bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Growth of Thick, IC Quality GaAs From a Flowing Solution
Authors: Crismant E. E. , Daly J. T. , Roberts C. B. , Schaafsma D.T. , Gerritsen H. J. , Karlsson S. K. F.
Published: March 2011

Single crystal layers of gallium arsenide have been grown on <111> and <100> oriented GaAs substrates using a flowing solution of gallium saturated with GaAs. With this novel technique, growth rates as high as 9.Oµm/min have been achieved for 5 minutes, while rates of approximately Aµmlmin are typically achieved for 20 minutes of growth. These figures are in good agreement with a previously developed theoretical model and are about two orders of magnitude greater than those for conventional, static solution, liquid phase epitaxy (LPE) for layer thicknesses greater than lµm. Undoped, p-doped and n-doped layers of high crystallographic and electronic quality have been grown. A description of the technique and some of the electro-optical properties are presented in this paper.
High Quality GaAs on Soi by MOCVD
Authors: Karam N.H. , Haven V. , Vernon S. , Ramdani J. , El-Masry N. , Haegel N.
Published: March 2011

Epitaxial GaAs films have been successfully deposited on three-inch Si wafers with a buried oxide by MOCVD. The SOI wafers were prepared using Separation by IMplantation of OXygen (SIMOX) process. High quality GaAs on SIMOX films, with dislocation density in the range of 2–6 × 106 cm-2, have been achieved using Thermal Cycle Growth (TCG) deposition technique. These films showed a 50-fold increase in the low temperature photoluminescence intensity over conventional deposition. We have also fabricated MESFET’s in GaAs on SIMOX with performance comparable to those fabricated in GaAs. The maximum measured transconductance was in the range of 175-180 ms/mm at a 1.5 µm gate length and a 5 µm source to drain separation. This is the first demonstration of large area, high quality and low defect density GaAs on SIMOX.
Epitaxial Growth of (100) GaAs on SOS using a Specifically Designed MOCVD System
Authors: Nishimura T. , Kadoiwa K. , Mitsui K. , Murotani T.
Published: March 2011

High quality (100) single domain GaAs layers are epitaxially grown on slightly misoriented (100) Si-on-(1102) sapphire(SOS) substrates by MOCVD. Epitaxial growth on a spherical SOS substrate reveals that R face (1102) should not be tilted toward C axis [0001], but toward [011] or [011] of Si. A new MOCVD system which has two reactors, one for Si cleaning, the other for GaAs deposition, is effective to obtain mirrorlike smooth surface. The X-ray FWHM of 10µm GaAs was reduced to 65 arcsec by the thermal cycle annealing.

A crack free 15 µm thick GaAs layer with a dislocation density of 3×106cm-2 is obtained by combining the thermal cycle annealing and the strained-layer superlattices.
The Role of an Interface Misfit Dislocation in Blocking the Glide of a Threading Dislocation in a Strained Epitaxial Layer
Authors: Freund L. B. , Ramirez J. C. , Bower A. F.
Published: March 2011

The glide of a threading dislocation in a strained layer may be impeded as it encounters interface misfit dislocations on intersecting glide planes. An estimate of the change in driving force on the threading dislocation during this interaction is discussed within the framework of elastic dislocation theory.
Influence of Off-Oriented Substrates on Heteroepitaxial Growth of (Ca, Sr)F2 Layers on Si (100)
Authors: Minemura Tetsuroh , Asano Junko , Tsutsui Kazuo , Furukawa Seijiro
Published: March 2011

Heteroepitaxial growth of CaxSr1-xF2 layers on Si (100) substrates by molecular beam epitaxy has been investigated for GaAs / fluoride / Si structures. The Si (100) substrates off-oriented toward [011] show no considerable influence on crystallinity of CaF2 and SrF2 epitaxial layers. The off - oriented substrates, however, influence a remarkable effect on CaxSr1-xF2 layers, resulting in poor crystallinity rather than good one. This influence of off-oriented Si (100) substrates on the heteroepitaxy of CaxSr1-xF2 layers was the opposite of that found in GaAs/Si (100) structures.
Strain in Epitaxial GaAs on CaF2/Si(111)
Authors: Schowalter L.J. , Ayers J.E. , Ghandhi S.K. , Hashimoto Shin , Gibson W.M. , LeGoues F.K. , Claxton P.A.
Published: March 2011

Epitaxial layers of (111) GaAs of approximately 1 µm thickness were grown on epitaxial CaF2 buffer layers which were either 140 or 380 nm thick on Si(111) substrates. The best nucleation temperature for the GaAs on CaF2/Si(111) we have observed was 620 °C. This resulted in high quality GaAs films which exhibited channeling minimum yields of 4%. The density of threading dislocations in the GaAs layers was observed by TEM to be ~108 cm-2. Double-crystal x-ray diffraction measurements showed that the strain (ε┴.) was less than 2.2×10-4 in both sets of GaAs samples. Ion channeling, however, revealed a large tetragonal strain of 3.5×10-3 (ε┴ = 1.7×10-3) in the thinner (140 nm) CaF2 buffer layers. By doing ion channeling with high energy (2.5 MeV) protons, it was possible to determine strain more accurately. Using this technique, we were able to set an upper limit for the tetragonal strain of 2.5×10-4 in both the GaAs (which implies ε┴ < 8×10-5 and CaF2 (ε┴ < 1.5×10-4) layers for the thicker (380 nm) CaF2 buffer layer structure. These results are in good agreement with the strain predicted from previous strain measurements of CaF2 epitaxial layers on Si.
Surface Stress Effect on the Elastic Moduli of Superlattice Thin Films
Authors: Cammarata R. C. , Sieradzki K. , Streitz F. H.
Published: March 2011

A thermodynamic model is presented which predicts a significant sample size effect on the elastic moduli of superlattice thin films possessing small bilayer repeat lengths. Owing to the presence of incoherent (incommensurate) interfacial stresses, biaxial in-plane strains are created which are approximately inversely proportional to the bilayer repeat length Λ. When Λ is of the order of 1 nm, these strains can be of the order of 1%, inducing nonlinear elastic behavior. This model is able to explain in a quantitative way the existence of a “supermodulus” effect in certain metallic superlattices.
Multilayered Metallic Thin Films Prepared by Dual-Bath Electrodeposition
Authors: Ross C.A. , Goldman L.M. , Spaepen F.
Published: March 2011

Electrodeposition is a fast and relatively inexpensive method for making metal multi-layered films. We present a dual bath electrodeposition technique capable of producing crystalline Ni/amorphous NiPx multilayers with repeat lengths of 20Å and above, of sufficient quality to give several low-angle x-ray reflections. The compositional and structural modulations of the films are analysed using x-ray diffraction and microscopy, and the effects of deposition parameters, such as the current density, are examined.
A Systematic Method for Extracting Structural Parameters from Low Angle X-Ray Reflectivity Measurements on Multilayers
Authors: Goldman L.M. , Atwater H.A. , Spaepen F.
Published: March 2011

X-ray diffraction is one of the main methods of determining the structure of multilayers. Low angle reflectivity measurements are particulary useful for multilayers containing polycrystalline or amorphous constituents, and for obtaining specific structural data. We present a method based on both kinematic and dynamic scattering calculations, and use it to extract specific structural parameters such as the roughness or diffuseness of the external surface, the thickness of the constituent layers, and the roughness or diffuseness of the internal interfaces. Results are given for a sputtered A1/A12O3 multilayer.
Characterization of Metal/Carbon Multilayers by Raman Spectroscopy
Authors: Allred David D. , Wang Qi , Gonzalez-Hernandez Jesus
Published: March 2011

Laser Raman spectroscopy has been found to be useful for characterizing amorphous semiconductor multilayers, especially the interfaces of multilayers. Recently, we have extended this technique to the characterization of magnetron sputtered multilayers commonly used as reflectors in soft x-ray optics. Unlike the multilayers previously studied which contained only semiconductors and dielectrics, these are generally semiconductor/metal multilayers. We report here on the Raman characterization of the most common class of multilayers used in soft x-ray optics, those that contain a high density metal like tungsten interspersed with layers of carbon. In all of the metal/carbon multilayers the dominate feature in the Raman spectra is due to a-C. The a-C spectra consists of a broad peak at about 1560 cm-1 (G-peak) and a shoulder at about 1400 cm-1 (D-peak). This can be deconvoluted with Gaussian line shapes to yield two peaks (one at about 1560 to 1570 cm-1 and the other at about 1380 to 1420 cm-1). Among the W/C multilayer samples peak positions and relative magnitudes changed little with carbon thickness over the range of 1 to 12 nm. Significant differences are, however, seen as the identity of the metal component is altered or, especially, as the preparations are varied. For example, the intensity ratio of the D-peak to G-peak was much larger for multilayer samples prepared under conditions of good plasma confinement.
Modulation Spectroscopy of Layered Structures
Authors: Glembocki O.J.
Published: March 2011

Modulation spectroscopies, such as electroreflectance and photoreflectance have become popular as room temperature probes of layered structures. Because of their derivative nature, one observes sharp optical features related to critical points in the dielectric function of the material under study. This allows us to obtain information such as alloy concentration, carrier density, well widths of quantum wells and thicknesses of the constituent layers in superlattices. In this paper, we will review the application of modulation spectroscopy to the study of optical and electronic properties of layered structures.
Photoluminescence Excitation Spectroscopy of Strained Ingaas/GaAs Quantum Wells
Authors: Koteles Emil S. , Owens D. , Elman B. , Melman P. , Bertolet D. , May Lau Kei
Published: March 2011

Photoluminescence excitation spectroscopy of exciton transitions has been utilized to obtain information about light-holes in strained InGaAs/GaAs single quantum wells. By monitoring their behavior with respect to that of heavy-holes, it was shown possible to ascertain whether or not the quantum wells were pseudomorphic (lattice matched but strained) or relaxed and, if strained, the magnitude of strain present. Thus the indium composition of the single QW layers was deduced. This method is advantageous since it is nondestructive, requires no special sample preparation, is accurate and can readily be extended to monitoring strain in QWs subjected to various processing steps associated with device fabrication.
Misfit Dislocation Nucleation and Interactions at GexSi1-x/Si Interfaces
Authors: Perovic D.D. , Weatherly G.C. , Houghton D.C.
Published: March 2011

In the study of elastic strain relaxation in semiconductor heterostructures, a number of misfit dislocation generation mechanisms have been suggested to account for the high interfacial dislocation density observed in these almost defect-free crystals. Several MBE-grown GexSi1-x/Si heterostructures, both in the as-grown and annealed condition have been studied using transmission electron microscopy. The results indicate that some of the popular theories of dislocation generation are less important or not applicable based on both theoretical and experimental considerations. Specifically, it will be shown that: (i) heterogeneous sources play a dominant role in the nucleation mechanisms, (ii) the strain relaxation behaviour during MBE growth may be different from that observed in metastable structures annealed after growth and (iii) the Hagen-S trunk multiplication mechanism is inoperative under most conditions in this system.
Optical Characterization of GaAsP Strained Layers Grown on (111)-Oriented GaP
Authors: Pistol M.-E. , Gerling M. , Gustafsson A. , Paulsson G. , Samuelson L. , Titze H.
Published: March 2011

Strained layers of indirect GaAsP have been grown on the (111)B-oriented surface of GaP by Metal-Organic Vapour Phase Epitaxy (MOVPE). These layers have been characterized by low-temperature photoluminescence (PL), electroreflectance (ER), secondary-ion mass spectroscopy (SIMS), and wavelength resolved imaging cathodoluminescence (CL). We have been able to follow the transition energies of the lowest X conduction band edge, as well as the higher Γ band edge of the strained layers, as a function of composition up to an As-concentration of 38 %. The experimental values of the transition energies are compared with predictions made from calculations based on deformation potential theory. CL allows us to directly observe the onset of dislocation formation, i. e. the critical thickness. The appearance and properties of the dislocation network revealed by CL are very different from those of the corresponding network when the strained layers are grown on (001)-oriented surfaces.
Characterization of an Asymmetric Triangular Multiple Quantum Well, by Variable Angle Spectroscopic Ellipsometry
Authors: Herzinger Craig M. , Snyder Paul G. , Woollam John A. , Evans Keith , Stutz C.E. , Jones R. , Merkel K.G. , Reynolds D.C.
Published: March 2011

Variable angle spectroscopic ellipsometry (VASE) was used to characterize a 20 period GaAs/Al(x)Ga(1-x)As multiple quantum well structure, grown by molecular beam epitaxy. The barriers were nominally 200 Å Al(.25)Ga(.75)As, and the well regions were grown to approximate a linearly graded composition, from x=0 to x=0.25, with total well width 200 Å. VASE data in the E1, E1,+Δ1. region were analyzed using four different models. It was founcЃ that the dielectric function of the cap GaAs layer was shifted to higher energy with respect to the bulk GaAs dielectric function.
Materials and Device Characteristics of Pseudomorphic AlGaAs-InGaAs-GaAs and AlInAs-InGaAs-InP High Electron Mobility Transistors
Authors: Ballingall J.M. , Ho Pin , Tessmer G J. , Martin P.A. , Yu T.H. , Chao P.C. , Smith P.M. , Duh K.H.G.
Published: March 2011

High electron mobility transistors (HEMTs) with single quantum well active layers composed of pseudomorphic IπGaAs grown on GaAs and InP are establishing new standards of performance for microwave and millimeter wave applications. This is due to recent progress in the molecular beam epitaxial growth of strained InGaAs heterostructures coupled with developments in short gate length (sub%0.2 µm) device fabrication technology. This paper reviews this progress and the current state-of-the-art for materials and devices.
The Kinetics of Si1-xGex/Si Relaxation using Large Area Dislocation Imaging Techniques
Authors: Houghton D.C. , Timbrell P.Y. , Baribeau J.-M.
Published: March 2011

Annealing experiments in the 450-1000 °C temperature range on various MBE grown Si1-xGex/(100)Si heterostructures have revealed an abrupt thermally activated transition from coherently strained to partially relaxed microstructures. Misfit dislocations at densities 1 to 104 cm-2 have been monitored using Nomarski interference microscopy of defect etched surfaces and charge collection microscopy (EBIC) of Si1-xGex/Si heterojunctions in the scanning electron microscope. The kinetics of misfit relaxation by dislocation glide can be characterized by a relaxation temperature which for 30 minute furnace anneals was ~500 °C for an uncapped Si0.83Ge0.17 stramed layer, and ~600 °C for a similar buried strained layer typical of heterojunction bipolar transistor geometries. Rapid thermal anneals (5s) delayed the onset of relaxation to higher temperatures (~ 200 °C increase) and allowed misfit dislocation velocities to be determined for the temperature range 500-900 °C. The activation energy for dislocation glide was found to be 2.2±0.1eV for a Si0.9Ge0.1/Si strained layer superlattice, 1.6±0.2eV for a Si capped Si0.88Ge0.12 layer and 1.6±0.2eV for a Si0.83Ge0.17 uncapped strained layer.
Strain-Controlled High Mobility in Modulation Doped Si0.5Ge0.5/Ge/Si1-xGex Hetero-Structures
Authors: Miyao Masanobu , Murakami Eiichi , Etoh Hiroyuki , Nakagawa Kiyokazu
Published: March 2011

Formation and characterization of a new hetero -structure of modulation doped p-Si0.5Ge0.5/Ge/Si1-xGex are comprehensively studied. In the MBE growth, thick Si1-xGex buffer layers are grown incommensurately at high temperature (520°C), and thin Si0.5Ge0.5/Ge layers are grown commensurately at low temperature (≦450°C). The strain field in the Ge channel layers can be precisely controlled by changing the Si composition (1-X) in the Si 1 -xGex buffer layers. As a result, a large energy discontinuity in the valence band (0.17 eV) is realized at the hetero -interface of p-Si0.5Ge0.5/Ge. This enables a high mobility of two -dimensional hole gas (4500 cm2/Vs) at 77 K.
Plastic Flow in Si/Ge Quantum Well Structures
Authors: Twigg M. E. , Godbey D. J.
Published: March 2011

Plastic flow is driven by excess stress, which can be calculated from lattice strain and dislocation line tension. In order to better understand and model plastic flow, we have derived an expression for the dislocation line tension in thin film structures for double kink (dislocation dipole) extension of a threading dislocation. From these calculations, we conclude that the presence of a free surface (i.e. the vacuum/solid interface) significantly reduces the line tension for an extended double kink. For the specific case of a 50nm thick Si0.7 Ge0.3 layer capped with lum of silicon, we find that the line tension is approximately 30% less than the estimate of an analogous model that neglects the influence of a free surface. Therefore, in order to obtain an accurate estimate of the excess stress for a double kink, one must allow for the influence of a free surface.
A Comparative Study of Gas Chemistry in Methane/Hydrogen and Acetylene/Hydrogen Gas Mixtures During Hot-Filament Vapor Deposition of Diamond
Authors: Wu Ching-Hsong , Tamor M. A. , Potter T. J. , Kaiser E. W.
Published: March 2011

The technology of low pressure chemical vapor deposition (CVD) of polycrystalline diamond films has advanced substantially in recent years [1–3]. However, fundamental understanding of the chemistry and physics occurring in this CVD process is still lagging. Although the key role that H atoms play in diamond CVD has long been recognized [4–6], the identity of the gaseous diamond precursors and the mechanism by which diamond is formed are still unclear. Only recently has interest in these critical issues grown. For example, theoretical predictions and quantum mechanical calculations of gas-solid reaction paths involving CH3 and CH3+ [7] or C2H2 [8] have been reported, and the thermodynamic analyses of diamond CVD processes have been examined [9,10]. In addition, experimental results and chemical models [11–16] have been presented in attempts to support specific species as the essential precursors of diamond growth. Nevertheless, no consensus has been reached concerning the growth species and mechanism in CVD diamond processes.
Deposition of Diamond Films by Scanning Oxy-Acetylene Flame
Authors: Tzeng Yonhua , Phillips Richard , Tin Chin C. , Chen Y. , Srivinyunon T. , Cutshaw Calvin
Published: March 2011

Diamond films have been deposited on silicon wafers by scanning an oxyacetylene flame against water-cooled silicon substrates. High quality diamond films about 20 um thick can be achieved by scanning the flame at a speed of about 0.2 mm per minute. The as-deposited films exhibit high electrical resistivity exceeding 1014Ωcm. Current voltage measurement shows the trap-dominated current conduction characteristics similar to that for dehydrogenated diamond films deposited by methane/hydrogen plasmas.
Growth of Device-Quality Homoepitaxial Diamond Thin Films
Authors: Geis M. W.
Published: March 2011

Diamond has an electric-field breakdown 20 times that of Si and GaAs, and a saturated velocity twice that of Si. This results in a predicted cut off frequency for high-power diamond transistors 40 times that of similar devices made of Si or GaAs. Boron is the only known impurity that can be used to lightly dope diamond. This p-type dopant has an activation energy of 0.3 to 0.4 eV, which results in high-resistivity material that is undesirable for devices. However, heavily boron doped diamond has a very small activation energy and a low resistivity and is of device quality. Transistors can be designed that use only undoped and heavily doped diamond. One of the steps in a device fabrication sequence is homoepitaxial diamond growth. Lightly and heavily doped homoepitaxial diamond films were characterized by scanning and transmission electron microscopy, x-ray diffraction, measurements of resistivity as a function of temperature, and secondary ion mass spectroscopy. It was found that under appropriate growth conditions these films are of device quality.
Characterization of Hollow-Cathode DC Discharge Growth of Diamond: Rotational Vibronic Emission In A CH4-H2 Discharge
Authors: Chu H. N. , Lefkow A. R. , Hartog E. A. Den , Jacobs J. , Sandstrom P. , Anderson L. W. , Lagally M. G. , Lawler J. E.
Published: March 2011

Experiments to study the temperature in the discharge produced using a dc spiral hollow cathode with CH4-H2 as the feed gas have been carried out during the rowth of diamond. Optical emission from the R branch of the 3d1 Σ v-O-2p Σ v-O rotational vibronic band are used to determine a rotational temperature. Limitations of this method are discussed.
Laser Assisted Techniques for Diamond and Diamondlike Thin Films
Authors: Rengan A. , Biunno N. , Narayan J. , Moyer P.
Published: March 2011

We have deposited diamond-shaped particles using a non equilibrium process of laser ablation from a solid graphite target in a hydrogen discharge. The nucleation on the heated silicon surface occurs in small regions of ∼ 0.1 to 0.5 mm covering a small fraction of the surface. The faceting of the crystals observed are mainly octahedral [111] faces. The results of using an eximer laser to ablate a graphite target are described. SEM micrographs show octahedral faceting. Micro Raman spectroscopy on the crystalline features exhibit two bands at 1348 and at ∼ 1600 cm−1. The peak position and large FWHM suggests the existence of disordered sp3 bonding or short range order existing in the film. Another possibility is the existence of a stress state in the crystal due to the non equilibrium nature and the high rate of growth of the crystals. We have also irradiated HFCVD grown diamond film with a XeCl UV- eximer laser. The results indicated that sp2 bonded graphitic and amorphous component are selectively ablated, enhancing the sp3 hybrid bonds in the film.
Epitaxial Growth of Diamond and Diamond Devices
Authors: Fujimori Naoji , Imai Takahiro , Nakahata Hideaki , Shiomi Hiromu , Nishibayashi Yoshiki
Published: March 2011

For the practical application of diamond semiconductor devices, the manufacture of planar-type devices is important. Homoepitaxial growth of diamonds would be a useful technique for making semiconducting diamond films. Homo-epitaxial growth of diamonds is achieved by microwave plasma CVD. The properties of epitaxial diamond films depend on the deposition condition and the substrate orientation. Boron doping was easily carried out by this method and boron doped films were determined to be ptype semiconductors. Properties of boron doped epitaxial films were found to be similar to those of natural IIb diamond. The Schottky junction on boron doped epitaxial films was obtained by the deposition of tungsten and aluminum. The Schottky properties of this combination were affected by the surface roughness of the epitaxial films. A field effect transistor and a light emitting device were successfully fabricated using boron doped epitaxial films and Schottky junctions.
Optical Characterisation of Nickel in Diamond
Authors: Nazaré Maria Helena , Neves Aj , Davies Gordon
Published: March 2011

Optical absorption and luminescence with zero-phonon lines at 1.401 and 1.404 eV is shown to contain fine structure induced by the isotopes of natural Ni. Uniaxial stress and magnetic field perturbations establish that the optical center has trigonal symmetry. A relationship is estimated between the concentration of Ni in these optical centers and the strength of the optical absorption.
Infrared Characterization of the Hydrogen Environments in Diamond Thin Films
Authors: LeGrice Y. M. , Buehler E. C. , Nemanich R. J. , Glass J. T. , Kobashi K. , Jansen F. , Machonkin M. A. , Tsai C. C.
Published: March 2011

CVD diamond films prepared under varying conditions have been investigated with IR and Raman spectroscopy. Raman spectroscopy was used to characterize the crystal structure, and ir absorption was used to determine the H bonding environments. The growth temperatures were varied in one series, while the CH4/H2 ratio was varied in another. The IR absorption of all the samples showed a weak broad band extending from approximately 2800 to 2970 cm−1 which was attributed to H bonded to sp3 C sites. There was no evidence of ir absorption at 3000 to 3200 cm−1 which would indicate H bonded to sp2 or sp1 C sites. For both series, the Raman measurements showed progression from diamond-like films to diamond films. The ir absorption showed a general trend of less H with more well ordered diamond structures. No sharp transition of the H incorporation vs the growth parameters was observed.
In-Situ Characterization of Thin Polycrystalline Diamond Film Quality by Thermal Wave and Raman Techniques
Authors: Pryor R. W. , Kuo P. K. , Wei L. , Thomas R. L. , Talley P. L.
Published: March 2011

In this paper, the thermal wave technique and microfocus Raman spectroscopy are used to measure the relative quality of thin diamond films deposited on silicon. The thermal wave technique uses a modulated heating laser beam, normal to the diamond film surface, to initiate a thermal wave which propagates into the film, the substrate, and the overlying gas(ses). The accompanying modulated gas density is then interrogated by a second (probe) laser beam. The probe beam is deflected by the corresponding periodic changes in the gradient of the refractive index of the gas. The measured probe beam deflection versus offset position is fitted, using a theoretical solution of the three-dimensional thermal diffusion equation for the gas/film/substrate system. The physically important fitting parameter is the thermal diffusivity of the diamond film. Thermal conductivities derived from our diffusivity measurements using this method compare well to previous measurements on similarly prepared films by other methods. Our measured values for the thermal conductivity of the highest-quality polycrystalline diamond films are of the order of 12 W/cm-K. Our measured values of thermal conductivity for diamond films range between this value and the thermal conductivity of graphite. We have also made measurements on bulk diamond using the thermal wave technique, and we obtain a thermal conductivity of 21 W/cm-K, in excellent agreement with values found in the literature. A multi-scan, microfocus ratio of “graphitic” material to diamond material for a relative assessment of film quality.
The Electronic and Optical Properties of Diamond; Do they Favour Device Applications?
Authors: Collins Alan T.
Published: March 2011

The electronic and optical properties of diamond are reviewed, with particular emphasis on current research into the production of semiconducting devices. Although many of the properties of diamond seem, at first sight, to be ideally suited to the development of high power microwave and optoelectronic devices, there are also a number of obstacles to be overcome before diamond may be successfully exploited for device applications.
Cyclic-Cluster Mindo/3 Computations of The Lattice Constant and Band Structure of Boron Nitride, Diamond and Silicon Carbide
Authors: Snyder Lawrence C. , Edwards Arthur H. , Deak Peter
Published: March 2011

We have employed a 32 atom cyclic-cluster and the Modified Intermediate Neglect of Differential Overlap (MINDO/3) method to compute the lattice constant, band structure, heat of formation and other properties of cubic boron nitride, diamond and silicon nitride. The computational scheme we have employed will permit studies of defects in these materials.
Electrical Characterization of Metal Contacts on Diamond Thin Films
Authors: Narducci Dario , Cuomo Jerome J. , Guarnieri C. Richard , Whitehair Stanley J.
Published: March 2011

Polycrystalline boron-doped diamond thin films were prepared by microwave-enhanced plasma-assisted chemical vapor deposition. Ti, V, Ta, Nb, Al, Mo and W contacts were prepared by physical vapor deposition and their behavior was studied as a function of the annealing temperature, atmosphere and duration. For Ti contacts, short heat treatments (less than 60 minutes) at 500 °C under argon atmosphere were found to make ohmic contacts for applied voltages up to 50 V. Longer annealing times, more reactive atmospheres, and higher temperatures degraded the contact characteristics. In order to obtain a more complete picture of the interface structure, the capacitance-voltage characteristics and the impedance spectra of the systems were measured between 10 K and 1000 K. The interface contribution to the overall dielectric behavior of the system shows much shallower depletion widths in Ti-diamond (ohmic) contacts than with the non-linear Nb and Ta contacts. The higher values of the contact resistance and the shallower depletion width with Ti can be explained in terms of formation of a thin carbide-like region at the metalsemiconductor interface. The space-charge region width as well as the distribution of localized states in the band gap were also determined. The effect of the microstructure on the electrical properties of the systems is discussed in comparison with the behavior of metal-contacts on single-crystal diamonds.
Properties of CVD Diamond/Metal Interface
Authors: Mori Yusuke , Kawarada Hiroshi , Hiraki Akio
Published: March 2011

Electric properties of the interface between metal and semiconducting CVD diamond formed by microwave plasma chemical vapour deposition (CVD) have been investigated. Much better rectifying property due to Schottky barrier has been obtained in the films formed with CO(5%)/H2 compared with CH4(0.5%)/H2. A high breakdown voltage (200 V) and a high rectification ratio (105) have been observed at the evaporated Al/diamond interfaces formed with CO(5%)/H2. In the point contact interfaces, where the metal-carbon reaction is not expected at room temperature, the rectifying and ohmic property depends on the electronegativity of metals.
A Diamond Silicon Heterojunction Diode
Authors: Ellison C. L. , Cohen R. M. , Hoggins J. T.
Published: March 2011

Thin diamond films were grown on low resistivity p-type Si wafers by microwave plasma assisted chemical vapor deposition. Using gold contacts, diode-like behavior was observed and forward bias current densities in excess of 5 A/cm2 were obtained. Reverse bias current densities were as low as 5 mA/cm2. Photocurrent was measured when photon energies larger than the Si bandgap were used to illuminate the heterojunction. The same photocurrent spectrum was measured even when the illumination spot was moved several centimeters away from the metal-diamond contact. Photovoltage. photocurrent and hot probe measurements have been used to infer the energy band diagram of the diamond-Si p-p heterojunction.
The Formation of Helical Dislocations in Silicon Substrates During Epitaxial Deposition of β- SiC
Authors: Aindow M. , Cheng T. T. , Pirouz P.
Published: March 2011

A study is presented of the dislocation content of (001) Si substrates after the formation of thin epitaxial “buffer layers” of beta-SiC by the pyrolysis of propane. Helical dislocations are observed running parallel to the interface and extending for many microns. The dislocation helices emanate from the substrate, have 1/2<110> Burgers vectors which are inclined to the interface, and do not lie on the {111} glide planes. This is consistent with the extension of dislocations in the substrate by climb. The extended segments are subsequently pinned and further climb gives rise to the observed helical configuration. These climb effects are presumably due to an excess of vacancies which are produced when Si interstitials migrate to the deposit in order to form SiC.
Some Observations on the Electrical Characterization of the Heteroepitaxially Grown Cubic SiC
Authors: Molnar B. , Kelner G.
Published: March 2011

This paper re-examines the electrical characterization of thin layers of cubic SiC, grown on (100) Si substrates. The resistivity and Hall coefficient for undoped SiC layers were measured between 10 K and 500 K. Electron spin resonance (ESR) and secondary ion mass spectrometry (SIMS) were used to identify and determine the nitrogen concentrations, which were higher than 1017/cm3. In all the samples examined the Hall measurements indicated impurity band conduction. Therefore, the temperature dependence of the resistivity has been used to derive an activation energy el. The value of el found to be in the range of 0.032–0.025 eV. The observed decrease in activation energy has been correlated with an increase in nitrogen concentration. The presence of substantial nitrogen leads to impurity band conduction and it is the most likely reason for the conflicting values reported for the dominant donor ionization energy by Hall and PL measurements.
Simple Graphitic Network Models of “Diamondlike” Carbon
Authors: Tamor Michael A. , Wu Ching-Hsong
Published: March 2011

Several highly disordered forms of carbon are termed “diamondlike” by virtue of their extreme hardness and significant optical gap. However, it is quite tempting to extend the analogy further and attribute these “diamondlike” properties to a high degree of local diamond order. Although an “amorphous diamond” character has been inferred from the optical properties in the 0-10 eV range, and the position of the π + σ plasmon peak in the electron energy loss spectrum, there is no direct evidence for such diamond order. However, there is a considerable body of work showing that DLC embodies a considerable degree of graphitic order which determines the optical gap and Raman spectrum. In order to determine to what extent a clearly non-diamond structure can exhibit specific “diamondlike” properties, we examine a simple structure derived from graphite. This “defected graphite” (DG) construct presumes an underlying graphitic structure which is insulating due to the strong localization of π -electrons by randomly distributed non-aromatic defects. Using specific defects suggested by experiment, the DG model reproduces a quite surprising array of observed properties of both hydrogenated and hydrogen-free “diamondlike” carbon.
Microstructural and Optical Characterization of GaN Films Grown by PECVD on (0001) Sapphire Substrates
Authors: Humphreys T. P. , Sukow C. A. , Nemanich R. J. , Posthill J. B. , Rudder R. A. , Hattangady S. V. , Markunas R. J.
Published: March 2011

Epitaxial GaN films have been grown by plasma-enhanced chemical vapor deposition (PECVD). The growth procedure utilizes a He gas discharge combined with the down-stream introduction of trimethylgallium (TMGa) and nitrogen. Both cubic [1111 and wurtzitic [0001] GaN epitaxial films have been achieved on (0001) sapphire substrates. Differences in substrate growth temperatures are believed to account for the different observed phases. A comparative study pertaining to the microstructural, optical and electrical properties of the α-GaN and β-GaN heteroepitaxial films is presented. Also reported for the first time is the Raman spectroscopy data for cubic GaN.
Thermal and Ion Bean Induced Reactions in Ni on BP
Authors: Kobayashi Naoto , Kumashiro Yukinobu , Revesz Peter , Li Jian , Mayer James W.
Published: March 2011

The solid phase reactions of Ni thin films with refractory wide bandgap semiconductor BP(100) were investigated both in the thermal process and the ion beam induced process with RBS, AES, XRD and XPS. In the thermal reaction process, reactions of Ni thin films with BP started around 350°C. Transient metastable phases were observed between 400°C and 450°C. The formation of the fully reacted crystalline phase with the mixture of NiB and Ni3P was observed at 450°C. At elevated temperatures above 600°C, mixture of phases with less Ni content was found to be formed. For the ion beam induced process inhomogeneous reaction was observed at LN2 and the reaction at RT showed an amorphous phase with the same composition as the first thermal phase. The reaction at 200°C induced the same crystalline phase as the first thermal phase. The reacted layer thickness as a function of the ion beam fluence between RT and 300°C increased linearly with the fluence by showing the thermal dependence with an activation energy of Ea=O.31±O, O6eV above 100°C.
The Role of Polarity on the Stability of Graphitic Compounds
Authors: Wentzcovitch Renata M. , Continenza Alessandra , Freeman A. J.
Published: March 2011

There is an old puzzle associated with the series of compounds formed by first row elements, C, BN, and BeO: similar to the other members of the family of octet semiconductors, these compounds exist in dense phases like diamond and zincblende, or hexagonal diamond (lonsdaleite) and wurtzite; however, whereas C and BN also exist in low density graphitic phases, BeO does not.
ZnGeP2: A Wide Bandgap Chalcopyrite Structure Semiconductor for Nonlinear Optical Applications
Authors: Xing G. C. , Bachmann K. J. , Posthill J. B. , Timmons M. L.
Published: March 2011

In this paper we report the growth and characterization of wide bandgap chalcopyrite structure semiconductor ZnGeP2 epitaxial layers by open tube MOCVD and ZnGeP2 single crystals by high-pressure vapor transport (HPVT). The electrical and optical properties of these crystals have been investigated by Hall measurements, absorption spectroscopy, photoconductivity and photoluminescence spectroscopy. The onset of the absorption edge for HPVT ZnGeP2 at 1.99 eV is in accord with the pseudodirect bandgap of this material. Both the meltgrown crystals and epitaxial layers show extended band tailing in the transparency range of ZnGeP2 depending on the growth conditions. Recently we have shown that epitaxial ZnGeP2 films can be grown with excellent surface morphology by MOCVD on (111) GaP substrates. These films should be suitable for phase matched second harmonic generation utilizing CO laser radiation in thick film heterostructures.
Microwave CVD of Diamond Using Methanol-Rare Gas Mixtures
Authors: Buck M. , chuang T. J. , Kaufman J. H , Seki H.
Published: March 2011

The deposition of diamond from a reactive vapor phase has been dominated by the use of very dilute gas mixtures of hydrocarbon molecules, usually methane, in hydrogen. Recently there have been reports using nitrogen and oxygen containing simple organics such as amines and alcohols which seem promising. The role of atoms other than hydrogen is still not very clear. There is need for more experimental data to further our understanding in this regard. Here we give a preliminary report on our investigation of deposition from methanol-rare gas mixtures using a small microwave reactor. An important result is that good diamond can be deposited from methanol without addition of hydrogen gas and the quality of the crystallites can be influenced by Ar in the plasma.
Fabrication and Characterization Studies of Semiconductor-Impregnated Porous Vycor Glass
Authors: Huber C. A. , Huber T. E. , Salzberg A. P. , Perez J. A.
Published: March 2011

Porous Vycor glass has been impregnated with semiconductors by pressure forcing the nonwetting semiconductor melt into the interconnected pores. Dense semiconductor mesh-like microstructures with a characteristic size of 50 Å can be fabricated by this technique. Measurements are reported which show the composites are suitable for both optical and transport studies, particularly those addressing quantum confinement of carriers and unusual electrical transport phenomena in this new class of materials.
Synthesis, Structural and Optical Characterization of II-VI Semiconductors Included in Sodalite-Type Hosts
Authors: Moran K. L. , Harrison W. T. A. , Gier T. E. , Dougall J. E. Mac , Stucky G. D.
Published: March 2011

Solid-state chemistry has been used to control both the size and the interconnection distance of small II-VI semiconductor moeities incorporated in zeolitic hosts with the sodalite-type structure. Structural characterization was carried out using X-ray Rietveld powder methods, and optical properties of these materials were also measured. These novel materials show quantum superlattice effects as evidenced by blue shifts in their optical absorption spectra.
Particle-Size Distribution of CdSe Quantum Dots Determined by Photoluminescence Spectroscopy
Authors: Prabhakar E.N. , Huber C.A. , Heiman D.
Published: March 2011

Particle-size distribution effects on the energy levels of semiconductor quantum dots are investigated. By examining the low temperature photoluminescence spectra of microcrystals of the binary semiconductor CdSe embedded in a glass matrix, the distribution of energy levels due to three-dimensional confinement is determined. Calculations of the electron-hole pair ground state energy provide a relation between confinement energy and particle diameter. This allows conversion of the photoluminescence lineshape directly into a distribution of particle radii and facilitates analysis of the observed properties of the material. With extension to other systems the technique can become a valuable tool in the study of semiconductor microparticle composites.
Thermal Annealing of Amorphous CoMnNiO Film on Oxidized Si Substrate
Authors: Hui Tan , Dong Qin , Mingde Tao , Chenglu Lin , Shichang Zou
Published: March 2011

Amorphous CoMnNiO film is doposited on oxidized Si substrate by RF sputtering equipment. Structure relaxation occurs in the amorphous CoMnNiO film when it is annealed below 550°C. Annealed in the range from 600°C to 1000°C, the amorphous film is converted into the polycrystal. After annealing in rich oxygen atmosphere, the amorphous film is transformed into spinel solid solution with stable structure and good electrical properties. The electrical conductivity will be reduced due to formation of low valence oxides when annealed without oxygen. As annealing temperature is higher than 1000°C, some spinel solid solutions will be resolved into low valence oxides CoO and NiO, reducing the conductivity of the CoMnNiO film.
Microcrystal Si Films Prepared by Remote Plasma CVD
Authors: Kim Sung Chul , Hwang Jung Tae , Lee Seung Kyu , Jung Chang Young , Soe Sung Moo , Koh Sung Ok , Chung Kwan Soo , Jang Jin
Published: March 2011

The effects of deposition temperature, rf power and hydrogen dilution ratio on the growth, structure and transport of p-type microcrystal(μc-) Si films deposited by remote plasma CVD have been investigated. While low substrate temperature and low rf power yield small grain sizes, high temperature and high rf power tend to supress the growth of grains. The etching of Si by hydrogen radicals plays an important role to grow μc-Si, but excess etching supresses the growth of crystallites. We obtained 400 A of grain size and 3.5 S/cm of room temperature conductivity for p-type μ-Si.
Fast-Pulse Excimer-Laser-Induced Processes in a-Si:H
Authors: Winer K. , Bachrach R.Z. , Johnson R.I. , Ready S.E. , Anderson G.B. , Boyce J.B.
Published: March 2011

The effects of fast-pulse excimer laser annealing of a-Si:H were investigated by measurements of electronic transport properties and impurity concentration depth profiles as a function of incident laser energy density. The dc dark conductivity of laser-annealed, highly-doped a-Si:H increases by a factor of ∼350 above a sharp laser energy density threshold whose magnitude increases with decreasing impurity concentration and which correlates with the onset of hydrogen evolution from and crystallization of the near-surface layer. The similarities between the preparation and properties of laser-crystallized a-Si:H and pc-Si:H are discussed.
Formation of Microcrystalline Silicon film by RMS Process
Authors: Wang Cheng , Parsons G.N. , Buehler E.C. , Nemanich R.J. , Lucovsky G.
Published: March 2011

We have deposited microcrystalline, gc-Si, silicon films by using RF reactive magnetron sputtering (RMS) at high substrate temperatures, Ts > 500°C, and at a relatively low partial pressure of hydrogen, PH = 0.40 mTorr, and at low Ts ∼200- 300°C, but with a higher PH > 2 mTorr. We have detected μc-crystallinity by Raman scattering and transmission electron microscopy. We discuss differences in the growth mechanisms for formation of μc-Si under these two deposition conditions.
Growth of Microcrystalline Silicon in Ultrathin Layers
Authors: Wu Y.-J. , Persans P. D. , Abeles B. , Wang S.-L.
Published: March 2011

We report recent studies of the crystallization of ultrathin (< 10 nm ) amorphous silicon layers clad by silicon dioxide. We observe changes in Raman scattering spectra which indicate that nanocrystalline silicon layers formed by crystallization of amorphous silicon continue to evolve structurally with further annealing. There is evidence for significant strain in crystallized material.
Optical Properties of Microcrystalline Silicon
Authors: Ingels Martin , Stutzmann Martin , Zollner Stefan
Published: March 2011

Optical properties of undoped, microcrystalline silicon are investigated by photothermal deflection spectroscopy, spectroscopic ellipsometry and Raman scattering. Samples are prepared by recrystallization of hydrogenated amorphous silicon in the temperature range 680 – 900°C. The increase of grain sizes with increasing annealing temperature and the disappearance of amorphous tissue lead to noticeable changes in the observed spectra. It is argued that much of the pertinent structural information of μc-Si can be obtained by a suitable combination of optical measurements alone.
Suppression of Acceptor Deactivation in Siucon by Disordered Surface Regions
Authors: Srikanth K , Ashok S.
Published: March 2011

Permeation of atomic hydrogen in p-type Si damaged with ion implantation or deposited with polycrystalline or amorphous Si has been studied. Following ion implantation or film deposition, atomic hydrogen was introduced by low energy H ion implantation or from an electron cyclotron resonance (ECR) plasma. Spreading resistance profiles indicate that deactivation of acceptor dopant boron atoms by atomic hydrogen is drastically reduced in silicon wafers with any of the above disordered surface layers, and secondary ion mass spectroscopy (SIMS) traces this reduction to the suppression of hydrogen movement into the crystalline Si substrate. Trapping of hydrogen or formation of molecular hydrogen at defect sites in the surface disordered regions apparently is responsible for this phenomenon.
Phonon States in Sic Small Particles
Authors: Sasaki Y. , Horie C. , Nishina Y.
Published: March 2011

Size dependence of optical phonon frequencies and that of phonon dampings of SiC small particles have been studied by analysing their Raman data. The particle size ranges from 30 nm to 1000 nm. Decrease in the TO-phonon frequency as well as the LT-splitting (the splitting between the LO- and TO-phonon) with decrease in the particle size are much larger than that expected from the spatial correlation model or that from the phonon confinement model. The phonon damping for the small particle consists of the usual temperature-dependent term and an excess damping term, which is independent of temperature. These results suggest that the scattering of the phonon at the particle surface plays a major role in determining the phonon states of the small particle. Our experimental data suggest that the surface phonon-polariton mode at the interface between the crystallites plays a minor role in the Raman spectrum of particles consisting of a number of crystallites.