Diffusion studies of Be-implanted GaAs by SIMS and electrical profiling

Secondary ion mass spectrometry (SIMS) has been used with differential resistivity and Hall effect measurements to study the 900°C diffusion of implanted Be in GaAs. Some outdiffusion of Be into the Si₃N₄ encapsulant occurs for surface Be concentrations above 1 × 10¹⁸cm^?3. However, excellent agreement between the electrical and atomic profiles indicates that 85–100% of the Be remaining after annealing is electrically active. The concentration-dependent diffusion observed for implanted Be in GaAs was not significantly altered in experiments using hot substrate implants, two-step anneals, or annealing with Ga and As overpressure.     

Effects of MBE growth conditions on carbon contamination in GaAs

The effects of growth and pre-growth conditions on the background concentration of carbon in high quality undoped GaAs layers grown by molecular beam epitaxy have been studied. Characterization of the layers by low temperature photoluminescence indicates that a growth temperature of 580°C minimizes carbon contamination, and extended pre-growth outgassing of the substrate under an As₄ over-pressure results in increased carbon concentrations. The carbon incorporation was found to be relatively insensitive to outgassing temperature above 615°C. Contrary to expectations, increasing the As/Ga flux ratio during growth resulted in larger carbon luminescence peaks.     

The epitaxial growth of Fe on GaAs(110): Development of the electronic structure and interface formation

The epitaxial growth of ultra-thin Fe films on GaAs(110) at a substrate temperature of 175° C has been studied by spin-resolved and spin-integrated photoemission with synchrotron radiation. Formation and evolution of the interface region have been followed for incremental Fe coverages Θ between 0.1 and 75 ML. The ordered growth of the overlayer is accompanied by reactive intermixing for metal coverage up to 15 ML followed by further As outdiffusion. The surface is ferromagnetically ordered by 6 ML.     

Implantation doping of germanium with Sb,As, and P

The ions of Sb, As, and P have been implanted into germanium at energies ranging from 200 keV to 700 keV. Annealing was performed at 400°C, 550°C, and 650°C. The doping profile was determined by differentialCV-measurements. Strong outdiffusion (80%) and diffusion into the bulk material was observed after annealing. The remaining doping concentration and the diffusion constants were determined by a computer fit at 650°C. We foundD _Sb=1.8×10⁻¹³ cm²/s,D _As=9×10⁻¹⁴ cm²/s andD _P=4×10⁻¹⁴ cm²/s. Lower values of the diffusion constant were determined when the samples were covered with a SiO₂ layer.     

Reaction of sputtered Pt films on GaAs

Pt/GaAs interface reaction has been investigated between 250–500°C. Schottky barrier Impatt diodes for microwave applications with this structure have an operating temperature of ～250°C and the solid state reaction at the interface can lead to degradation of the device. Using RF sputtered Pt films on (100) GaAs, the reaction has been investigated with the help of X-ray diffraction, Auger spectroscopy, Rutherford backscattering and electrical resistivity measurements.The reaction starts by a rapid diffusion and dissolution of Ga in Pt and is slowed down by the formation of PtAs₂ at the interface which acts as a barrier for further Ga diffusion and reaction. Five different Pt-Ga phases and PtAs₂ were identified at various stages of the reaction. The final reaction products are PtAs₂ and GaPt. The reaction becomes self limited (up to 500°C) for Pt films thicker than ～2000 Å, probably due to extremely slow diffusion of Ga through the interfacial PtAs₂. Electrical resistivity data seem to indicate that Pt₃Ga is more resistive than PtGa which is the final equilibrium Pt-Ga compound observed in this reaction.     

Temperature and reconstruction dependence of the initial Al growth on GaAs(001)

The development of the interface between Al and MBE-grown GaAs(001) surfaces has been analyzed up to a mean Al coverage of 0.5 nm. Interdiffusion, chemical reactivity and nucleation have been studied by Auger electron spectroscopy and reflection high energy electron diffraction for the c(2 × 8) and the (4 × 6) surface reconstructions in the temperature interval 268 to 673 K. Above 550 K no nucleation was observed and the growth process was governed by As outdiffusion followed by formation of AlAs. At lower temperatures three characteristic regions of Al coverage were found. The different growth mechanisms in these regions are discussed. An AlGa exchange reaction was observed only on the Ga-rich (4 × 6) structure where it was also correlated to the nucleation. The particular deposition measurement procedure used was found to be an important parameter, since interdiffusion was observed even at room temperature. The coverage at which 3D nucleation occurred was dependent on both substrate temperature and surface reconstruction but always appeared between 1.5 and 3.5 monolayer coverage. A strong temperature dependence of the nucleation was observed.     

Manganese-related luminescence in GaInAs/AlInAs multiple quantum wells grown on InP by molecular beam epitaxy

Two Mn-related luminescence peaks have been observed in a series of nominally undoped Ga_0.47In_0.53As/Al_0.48In_0.52As multiple quantum wells (MQW) grown lattice-matched on InP substrates by molecular beam epitaxy. These two peaks correspond to on-center and on-edge impurity states, respectively. The origin of the Mn impurities is outdiffusion from the Fe-doped semiinsulating InP substrate into the epitaxial layer. The binding energy of Mn acceptors, determined to be 53±3 meV in bulk-like Ga_0.47In_0.53As, increases to 80±5 meV for the on-center Mn state in a 58 Å MQW. The strong well-width dependence of the binding energy is explained in terms of the unique behavior of the Mn impurity in III–V semiconductors. The Mn in Ga_0.47In_0.53As and Ga_0.47In_0.53As/Al_0.48In_0.52As MQWs behaves predominantly as a deep impurity.On leave from: A. F. Ioffe Physicotechnical Institute, Leningrad, USSR     

Light scattering in transition metal diselenides CoSe2 and CuSe2

Raman scattering techniques have been used to investigate the long- wavelength optical phonon spectrum of the pyrite-type transition metal diselenides CoSe₂ and CuSe₂. Of the five Raman-active phonon peaks expected by group theory only one has been observed in CoSe₂ and three in CuSe₂ at 300 and 77°K. Overtone scattering is also observed in CuSe₂. As these materials are highly conducting it is concluded that appreciable damping by free carriers obscures the observation of the missing modes.     

Influences of As flux on the lattice constants, magnetic and transport properties of (Ga, Mn)As epilayers

A series of (Ga, Mn)As epilayers have been prepared on semi-insulating GaAs (001) substrates at 230  ^°C by molecular-beam epitaxy under fixed temperatures of Ga and Mn cells and varied temperatures of the As cell. By systematically studying the lattice constants, magnetic and magneto-transport properties in a self-consistent manner, we find that the concentration of As antisites monotonically increases with increasing As flux, while the concentration of interstitial Mn defects decreases with it. Such a trend sensitively affects the properties of (Ga, Mn)As epilayers.     

Alignment effects on implantation profiles in silicon

Abstract

Dual species ion implants of Se in conjunction with Ga implant in Cr-doped semi-insulating GaAs have been carried out. Electron concentration and mobility profiles have been investigated for annealed samples using differential Hall-effect and sheet-resistivity measurements.

It has been shown that the dnal implantations give high maximum electron concentrations above 1 × 10¹⁹ cm^?3 when those samples are annealed at 950°C using a low oxygen content CVD Si₃ N₄ encapsulant. Experimental results indicate that the major part of the enhanced maximum electron concentrations arise from Se donors on As vacancy sites.     

Kinetic study of the thermoluminescence glow curve of natural dolerite

T _m–T _stop and glow curve deconvolution methods have been used to determine the number of glow peaks and kinetic parameters (activation energy E and frequency factor s) associated with the glow peaks in a natural dolerite. The T _m–T _stop method indicated that the glow curve of the mineral is the superposition of at least seven first-order components, whereas deconvolution analysis indicated the presence of at least eight peaks. A possible reason for this discrepancy is given. The kinetic parameters of the eight peaks are presented and used to estimate the lifetimes of the glow peaks. The lifetimes of the peaks at 120.8 and 143 °C are few days. For application in dosimetry and dating, we suggest the use of a preheat temperature around 170 °C to ensure the complete removal of these peaks with small lifetimes.     

Local structure around Zn and Ga in solution‐processed In–Ga–Zn–O and implications for electronic properties

We study by X‐ray absorption spectroscopy the local structure around Zn and Ga in solution‐processed In–Ga–Zn–O thin films as a function of thermal annealing. Zn and Ga environments are amorphous up to 450 °C. At 200 °C and 450 °C, the Ga atoms are in a β‐Ga₂O₃ like structure, mostly tetrahedral gallium oxide phase. Above 300 °C, the Zn atoms are in a tetrahedral ZnO phase for atoms inside the nanoclusters. The observed formation of the inorganic structure above 300 °C may be correlated to the rise of the mobility for IGZO TFTs. The Zn atoms localized at the nanocluster boundary are undercoordinated with O. Such ZnO cluster boundary could be responsible for electronic defect levels. Such defect levels were put in evidence in the upper half of the band gap. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Thermoluminescence in two varieties of jadeite: Irradiation effects and application to high dose dosimetry

The thermoluminescence properties of white (WJ) and green (GJ) mineral jadeite have been investigated with a view to be of use in high dose dosimetry. WJ presented glow curve with 110, 190 and 235 °C peaks. All these peaks grow with radiation dose. The glow curve of GJ the green variety has TL peaks at 140, 210, 250 and 330 °C. We also observed that there is a difference between the TL glow curves for both samples, irradiated with gamma and electron. As expected the green jadeite can be used for measurement of dose as high as 50 kGy.     

Defect and photoluminescence profiles from thermally converted Cr-doped GaAs

Specimens of Cr-doped semi-insulating (SI) GaAs have been annealed in quartz ampoules under vacuum at elevated temperatures. Some samples, depending on temperature and time of anneal, were partially or wholly converted to p-type. In these cases CV measurements have been combined with serial sectioning to produce carrier concentration profiles. The As overpressure dependencies indicate acceptors to be associated with Ga vacancies. The diffusion coefficient of the Ga vacancies was estimated to be about 3.35 × 10^-14cm²sec^-1 at 950°C. Low temperature photoluminescence on the converted samples show a reasonably good correspondence between carrier distribution profile and the intensity of copper luminescence peak on photoluminescence spectra taken at various depth in the crystals.     

As-rich (2 × 2) surface reconstruction on GaAs(111)A

The atomic structures and the formation processes of the Ga- and As-rich (2×2) reconstructions on GaAs(111)A have been studied. The Ga-rich (2×2) structure is formed by heating the As-rich (2×2) phase, but the reverse change hardly occurs by cooling the Ga-rich surface under the As₂ flux. Only when the Ga-rich (2×2) surface covered with amorphous As layers was thermally annealed, the As-rich (2×2) surface is formed. The As-rich (2×2) surface consists of As trimers located at a fourfold atop site of the outermost Ga layer, in which the rest-site Ga atom is replaced by the As atom.     

TL–ESR correlation studies in LiMgPO4:Tb,B phosphor

Defect centers formed in irradiated LiMgPO₄:Tb,B phosphor have been investigated using the electron spin resonance technique. O^?, BO₃^2?, PO₂^?, and F⁺ are some of the centers observed in the gamma-irradiated phosphor. The phosphor exhibits thermoluminescence (TL) peaks at around 110°C, 175°C, and 260°C. An attempt has been made to determine the correlation between the defect centers and the observed TL peaks.     

Surface reactions of TiCl4 and Al(CH3)3 on GaAs(100) during the first half-cycle of atomic layer deposition

GaAs(100) was exposed to pulses of trimethylaluminum (TMA, Al(CH₃)₃) and titanium tetrachloride (TiCl₄) to mimic the first half-cycle of atomic layer deposition (ALD). Both precursors removed the 9.0 ± 1.6 Å-thick mixed oxide consisting primarily of As₂O₃ with a small Ga₂O component that was left on the surface after aqueous HF treatment and vacuum annealing. In its place, TMA deposited an Al₂O₃ layer, but TiCl₄ exposure left Cl atoms adsorbed to an elemental As layer. This suggests that oxygen was removed by the formation of a volatile oxychloride species. A small TiO₂ coverage of approximately 0.04 monolayer remained on the surface for deposition temperatures of 89 °C to 135 °C, but no TiO₂ was present from 170 °C to 230 °C. The adsorbed Cl layer chemically passivated the surface at these temperatures and blocked TiO₂ deposition even after 50 full ALD cycles of TiCl₄ and water vapor. The Cl and As layers desorbed simultaneously at higher temperature producing peaks in the temperature programmed desorption spectrum in the range 237–297 °C. This allowed TiO₂ deposition at 300 °C in single TiCl₄ pulse experiments. On the native oxide-covered surface where there was a higher proportional Ga oxide composition, TiCl₄ exposure deposited TiO₂.     

Temperature dependent surface and spectral modifications of nano V<Subscript>2</Subscript>O<Subscript>5</Subscript> films

Nanocrystalline V₂O₅ films have been deposited on glass substrates at 300°C substrate temperature using thermal evaporation technique and were subjected to thermal annealing at different temperatures 350, 400, and 550°C. X-ray diffraction (XRD) spectra exhibit sharper and broader characteristic peaks respectively indicating the rearrangement of nanocrystallite phases with annealing temperatures. Other phases of vanadium oxides started emerging with the rise in annealing temperature and the sample converted completely to VO₂ (B) phase at 550°C annealing. FESEM images showed an increase in crystallite size with 350 and 400°C annealing temperatures followed by a decrease in crystallite size for the sample annealed at 550°C. Transmission spectra showed an initial redshift of the fundamental band edge with 350 and 400°C while a blue shift for the sample annealed at 550°C, which was in agreement with XRD and SEM results. The films exhibited smart window properties as well as nanorod growth at specific annealing temperatures. Apart from showing the PL and defect related peaks, PL studies also supported the observations made in the transmission spectra.     

Ferromagnetic resonance in epitaxial (Bi,Lu)3(Fe,Ga)5O12(210) films

Ferromagnetic resonance in epitaxial (Bi,Lu)₃(Fe,Ga)₅O₁₂ films grown on Gd₃Ga₅O₁₂(210) substrates is investigated. The spectrum contains a number of peaks, the most intense of which is related to the bulk of the film and the transition layer at the film-substrate interface. Most of the film volume is characterized by reduced magnetic anisotropy. The azimuthal and polar dependences of the resonance field exhibit 180° symmetry.