XPS) combined with Auger electron spectroscopy (AES) have been used to study the oxides from a Si0.5Ge0.5 alloy grown by molecular beam epitaxy (MBE). The oxidation was performed at 1000 degrees C wet atmosphere. The oxide consists of two layers: a mixed (Si,Ge)O-x layer near the surface and a pure SiOx layer underneath. Ge is rejected from the pure SiOx and piles up at the SiOx/SiGe interface. XPS analysis demonstrates that the chemical shifts of Si 2p and Ge 3d in the oxidized Si0.5Ge0.5 are significantly larger than those in SiO2 and GeO2 formed from pure Si and Ge crystals.

NiO removal of Ni/Au Ohmic contact to p-GaN after annealing

The Ni/Au contact was treated with oxalic acid after annealing in O_2 ambient, and its I-V characteristic showed the property of contact has been obviously improved. An Auger electron spectroscopy (AES) depth pro-file of the contact as-annealed showed that the top layer was highly resistive NiO, while an X-ray photo-electron spectroscopy (XPS) of oxalic acid treated samples indicated that the NiO has been removed effectively. A scanning electron microscope (SEM) was used to observe the surface morphology of the contacts, and it was found that the lacunaris surface right after annealing became quite smooth with lots of small Au exposed areas after oxalic acid treatment. When the test probe or the subsequently deposited Ti/Au was directly in contact with these small Au areas, they worked as low resistive current paths and thus decrease the specific contact resistance.