bluuebunny/crossref_metadata_2025 huggingface dataset:
Conduction Mechanisms In Crystallized Silicon Films On Molybdenum Substrates
Authors: Palmer J. , Yi J. , Wallace R. , Anderson W.
Published: March 2011

Hydrogenated Amorphous silicon films deposited on molybdenum sheet metal substrates have been crystallized by thermal annealing at 850°C for 4 hours in a nitrogen atmosphere. X-ray diffraction and scanning electron microscopy results indicated that the average grain size in the crystallized films was approximately 200A. Palladium contacts were fabricated and the resulting Pd/Si/Mo structures were electrically characterized. Current-voltage-temperature measurements for phosphorus doped and undoped annealed samples resulted in a J “V characteristic consistent with space-charge-limited current. Using this data, Mobility as a function of temperature from 100K-300K was obtained. In phosphorus doped samples, the mobility appeared to be limited by energy barriers at the grain boundaries. In undoped samples, a σ “T’ exp (-b/T’) temperature dependence consistent with variable-range hopping conduction was observed.
Amorphous Silicon Crystallization For Tft Applications
Authors: Yi J. , Wallace R. , Sridhar N. , Chung D. D. L. , Anderson W. A.
Published: March 2011

Thin film hydrogenated Amorphous silicon (a-Si:H) was deposited on Molybdenum (Mo) substrates by d.c. glow discharge. We investigated the a-Si:H crystallization using four anneal techniques; nitrogen atmosphere furnace, vacuum, rapid thermal anneal (RTA), and excimer laser anneal. Anneal temperature ranged from 100 to 1200 °C. Excimer laser energy per pulse ranged from 90 to 340 M.J. Transmission electron Microscopy (TEM) revealed microstructure of crystallized Si film with grain size over 0.5 μm. X-ray diffraction (XRD) and Raman spectroscopy were employed to determine the degree of crystallization. The a-Si:H started to crystallize at temperatures over 600 °C. An 850 °C anneal reduced film resistivity to 10s (ω-cm) for intrinsic and 1 (ω-cm) for n-type. Coplanar type thin film transistors (TFT) with gate channel length of 25 μm and width of 220 μm were fabricated with various insulating layers; if sputtered SiO2, Si3N4, BaTiO3, MgO, and evaporated SiO. The first two exhibited the least leakage current. The as-grown intrinsic a-Si:H field effect mobility was around 0.03 (cmVV.s) and delay time was 5×10−7 s. The solid phase crystallized silicon film exhibited high leakage current. The delay time of an excimer laser anneal treated TFT was reduced to 2.5×10−7 s. Crystallized Si film mobility was improved to 15 (cm2 /V.s).
Laser Annealing of Hydrogenated Amorphous Silicon Thick Films
Authors: Sridhar Nagarajan , Chung D. D. L. , Anderson W. A. , Fu L. P. , Petrou A.
Published: March 2011

Hydrogenated amorphous silicon thick films deposited by dc glow discharge on molybdenum substrates were annealed by a pulsed Nd:glass laser. Mass spectrometry showed hydrogen remaining in all the laser annealed films. The amount of hydrogen remaining decreased with decreasing scan rate. The hydrogen evolved upon heating at 365 °C and mainly at 658 °C before laser annealing, but at 365, 575 (Mainly) and 645 °C after laser annealing, indicating weakening of the silicon-hydrogen bonding after laser annealing. The presence of hydrogen inhibited crystallization, as indicated by Raman scattering. The photo and dark conductivity of the film increased by one and three orders of magnitude respectively with increasing laser energy density up to 12 J/cm2 at a fixed scan rate. This Means that the photoresponse was decreased with laser annealing, in spite of the associated increase in crystallinity. This photoresponse decrease is attributed to the hydrogen evolution.
Transient Phases and their Transition Temperatures of A-Si in Non-Isothermal Processes
Authors: Suzuki Masakuni , Kitagaffa Akio
Published: March 2011

The heating rate dependence of the phase transition temperature was formulated based on the temperature dependence of nucleation of a new phase. The glass transition temperature of a-Si was explained in terms of van der Waals fluid of a-Si pseudo-Molecules which are produced by the fragmentation of continuous random networks of Si atoms. Transient phases and their transition temperatures as a function of the heating rate are summarized in the phase diagram.
Physical Studies of A Series of Main-Chain Liquid Crystalline Polymers With Long Soft Segment
Authors: Wu Bing , Lillya C. Peter , Stein Richard S.
Published: March 2011

A series of Main-chain liquid crystalline polymers with long and polydisperse soft segments has been synthesized. The thermal properties of these polymers have been characterized by differential scanning calorimetry, optical microscopy and wide angle X-ray diffraction. Unexpectedly, these polymers have a strong tendency to form purely smectic Mesophases. The degree of ordering of these polymeric mesophases is Much higher than that of the mesophase formed by a low molecular weight Model compound with the same Mesogen. The soft segment length effects on thermal behavior of such segmented copolymers have been elucidated. A semi-quantitative theory has been formulated to interpret these observations. A phase diagram relating thermal properties to soft segment length has been proposed.
Copper-Matrix Molybdenum Particle Composite as a Low-Thernal-Expansion Conductor
Authors: Yih Pay , Chung D. D. L.
Published: March 2011

Powder metallurgical fabrication of Cu/Mo composites containing 33–73 wt.% Mo was carried out by using either Cu coated Mo powder or a mixture of Cu and Mo powders. The former yielded Cu/Mo composites of greater density, hardness, compressive yield strength and abrasive wear resistance, and lower electrical resistivity and coefficient of thermal expansion than the latter. This is attributed partly to the lower porosity of the former composites and partly to the separation of the adjacent Mo particles in the former composites and the partial linkage of the adjacent Mo particles in the latter composites.
Au/Ti and Au/Ni-Cr Metallization of CVD Diamond Substrates for Multichip Module Applications
Authors: Chilakamarri Prasad , Meyyappan Ilango , Naseem H. A. , Brown W. D.
Published: March 2011

Multichip Modules (MCMs) have recently received widespread attention in the electronics industry. Owing to its high thermal conductivity, CVD diamond holds great promise for solving thermal management problems in MCMs. Also, large diameter free standing diamond substrates have recently become available. It is thus necessary to develop a reliable metallization for diamond substrates. As Au does not adhere to diamond, refractory metals, viz., Ti, W and Mo have been used as glue layers, as they form carbides above 800 °C. Since CVD diamond looses its properties at these temperatures, there is a need to obtain adherent metallizations at much lower temperatures. In the work reported here, tenaciously adherent Au/Ti and Au/Ni80-Cr20 metallization systems were sputter deposited on CVD diamond substrates for potential use as interconnects in MCMs. The adhesion values obtained by Sebastian V stud pull tester were in the range of 12 Kpsi, with post-deposition anneal temperature as low as 150 °C. The key to good adhesion was preconditioning of the diamond surface using in-situ sputter-etch technique. The effect of post-deposition annealing (up to 450 °C) on the interdiffusion of Au with the underlying metals was studied using AES, EDX, Optical Microscopy and sheet resistance measurements. Results indicate mixing of C from diamond with refractory metals at low temperatures which may be contributing to strong adhesion.
Z-Axis Anisotropic Electrically Conducting Polymer-Matrix Composite Film
Authors: Li Lin , Chung D. D. L.
Published: March 2011

A z-axis anisotropic electrically conducting polymer-matrix composite film was developed. It comprised 25 vol.% copper coated polyether sulfone particles and a polyimidesiloxane matrix. Each particle protruded from both sides of the film and provided a conducting path along the z-axis. A z-axis pressure of 40 kPa resulted in a z-axis electrical resistivity of 2 ohm.cm for the overall film (i.e., 5 × 10-2 ohm.cm for a conducting path); subsequent pressure removal caused the resistivity to rise to 7 ohm.cm only. The film exhibited negligible stress relaxation and a low modulus of 1.67 GPa.
Optical Properties of Low Dielectric Constant Polyimides and Effects of Orientation
Authors: Rich David C. , Cebe Peggy , Clair Anne K. St.
Published: March 2011

Control of the refractive index in low dielectric constant polyimides through modification of chemistry and structure was investigated. The optical refractive indices of several low dielectric constant polyimides were measured, and the effects of orientation on optical anisotropy were determined. Refractive index in these polyimides was found to decrease with increasing fluorine content due primarily to the low electronic polarizability of the fluorine-carbon bonds. In zone drawn polyimides, refractive index was found to increase substantially in the direction of the draw, but decrease substantially normal to the draw direction. This was explained in terms of the preferential alignment of the polymer chains.
An Assessment of Au Wire Bump Thermo-Mechanical Integrity in GaAs/Al2O3 Flip Chip Modules
Authors: Lin Jong-Kai , Hileman Bennett , Lee Russ , O'brien Richard , Sharma Ravi
Published: March 2011

The flexibility and cost advantages of the wire bumping process are making it increasingly attractive as an alternative bumping method for low I/O flip chip technologies. In this study, electrical measurements from DC to 8.1 GHz and die shear experiments are used to assess the thermo-mechanical integrity of Au/2%Pd wire bumped GaAs/Al2O3 flip chip modules. Finite Element Modeling results for in-process and in-service temperature cycling indicated that the maximum stress of the flip chip module is well below the failure stresses for GaAs, Al2O3 and the Au interconnect. These results are validated by data from thermal cycling experiments. Average shear strength after thermal cycle, thermal shock, and thermal aging (MIL-STD-883C, Condition C) was 64 grams/bump. Electrical characterization (from 45 MHz to 8.1 GHz) using a coplanar waveguide flip chip test structure showed no thermal stress-induced microwave energy losses.
Diode Laser-Assisted Deposition of Gold and Copper from Thin Organometallic Films
Authors: Evoy Stephane , Bernier Marie-Hélène , Izquierdo Ricardo , Pieri Fabrice , Meunier Michel , Sacher Edward
Published: March 2011

We have developed a simple, compact and economical diode laser-assisted process for the direct writing of gold and copper on polyimide. Gold precursor films were deposited by spin-coating a commercially available organometallic compound onto the substrate. The local pyrolysis of these films was induced by the focused beam of an AlGaAs diode laser array ( Pmax = 1 W, λ = 796 nm). Direct writing was achieved in open air while moving the substrate at speeds up to 15 mm/s. Gold lines 13–17 μm wide, ∼0.1 μm thick, and having a resistivity of 30 μΩ·cm, were obtained on polyimide with good reproducibility using writing speeds > 10 mm/s. Following a simple annealing process, these gold lines successfully activated the electroless plating of copper. After 45 min of plating, 2 μm thick Cu/Au conductors, having a resistivity of 8 μΩ·cm, were deposited. A commercially available copper precursor was also studied for the direct deposition of copper.
A New Technique to Generate Conductive Paths in Dielectric Materials
Authors: Desilva M. J. , Pedraza A. J. , Lowndes D. H. , Godbole M. J.
Published: March 2011

We have developed a new two-step process to generate a metallic pattern on dielectric materials. This method employs ultraviolet (uv) laser irradiation followed by electroless deposition. A few laser pulses are required to generate the pattern. After immersion in an electroless bath, the metal film is deposited only on the uv exposed area. Results of the application of this method to aluminum nitride and alumina are presented. The laser irradiation step is very fast, and the electroless deposition is simplified because it does not require any special seeding to promote activation, i.e. laser irradiation activates the dielectric surface for electroless deposition. In addition, the laser-induced activation of the insulator is maintained for a very long time allowing electroless deposition to be performed many months after irradiation. Patterns in the tens of microns can be produced on laser-exposed substrates. Pull tests have been performed to determine the bond strength. We have found that the bond strength can be further increased by annealing.
Real-Time in Situ Monitoring of Defect Evolution at Widegap II-VI/GaAs Heterointerfaces during Epitaxial Growth
Authors: Rouleau C.M. , Park R.M.
Published: March 2011

We report the real-time in situ observation of heterointerface dislocation formation during the growth of lattice-mismatched widegap II-VI/GaAs heterostructures. Such observations were made by employing a near-normal incidence HeNe laser probe during epitaxial growth which generated both a laser reflection interferometry (LRI) signal as well as an elastically scattered laser light (ELLS) signal. We believe that the scattered light signal is generated at the II-VI/GaAs heterointerface based on the observation of a π phase difference between the LRI and the ELLS signals which were monitored simultaneously. We suggest, therefore, that the observed ELLS signal is a consequence of dislocation formation at the heterointerface which occurs due to plastic deformation in lattice-mismatched systems.
Contactless Electromodulation Characterization of Compound Semiconductor Surfaces and Device Structures
Authors: Woodall J.M.
Published: March 2011

This paper will review the use of contactless electromodulation methods, such as photoreflectance (PR) and contactless electroreflectance (CER), to characterize the electronic properties of compound semiconductor surfaces exposed to different growth and post-growth conditions. Also the characterization of properties critical to device performance can be evaluated. For example, using PR and CER it has been found that there is a lower density of surface hole traps than electron traps in certain as-grown MBE (001) GaAs samples and that this condition persists even after air exposure. This behaviour is in contrast to other samples, including both bulk and MBE grown (001) surfaces in which the Fermi level is pinned mid-gap for both n- and p-type structures. We also have observed that Ar+ bombardment under UHV conditions results in Fermi level pinning close to the conduction band edge and that thermal annealing restores mid-gap pinning. Finally, using PR we are able to characterize the electric fields and associated doping levels in the emitter and collector regions of heterojunction bipolar transistor structures (fabricated from III-V materials), thus demonstrating the ability to perform inprocess evaluation of important device parameters.
Optical Characterization of InGaAs/InP Quantum Wires and Dots
Authors: Gu S.Q. , Reuter E. , Xu Q. , Chang H. , Panepucci R. , Adesida I. , Bishop S.G.
Published: March 2011

High resolution electron beam lithography and reactive ion etching in methane-hydrogen (CH4/H2) plasmas have been used to fabricate InGaAs/InP open quantum well wires (QWW) with widths ranging from 200 to 40 nm and quantum dots (QD) with diameters ranging from 600 to 100 nm. Low temperature photoluminescence (PL) spectra were investigated in these nanostructures as a function of excitation intensity, wire width, and dot diameter. The peak emission of the dry-etched 40 nm wires is shifted to higher energies by about 2 meV as compared to 100 nm wires. This “open wire” result is consistent with results reported for buried InGaAs/InP wires of the same width. The blue-shift of the PL peak reaches 10 meV in QDs as their diameters decrease to 100 nm. The magnitude of the observed blue shift in the QDs is larger than the blue-shift predicted on the basis of quantum confinement for the same size dots.
Photoreflectance Study of Modulation-Doped GaAs/GaAlAs Quantum Dots Fabricated by Reactive-Ion Etching
Authors: Wang P.D. , Torres C.M. Sotomayor , Holland M.C. , Qiang H. , Pollak F.H. , Gumbs G.
Published: March 2011

Using contactless photoreflectance at 300K and 77K we have investigated the intersubband transitions from two modulation-doped GaAs/GaAlAs quantum dot (QD) arrays fabricated by reactive-ion etching (RIE). The samples consisted of 8 nm decoupled GaAs/GaAlAs quantum wells with dot sizes (lateral dimensions) of 60 and 100 nm. The lineshapes of the “IC-IH” and “IC-IL” features were indicative of a screened exciton, i.e., the derivative of a broadened twodimensional density of states (step function), due to the presence of the electron gas. On the other hand, even at 300K the “2C-2H“ features exhibited a well-defined sharp excitonic lineshape, i.e., derivative of a Gaussian profile. Even at room temperature it is possible to detect the effects of the lateral quantum confinement. We have observed a 2 meV blue shift of the “2C-2H” feature of the 60 nm QD array in relation to the 100 nm QD array. At 77K we have found evidence for a “parabolic-like” in-plane confining potential on the smaller QD array. This experiment demonstrates the considerable utility of PR in studying these reduced dimensional systems.
Influence of Growth Conditions on the Modulation Mechanism of Photoreflectance Spectra of Single InGaAs/InAlAs Quantum Wells
Authors: Baltagi Y. , Bru C. , Benyatrou T. , Garcia-Perez M.A. , Guillot G. , Gendry M. , Leclercq J.L , Drouot V. , Hollinger G.
Published: March 2011

Using Photoreflectance (PR) measurements, we have investigated In0.53Ga0.47As single quantum wells (SQW) with In0.52Al0.48As barriers grown by MBE on InP substrates. Unusual lineshapes of PR spectra are observed for the fundamental transition in some of the SQW. This phenomenon is shown to be independent on the widths of both the SQW (5nm or 10nm) and the surface barrier layer (between 65nm and 300nm). PR spectra are recorded at different temperatures and in different samples, as well as with a secondary pump laser beam. From these measurements, it is concluded that interface defects exist in the SQW grown at 525°C without growth interruption. Such defects are clearly evidenced in room temperature PR experiments and confirmed by PL measurements.
Raman Scattering Characterization of Ultrathin Films of β-SiC
Authors: Choo Ahn Goo , Tlali Spirit , Jackson Howard E. , Li J. P. , Stecki Andrew J.
Published: March 2011

Raman scattering has been used to characterize ultrathin films of β-SiC, ranging in thickness from 38 nm to 240 nm. These films were prepared on the surface of a <100> Si substrate by a carbonization process at a temperature of 1300°C. In each case, the LO phonon near 970 cm−1 and the TO phonon near 795 cm−1 are observed, indicating the formation of β-SiC crystal. The Raman linewidths and peak positions indicate evidence of nonuniform stress and disorder. The Raman intensity of the TO phonon is nearly twice the intensity of the LO phonon measured both with and without the Si substrate, which indicates that the crystal growth was not entirely confined in the <100> direction.
Real-Time Thermo-Mechanical Property Evaluation of Thin Films
Authors: Rogers John A. , Nelson K. A.
Published: March 2011

We describe an experimental method capable of evaluating the elastic and loss moduli and the thermal diffusivity in thin films. The versatility of the technique is demonstrated with data scans from several films of technological interest.
Hydrocarbon Ecr Reactive Ion Etching of III-V Semiconductors with Sims Plasma Probe Diagnostics
Authors: Melville Douglas L. , Simmons J.G. , Thompson D.A.
Published: March 2011

The advantages of in-situ SIMS plasma probe diagnostics are highlighted in low pressure hydrocarbon ECR reactive ion etching (RIE) of III-V materials. Three aspects of the RIE process are investigated. First, the dominant ion species in a CH4/H2/Ar plasma are recorded at various chamber pressures, ECR powers, CH4/(CH4+H2) gas flow ratios and microwave cavity tuning. These studies have improved our understanding of the effects of these parameters on the relative concentrations of reactive precursor species in the plasma and have led to more rapid optimization of the etch system. Secondly, SIMS has been used for identification of reaction products from the III-V surface at the optimized plasma conditions. The Ar diluted mixture gives rise to significant levels of group V hydrides and organometallic compounds and the dominant group III volatile ions have been positively identified as dimethyl species. The third and final aspect reported is the application of volatile product identification to endpoint detection. In lcm2 multiple quantum well samples, layers as thin as 50Å are easily distinguishable.
In-Situ Monitoring by Mass Spectrometry for GaAs Etched with An Electron Cyclotron Resonance Source
Authors: Kahaian D. J. , Pang S. W.
Published: March 2011

Quadrupole mass spectrometry (QMS) has been used as an in-situ diagnostic technique for GaAs etched with an electron cyclotron resonance source. Changes in the detected signal intensities for reactive species and etch products have been related to corresponding changes in the etch rate as several process parameters were varied. The detected 75As+ and to a lesser degree, 35C1+ and 70C12+, were observed to follow etch rate as microwave power, rf power, source to sample distance, temperature, and pressure were varied. The self-induced dc bias (IVdcl) determines the etch rate dependence on etch time. The time delay before saturation of the monitored 75As+ signal corresponding to a constant etch rate is inversely proportional to IVdcl. The addition of N2/O2 in a 4:1 ratio to constitute 15% of the total discharge resulted in a 95% decrease in the intensity of the monitored 75As+ signal. The measured etch rate decreased by 75%.
AIGaAs Microelectronic Device Processing Using an as Capping Layer
Authors: Grepstad J.K. , Husby H. , Bernstein R.W. , Fimland B.-O.
Published: March 2011

The case for incorporating an arsenic capping layer in compound semiconductor device processing has been investigated with x-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED) and scanning electron microscopy (SEM). The As cap was found to be stable upon exposure to common processing chemicals, such as acetone, photoresist, developer, and N-methyl-2-pyrrolidone, a common polyimide solvent. A clean, c(4×4)-reconstructed GaAs(001) surface was recovered after thermal desorption of the cap in ultra-high vacuum, for a sample exposed to standard (maskless) photolithography. We also report a new technique for reactive decapping at room temperature, using a beam of hydrogen radicals (H*). Pattern definition in the As cap with ∼ 5 μm linewidth was demonstrated, using this technique. However, XPS and SEM data for the H*-etched specimens showed clear evidence of superficial gallium (sub)oxide and of As residues along the photoresist mask edges. This novel method of As cap patterning thus needs further refinement, before being useful to III-V device processing.
Optical Emission End-Point Detection for Via Hole Etching in InP and GaAs Power Device Structures
Authors: Pearton S. J. , Ren F. , Abernathy C. R. , Constantine C.
Published: March 2011

Narrow (∼30 μm ϕ) via holes have been etched in both InP and GaAs substrates using either C12/CH4/H2 /Ar or BC13/C12 discharges, respectively. High density (∼5×1011 cm−3), low pressure (1 mTorr for C12/CH4/H2/Ar or 15 mTorr for BC13/C12) conditions, combined with sidewall passivation obtained using AZ 4620 photoresist masks, produce the correct profiles for subsequent metallization to complete the via connection. Optical emission monitoring of the 417.2 nm Ga line during GaAs etching or of the 325.6 nm In line during InP etching provided a sensitive, non invasive and reliable indicator of endpoint for both types of substrates. The intensity of these lines was proportional to the microwave input power at fixed dc bias and pressure. The via holes are suitable for a range of InP and GaAs microwave power devices, including Heterojunction Bipolar Transistors and High Electron Mobility Transistors.
Real-time Monitoring and Control of Silicon Epitaxy Using Emission Fourier Transform Infrared Spectroscopy
Authors: Zhou Z.H. , Kim H. , Reif Rafael
Published: March 2011

Real-time epi-film thickness is measured by an Emission Fourier Transform Infrared Spectrometer (E/FT-IR). The E/FT-IR takes advantage of the heated wafer as the source of IR radiation. In our experiments, wafers were cleaned using in-situ ECR hydrogen plasma followed by film growth. The cleaning and deposition processes were monitored in real-time using the E/FT-IR technique. We have demonstrated the application of E/FT-IR for observing real-time growth rates and incubation times. Based on these real-time observations, the predeposition plasma cleaning process and the deposition process can be effectively monitored and controlled in real-time. Application of E/FT-IR in optimizing the predeposition hydrogen plasma cleaning process was demonstrated.
Relationship Between Minority Carrier Parameters and Solar Cell Characteristics of Electromagnetic Cast Polycrystalline Silicon
Authors: Suzuki Eiichi , Kaneko Kyojiro , Nunoi Toru
Published: March 2011

The relationship between minority carrier properties and solar cell characteristics of electromagnetic (EM) cast polycrystalline Si has experimentally been investigated. The minority carrier lifetime τ and diffusion coefficient D were evaluated by a novel dual mercury probe method. The solar cell characteristics, e.g., a conversion efficiency η were measured by fabricating experimental solar cells using the corresponding wafers. The wafer showing high-η (13.1%) has relatively high τ (av. 8.2 μs) with small variation of I) (av. 29.6 cm2/s). On the contrary, the low-η (11%) wafer shows low τ (av. 1.1 μs), including some inferior portions with very low τ of less than 0.5 μs. It is also shown that D drastically deteriorates with decreasing τ if τ is less than around 2 μs. To realize high efficiency polycrystalline solar cells, the wafers with high value of τ and without considerably low-τ portions are needed.
Surface Photovoltage Measurement of Minority Carrier Diffusion Lengths Exceeding Wafer Thickness: Application to Iron Monitoring with Part Per Quadrillion Sensitivity
Authors: Kontkiewicz A.M. , Lagowski J. , Dexter M. , Edelman P.
Published: March 2011

We discuss an approach to iron concentration determination in silicon, based on wafer-scale surface photovoltage measurement of the minority carrier diffusion length in the millimeter range. The approach combines two novel aspects: it overcomes the diffusion length to wafer thickness ratio limitation of previous SPV methods, and it employs iron separation from other recombination centers using rapid photo-dissociation of iron-boron pairs. The wafer thickness limitation was eliminated by using the correct theoretical SPV wavelength dependence instead of simplified asymptotic diffusion length form adopted in all previous treatments and valid only for diffusion lengths much shorter than the wafer thickness. Photo-dissociation of Fe-B pairs and measurement of the corresponding decrease of the L value (caused by creation of iron intersticials) enables iron detection in typical silicon wafers in times of seconds with a sensitivity in the low 108 atoms/cm3 range.
Use of Synchrotron White Beam X-Ray Topography to Characterize IR Detector Manufacturing Processes
Authors: Dudley M. , Wu Jun , Larson D. J. , Dimarzio D.
Published: March 2011

It has been have demonstrated that synchrotron white beam x-ray topography can be used to characterize IR detector materials at nearly every stage in the manufacturing cycle, including: as-grown CdZnTe single crystal boules; substrate wafers cut from different positions in the boules; thin films grown on characterized wafers; and HgCdTe focal plane arraystructures. Special diffraction geometries have been developed, taking advantage of the broad wavelength spectrum, large beam size, and high intensity of the synchrotron radiation source, to enable rapid and non-destructive assessment of defect densities and strain distributions after each processing step. This diagnostic method has important implications for increasing the producibility of focal plane arrays. Boule characterization can reveal defects, grain orientation, interfaces and strains, and provides guidance for optimal slicing. Wafer characterization produces multiple topographic images, providing both defect mapping and depth profiling in a single exposure. Finally, x-ray topography of HgCdTe focal plane array test articles reveals subsurface damage not observable by optical or IR microscopy. The applicability of this technique to evaluate yield, quality, and reproducibility will be discussed.
Effects of Halogen-Containing Gas Plasma and Rapid Thermal Anneal Treatment on the Reactive Ion Etched Silicon
Authors: Kwon Kwang-Ho , Kim Bo-Woo , Park Hyung-Ho , Kang Jin-Yeong , Yeom Gun-Yung
Published: March 2011

The effects of SF6 and NF3 gas plasma treatments, and succesive rapid thermal anneal (RTA) treatment for the recovery of modified silicon surface due to CHF3/C2F6 plasma have been investigated using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). XPS analyses have revealed that NF3 and SF6 plasma treatments are effective for the removal of residue layer. SIMS results show that penetrated impurities in the contaminated silicon substrate reduce through the additional RTA treatment. The effects of NF3, SF6 plasmas, and additional RTA treatments for the recovery of reactive ion etched silicon surface has been also studied by measuring the electrical performance of the silicon devices.
A New Environmentally Stable Posyitve Tone Chemically Amplified Resist System - KRS
Authors: Iiuang Wu-Song , Kwong Ranee , Katnani Ahmad , Khojasteh Maitoud , Lee Kim Y.
Published: March 2011

It is known that one of the main shortcomings of chemically amplified resist systems is their sensitivity to airborne base contaminants. The contaminants cause unpredictable linewidth variations deeming the resist incompatible with manufacturing. Besides other issues, this drawback has greatly contributed to the slow introduction of DUV into manufacturing and discouragcd most semiconductor manufactures from including DUV in their strategic plans. In this paper, we present a new positive tone chemically amplified photoresist system which is resilient to airborne base contaminants and it shows stable linewidth for more than 24 hours delay between exposure and development. This resist has high sensitivity (17-18 mj/cm2), high contrast (7), high resolution (0.35 um with λ = 248 rm and NA = 0.37) and large process latitude in deep-UV lithography. This resist also exhibits high resolution (0.1 um in 0.35 um thick resist) in E-beam lithography at a sensitivity of about 10 uC/cm2. Both lithographic systems (deep-UV and E-beam) yield nearly vertical profiles in the resist images.
Infrared and Ultraviolet Analysis of Dual-Ion Implanted Gaas
Authors: Lacquet Beatrys M. , Aizenberg Gustavo E. , Swart Pieter L.
Published: March 2011

Semi-insulating <100> GaAs was implanted with 170 ke V H+ and P+ ions at room temperature using a PH3 source. Fourier analysis of the bilinear transformed optical reflectance data in the infrared region of the spectrum indicated the presence of two damaged layers at different depths from the surface: (i) a deep inhomogeneous layer of low damage produced by the protons and (ii) a thin amorphized surface layer which was produced by phosphorus ions. The position and refractive index at the peak of the assumed gaussian damage profile caused by the protons, as well as the standard deviation of the profile, were estimated rapidly from the processed data. The thickness and refractive index of the surface layer were also estimated from this analysis. The presence of the amorphized surface layer was evident from the reflectance in the ultraviolet where shift and broadening of the reflectance peaks associated with the Van Hove singularities, were observed.
Reliable Impurity Identification in Inp
Authors: Schnoes M. L. , Harris T. D. , Pearton S. J. , Di Giuseppe M. A. , Bhat R. , Cox H. M.
Published: March 2011

Low temperature, resonantly excited photoluminescence (PL) has proven to be the method of choice for impurity identification in GaAs. InP has suffered from insufficient impurity binding energy data to benefit similarly. We will report results of selectively-excited donor-acceptor pair spectroscopy for acceptor identification in InP. Ion implantation doping of high purity InP is used for generation of known impurity samples. Progress toward a complete database of acceptor binding energies in InP is reported. We will discuss the results of high magnetic field low temperature resonant photoluminescence spectroscopy for donor identification in InP. The success of donor ion implantation studies will be included. This data should provide direction for efforts in growing high purity InP by MOCVD and gas source MBE.
Correlation Between Electrical Properties and Residual Defects in Se+-Implanted InP After Rapid Thermal Annealing
Authors: MÜller P. , Bachmann T. , Wendler E. , Wesch W. , Richter U.
Published: March 2011

>100> -semiinsulating InP was implanted with 600 keV Se-ions at temperatures between 300K and 425K with an ion dose of 1 ×1014 cm−2. After capping the samples with about 120 nm siliconoxynitride annealing was performed at 700°C up to 975°C using a graphite strip heater system. The annealed samples were analyzed with Rutherford backscattering, electron microscopy and conventional Hall measurements. The results show, that a strong correlation exists between defects remaining after annealing (for instance dislocations, loops, microtwins) and the measured electrical properties. An implantation temperature ≦ 395K and annealing at least at 800°C for 50 s is necessary to obtain high performance electrically active layers. The activation of selenium in InP can be well described using a simple thermodynamical model. The model yields an activation energy of EA = (1.0 ± 0. 1) eV which can be understood as the energy necessary to split-up selenium-vacancy-complexes and a diffusion energy of Ed = (2.0 ± 0.2) eV representing material transport of the semiconductor material.
Deep Level Characterization and Passivation in Heteroepitaxial Inp
Authors: Chatterjee B. , Ringel S. A. , Sieg R. , Weinberg I. , Hoffman R.
Published: March 2011

Deep levels in MOCVD grown p-InP on GaAs substrates have been investigated by Deep Level Transient Spectroscopy (DLTS). The effect of hydrogenation on the electrical activity of these levels has been studied through a combination of DLTS and Photoluminescence (PL) measurements. DLTS measurements indicate a drop of trap density from σ 5 × 1014 cm−3 to σ 1 × 1012 cm−3 after hydrogenation. Annealing at 400°C reactivated only the dopants, while temperatures above 600°C were necessary for deep-level reactivation. This combined with a logarithmic dependence on fill pulse time, indicate that at least one broad DLTS peak is associated with dislocations. The PL the DLTS results show that the dislocation related traps are passivated by hydrogen, preferentially over the dopants and that a wide annealing window exists for dopant reactivation.
Photoluminescence Fatigue in Laterally-Ordered (GaP)2/(InP)2 Short-Period-Superlattices (SPS) Grown by Molecular Beam Epitaxy
Authors: Liu X. C. , Gu S. Q. , Reuter E. E. , Bishop S. G. , Chen A. C. , Moy A. M. , Cheng K. Y. , Hsieh K. C.
Published: March 2011

Spontaneously laterally ordered (GaP)2/(InP)2 short period superlattices (SPS) grown by Molecular Beam Epitaxy (MBE) on nominal (100) GaAs substrates have been studied by photoluminescence (PL) spectroscopy. The samples studied included SPS comprising 110 pairs of (GaP)2/(InP)2 (total thickness σ90 nm) and multiquantum well structures in which quantum wells comprising 12 pairs of (GaP)2/(InP)2 SPS layers (thickness σ10 nm) are alternated with lattice-matched GaInP random alloy barrier layers. The 5K PL spectra include a σ1760 meV nearband edge band, and a much broader, lower energy (σ1670 meV) luminescence band that exhibits an unusual fatiguing behavior; its intensity diminishes monotonically during continuous illumination by the exciting light. This fatigued PL state is metastable at low temperatures. In the quantum well structure, although the relative intensity of the lower energy band is significantly weaker in comparison to the higher one, the fatiguing behavior still exists. However the fatiguing rate is slower in quantum well structures than that observed in the thick SPS film.
Space Distribution of Deep Levels in SiGe/Si Heterostructure
Authors: Rong Zhang , Kai Yang , Shulin Gu , Yi Shi , Hongbin Huang , Ronghua Wang , Ping Han , Liqun Hu , Youdou Zheng , Qi Li
Published: March 2011

The small-pulse DLTS had been developed to measure distribution of deep levels in CVD grown SiGe/Si heterostructure before and after thermal processing at 800°C. Changes of defect states was found and after processing the original single deep level 0.62eV under the condition band split into two separated traps. A new weak deeper trap signal was found only in the just relaxed region. It could be Ge-related defect complex with misfit dislocations.
Occurrence of Ground and Excited-State Impurity Bands in Silicon Inversion Layers: Electric Field Effects
Authors: HipÓlito O. , LeÃO Salviano A. , Ferreira Da Silva A.
Published: March 2011

We investigate the effects of charged impurities in n-type Silicon inversion layers. We show the occurrence of ground and excited-state impurity bands as a function of electric field and concentration. Also the effects of disorder and for given impurity concentrations, the lowest excited band play an essential role in the optical and transport measurements. For high electric fields the impurity bands go to the ideally 2D separated bands.
Optical Spectroscopy of Defects in GaAs/AlGaAs Multiple Quantum Wells.
Authors: Monemar B. , Holtz P. O. , Bergman J. P. , Zhao Q.X. , Harris C.I. , Ferreira A. C. , Sundaram M. , Merz J.L. , Gossard A.C.
Published: March 2011

The study of electronic properties of GaAs/AlGaAs quantum wells (QWs) has traditionally been focused on intrinsic phenomena, in particular the free exciton behaviour. Defects and impurities have often been regarded as less relevant compared to the case of bulk semiconductors. Doping in QWs is important in many applications, however, and recently the knowledge about the structure of shallow donors and acceptors from optical spectroscopy has advanced to a level comparable to the situation in bulk semiconductors. A dramatic difference from the bulk case is the common occurrence of localisation effects due to interface roughness in QW structures. The recombination of bound excitons (BEs) differs drastically from bulk, BE lifetimes decrease with decreasing well thickness Lw, but increase with decreasing barrier thickness Lb (at constant Lw) below Lb=70Å. Exciton capture at impurities is a process which is strongly influenced by the localisation potentials from the interface roughness. The recombination process in doped QWs involves a nonradiative component, for shallow acceptors an excitonic Auger process has been identified. Deep nonradiative defects in the (MBE grown) QW as well as in the barrier material are manifested in measurements of the PL decay time vs temperature. In undoped multiple QWs the decay times vs T are consistent with thermal emission out of the well into the barrier, where nonradiative recombination via deep level defects occur. Nonradiative recombination in the well itself can be studied in electron-irradiated structures. Preliminary data also demonstrate the feasibility of hydrogen passivation of dopants as well as deep levels in the QW structures.
Carbon Doping of InGaAs for Device Applications
Authors: Stillman G.E. , Stockman S.A. , Colomb C.M. , Hanson A.W. , Fresina M.T.
Published: March 2011

Carbon has gained wide acceptance as a p-type dopant for GaAs-based device structures due to its low atomic diffusivity. Carbon doping of InGaAs, however, is complicated by the amphoteric nature of C and difficulty in incorporating C efficiently during epitaxial growth. We have achieved hole concentrations as high as 7x1019 cm−3 in CC14-doped InGaAs grown at low temperature by MOCVD. Growth-related issues include the effect of CCl4 on the alloy composition due to etching during growth, and the incorporation of hydrogen, which passivates the C acceptor and reduces the hole concentration during growth and during the post-growth cool-down. The effect of H passivation on minority carrier transport has been characterized by the zero-field time-of-flight technique. High frequency InP/InGaAs HBTs with a C-doped base have been demonstrated with ft = 62 GHz and fmax = 42 GHz, which is comparable to the best performance reported for MOCVD-grown InP/InGaAs HBTs.
Dislocation Distribution in Graded Composition IngaAs Layers
Authors: Molina S.I. , Gutiérrez G. , Sacedón A. , Calleja E. , García R.
Published: March 2011

The defect distribution of a graded composition InGaAs layer grown on GaAs by MBE has been characterized by TEM (XTEM, PVTEM, HREM). The observed configuration does not correspond completely with that theoretically predicted. Dislocation misfit segments are in a quantity much bigger than in constant composition layers. Dislocation density is quite uniform up to a certain layer thickness t1. Few dislocations are observed between this t1 thickness and a larger thickness t2. Dislocation density is below the detection limit of XTEM for thicknesses bigger than t2. Some dislocations are observed to penetrate in the GaAs substrate.

Several mechanisms (reactions between 600 dislocations, Hagen-Strunk and modified Frank-Read processes) are proposed to explain the interactions of dislocations in the epilayer and their penetration in the substrate.
Raman Scattering by Lo Pronon-Plasmon Coupled Mode in Heavily Carbon Doped P-Type InGsAs
Authors: Qi Ming , Luo Jinsheng , Shirakashi Junichi , Tokumitsu Eisuke , Nozaki Shinji , Konagai Makoto , Takahashi Kiyoshi
Published: March 2011

The Raman scattering from LO phonon–plasmon coupled (LOPC) mode in heavily carbon doped p–type InxGa1–xAs grown by metalorganic molecular beam epitaxy (MOMBE) was studied experimentally. Only one LOPC mode appears between the GaAs–like and InAs–like LO modes was observed. The peak position of the LOPC mode is near the GaAs–like TO mode frequency, and is not sensitive to the hole concentration. The intensity of the mode increases with increasing the carrier concentration while the two LO modes decrease and become unvisible under the higher doping level. The hole concentration dependence of the linewidth and intensity of the LOPC mode is very similar to that in p–type GaAs. It was shown that the plasmon damping effect plays a dominant role in the p–type doping case.
Dipole Relaxation Current in N-Type AIxGa1-xAs
Authors: Scalvi Luis V.A. , Oliveira L. , Li M. Siu
Published: March 2011

Thermally stimulated depolarization current (TSDC) spectra are reported for AlxGa1-xAs alloys with direct and indirect bandgap for the first time. The experimental data reveal the presence of electric dipoles in both samples which are interpreted by using the negative-U DX center model. These data are fitted by a relaxation time distribution approach yielding average activation energies in close coincidence with the DX center binding energy value.
Theory of Rare-Earth Impurities in Semiconductors
Authors: Delerue C. , Lannoo M.
Published: March 2011

The theory of rare-earth impurities in semiconductors is reviewed. Results of Green's function calculations are presented. The particular case of Ytterbium (Yb) in InP is analyzed in detail. We show that the optical transitions of Yb in InP and their Zeeman splitting can be interpreted by a small coupling between quasi degenerate 5d and 4f states. It also explains the observed lifetimes. This model is coherent with the attribution of the Ec-30 meV level to the Yb3+/Yb2+ acceptor level as proposed recently. We detail the mechanism which allows the energy transfer between a free exciton and the rare-earth impurity. The conditions required for an efficient luminescence are analyzed.
Rh: a Dopant with Mid-Gap Levels in InP and InGaAs and Superior Thermal Stability
Authors: Scheffler H. , Srocka B. , Dadgar A. , Kuttler M. , Knecht A. , Heitz R. , Bimberg D. , Hyeon J.Y. , Schumann H.
Published: March 2011

We investigate the influence of Rh-doping on electrical properties of InP and InGaAs. Deep level transient spectroscopy carried out on Rh-doped as well as undoped reference samples reveals a single Rh-related deep level in both semiconductors. While a Rh-related electron trap in InGaAs is situated at EC-0.38eV a Rh-related hole trap is found to exist in InP approximately 0.73 eV above the valence band edge. The internal reference rule for 3d transition metal deep levels is found to be valid for these 4d transition metal levels: their energy is constant across the InGaAs/InP heterojunction. We conclude these levels to be the single acceptor states of Rh substitutionally incorporated on cation sites.
Hydrogenation of Gallium Nitride
Authors: Brandt M. S. , Johnson N. M. , Molnar R. J. , Singh R. , Moustakas T. D.
Published: March 2011

A comparative study of the effects of hydrogen in n-type (unintentionally and Si-doped) as well as p-type (Mg-doped) MBE-grown GaN is presented. Hydrogenation above 500°C reduces the hole concentration at room temperature in the p-type material by one order of magnitude. Three different microscopic effects of hydrogen are suggested: Passivation of deep defects and of Mg-acceptors due to formation of hydrogen-related complexes and the introduction of a hydrogenrelated donor state 100 meV below the conduction band edge.
Optical Spectroscopy of a Nitrogen-Hydrogen Complex in ZnSe
Authors: Wolk J. A. , Ager J. W. , Duxstad K. J. , Haller E. E. , Taskar N. R. , Dorman D. R. , Olego D. J.
Published: March 2011

We have observed two local vibrational modes related to H bonded to N acceptors in ZnSe samples grown by metal organic vapor phase epitaxy. The modes have been seen in both infrared and Raman spectroscopy. The new mode seen at 3194 cm-1 is assigned to an N-H stretching vibrational mode and the mode found at 783 cm-1 is tentatively assigned to an N-H wagging vibrational mode. Polarized Raman spectroscopy was used to determine that the symmetry of the defect complex is C3v, which implies that the H atom is in either a bonding or anti-bonding position.
Stoichiometry Related Phenomena in Low Temperature Grown GaAs
Authors: Missous M. , O'Hagan S.
Published: March 2011

The growth of GaAs at low temperatures (LT-GaAs) at or below 250 °C, under standard Molecular Beam Epitaxy (MBE) growth conditions, usually results in a massive incorporation of excess As in the lattice which then totally dominates the electrical and optical characteristics of the as grown material. We report on new phenomena associated with the growth of GaAs at 250 °C and we show, for the first time, data on highly electrically active doped material. By careful control of the growth conditions, namely As4/Ga flux ratios, material in which total defect concentrations of less than 1017 cm-3, well below the huge 1020 cm-3 that is normally obtained in LT-GaAs, can be achieved thereby demonstrating that high quality GaAs can in effect be grown at extremely low temperatures.
Femtosecond Probe-Probe Transmission Studies of Lt-Grown Gaas Near the Band Edge
Authors: Radousky H. B. , Bello A. F. , Erskine D. J. , Dinh L. N. , Bennahmias M. J. , Perry M. D. , Ditmire T. R. , Mariella R. P.
Published: March 2011

We have studied the near-edge optical response of a LT-grown GaAs sample which was deposited at 300 °C on a Si substrate, and then annealed at 600 °C. The Si was etched away to leave a 3-micron free standing GaAs film. Femtosecond transmission measurements were made using an equal pulse technique at four wavelengths between 825 and 870 nm. For each wavelength we observe both a multipicosecond relaxation time, as well as a shorter relaxation time which is less than 100 femtoseconds.