bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and operation of a valved solid-source As2 oven for molecular beam epitaxy
Authors: Miller D. L. , Bose S. S. , Sullivan G. J.
Published: July 2002

The design and operation of a valved solid-source of arsenic for molecular beam epitaxy is described. The addition of a throttle valve to a solid-charge arsenic source allows the arsenic flux to be varied rapidly and controllably during epitaxial growth with a time constant of <1 s. In addition to the novel valve, the arsenic source assembly includes a large reservoir, a thermal cracking zone for the production of As2, and provisions for adding an exit aperture ionization gauge for feedback flux control. Low-temperature photoluminescence from undoped GaAs grown with this source exhibited a neutral donor-bound exciton peak with full width at half-maximum of 0.128 meV, and lightly silicon-doped GaAs exhibited a mobility of 73 000 cm2/V s at 77 K, corresponding to ND =1.3×1015/cm3 and NA =2.0×1014/cm3.
Radiation stability of SiC and diamond membranes as potential x-ray lithography mask carriers
Authors: Wells G. M. , Palmer S. , Cerrina F. , Purdes A. , Gnade B.
Published: July 2002

In this paper we report on the radiation stability of silicon carbide and diamond membranes as potential x-ray lithography mask carriers. Silicon carbide membranes have been produced by epitaxial chemical vapor deposition (CVD). Diamond membranes have been produced in tension with diameters up to 2.5 cm using a microwave plasma CVD process. The stability of these membranes upon exposure to x rays has been studied. The materials were characterized before and after irradiation for their stress, Young’s modulus, infrared absorption from 2.5 to 25 μm, and visible transmission from 300 to 800 nm. The x-ray exposures were performed using the Center for X-ray Lithography beamlines at the Aladdin synchrotron at the University of Wisconsin. These beamlines provide a broadband x-ray spectrum from 900 to 5000 eV. Incident doses of 6700 and 2400 J/cm2 were delivered to the silicon carbide and diamond samples, respectively. Both materials were found to be stable for these exposure levels within the accuracy of the experimental methods.
Extreme ultraviolet resist and mirror characterization: Studies with a laser plasma source
Authors: Kubiak Glenn D. , Outka Duane A. , Rohlfing Celeste M. , Zeigler John M. , Windt David L. , Waskiewicz Warren K.
Published: July 2002

A monochromatized laser-produced plasma source of extreme ultraviolet (XUV) radiation has been used to study resists and reflective multilayers for use in projection x-ray lithography. We report the characterization of near-edge x-ray absorption fine structure (NEXAFS) spectra, exposure sensitivity, and contrast of selected polysilane resists at photon energies near 100 eV, where projection x-ray lithography is being developed. We find absorption resonance features in the NEXAFS spectra which we assign based on ab initio quantum chemical calculations to excitation into Si–Si and Si–C σ* orbitals. Using monochromatized XUV exposures on the Si–Si σ* resonance at 105 eV, followed by solvent dissolution development, we have measured the exposure sensitivity curves of these resists. We find sensitivities in the range of 600–3000 mJ/cm2 and contrasts in the range from 0.5–1.4, depending on the polysilane side chain. Exposure sensitivity measurements have also been performed below the edge at 92 eV where we find only minor differences from the results at 105 eV, which can be accounted for by a simple decrease in film absorption. The variation in Mo/Si multilayer mirror reflectance as a function of wavelength has also been measured for two mirrors having nearly identical layer periods, but different numbers of layer pairs (N). Increasing N from 20 to 40 is seen to increase the first order peak reflectance from 39%±2% to 50%±3% and to narrow the reflectance bandwidth from 7% to 5.6%. These results are in accord with calculations which use optical constants from the literature and a Debye–Waller interfacial roughness factor to account for interfacial reflectance losses.
Scanning tunneling microscopy study of a polyimide Langmuir–Blodgett film
Authors: Fujiwara Ichiro , Ishimoto Coe , Seto Jun’etsu
Published: July 2002

The microscopic molecular structure of a polyimide Langmuir–Blodgett (LB) film monolayer was studied by scanning tunneling microscopy (STM) and molecular simulation. An STM image of a polyimide monolayer on graphite showing the polymer chains was observed for the first time. The STM image directly indicated that the alignment direction of the polymer chains of polyimide is parallel to the deposition direction of the LB film. In order to investigate the microscopic interpretation of the molecular structure theoretically, molecular dynamics calculations of the optimum polyimide structure on graphite were carried out. The polyimide chain on graphite has a zigzag structure with bends at the ether-bonded oxygen atoms. The distance between oxygen atoms at successive bends is 17.8 Å and the bend angle is about 119 deg. These values are in fair agreement with the STM image. Therefore, it was confirmed that the STM image can be interpreted as showing the individual molecular chains of the polyimide monolayer.
Scanning tunneling microscopy of quasi-one-dimensional organic conductors
Authors: Pan S. , de Lozanne A. L. , Fainchtein R.
Published: July 2002

We have used a variable temperature ultrahigh vacuum (UHV) scanning tunneling microscope to study the quasi-one-dimensional organic conductor, tetrathiafulvalene-tetracyanoquinodimethane. The experiment has been performed in air and UHV, at temperatures ranging from 10 to 300 K. High resolution images obtained both in air and UHV clearly revealed a one-dimensional structure. The molecular positions and orientations deduced from the real space images are in good agreement with the lattice parameters obtained from other experimental methods. Below 80 K, a commensurate 2kF charge density wave modulation in real space appeared, and its associated energy gap of about 100 mV was also observed at lower temperatures.
Characterization of CdTe, HgTe, and Hg1−xCdxTe grown by chemical beam epitaxy
Authors: Wagner B. K. , Rajavel D. , Benz R. G. , Summers C. J.
Published: July 2002

Detailed characterization of chemical beam epitaxially (CBE) grown CdTe and Hg1−xCdxTe layers are reported. These characterizations include photoluminescence, infrared transmission, energy dispersive x-ray analysis, and variable temperature (10–300 K) Hall effect and resistivity measurements. The results indicate that high quality HgCdTe layers can be grown by CBE.
Studies of nucleation and growth morphology of boron-doped diamond microcrystals by scanning tunneling microscopy
Authors: Everson M. P. , Tamor M. A.
Published: July 2002

We report on a study of nucleation and growth morphology of diamond microcrystals formed by microwave enhanced chemical vapor deposition. By doping diamonds with boron, sufficient conductivity is achieved that they may be directly imaged by scanning tunneling microscopy with near-atomic resolution. We demonstrate the first application of work function and dI/dV imaging of diamond. These techniques offer the ability to identify nuclei too small to be recognized by their characteristic cubo-octahedral shape, and may enable identification of nucleation sites before diamond growth begins.
Formation of cobalt silicide under a passivating film of molybdenum or tungsten
Authors: Yang Fann-Mei , Chen Mao-Chieh
Published: July 2002

A very simple and reproducible cobalt silicide process with Mo/Co or W/Co bilayer metallization to overcome the oxidizing liability of Co annealed in a normal flowing-nitrogen furnace has been developed. Cobalt is deposited on blank and patterned silicon wafers in an electron-beam evaporation system followed by Mo (or W) deposition without breaking the vacuum. The cobalt silicidation is carried out using a two-step annealing process. The first annealing is performed at a temperature ranging from 400 to 600 °C, during which the role of the upper layer of Mo (or W) is to protect the underlying Co layer from being oxidized while not disturbing the cobalt’s silicidation process. Perfect selective etching of Mo (or W) can be accomplished by a NH4OH+H2O2+(2–3)H2O solution. The second annealing is performed at a higher temperature of 750 °C to completely transform the CoSi obtained in the first annealing into CoSi2 and induce grain growth of CoSi2, thus lowering the resistivity. X-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and sheet resistance measurement are used to characterize the silicide phase and microstructure.
Scanning tunneling microscopy observations of metallic clusters Pd561 and Au55 and the implications of their use as a well defined tip
Authors: van de Leemput L. E. C. , Gerritsen J. W. , Rongen P. H. H. , Smokers R. T. M. , Wierenga H. A. , van Kempen H. , Schmid G.
Published: July 2002

We investigated ligand stabilized clusters Au55(PPh3)12Cl6 and Pd561(phen)38±2O≊200 on gold and graphite substrates with scanning tunneling microscopy (STM) under atmospheric conditions. We were able to image dense layers of clusters as well as free-lying clusters. Clusters are frequently picked up by the tip. This results in a tip with a well defined shape and electronic structure. Analysis of images of clusters scanned with another cluster attached to the tip can yield direct information on the tunnel distance. We found a tunnel distance of 24±5 Å.
Laser and thermal annealed Si(111) and Si(001) surfaces studied by scanning tunneling microscopy
Authors: Tarrach G. , Wiesendanger R. , Bürgler D. , Scandella L. , Güntherodt H.-J.
Published: July 2002

We used scanning tunneling microscopy to study the local structure of the Si(111)7×7 and Si(001)2×1 reconstructions in the vicinity of step edges and to investigate the transition from order to disorder on laser-irradiated Si(111). Atomic resolution even in the presence of multiple steps and characteristic defects on the lower terrace at the step edges are reported for the Si(111) surface. Furthermore, we achieved atomic resolution in several regions exhibiting different degrees of disorder after laser irradiation. These measurements are compared to a simple geometric model using pair-correlation functions. High-resolution images of the Si(001)2×1 reconstruction reveal buckled dimers near defects and monatomic type A steps when probing the empty states of the sample.
Interaction between Al–Si–Cu alloys and MoSi2
Authors: Fukada Shin-ichi , Suwa Motoo , Koubuchi Yasushi , Onuki Jin
Published: July 2002

The interaction at the metal–metal interface of the Al–Si–Cu/MoSi2 bilayer system has been investigated as a function of the Cu concentration. The Al in the Al–Si–Cu alloy reacts with the MoSi2 at temperatures above 400 °C. Al atoms diffuse into the MoSi2 and the excess Si diffuses into the Al layer. After the reaction, the amorphous MoSi2 becomes crystalline Mo(Al,Si)2. The excess Si in the MoSi2 layer forms precipitates in the Al layer. The Cu concentration in the Al alloy affects the reaction rate with 1% Cu having the largest effect followed by 0.5% Cu and then 3% Cu. A model is presented that explains this phenomenon. The Al–Si alloy without Cu does not react with MoSi2 below 450 °C.
Temperature measurement during implantation at elevated temperatures (300–500 °C)
Authors: Vandenabeele Peter , Maex Karen
Published: July 2002

Using an optical fiber thermometer, wafer temperature was measured during implantation at elevated temperatures. The wafer was mounted on a chuck which was resistively heated to 400 °C. Ar was implanted at an energy of 200 keV and a current in the range of 0–750 μA. Due to poor thermal contact between the chuck and the wafer, wafer temperature could be different from chuck temperature. The wafer temperature varied from ∼300 to 500 °C as a function of implantation current. The wafer temperature was also dependent on the optical properties of the wafer. A model was developed which took the optical properties of the wafer and the chuck into account.
Increase in silicon charge coupled devices speed with focused ion beam implanted channels
Authors: Murguia J. E. , Shepard M. I. , Melngailis J. , Lattes A. L. , Munroe S. C.
Published: July 2002

The clocking frequency of long channel CCDs is limited by the time taken to transfer charge from one well to the next. The bulk of the charge transfers rapidly by Coulomb repulsion but residual charge has to transfer by thermal diffusion, which is a slow process. If the n-type dopant density has a gradient in the direction of current flow, a built-in electric field is created, speeding up the charge transfer process. The focused ion beam system is uniquely suited to implant such a gradient of doping and has been used to implant buried-channel CCDs with 26-μm-long storage gates. The devices built to demonstrate this concept were shallow-buried-channel CCDs driven by 2-phase 5-V clocks. Arsenic ions were implanted at an energy of 220 keV and a gradient of doping increasing from 0 to 1.5×1011 ions/cm2 was superimposed on a uniform phosphorus implant. The challenge here was to get a low, monotonically increasing implant dose. Defocusing of the 25-pA As+ + beam to a diameter of ∼1 μm was found to be necessary. The maximum operating (clocking) frequency of the graded-implant devices was 41 MHz compared to a maximum frequency of 2.5 MHz for the same devices with uniformly doped channels. Such long-channel CCDs are of interest in 2-dimensional imaging applications and signal processing applications where high well charge capacity is needed without compromising speed or charge transfer efficiency.
Dry-etch monitoring of III–V heterostructures using laser reflectometry and optical emission spectroscopy
Authors: Collot P. , Diallo T. , Canteloup J.
Published: July 2002

Reactive ion etching of III–V heterostructures was monitored using laser interferometry at 632.8 nm and optical emission spectroscopy (OES) between 200 and 800 nm, simultaneously. Three standard plasma chemistries were investigated: (i) CCl2F2/He for the selective etching of GaAs on AlGaAs, (ii) SiCl4/He for the nonselective etching of GaAs/AlGaAs heterostructures, and (iii) CH4/H2 for the etching of In-based III–V compounds. Laser interferometry provided local monitoring of etch rate, independent of etch chemistry. During GaAs and AlGaAs etching, optical emission from etch products was detected, identified, and selected to monitor etching. Using AlCl emission line at 261.4 nm, accurate etch monitoring of GaAs/AlGaAs heterostructures in SiCl4 -based plasma was demonstrated. The high resolution capacity of OES thereby allowed the discrimination of AlGaAs layers as thin as 5 nm. Accurate etch monitoring of InP/In0.53GaAs heterostructures in CH4/H2 plasma was also demonstrated using the In atomic emission line at 325.6 nm: detection of In0.53GaAs layers as thin as 3 nm was possible. The combination of laser interferometry and OES was shown to be a suitable tool for III–V device etching.
Interface formation and film morphology for growth of Fe and Co on ZnSe(001)
Authors: Jonker B. T. , Prinz G. A. , Idzerda Y. U.
Published: July 2002

We have studied the growth of Fe and Co films on ZnSe(001) epilayers and GaAs(001) bulk substrates with electron forward scattering in the form of Auger electron diffraction (AED), and with x-ray photoelectron spectroscopy (XPS) and reflection high energy electron diffraction to determine the mode of film growth and the formation of the interface. The coverage dependence of the AED forward scattering peaks is modeled and compared with the experimental data obtained for these overlayer systems. We find that the growth of Fe on ZnSe(001) at 175 °C proceeds in a predominantly layer-by-layer fashion, while a more three-dimensional growth mode occurs on the oxide-desorbed GaAs(001) substrate for both Fe and Co overlayers. Deposition of Co on the ZnSe(001) epilayers results in poorly ordered multicrystalline growth. The XPS data show that the metal/ZnSe interface is less reactive than the corresponding interface with the GaAs(001) substrate.
High quality rapid thermal annealing of InP and GaAs substrates under low pressure tertiarybutylphosphine and tertiarybutylarsine ambients
Authors: Katz A. , Feingold A. , Pearton S. J. , Abernathy C. R. , Geva M. , Jones K. S.
Published: July 2002

High quality rapid thermal annealing of InP and GaAs at elevated temperatures was achieved in a load-locked rapid-thermal-low-pressure-metalorganic-chemical-vapor deposition (RT-LPMOCVD) reactor, under phosphorus and arsenic controlled ambient, using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBA) organometallic liquid sources. Damage-free surfaces of InP and GaAs were obtained for temperatures up to 700 °C for InP under TBP ambient, or above 900 °C for GaAs under TBA ambient, respectively. Annealing the III–V substrates at low protective ambient pressure (50 mTorr) provided an excellent surface protection through the heating cycle without resulting in deposition of the group-V elements on the surface and without reducing the efficiency of the process.
Sulfur bonding to GaAs
Authors: Shin J. , Geib K. M. , Wilmsen C. W.
Published: July 2002

This paper presents experimental results on sulfur bonding to etched GaAs surfaces which have an As/Ga ratio ranging from 0.6 to 6.0. The source of the sulfur was either a liquid solution of Na2S or (NH4)2S, or gaseous H2S applied in a N2 purged glove box. Angle resolved x-ray photoelectron spectroscopy (XPS) spectra was obtained from ∼40 different samples in order to determine the concentration of the various surface chemical species and their bonding state. Most of the experiments were conducted with H2S exposed samples at substrate temperatures from 30 to 350 °C. Sulfur is shown to bond to both Ga and As. The amount of bonding to each depends on the As/Ga ratio. This is true for both H2S and the liquid S solutions. Only one S–As bonding state was observed, independent of the S treatment process. S was observed to bond to elemental As and substrate As with the same binding energy and concentration. H2S exposed surfaces had a higher concentration of S than did those that were treated with Na2S or the (NH4)2S.
Ballistic electron emission microscopy, current transport, and p-type δ doping control of n-isotype InAs–GaAs heterojunctions
Authors: Shen T.-H. , Elliott M. , Fowell A. E. , Cafolla A. , Richardson B. E. , Westwood D. , Williams R. H.
Published: July 2002

Ballistic electron emission microscopy (BEEM) and the conventional I-V technique have been applied to study the band discontinuity at a relaxed InAs–GaAs heterojunction grown by molecular-beam epitaxy (MBE). A conduction band discontinuity ΔEc of 0.72 eV has been determined from the measurements and from appropriate numerical modeling of the interface. The lateral variation of the conduction band discontinuity has been successfully probed with BEEM with a view to establishing the influence of misfit disclocations on the barrier height. Experiments are also reported where the conduction band offset has been significantly modified by appropriate δ doping close to the interface. Doping with Be has enabled values of the effective barrier as high as 1.2 eV to be obtained. These investigations are also well described by numerical modeling.
Auger electron spectroscopy and Rutherford backscattering characterization of TiNx/TiSiy contact barrier metallization
Authors: Kottke M. , Gregory R. , Pintchovski F. , Travis E. , Tobin P. J.
Published: July 2002

We have studied both the formation and integrity of TiNx/TiSiy bilayer films formed by reacting sputter deposited Ti films on Si substrates in nitrogen containing ambients. Auger electron spectroscopy and Rutherford backscattering spectrometry have been used to characterize the formation and properties of these bilayer films as a function of the ambient composition, the substrate doping, and the method of heating [furnace or rapid thermal annealing (RTA)]. We have also characterized the B and As substrate dopant redistribution which occurs during the bilayer formation. Barrier integrity was measured by depositing 2 kÅ of Al–Si(1%)–Cu(1%) on top of the TiNx/TiSiy bilayers and thermally stressing the films at 450 °C for times ranging from 0.5 to 6.0 h. The metallurgical breakdown of the Al/barrier/Si was characterized by Auger depth profiling and the integrity of the barriers was correlated with the various parameters of the barrier formation. It is concluded that the properties of the nitride/silicide bilayer as a whole (rather than the nitride layer alone) must be considered in order to optimize the barrier performance. In particular, barriers with incompletely reacted Ti layers show inferior performance relative to those with more completely reacted Ti layers, and this characteristic is of greater importance than the nitride thickness in determining the barrier integrity. Barrier effectiveness is diminished by either p+ or n+ substrate doping through the dopant induced inhibition of the silicidation reaction. Native oxides prevalent on n+ substrates and their effect on the silicidation reaction have also been studied.
Strain-induced lateral confinement of excitons in GaAs/AlGaAs quantum well by chemical dry etching
Authors: Tan I.-H. , Lishan D. G. , Mirin R. , Jayaraman V. , Yasuda T. , Prater C. B. , Hu E. L. , Bowers J. E. , Hansma P. K.
Published: July 2002

HCl radical beam etching has been used to produce strain-induced lateral confinement of excitons in a GaAs quantum well. This confinement was generated by etching a grating pattern into a strained layer of In0.35Ga0.65As which overlies the GaAs quantum well. Atomic force microscopy was used to examine the etched surface morphology. Photoluminescence and excitation photoluminescence spectroscopy were used to detect the optical transitions. The after-etch photoluminescence intensity and the systematic peak shift with etch time indicate the degree of control and low-damage nature of the etch process used.
Conductance quantization in a GaAs electron waveguide device fabricated by x-ray lithography
Authors: Chu W. , Eugster C. C. , Moel A. , Moon E. E. , del Alamo J. A. , Smith Henry I. , Schattenburg M. L. , Rhee K. W. , Peckerar M. C. , Melloch M. R.
Published: July 2002

We report on the fabrication of AlGaAs/GaAs split-gate electron waveguide devices of lengths between 0.1 and 2 μm using x-ray lithography, and the measurements of these devices at liquid-helium temperatures and up to 15 K. An x-ray mask (parent mask) was fabricated using e-beam lithography and replicated using proximity x-ray lithography (λ=1.32 nm) to generate a replica (daughter) mask. The daughter mask was then aligned to patterns on a high-mobility AlGaAs/GaAs sample and x ray exposed using a conformable mask fixture. The conductance of the electron waveguides was measured as a function of the split-gate bias. Sharp 2e2/h conductance steps were observed in devices up to 0.75 μm long at T=2 K. The features in the conductance remain visible up to 15 K.
Fabrication of nonconventional distributed feedback lasers with variable grating periods and phase shifts by electron beam lithography
Authors: Kaden C. , Griesinger U. , Schweizer H. , Pilkuhn M. H. , Stath N.
Published: July 2002

Distributed feedback (DFB) lasers for a wide range in emission frequency have been fabricated in the AlGaAs system. Gratings with periods around 110 nm have been defined by electron beam lithography and dry etching. Two approaches are discussed to reach extremely fine tuning of the emission frequency, which becomes more and more essential the higher the band gap of the material and with that, the emission frequency of the laser. To reach single mode emission, phase shifts in the grating structure have been realized. A flat photon density distribution to reduce spatial hole burning could be achieved by distributing the π/2 phase shift by using four λ/16 phase shifts. In addition, resonators have been fabricated where the phase shift is spread over a wide region in the center of the resonator which corresponds to the introduction of a phase arranging zone with a slightly larger effective grating constant. The laser structures have been tested by optical pumping. DFB emission could be observed over a wide range in frequency at room temperature. The resonators with the distributed phase shifts show stable single mode operation.
Comparative mobility degradation in modulation-doped GaAs devices after e-beam and x-ray irradiation
Authors: Ghanbari R. A. , Burkhardt M. , Antoniadis D. A. , Smith Henry I. , Melloch M. R. , Rhee K. W. , Peckerar M. C.
Published: July 2002

We report on measured Hall mobility versus temperature for high-quality modulation-doped AlGaAs/GaAs samples after exposure by electrons and x rays at doses and energies typically used in lithography. We find that bare samples exposed by 50 keV electrons suffered significant mobility degradation over the temperature range of 4.2–300 K (as much as a factor of 30). X-ray-exposed samples did not show any mobility degradation. Two-dimensional electron densities were not dramatically affected by either exposure technique, although e-beam exposed samples did show a slight decrease in carrier density. Our results are consistent with previous reports of mobility degradation in some e-beam evaporators.
Magnetically enhanced triode etching of large area silicon membranes in a molecular bromine plasma
Authors: Wolfe J. C. , Sen S. , Pendharkar S. V. , Mauger P. , Shimkunas A. R.
Published: July 2002

The optimization of a process for etching 125 mm silicon membranes formed on 150 mm wafers and bonded to Pyrex rings are discussed. A magnetically enhanced triode etching system was designed to provide an intense, remote plasma surrounding the membrane while, at the same time, suppressing the discharge over the membrane itself. For the optimized molecular bromine process, the silicon etch rate is 40 nm/min and the selectivity relative to SiO2 is 160:1.
Influence of shifter errors on the printability of L/S structures using the alternated phase-shifting design: Simulations and experiments
Authors: Op de Beeck Maaike , Ronse Kurt , Kamon Kazuya , Fujinaga Masato , Kusunose Hal , Morimoto Hiroaki
Published: July 2002

It is well-known that many improvements concerning resolution and focus latitude can be obtained by the use of phase-shifting masks. Different phase-shifting mask designs are proposed already, and one of the most suitable designs for periodical structures is the alternated shifter design. If such phase-shifting masks are investigated, it is assumed that all shifter parameters are ideal. A major problem, however, is the production of such an ideal phase-shifting mask with perfect shifter parameters. In this work, the influence of shifter parameters such as transparency, thickness, and sidewall slope are studied for the alternated phase-shifting design. The investigation is carried out by simulations and by experiments, and for various coherence factors. It is found that all shifter deviations cause linewidth differences between shifter and quartz lines, often resulting in a reduced depth-of-focus (DOF). Especially if various deviations occur simultaniously, the DOF reductions are important, putting stringent demands on mask processing in order to obtain tolerable shifter deviations. In order to print L/S down to 0.3 μm with reasonable DOF for production applications, the shifter transparency and thickness should not deviate more than 5% from their ideal values.
Gas-source molecular-beam epitaxy growth of InxGa1−x−yAlyP
Authors: Hafich M. J. , Lee H. Y. , Crumbaker T. E. , Vogt T. J. , Silvestre P. , Robinson G. Y.
Published: July 2002

InxGa1−x−yAlyP, with y=0.0 to y=0.52, has been grown lattice matched to GaAs substrates using the technique of gas-source molecular-beam epitaxy. Growth conditions were established that resulted in conducting quaternary layers for both n-type Si doped and p-type Be doped samples. Si doped quaternary layers had a significantly reduced electron concentration at room temperature that varied with the AlP content in the InGaAlP layer. Intentionally doped InGaAlP layers exhibited room temperature photoluminescence for AlP mole fractions up to y=0.37; photoluminescence peak energies were 1.9 eV when y=0.0 (InGaP) to 2.3 eV when y=0.37 and decreased in intensity for increasing y.
Photoluminescence study of the effects of growth interruption on integer and fractional monolayer AlGaAs/GaAs quantum wells
Authors: Block T. R. , Neikirk D. P. , Streetman B. G.
Published: July 2002

A set of quantum wells containing wells of integer n and integer plus half-monolayer n+1/2 thickness were grown. The photoluminescence of these samples contained distinct peaks for both the n and n+1/2 wells. The structure was regrown with growth interruption between layers. With sufficiently long interrupt times (∼60 s) the peaks due to the n+1/2 wells disappeared leaving only peaks from wells of integer monolayer thickness. This result can be interpreted in terms of structural changes at the interfaces such as island coalescence. The intensity of the peaks and shifts in their energy also provide a measure of contamination and microroughness.
Properties of ZnSxSe1−x–Zn1−yCdySe quantum well structures
Authors: Ren J. , Bowers K. A. , Cook J. W. , Schetzina J. F.
Published: July 2002

Molecular-beam epitaxy has been employed to grown ZnSxSe1−x–Zn1−yCdySe multilayers. Double heterostructures consisting of a multiple quantum well structure of ZnSxSe1−x–Zn1−yCdySe sandwiched between ZnSxSe1−x have also been fabricated. Photopumped stimulated emission has been observed from these structures. In addition, double heterostructures with n-type and p-type ZnSxSe1−x cladding layers emit bright blue electroluminescence at 2.601 eV (476 nm) at room temperature.
Interface stoichiometry dependence of the Schottky barrier height of CoGa and GaAs
Authors: Kuo T. C. , Wang K. L. , Arghavani R. , George T. , Lin T. L.
Published: July 2002

The Schottky barrier formation of CoGa on (100)n-GaAs is investigated. CoGa is grown by molecular-beam epitaxy, and the epitaxial orientation is controlled by the initial growth conditions of the GaAs substrate. Schottky diodes with three different phases of CoGa: (100)CoGa, (110)CoGa and mix of (100) and (110)CoGa, are fabricated and Schottky barrier heights are measured by I–V, C–V, and internal photoemission. All these three types of diodes have different values of barrier height, indicating that the mechanisms of the barrier formation for these three phases are different. The plausible mechanisms for the change of the Fermi level pinning position of these phases are discussed. Finally, the temperature dependence of the Schottky barrier height is also examined and the barrier height is found to be constant from 150 to 300 K for all of the phases.
Effect of Γ–X mixing on electron tunneling times in GaAs/AlAs double barrier heterostructures
Authors: Ting D. Z.-Y. , McGill T. C.
Published: July 2002

The effect of Γ–X mixing on electron tunneling time in GaAs/AlAs symmetric double barrier heterostructures is studied theoretically using an empirical tight-binding band structure model. It is found that the Γ quasibound state tunneling times can be shortened or lengthened by Γ–X mixing, depending on whether the AlAs barriers consist of an even or odd number of monolayers. This is attributed to the interference between the Γ and X conduction channels in the AlAs barriers.
Surface morphology of molecular-beam epitaxially grown Si1−xGex layers on (100) and (110) Si
Authors: Pike W. T. , Fathauer R. W. , Anderson M. S.
Published: July 2002

The surface morphology and dislocation structure of Si1−xGex layers grown on (100) and (110) Si substrates have been investigated using atomic force microscopy, and scanning and transmission electron microscopy. The layers, which have up to a 1.2% lattice mismatch with the substrates, were grown by molecular-beam epitaxy at 550 °C at thicknesses above those required for the introduction of dislocations. Si1−xGex layers grown on (100) show a crosshatch morphology which is correlated to the underlying misfit dislocation network. Annealing greatly enhances the surface roughness producing a partial islanding growing on the pre-existing crosshatch morphology. On the (110) substrates no annealing is necessary to produce a roughened surface. The roughened surface morphology is analyzed as a strain-reducing growth mode which enables partial relaxation of the near-surface atomic planes.
Si(100) and Ge(100) core-level shifts: A reevaluation
Authors: Yang X. , Cao R. , Terry J. , Pianetta P.
Published: July 2002

High resolution core level photoemission was used to study the Si 2p core levels of the clean Si(100) surface and other related surfaces, and the Ge 3d core level of the clean Ge(100) surface and other related surfaces. Two surface components S and S′ for the Si 2p core level from the clean Si(100) surface have been resolved. The S and S′ components were resolved for the Ge 3d core level from clean Ge(100) surface for the first time. On both surfaces, S and S′ components are identified to be the contribution from surface dimer atoms and the subsurface layer, respectively.
Fabrication of ultrahigh quality vertical facets in GaAs using pattern corrected electron beam lithography
Authors: Hagberg Mats , Jonsson Björn , Larsson Anders
Published: July 2002

Extremely high quality vertical structures, suitable for integrated optical components, have been fabricated in GaAs using electron beam lithography and chemically assisted ion beam etching. By using the directly exposed electron beam resist as etch mask all quality degrading intermediate pattern transfers were eliminated, resulting in high resolution and reproducibility. In order to obtain a vertical mask profile and high durability, pattern corrected exposure and heat treatment of the electron beam resist was employed. The pattern correction of the resist exposure was studied using an exposure simulation program. Calculations, based on an estimation of the facet roughness using a scanning electron microscope, suggest optical scattering ratios as low as 0.6% and 7.1% for external and internal reflection of 850 nm light, respectively.
Lattice tilt and dislocations in compositionally step-graded buffer layers for mismatched InGaAs/GaAs heterointerfaces
Authors: Kavanagh K. L. , Chang J. C. P. , Chen J. , Fernandez J. M. , Wieder H. H.
Published: July 2002

The strain relaxation and dislocation densities of a compositionally step-graded InGaAs/GaAs buffer layer have been investigated. The structural results were correlated with the electrical properties of an In0.3Ga0.7As/In0.29Al0.71As modulation doped heterostructure grown on top. The buffer was a three step InxGa1−xAs structure each layer 300 nm thick and each In composition step x=0.1. X-ray rocking curve analysis measured a tilt about an in-plane <110≳ axis of about 0.3° per step. At the top interface of the buffer the density of misfit dislocations evaluated by electron microscopy was comparable to the number required to account for this tilt. Thus, the 60° burgers vectors for the majority of dislocations along one in-plane line direction was restricted to a maximum of two rather than the usual four possibilities. The electron mobility in the two-dimensional electron gas channel showed a small assymetry (4%) in the two in-plane <110≳ directions and was highest in the direction parallel to the tilt axis. The sheet electron concentration was 1.2×1012/cm2 with peak mobilities of 9300 and 31 000 cm2/V s at room temperature and 77 K, respectively.
Role of defects in the passivation of III–V semiconductor surfaces modified by alkali metals: O2/Rb/p- and n-type GaSb(110)
Authors: Schirm K. M. , Soukiassian P. , Mangat P. S. , Hurych Z. , Soonckindt L. , Bonnet J. J.
Published: July 2002

The effect of rubidium overlayers is investigated on the room-temperature oxidation of GaSb(110) surfaces by means of core-level and valence-band photoemission spectroscopy using synchrotron radiation. The presence of Rb enhances the oxidation rate of the GaSb(110) by at least six orders of magnitude and results in the formation of mixed Ga2O3 and Sb2O5 oxides. A strong reaction between the Rb overlayer and the GaSb surface is found to be essential for a complete oxidation, thus stressing the role of surface defects similarly to the previously observed case of alkali metal-promoted nitridation of GaAs(110) and InP(110) surfaces. This is in strong contrast to the behavior observed for alkali metal promoted oxidation or nitridation of an elemental semiconductor like silicon where no reaction occurs between the catalyst and the substrate. These results suggest that the presence of surface defects appear to play, in general, an important role in alkali-metal-promoted reactions of III–V compound semiconductors. Surprisingly, the interfaces formed with the p-type (Zn-doped) GaSb(110) samples are significantly more reactive than the n-type (Te-doped) one which suggests that the nature of the dopant might be of relevance in the formation of reactive interfaces.
Surface reconstruction, steps, and ordering in semiconductor alloys grown from vapor phase
Authors: Ogale S. B. , Madhukar A. , Joshi S. Y. , Viswanathan R.
Published: July 2002

The role of [110] and [1̄10] steps on GaAs(001) substrate in influencing ordering in III–III–V alloys is examined via the example of AlGaAs. Semiempirical potentials and the simulated annealing approach are employed to examine the energy of various configurations of cation clusters of increasing size. The steps are shown to significantly influence ordering, and the differences in symmetries at different steps are shown to affect the subvariant of CuPt–B type ordering realized, consistent with recent experiments.
Interfacial atomic structure and band offsets at semiconductor heterojunctions
Authors: Dandrea R. G. , Duke C. B. , Zunger Alex
Published: July 2002

The relationship between interfacial atomic structure and band offsets at semiconductor heterojunctions is explored through first-principles local density functional calculations. In particular, the effects of variations in interfacial geometry are analyzed for (001) interfaces between III–V/III–V materials. For the AC/BC case of a common atom, isovalent A–B intermixing in the noncommon atomic planes near the interface does not affect the band offset, even in the case of large lattice-mismatched systems. For quaternary AB/CD systems, there are two possible chemically abrupt interfaces (A–D or B–C); these can have offsets that differ by up to 80 meV. In those cases where the chemically abrupt AB/CD offset depends on the interfacial identity, intermixing leads to offset variations which are directly related to the offset difference between the chemically abrupt A–D and B–C interfaces. The differing behavior of common-atom versus noncommon-atom systems is analyzed in terms of the symmetry of the nearest-neighbor environment surrounding an atomic site of a composition change.
Analysis of excess carrier lifetime in p-type HgCdTe using a three-level Shockley–Read model
Authors: Tyan Y. L. , Schimert T. R. , Claiborne Lewis T.
Published: July 2002

A three-level Shockley–Read model for p-type Hg vacancy-doped HgCdTe is proposed which leads to an accurate prediction of excess carrier lifetime versus temperature. The three levels included in the model are the two shallow Hg vacancy acceptor levels treated as a divalent acceptor and the deep trap level treated as an independent level. The rate equations obtained are solved using the full eigenvalue spectrum of the theory. The transient decay of excess carriers is found to be exponential with the exception of a slight departure in the initial decay at higher temperatures (200–300 K). The Hg vacancy density and deep-level density together with a compensating donor density are included in modeling the equilibrium carrier statistics. The treatment of the Hg vacancy as a divalent acceptor is found to significantly impact the equilibrium carrier concentration and hence the excess carrier lifetime. Wafer-to-wafer variation in excess carrier lifetime is attributed to differences in x value and acceptor and compensating donor densities while keeping the capture cross sections and divalent Hg vacancy ionization energies fixed. In this way the effect of compensation on excess carrier lifetime can be evaluated.
Laser-induced reactions of semiconductor surfaces
Authors: Qin Q. Z. , Li Y. L. , Lu P. H. , Zhang Z. J. , Jin Z. K. , Zheng Q. K.
Published: July 2002

Laser-induced reactions of Ge(111), Si(111), GaAs(100), and InP(100) surfaces with chlorine under 355-, 560-, and 1064-nm laser irradiation have been investigated using a supersonic beam technique and time-resolved mass spectrometry. It has been found that the reaction yields depend not only on the laser fluence and wavelength, but also on the translational energy of the incident chlorine molecules. A possible mechanism of laser-induced reactions is proposed.
On the determination of dopant/carrier distributions
Authors: Vandervorst W. , Clarysse T.
Published: July 2002

Accurate determination of dopant and carrier distributions for ultra-large-scale integrated devices poses stringent requirements to the analysis tools used. In assessing their potential one has to investigate their properties with respect to near-surface quantification, depth resolution, quantification for multilayers as well as the aspects of reproducibility, sensitivity, and generality in the application. In this article these aspects are discussed for the dopant profiling techniques Rutherford backscattering spectroscopy, secondary ion mass spectrometry, and the carrier profiling methods spreading resistance profiling, capacitance–voltage, scanning tunneling microscopy, and transmission electron microscopy.
Particle contamination on a silicon substrate in a SF6/Ar plasma
Authors: Smadi Mithkal M. , Kong George Y. , Carlile Robert N. , Beck Scott E.
Published: July 2002

Particle contamination on silicon wafers exposed to a SF6/Ar plasma is examined as a function of five critical plasma parameters using response surface methodology. Plasma parameters explored are 13.56 MHz rf power, pressure, process gas flow rate, 100 KHz wafer electrode power, and etch time. The experiment is conducted in a Tegal MCR-1 single wafer reactor operated in the triode mode. Particle count is found to increase linearly as a function of 13.56 MHz rf power, 100 KHz power, and etch time. Also, the particle count has a quadratic dependence as a function of process gas flow rate. Surprisingly, in the pressure range explored, particle deposition on the wafers is found to be independent of pressure. Auger and EDX chemical analysis of the particles reveals the presence of silicon, fluorine, oxygen, sulfur, and aluminum.
Secondary ion mass spectrometry–spreading resistance profiling study on the outdiffusion from poly- and monocrystalline cobaltsilicide
Authors: Elst K. , Vandervorst W. , Clarysse T. , Eichhammer W. , Maex K.
Published: July 2002

The aim of the present work is to investigate the outdiffusion of implanted boron from polycrystalline CoSi2 overlayers into silicon. A detailed investigation is carried out on the secondary ion mass spectrometry (SIMS) quantification problems (matrix effects, interface roughness) applied to the determination of outdiffusion lengths and interface concentrations on mono and polycrystalline CoSi2 overlayers. Comparative studies using spreading resistance profiling (SRP) are performed to assess the electrical performance of the outdiffused samples. The similarity in the behavior with polycrystalline silicon has led to the incorporation of outdiffusion from poly CoSi2 into poly-Si models.
An AlSb–InAs–AlSb double-heterojunction P-n-P bipolar transistor
Authors: Pekarik John J. , Kroemer Herbert , English John H.
Published: July 2002

We report the experimental demonstration of AlSb–InAs P-n-P double-heterojunction bipolar transistors. The devices exhibited net current gain and supported a substantial collector voltage of VCE≳2.5 V. The device structure was grown by molecular-beam epitaxy on a (001)-oriented p+ GaAs substrate. The base thickness was 100 nm, with a degenerate n-type base doping level (Si) of 2×1018 cm−3. The p-type emitter and collector doping levels (Be) were 5×1016 cm−3. The collector currents obeyed a typical Gummel relation, with parameters close to those expected from theory, making allowance for the high degree of degeneracy and the nonparabolicity in the InAs base region. However, the base currents were still high, apparently due to extensive interface recombination via unknown defects at the InAs–AlSb emitter-base junction. The base currents could be described well by a Sah–Noyce–Shockley model, modified to account for the unusual abrupt staggered lineup heterojunction and the degeneracy on the InAs side.
Resolution limits in electron-beam induced tungsten deposition
Authors: Kohlmann-von Platen K. T. , Chlebek J. , Weiss M. , Reimer K. , Oertel H. , Brünger W. H.
Published: July 2002

Electron-beam induced deposition of tungsten from the precursor gas W(CO)6 was investigated with the aim of determining the resolution limiting parameters. By exploring the effect of the beam energy and current, the resolution was found to correlate to the expected behavior of the beam diameter. To achieve a more accurate description of the deposition process, the time dependence of the needle height and diameter at the base was determined for deposition times ranging from 5 to 180 s. The measurements enabled a mathematical description of the needle surface as a function of time, and, therefore, the determination of the surface growth. The results exhibit that electron scattering cannot explain the observed growth. For that reason, the surface growth was correlated to the number of secondary electrons (SE) emitted by the primary e beam from the needle surface considering the Gaussian intensity distribution of the e beam and the angle dependence of the SE yield. These assumptions result in a good agreement of the number of SE with the surface growth and demonstrate that the beam diameter mainly limits the deposit resolution. As a consequence, by using a proper e-beam system, a resolution of 1 μm high needles in the order of 50 nm is obtainable.
Characterization of low energy ion-induced damage using the multiple quantum well probe technique with an intervening superlattice
Authors: Green D. L. , Hu E. L. , Petroff P. M. , Liberman V. , Nooney M. , Martin R.
Published: July 2002

Observations of low energy ion-induced damage of III–V semiconductor materials indicate that the ion damage penetrates much more deeply than simple projected ion range theory would suggest. Our present experiments are aimed to investigate two proposed mechanisms of this low energy, long range ion-induced damage: namely, (1) ion channeling and (2) defect generation and diffusion. Accordingly, we have designed a set of well-controlled ion exposure experiments based on the multiple quantum well (MQW) probe technique. Our experimental approach incorporates both the use of structural variations of our MQW probe structures and Ar ion beam parameter variations. An intervening superlattice placed in the surface barrier region of one of our MQW probe structures is effective in reducing observed defects. Bombardment carried out at a variety of substrate temperatures (78 K, room temperature, and 150 °C) reveal decreased damage profiles at the lowest temperature.
Antimony δ doping by low energy implantation in molecular-beam epitaxy Si layers
Authors: Gergam E. , Charki H. , Lazzouni M. , Vapaille A. , Prudon G.
Published: July 2002

Silicon layers, δ doped, have been processed by molecular-beam epitaxy with an implantation of 1 keV Sb ions during Si growth interruption. Characterization of these layers shows that all the implanted ions are incorporated and are electrically active. The thickness of the ‘‘doped plane’’ can be estimated between 2 and 5 nm. Carrier mobility enhancement is observed in these layers for longitudinal transport.