bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of electrical damage induced by CH4/H2 reactive ion etching of molecular beam epitaxial InAlAs
Authors: Achouche M. , Clei A. , Harmand J. C.
Published: July 2002

In this article, we report investigations on the effects of methane/hydrogen (CH4/H2) reactive ion etching (RIE) of InGaAs/InAlAs/InP heterostructure materials for high electron mobility transistors, and especially on the electrical properties of the InAlAs layer after dry recess etching of the InGaAs cap layer. The ion etching induced damages in the barrier layer InAlAs are evaluated by diode current–voltage and capacitance–voltage measurements and deep-level transient spectroscopy (DLTS). The I–V data indicate that RIE lowers the Schottky barrier height (φb) and increases the ideality factor. Using low pressure (10 mTorr) RIE processes, with various self-bias voltages, shows that the use of low ion energy is necessary to get good Schottky contacts. Rapid thermal annealing at 400 °C is shown to induce a limited decrease of the dry etching induced defects. However, full recovery of the electrical properties is not achieved. A significant improvement of the Schottky diode electrical characteristics and DLTS spectra is observed after wet etching a 60 Å thick InAlAs layer before metal deposition, indicating that the main damages are concentrated within a short distance from the surface.
High stability heterojunction bipolar transistors with carbon-doped base grown by atomic layer chemical beam epitaxy
Authors: Driad R. , Alexandre F. , Juhel M. , Launay P.
Published: July 2002

We report the improved thermal stability of heavily C-doped GaAs layers using atomic layer chemical beam epitaxy (ALCBE). The use of ALCBE improves the crystal quality and reduces hydrogen incorporation in the epilayers by about a factor of 2, resulting in enhanced electrical dopant activity as compared to conventional growth techniques. This process has been successfully applied to the fabrication of InGaP/GaAs heterojunction bipolar transistors (HBTs) with a highly C-doped base grown by ALCBE and other layers grown by conventional CBE. Dc current gains up to 150, for a base doping layer of 3×1019 cm−3, have been obtained. Moreover, the thermal stability of these devices is increased, as indicated by a post-growth annealing (650°C, 60 min) which induces only a slight current gain degradation of about 20% at high collector currents, to be compared to a degradation of 60% for HBTs conventionally grown by CBE.
Layer-by-layer removal of GaAs(110) by bromine
Authors: Cha C. Y. , Weaver J. H.
Published: July 2002

Scanning tunneling microscopy results show that heating a nearly saturated Br–GaAs(110) 2×1/c(2×2) surface to 600 K leads to a random distribution of single-layer deep vacancy islands. These islands expand via continued etching upon heating to 700 K. Subsequent exposure to Br2 at 625 K results in complete removal of the first layer via step retreat. Accordingly, monolayer etching can be achieved. The different etching pathways of the exposure-annealing treatment and that of continuous etching are discussed.
Low resistance (∼1×10−6 Ω cm2) Au/Ge/Pd Ohmic contact to n-Al0.5In0.5P
Authors: Hao P. H. , Wang L. C. , Ressel Peter , Kuo J. M.
Published: July 2002

A Au (1000 Å)/Ge (100 Å)/Pd (100 Å) contact scheme has been investigated to form low resistance Ohmic contact to n-Al0.5In0.5P (Eg=2.3 eV) with a minimum contact resistivity of about 1×10−6 Ω cm2. The surface morphology of this contact remained smooth after annealing at 425 °C for 1 min. Front side secondary ion mass spectrometry depth profiles of this contact structure under different annealing conditions were performed. It is found that the outdiffusion of indium due to the reactions between the metallization and the Al0.5In0.5P substrate in conjunction with the indiffusion of Ge into the substrate is responsible for the Ohmic contact formation. The germanide formation is believed to be responsible for the smooth surface morphology. The contact resistivity of this contact remained ∼2×10−6 Ω cm2 after aging at 350 °C for 31 h.
Strained coherent InAs quantum box islands on GaAs(100): Size equalization, vertical self-organization, and optical properties
Authors: Xie Qianghua , Kobayashi N. P. , Ramachandran T. R. , Kalburge A. , Chen P. , Madhukar A.
Published: July 2002

Evolution of the size distribution of InAs islands is examined via in situ ultrahigh vacuum atomic force microscope for samples grown via molecular beam epitaxy with InAs deposition at and just above the critical value for two- to three-dimensional growth mode transition. An initial independent island formation and growth followed by a global tendency towards island lateral size equalization is observed. The strain fields induced by the InAs islands in the subsequently grown GaAs cap layer are exploited to fabricate vertically self-organized multiple sets of islands. Optical properties of such vertically self-organized quantum box islands are examined via photoluminescence spectroscopy. Microtwins of very low linear density (<1/μm), originating from the edge of the topmost set of islands are found for the samples with multiple sets of islands and are shown to be the type of defect that appears first to relax the accumulated strain around the multiply stacked islands.
Combination of fluorescence in situ hybridization and scanning force microscopy for the ultrastructural characterization of defined chromatin regions
Authors: Fritzsche W. , Takács L. , Vereb G. , Schlammadinger J. , Jovin T. M.
Published: July 2002

Although the internal arrangement of interphase chromatin is still a matter of conjecture, there exists a large body of evidence for the compartmentalization of chromosomal domains. A study based on combined scanning force and optical microscopy of supramolecular chromatin spreads produced by isotonic lysis of cells suspended in phosphate-buffered saline has been conducted. The ultrastructure of fluorescent labeled chromosomes was resolved with the topographical contrast provided by the scanning force microscope. Fluorescence in situ hybridization was used to label specific DNA sequences. The location of different pericentromeric chromosome regions was determined by fluorescence microscopy and correlated with scanning force microscope topography. Using a single DNA probe, discrimination between labeled chromosome pairs of an aneuploid cell was possible, based on the different intensities of fluorescence signals. The results show that the in situ hybridization technique with fluorescence labeling is compatible with scanning force microscopy. The combination of these methods can be used for the specific identification and lateral localization of DNA sequences in spread chromatin, opening the possibility for the ultrastructural characterization of defined genes in the scanning force microscope.
Minimizing the size of force-controlled point contacts on silicon for carrier profiling
Authors: Snauwaert J. , Blanc N. , De Wolf P. , Vandervorst W. , Hellemans L.
Published: July 2002

The spatial distribution of charge carriers in semiconducting structures can be derived from conductive properties. In this report silicon cantilevers with integrated tips and coated with boron-doped chemical vapor deposited diamond have been used for the first time to establish electrically reliable point contacts on silicon. The relation between the applied force and the nanoindentation characteristics has been investigated in a range from 10 to 150 μN. The threshold value necessary to pierce the native oxide layer has been obtained and is found to depend on the peculiar coating of each tip. The data are correlated with the current–voltage characteristics of the contacts. The impedance of point contacts on homogeneously doped p- and n-type silicon with known resistivity has been measured and calibration curves have been plotted for nanospreading resistance probe measurements. It is found that only above the threshold for plastic deformation can useful electrical characterizations be performed.
International intercomparison of scanning tunneling microscopy
Authors: Barbato G. , Carneiro K. , Cuppini D. , Garnaes J. , Gori G. , Hughes G. , Jensen C. P. , Jo/rgensen J. F. , Jusko O. , Livi S. , McQuoid H. , Nielsen L. , Picotto G. B. , Wilkening G.
Published: July 2002

Because scanning probe microscopes produce three-dimensional data of almost any solid they have a strong potential as metrological tools. Results are presented from the first international intercomparison between four national metrology laboratories. On three-dimensional calibration standards the mean deviations between instruments were typically <2% in the x direction, <5% in the y direction, and <10% in the z direction. Eight samples were circulated for roughness measurements and 19 roughness parameters were calculated for each image. In the range where the scanning probe microscope measurements overlapped with classical techniques (profilometers) the agreement was good. Also a gauge block of hardened steel (≊900 HV) with an array of Vickers indentations having diagonal lengths ranging from 3 to 60 μm was circulated and measured.
Electron trajectories and light emitting images of starlike thin-film field emitters
Authors: Kaneko Akira , Sumita Isao
Published: July 2002

Electron trajectories and light emitting images for the electron emission from a single starlike thin-film field emitter and a 200-μm-sq field emitter array have been studied. In the early stage of electron emission from the starlike field emitters, a unique light emitting image appeared on a phosphor screen. The image consisted of an upper hornlike and a lower mountainlike pattern, their geometrical configuration roughly agreeing with the simulation results of electron trajectories using a finite integral equation method code. From the observation of the light emitting images for the starlike field emitters, we found that the images of the starlike field emitters resulted from overlapping electron beams emitted from the four apices of each field emitter. The emitted electrons had an electron emitting angle of 40° and a horizontal electron spread angle of 30°–40° at an anode voltage of 340 V. An increase in the anode voltage to 680 V reduced the vertical electron emitting angle to 30°.
Direct measurement of laser momentum transfer to dense media by means of atomic force microscopy cantilevers
Authors: Labardi M. , La Rocca G. C. , Mango F. , Bassani F. , Allegrini M.
Published: July 2002

Various Gedanken experiments have been proposed in the past to test the expression for the electromagnetic energy-momentum tensor in a material medium and hence the ratio of the momentum to the energy carried by the electromagnetic wave in a dielectric medium. We suggest a real experiment, based on the use of atomic force microscopy microcantilevers. We discuss the phenomenological theoretical framework and the feasibility of our proposal. We report preliminary experimental results obtained in air and water to test the performance of our setup.
Surface modification of InP by diffraction-patterning utilizing laser dry etching
Authors: Prasad Manoj , Ruda Harry E. , Dubowski Jan J.
Published: July 2002

Laser based dry etching of semiconductors offers a useful way of integrating patterning with growth for optoelectronic device development. In this article we demonstrate XeCl excimer laser based dry etching of InP. Experiments were carried out using a 10% gas mixture of chlorine diluted in helium. Studies were made of the effect of laser fluence on the etching process and how this influences pattern development. Based on these studies, surface electromagnetic waves were used to form ripple patterns and the optimum conditions for interference pattern development are reported. These studies show that a relatively low fluence is not conducive to pattern development. We also utilize diffraction from slits of different shapes in tandem with laser dry etching for the patterning of structures in semiconductors. This technique offers the potential to develop relatively damage-free structures. These structures may be suitable for devices used in a number of applications such as telecommunications.
Compression in transconductance at low gate voltages in submicron GaAs metal semiconductor field-effect transistors
Authors: Ahmed M. M.
Published: July 2002

In submicron GaAs metal semiconductor field-effect transistors, the shift in the transconductance (gm) peak towards the high negative gate voltage end is often observed. Factors causing this abnormality were investigated. It is believed that if the surface potential and the Schottky barrier potential are of the same order of magnitude then there will be a strong probability that the peak gm value will appear at high negative gate voltages rather than near zero gate bias. It was shown that under these circumstances the drain current at low gate biases is not under the direct influence of gate depletion but rather is controlled by surface depletion in the gate-drain gap. At high negative gate voltages, depletion under the gate has the dominant effect on channel current, and the device exhibits an improved performance. Recessed gate technology is thought to be a solution to eliminate the surface state effects of a free drain-source surface. It was shown that a simple gate recess will not eliminate the possibility of gm compression and shift unless the Schottky barrier potential is greater than the free-surface potential.
Role of rate window, transient time, and reverse bias field on the deep levels of LT-GaAs by field effect transient spectroscopy
Authors: Halder N. C. , Goodman T.
Published: July 2002

We have investigated the effect of rate window, transient time, and reverse bias field on the deep levels in molecular beam epitaxy (MBE) grown, Si-doped, low temperature (LT) GaAs by field effect deep level transient spectroscopy (FEDLTS). As far as we know, this is the first successful paper on LT-GaAs investigated by FEDLTS. The applied rate window (R=t2/t1) ranged from 5 to 8 with interval 1, transient time from 5 to 50 s, and reverse bias field from −0.5 to −4×105 V/cm. The capacitance transients (CT) were recorded from 70 to 380 K at temperature intervals of 0.5, 1, or 2 K and analyzed by modulating function waveform analysis. The CT were relatively strong marked by very short growth time (∼5 s). At the measurement transient time greater than 5 s, the CT began to deteriorate showing no further resolution. On the other hand, the FEDLTS spectra were quite dense due to a large number of overlapping deep levels which were found to be very sensitive to the selection of rate window, measurement transient time, and reverse bias electric field. LT-GaAs was found to posses as many as nine electron trap levels in contrast to five deep trap levels observed in MBE-grown, Si-doped, high temperature GaAs studied earlier.
Application of poly(methyl methacrylate) ultrathin resist supported by a flowing subphase method in electron-beam fabrication of a 4 in. high-resolution mask
Authors: Gu Ning , Qian Feng , Hong Qinyue , Lu Zuhong , Wei Yu , Yu Xiangdong , Peng Li , Zhang Zhongyi , Zhao Lixing , Zhang Haiping , Liu Yong Kuan
Published: July 2002

A recently designed Langmuir trough using a steady-laminar flowing subphase is exploited to support polymer monolayers. The ultrathin poly(methyl methacrylate) (PMMA) films prepared by this technique have been explored as high-resolution electron beam resists. The lithographic exposure conditions of Langmuir–Blodgett PMMA films were investigated and the results of fabricating a 4 in. mask with 0.38 μm in feature linewidth and 0.5 μm in resolution were achieved by using the Jeoptic ZBA-23 electron-beam machine as the exposure tool.
Single step lithography for double-recessed gate pseudomorphic high electron mobility transistors
Authors: Grundbacher R. , Adesida I. , Kao Y.-C. , Ketterson A. A.
Published: July 2002

An asymmetric double-recessed gate process achieved through a single lithography step and a combination of wet and dry etching techniques is presented. The double-recessed gate process is beneficial in the fabrication of InGaAs/AlGaAs/GaAs pseudomorphic high electron mobility transistors (PHEMTs) because breakdown voltage is enhanced while surface effects on the drain side of the gate are minimized. In contrast to conventional processes that require two lithography steps, the current process requires only a single lithography step for the asymmetric placement of a T-gate in a wide recess trench. The process utilizes a four-layer resist of polymethylmethacrylate (PMMA) and P(MMA-MAA) exposed by electron beam lithography. Upon development of the resist, a wet selective etch (citric acid:H2O2) is used to define the wide recess trench and then a dry selective etch (SiCl4/SiF4) is used to recess a narrow trench (within the wide recess trench) in which the gate foot rests. This technique can achieve gate lengths of 0.15μm and drain-side wide recess dimensions from 0.15 to 0.55μm while the source-side recess width is kept at or below 0.15 μm. Device results show improved breakdown voltages and output conductance with only slight reduction in transconductance and drain current for the PHEMTs fabricated using the technique as compared to PHEMTs fabricated using a trilayer T-gate process.
Effect of plasma polymerization film on reducing damage of reactive ion etched silicon substrates with CHF3+O2 plasmas
Authors: Kimizuka Masakatsu , Ozaki Yoshiharu , Watanabe Yoshio
Published: July 2002

The damage generated in reactive ion etched Si using CHF3 added with O2 is studied using a metal-contamination-free reactor. The measurements of the photoconductive decay curve on the etched Si substrates indicate that carrier recombination lifetime decreases as the flow rate of oxygen increases. Physical analysis x-ray photoelectron spectroscopy and secondary ion mass spectrometry show that plasma polymerized film consisting of carbon and fluorine can be seen on the etched Si substrate in the low oxygen flow rate region. The thickness of the film depends inversely on the oxygen flow rate. It becomes clear that thick plasma polymerization film protects the substrate from ion bombardment that results in damage.
Influence of plasma gas and postcleaning on the electrical characteristics of plasma-exposed Al/n-Si Schottky diodes
Authors: Kuroda Tsukasa , Lin Zhangda , Iwakuro Hiroaki , Sato Shinji
Published: July 2002

The influence of plasma exposure at self-bias voltages less than 200 V on electrical characteristics of Al/n-Si diodes was examined. In particular, the influence of chemical cleaning on the electrical characteristics of plasma-exposed diodes was examined. In Ar, N2, and O2 plasma exposure followed by postcleaning, the electrical characteristics were the same as that of a nonplasma-exposed diode. The postcleaning treatment removed the damage layer formed during plasma exposure. On the other hand, in the diodes exposed to H2 and H2-containing plasma followed by the postcleaning treatment, the electrical characteristics was not improved by the postcleaning treatment: the Schottky barrier height increased. The H-incorporated zone was not removed by the postcleaning treatment.
Fabrication of nanometer-size Si wires using a bevel SiO2 wall as an electron cyclotron resonance plasma etching mask
Authors: Ishii Kenichi , Suzuki Eiichi , Sekigawa Toshihiro
Published: July 2002

We have investigated a fabrication technique of nm size Si wires utilizing a bevel SiO2 wall on a (111) surface as an electron cyclotron resonance (ECR) plasma etching mask. The bevel (111) surface is obtained by anisotropic etching of a (100) silicon-on-insulator layer. Small-size Si wires of around 20–25 nm are successfully obtained underneath the bevel SiO2 wall. It is shown that a local oxidation of silicon process to form the bevel SiO2 wall affects the cross-sectional shape of the small-size Si wires in the ECR plasma etching process. It is also indicated that a self-limiting oxidation takes place in such small-size Si wires. By thermal oxidation of the small-size Si wires, an ultrasmall cross-sectional size of around 1×nm2 is realized. In addition, a Coulomb blockade effect is observed in an experimental nm size Si wire metal-oxide-semiconductor field-effect transistor.
1 μm range comparative length measurement using a regular crystalline lattice and a dual tunneling unit scanning tunneling microscope
Authors: Aketagawa Masato , Takada Koji , Suzuki Seiki , Sasaki Shigetoshi , Takahashi Hideaki
Published: July 2002

This article presents a potential image processing method for determining the in-plane geometrical distortion of a scanning tunneling microscope (STM) image and calibrating it using a regular crystalline lattice, and describes the results obtained in comparative length measurements in the range of about 1 μm using a regular crystalline lattice as a reference scale and a dual tunneling unit-STM (DTU-STM) as a detector. The method is based on two-dimensional fast Fourier transform analysis. The DTU-STM with one X-Y stage and two tunneling units independently controlled in the Z-axis direction was utilized for comparative length measurement. To improve the measurement accuracy, the present method is used to process the raw images obtained from the DTU-STM. The results of experiments, in which the cleaved surface of highly oriented pyrolytic graphite is used as a reference scale for measurement of lengths on the order of 1 μm, demonstrate the feasibility of the present image processing method and the possibility of comparative length measurement with subnanometer resolution using the DTU-STM.
Fabrication and analysis of extreme ultraviolet reflection masks with patterned W/C absorber bilayers
Authors: Voorma H.-J. , Louis E. , Koster N. B. , Bijkerk F. , Zijlstra T. , de Groot L. E. M. , Rousseeuw B. A. C. , Romijn J. , van der Drift E. W. J. M. , Friedrich J.
Published: July 2002

We report on a novel procedure developed for the fabrication of reflection masks for extreme ultraviolet lithography. The procedure involves the deposition and patterning of an absorber bilayer (40 nm W and 25 nm C) on Mo/Si multilayer blanks. The C layer is used to protect the underlying Mo/Si multilayer structure during processing and repair. The pattern is written with an e-beam pattern generator into EPR resist and is transferred into the absorber bilayer with three consecutive rf etching processes. We have investigated the effect of the full mask making procedure on the multilayer reflectivity using 13 nm radiation. The procedure causes some oxidation of the top Si layer of the multilayer, an effect which is confirmed by XPS measurements. However, the method does not affect the multilayer reflectivity to within narrow tolerances. The profiles of patterns in the absorber layer are inspected with a SEM, showing patterns with a feature size of 250 nm and side wall slope angles of 80°. An indication is found that cleaning of the substrate with ion etching prior to the fabrication of the mask blanks reduces the defect density.
Raman monitoring of molecular beam epitaxial growth of GaN on GaAs (100) and Si (111)
Authors: Drews D. , Schneider A. , Zahn D. R. T.
Published: July 2002

Epitaxial layers of GaN were grown by molecular beam epitaxy on GaAs (100) and Si (111) substrates. Nitrogen was provided from a rf-plasma source while elemental Ga was evaporated from a Knudsen cell. The growth process was performed in an ultrahigh vacuum chamber that is optically aligned with a multichannel Raman spectrometer. This setup allows Raman spectra to be taken online, i.e., during the growth process. Utilizing resonant Raman scattering conditions, spectra with a sufficient signal-to-noise ratio were taken even at the growth temperature of 600 °C. For both substrates the evolution of compressive strain at the interface was monitored from the frequency shift of the substrate phonons in the initial phase of the growth process.
Gas phase and surface reactions in subatmospheric chemical vapor deposition of tetraethylorthosilicate-ozone
Authors: Gill William N. , Ganguli Seshadri
Published: July 2002

A new physical-chemical model, which applies over a wide range of operating pressures, describes the gas phase and surface reactions in subatmospheric chemical vapor deposition of silicon dioxide for producing inter-layer dielectrics in a cold-wall reactor. Tetraethylorthosilicate (TEOS) reacts in the gas phase to form an intermediate which is adsorbed and reacts on the surface to produce a silicon dioxide film. The results compare favorably with experimental data over a pressure range of 100–600 Torr and a temperature range of 370–500 °C. The concentration distributions of TEOS, intermediate and ozone in the gas phase and their ratios at the surface of the wafer are determined to study gas phase nucleation and the relationship between composition distributions and film quality. Previous models based on low pressure data in the range of 30–90 Torr need to be modified to predict accurately the rates of deposition from 100 Torr to atmospheric pressure. Gas phase reactions cause the maximum in the deposition rates to shift to higher pressures at lower deposition temperatures, both in the model and experiments. At higher pressures, particulates are formed by the gas phase reactions which must be included to represent properly the chemical dynamics of the process. The deposition rate increases up to an asymptotic value as the TEOS flow rate is increased; above this level no further increase in growth rate occurs. This is a consequence of the basic mechanism of the surface reaction which predicts the asymptotic behavior observed.
Study of Ohmic contact resistance to Ga(1−X)In(X)As/InP composite channel InP high electron mobility transistors for X=35% to X=81%
Authors: Shealy J. B. , Matloubian M. , Liu T. , Ngo C.
Published: July 2002

This article reports the performance of alloyed Ohmic contacts to Ga(1−X)In(X)As/InP composite channel InP high electron mobility transistors for various indium compositions, from X=35% to X=81%. Both strained and pseudomorphic structures were utilized to observe the impact of the indium concentration on electron mobility, carrier concentration, sheet resistance, and specific contact resistance. The lowest specific contact resistance (Rt<0.16 Ω mm) was obtained for strained structures with indium concentrations of 74% and 81%. For strained structures with indium concentrations of 35%, we observe specific contact resistance of 0.35 Ω mm.
Possible multistranded DNA induced by acid denaturation–renaturation
Authors: Li Jian Wei , Tian Fang , Wang Chen , Bai Chun Li , Cao En Hua
Published: July 2002

λ-DNA Hind III was denatured by HCl, renatured by NaOH, and completely digested by DNase I sequentially. The produced mixture was separated by gel filtration, and one component was obtained which showed resistance to the digestion of DNase 1. The results of atomic force microscopy (AFM) studies on this component indicated that an unusual form of DNA was presented, with the height 13 times that of double-stranded DNA. The renatured and partially digested λ-DNA Hind III was also studied by AFM, and the images revealed both the duplex DNA and the unusual DNA. By comparison with known results, it is suggested that the unusual DNA is a multistranded DNA rather than a simple supercoil.
Frequency modulation detection high vacuum scanning force microscope with a self-oscillating piezoelectric cantilever
Authors: Chu Jiaru , Itoh Toshihiro , Lee Chengkuo , Suga Tadatomo , Watanabe Kazutoshi
Published: July 2002

This article attempts to describe a novel high vacuum scanning force microscope (HV-SFM) using a self-oscillating piezoelectric cantilever in frequency modulation (FM) mode. Since no external deflection sensor or external vibrator is needed, the new HV-SFM is very simple and easy to handle in vacuum conditions in comparison with conventional systems using optical sensors. FM detection is used to detect the force gradient acting on the end of the piezoelectric cantilever because it gives higher response speed in vacuum conditions compared to the commonly used slope detection. The unimorph cantilever consists of a 1.0 μm thick Pb(Ti,Zr)O3 (PZT) layer on a SiO2 elastic base, which becomes self-oscillating when an ac voltage is applied to the piezoelectric layer. The 160 μm long piezoelectric cantilever has successfully been oscillated at its natural resonance frequency of 117 kHz by connecting its piezoelectric layer directly into the FM loop, which applies positive feedback to the piezoelectric charge current caused by cantilever vibration. The shift in oscillation frequency of the FM loop, or the shift of cantilever resonance frequency due to force gradient acting on the cantilever end, is measured as a SFM feedback signal. At a frequency shift of 80 Hz, the force gradient and the force acting on the cantilever tip were calculated as 0.012 N/m and 0.02 nN, respectively, from an obtained force curve. At that set point, high-resolution images of a gold film have been obtained. The constructed FM detection noncontact SFM with a self-oscillating PZT cantilever has proven to be stable and easy to handle in vacuum conditions.
Characterization of AL–Y alloy thin films deposited by direct current magnetron sputtering
Authors: Liu Y. , Singh R. , Poole K. , Diefendorf R. J. , Harriss J. , Cannon K.
Published: July 2002

Thin films of Al-1.27 wt %Y were deposited by dc magnetron sputtering. Adding yttrium to the aluminum drastically reduced the metal’s grain size and also improve the uniformity of grain size distribution. Upon annealing at a temperature of 450 °C for 30 min, grain growth was insignificant, while the electrical resistance dropped from 6.05 to 2.95 μΩ cm. The as deposited films consisted of Al4Y and α-Al supersaturated with yttrium. After annealing, β-Al3Y precipitated instead of α-Al3Y. The Al–Y films had much higher resistance to hillock formation than did Al-1 wt %Si films.
Low damage thermally assisted electron cyclotron resonance etch technology for wide bandgap II-VI materials
Authors: Kümmell T. , Bacher G. , Forchel A. , Nürnberger J. , Faschinger W. , Landwehr G. , Jobst B. , Hommel D.
Published: July 2002

A flexible and low damage dry etch technology for the fabrication of ZnSe-based nanostructures is presented. Thermally assisted electron cyclotron resonance etching using gas mixtures of chlorine compounds and Ar and N2, respectively, combines plasma etching at low ion energies with process temperatures between 60 and 250 °C. With increasing process temperatures, rising etch rates and reduced surface roughness indicate a thermal activation of the etching process. The etch profile can be controlled by varying the plasma power causing a transition from partially physical to prevailing chemical etch properties. High quantum efficiencies in CdZnSe/ZnSe quantum wires with lateral sizes down to 20 nm were obtained, indicating a significantly reduced etch damage compared to conventionally dry etched II-VI nanostructures. The potential of the etch technology is demonstrated by realizing quantum wires with a blue shift of the photoluminescence signal (e.g., 8 meV for 20-nm-wide wires) caused by lateral carrier confinement effects.
Novel structure of a silicon field emission cathode with a sputtered TiW gate electrode
Authors: Kang Sung Weon , Lee Jin Ho , Yu Byoung Gon , Cho Kyoung-Ik , Yoo Hyung Joun
Published: July 2002

A novel technique for a gated silicon field emission cathode is proposed in order to decrease the spacing between the tip and the gate electrode of the device, which leads to low voltage operation. This technique is based on the filling characteristics of the sputtered Ti0.1W0.9 layer, which is used as the gate electrode in the shadowed area surrounding the tip with good step coverage. This process is completely compatible to conventional 1.2 μm complementary metal–oxide–semiconductor standard processes. The experimental results indicate that the diameter of the gate hole is greatly reduced to a subhalf-micron dimension (∼0.4 μm) even when starting with an initial mask size of 1.2 μm. The I–V characteristics of the cathodes show low turn-on voltages (∼25 V) in high vacuum (<3.0×10−7 Torr). The Fowler–Nordheim plots also show good linearity.
Analysis and optimization of force sensitivity in atomic force microscopy using optical and electrical detection
Authors: Ho Francis , Yamamoto Yoshihisa
Published: July 2002

Atomic force microscopy is a versatile tool for ultrasensitive measurement. We explore the fundamental and practical limits to force sensitivity that are imposed by optical and electrical deflection sensing techniques, and present a method for designing cantilevers to optimize force sensitivity. We calculate the optimized force sensitivity to be 1.2×10−18  N/ Hz at a temperature of 4 K, using a gallium arsenide piezoresistive cantilever with dimensions w=0.1  μm, t=0.1  μm, and L=81  μm, and mechanical quality factor Q=104. The optimized force sensitivities obtained using silicon piezoresistive and optical detection are not far behind.
Optical reflectance thermometry for rapid thermal processing
Authors: Guidotti Daniel
Published: July 2002

Temperature control during rapid thermal processing continues to be subjected to pressures for improved reliability by advanced semiconductor device manufacturing requirements. A very simple, inexpensive, and compact temperature sensor, based on the temperature dependence of the reflectivity of materials, has been developed here at IBM. While this sensor is directly applicable to metals, semiconductors, and insulators, we emphasize here only application to silicon, for which the optical reflectance thermometer (ORT) is continuously applicable from well below room temperatures to the melting point with a response time of less than 1 ms. The operation of this thermometer is demonstrated in a conventional rapid thermal anneal (RTA) chamber. When the RTA temperature cycle is controlled by the ORT, repeatability of ±3 °C is routinely obtained for steady-state dwell times as short as 0.4 s at 987 °C and slew rates as high as 445 °C/s. The actual sample temperature is continuously recorded as a function of time.
Temperature independent lifetime in InAlAs quantum dots
Authors: Arlett J. , Yang F. , Hinzer K. , Fafard S. , Feng Y. , Charbonneau S. , Leon R.
Published: July 2002

Continuous wave and time-resolved photoluminescence (PL) measurements were performed in order to understand the temperature and power dependence of the luminescence from visible quantum dots (QDs). The PL decay rate is found to be independent of temperature up to 100 K, confirming the high quality of the QDs. However, the intensity of the luminescence decays rapidly, which proved to be due to nonradiative recombination in the barriers, preventing the carriers from reaching the QDs. The dependence of the decay rate on incident power was also studied at 4.2 K. Excited state emission was seen at this temperature.
In situ relaxed Si1−xGex epitaxial layers with low threading dislocation densities grown on compliant Si-on-insulator substrates
Authors: Yang Z. , Alperin J. , Wang W. I. , Iyer S. S. , Kuan T. S. , Semendy F.
Published: July 2002

High quality relaxed Si0.6Ge0.4 films as thick as 1.0 μm have been achieved as grown on silicon-on-insulator (SOI) substrates with 200 Å Si(100)-oriented compliant substrates. This represents the thickest relaxed layers grown by this technique. A greater than five order of magnitude reduction in threading dislocation density was achieved by compliant growth compared to growth on unmodified Si(100) substrates. Additionally, for the first time (to the best of our knowledge) we show that it is not necessary to separate the growth and relaxation processes, and relaxation during growth is governed by the nature of the compliant substrate structure that causes dislocations to terminate at the unique crystalline-amorphous SiO2 interface. Results indicate that utilizing SOI as a compliant substrate which is effective in producing high quality Si1−xGex films can be extended to other films, where film relaxation (via dislocation nucleation and growth) cannot be conveniently separated from the synthesis method (e.g., SiC).
Growth of GaN on lithium gallate substrates for development of a GaN thin compliant substrate
Authors: Doolittle William A. , Kropewnicki Tom , Carter-Coman C. , Stock S. , Kohl Paul , Jokerst Nan Marie , Metzger Robert A. , Kang Sangbeom , Lee Kyeong Kyun , May Gary , Brown April S.
Published: July 2002

Since we have found that an entire substrate can be chemically removed in less than 5 min and since GaN is impervious to chemical etching, the GaN on lithium gallate (LGO) system is an excellent template (due to near infinite etch selectivity) for developing a thin film/compliant GaN substrate. Here we report on our efforts to grow GaN on LGO, including improvement of the atomic surface morphology using pregrowth pretreatments. We also report the first transferred thin film GaN substrate grown on LGO, transferred off of LGO and mounted on GaAs. With this approach, (InAl)GaN alloys can be grown on thin GaN films, implementing a “compliant” substrate for the nitride alloy system. In addition, the flexibility of bonding to low cost Si, metal or standard ceramic IC packages is an attractive alternative to SiC and hydride vapor phase epitaxy GaN substrates for optimizing cost verses thermal conductivity concerns. We have demonstrated high quality growth of GaN on LGO. X-ray rocking curves of 145 arcsec are shown on a 0.28 μm thick films. For the first time, we present data on the out-of-plane crystalline quality of GaN/LGO material. Likewise, we show two orders of magnitude improvement in residual doping concentration and factors of 4 improvement in electron mobility. We show substantial vendor to vendor and intravendor LGO material quality variations. We have quantified the desorption of Ga and Li from the surface of LGO at typical growth temperatures using in situ desorption mass spectroscopy and x-ray photoelectron spectroscopy.
Process characterization of plasma enhanced chemical vapor deposition of silicon nitride films with disilane as silicon source
Authors: Nallapati G. , Ajmera P. K.
Published: July 2002

Process characterization details are reported for the first time, to the best of our knowledge, for plasma enhanced chemical vapor deposition of silicon nitride films using disilane as silicon source. Respectable deposition rates have been realized even under the conditions of low mass flow rates of disilane (<1 sccm) and large dilution of process gases with helium. The film uniformity (<±3% thickness variation across 4 in. diameter wafers) and process repeatability in this gas system were found to be excellent. The deposition rates were examined as a function of gas flow ratio, rf power, process pressure, and deposition temperature. Similar to a silane based process, two regimes of operation, namely ammonia-rich and disilane-rich, were identified. Films deposited at the boundary of these two regimes were nitrogen rich and had deposition rates that were dependent only on disilane to ammonia flow ratio and rf power and nearly independent of process pressure and deposition temperature. The hydrogen concentration of these films was found to be nearly constant over the investigated range of ammonia to disilane flow ratio values varying from 4 to 20. Also, the variation in H concentration in these films with deposition temperature was smaller than what is reported for silane based films. The choice for process parameters based on rf power, utilization of disilane, deposition rate, and film stoichiometry is given.
Environmental effect on the electron emission from diamond surfaces
Authors: Zhirnov V. V. , Liu J. , Wojak G. J. , Cuomo J. J. , Hren J. J.
Published: July 2002

Electron emission from silicon field emitters with a thin coating of diamond were studied during exposure to varying pressures of Ne, He, H2, and D2. Introduction of Ne and He at pressures >10−4 Torr suppressed the emission current. Conditioning of field emitters in a 10−5 Torr helium ambient improved the emissivity. After hydrogen and deuterium exposure, a continuous emission current was measured below the initial threshold voltages for electron emission. The effects of deuterium were significantly greater than for hydrogen. We believe this phenomenon is due to the formation of a surface dipole layer of hydrogen or deuterium, bonded to the surface carbon atoms, which lowers the electron affinity of the diamond surface.
Electron emission from patterned diamond flat cathodes
Authors: Tolt Z. Li , Fink R. L. , Yaniv Zvi
Published: July 2002

A substrate predeposition treatment process is used to pattern and enhance the emission properties of diamond flat cathode films. An advantage of this process is that diamond grit abrasive process steps are not required for the enhanced emission properties. The predeposition treatment also eliminates the possibility of degrading cathode performance resulting from postgrowth processes.
Quantification of metal contaminants on GaAs with time-of-flight secondary ion mass spectrometry
Authors: Schröder-Oeynhausen F. , Burkhardt B. , Fladung T. , Kötter F. , Schnieders A , Wiedmann L. , Benninghoven A.
Published: July 2002

We have shown that small concentrations of metal atoms on UV/ozonized GaAs wafer surfaces can be quantitatively determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS). As standard reference materials, we produced defined submonolayer concentrations of Ca, Mg, Al, Cu, Zn, Si, Ni, Cr, Co, and Fe on the wafer surface by sputter deposition from different single- and multielement targets. The concentrations of the elements with m>27 u involved in these calculations were verified independently by total reflection x-ray fluorescence spectroscopy. For all ten metals, a linear relation exists between the relative metal signal Me+/71Ga+ and the surface concentration of the metal. By this relation we established TOF-SIMS sensitivity factors for these metals on UV/ozonized GaAs. The detection limits for almost all elements are in the order of 109 atoms/cm2.
Al
1−x
In
x
As
1−y
Sb
y
/
GaSb
heterojunctions and multilayers grown by molecular beam epitaxy for effective-mass superlattices
Authors: Washington D. , Hogan T. , Chow P. , Golding T. , Littler C. , Kirschbaum U.
Published: July 2002

Al 1−x In x As 1−y Sb y epilayers and Al1−xInxAs1−ySby/GaSb multilayers (0.5⩽y⩽1.0) have been grown by molecular beam epitaxy on GaSb (100) substrates as part of an investigation for potential use of this material’s system as kinetic heterojunctions (KHJs). Viable KHJ’s require lattice matching and a zero-conduction-band offset to GaSb, necessitating a high degree of compositional control. Therefore, a detailed study of the growth of Al1−xInxAs1−ySby epilayers has been conducted. Synthesis of the arsenide/antimonide quaternary system is problematic due to the miscibility gap throughout the composition range, therefore, the compositional dependence on the Sb:As flux, Sb:In flux, and substrate temperature has been studied. In situ reflection high-energy electron diffraction was used to monitor the surface reconstruction during growth. Crystalline quality and composition of single layer and multilayer samples have been determined by double-crystal x-ray diffraction and electron dispersion spectroscopy. Hall-effect measurements were performed to determine layer mobility and conductivity.
Optimization of the aluminum composition in In0.5(AlxGa1−x)0.5P/In0.2Ga0.8As high electron mobility transistors for power applications
Authors: Kuo J. M. , Wang Y. C. , Lothian J. R. , Tsai H. S. , Chen Y. K. , Mayo W. E.
Published: July 2002

We have optimized the In0.5(AlxGa1−x)0.5P/In0.2Ga0.8As high electron mobility transistor’s (HEMT’s) design by considering the material aspects of conduction band discontinuity, indirect-to-direct band electron transfer, donor-related deep levels, and the Schottky barrier height of this material system. We found that the In0.5(AlxGa1−x)0.5P/In0.2Ga0.8As HEMTs with 0.2⩽x⩽0.3 have the best device performance. For 1 μm×5 mm In0.5(AlxGa1−x)0.5P/In0.2Ga0.8As double heterostructure HEMTs, power-added efficiency (PAE) of 65.2% and 68.2% at 850 MHz was demonstrated at 1.2 and 2 V drain biases, respectively. These are the highest PAEs ever reported for 1 μm gate-length HEMTs. At 1.9 GHz and 2 V drain bias, the maximum output power was 25 dBm with a maximum PAE of 53% and linear gain of 8.3 dB. These results demonstrate that the new In0.5(AlxGa1−x)0.5P/In0.2Ga0.8As HEMTs have great potential for one-battery-cell operated wireless communication applications.
Field emission from nitrogen doped tetrahedral amorphous carbon prepared by filtered cathodic vacuum arc technique
Authors: Cheah L. K. , Shi X. , Tay B. K. , Sun Z.
Published: July 2002

A study of field emission from nitrogen doped tetrahedral amorphous carbon (ta-C:N) films prepared by the filtered cathodic vacuum arc (FCVA) deposition technique is reported. Field emission from ta-C:N films deposited on Si substrates was investigated in a diode configuration at room temperature and base pressure of 2.0×10−6 Torr. The J–E curves shift significantly towards the low potential side with increasing nitrogen concentration. The lowest field at which field emission was obtained was 10 V μm−1. A current density of 0.1 mA mm−2 (assuming the entire film surface is emitting) at 50 V μm−1 was obtained from these films. Electronic parameters, i.e., the band gap energy and activation energy were measured in order to construct an energy band diagram for the heterojunction structure, and the field emission mechanism is proposed based on this structure.
Soft x-ray emission studies of the bulk electronic structure of AlN, GaN, and Al0.5Ga0.5N
Authors: Smith Kevin E. , Duda Laurent C. , Stagarescu Cristian B. , Downes James , Korakakis Dimitris , Singh Raj , Moustakas Theodore D. , Guo Jinghua , Nordgren Joseph
Published: July 2002

The electronic structure of wurtzite GaN, Al0.5Ga0.5N, and AlN has been studied using synchrotron radiation excited soft x-ray emission spectroscopy. In particular, the elementally resolved partial densities of states has been measured and found to agree well with calculations. The shift in energy of the valence band maximum as x varies from 0 to 1 in AlxGa1−xN was measured by recording N K-emission spectra, and found to be linear. Furthermore, N K-emission spectra revealed resonantlike hybridization of N 2p and Ga 3d states at 19 eV below the GaN valence band maximum. The spectral intensity of this feature is proportional to Ga content.