bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of Delta Doped Al0.25Ga0.75N and GaN Epitaxial Layers
Authors: Flynn Jeffrey S. , Wallace Leah G. , Dion Joe A. , Hutchins Edward L. , Antunes Helder , Brandes George R.
Published: April 2011

Delta doping (paused growth doping) was investigated as an alternative to uniformly distributing the dopant in the nitride semiconductor layer. In this work, delta doped layers were produced in MOVPE-grown AlGaN and GaN layers at a susceptor temperature of 1220°C by turning off the group III precursors (TMG and TMA) and introducing into the reactor a silicon precursor Si2H6 (disilane) for a fixed period (pause time) before growth was restarted. The compositional and electrical properties as a function of aluminum content and dopant flux were investigated for nitride layers on 2 inch c-plane sapphire substrates. Secondary ion mass spectroscopy (SIMS) measurements revealed a sharp silicon peak with a FWHM of 5.7 ± 0.6 nm for an Al0.25Ga0.75N sample and 10.0 ± 0.6 nm for a GaN sample with sheet charges of 7.9×1012 cm−2 and 9.9×1012 cm−2,respectively. Room temperature Hall mobility as high as 265 cm2 V−1s−1 for a sheet charge 7.9×1012 cm−2 was demonstrated for delta doped Al0.25Ga0.75N layers, but the mobility enhancement saturated and then decreased with increasing sheet charge. Room temperature sheet charge increased with increasing dopant flux for delta-doped AlGaN and GaN layers. Sheet charge density as high as 2.2×1013 cm−2 and 1.3×1013 cm−2 was measured at room temperature for Al0.25Ga0.75N and GaN delta doped layers, respectively. Under identical doping conditions, the Hall sheet charge of the delta doped Al0.25Ga0.75N layer was approximately half as large as GaN layers. The impurity and electrical characteristics of the delta doped layers are further discussed.
Comparative morphology of AuTiAlTi, AuPdAlTi and AuAlTi ohmic contacts to AlGaN/GaN
Authors: Fay M W , Moldovan G , Harrison I , Balmer R. S. , Hilton K P , Hughes B T , Uren M J , Martin T , Brown P D
Published: April 2011

AuTiAlTi, AuPdAlTi and AuAlTi ohmic contacts to AlGaN/GaN layers rapid thermal annealed at temperatures up to 950°C have been characterised using conventional and chemical transmission electron microscopy techniques. The relationship between the as-deposited metallic structure, annealing temperature, post-anneal interfacial microstructure and contact resistance is examined.

The presence of a TiN interfacial layer is found to correlate with the onset of ohmic behaviour. Ti and Pd barrier layers are found to be ineffective at stopping the diffusion of Au to the interface. Au is implicated in the development of the inclusions, which are associated with threading dislocations. Once activated, the presence of the inclusions has little influence on the ohmic behaviour of the sample.
Activation of Mg acceptors in GaN:Mg monitored by electron paramagnetic resonance spectroscopy.
Authors: Matlock D. , Zvanut M. E. , DiMaio Jeffrey R. , Davis R. F. , Henry R. L. , Koleske Daniel , Wickenden Alma
Published: April 2011

Hydrogen removal from Mg-doped GaN is necessary to activate p-type conductivity, but the exact chemical process is not yet clear. We have investigated this issue by monitoring the intensity of an electron paramagnetic resonance (EPR) signal attributed to Mg through a series of isochronal and isothermal anneals between 600 and 1000 °C. Measurements made on GaN:Mg epitaxial layers deposited on SiC and annealed between 700 and 850 °C indicate that the Mg-related EPR signal increases with temperature as expected for depassivation of a Mg complex by removal of hydrogen. However, data obtained outside this temperature range suggest that additional processes may occur. For example, as-deposited films contain a signal resembling the Mg acceptor that is quenched by a 650 °C N2 anneal. Also, for all samples, N2 annealing at T>850 °C irreversibly decreases the signal thought to be due to Mg. Although the presence of the signal in the as-grown films is not fully understood, the effects observed at T>850 °C may be attributed to preferential N-desorption from Mg-N-H complexes.
Microstructural Defects in Mg-doped AlGaN Layers Grown by Metalorganic Chemical Vapor Deposition
Authors: Cho Hyung Koun , Yang Gye Mo
Published: April 2011

We have investigated the formation of inversion domain boundaries in Al0.13Ga0.87N layers grown on sapphire substrates by metalorganic chemical vapor deposition using transmission electron microscopy. By increasing the Mg source flow rate, the reduction of dislocation density occurred up to the Mg source flow rate of 0.103 μmol/min. While the vertical type inversion domain boundaries (IDBs) were observed in the Al0.13Ga0.87N layers grown with the low Mg source flow rate, the IDBs in the Al0.13Ga0.87N layers grown with the high Mg source flow rate have horizontally multifaceted shapes. The change of polarity by the IDBs of horizontal type also resulted in the 180°rotation of pyramidal defects within the same AlGaN layer. Therefore, We found that the Mg source flow rate affects significantly the dislocation density, the type of IDBs, and the shape of pyramidal defects in AlGaN layers.
The First Wafer-fused AlGaAs-GaAs-GaN Heterojunction Bipolar Transistor
Authors: Estrada Sarah , Stonas Andreas , Huntington Andrew , Xing Huili , Coldren Larry , DenBaars Steven , Mishra Umesh , Hu Evelyn
Published: April 2011

We describe the use of wafer fusion to form a heterojunction bipolar transistor (HBT), with an AlGaAs-GaAs emitter-base fused to a GaN collector. In this way, we hope to make use of both the high breakdown voltage of the GaN and the high mobility of the technologically more mature GaAs-based materials. This paper reports the first dc device characteristics of a wafer-fused transistor, and demonstrates the potential of wafer fusion for forming electronically active, lattice-mismatched heterojunctions. Devices utilized a thick base (0.15um) and exhibited limited common-emitter current gain (0.2–0.5) at an output current density of ∼100A/cm2. Devices were operated to VCE greater than 20V, with a low VCE offset (1V). Improvements in both device structure and wafer fusion conditions should provide further improvements in HBT performance. The HBT was wafer-fused at 750°C for one hour. Current-voltage characteristics of wafer-fused p-GaAs/n-GaN diodes suggest that the fusion temperature could be reduced to 500°C. Such a reduction in process temperature should mitigate detrimental diffusion effects in future HBTs.
The Effect of Growth Stoichiometry on the GaN Dislocation Core Structure
Authors: Baines Marcus Q. , Cherns David , Hsu Julia W. P. , Manfra Michael J.
Published: April 2011

Plan-view transmission electron microscopy was used to study the core structures of different dislocations in (0001) GaN layers grown under Ga-rich and Ga-lean conditions by molecular beam epitaxy. In Ga-rich samples at least one third of mixed type dislocations were open-core, and edge dislocations were observed to be closed-core. In contrast, under Ga-lean conditions, all dislocations were observed to be closed-core, and many were associated with pits at the sample surface. High resolution studies of the open core dislocations revealed that many were decorated with a disordered deposit, the origin of which is discussed.
Study on Cubic GaN Growth on (001) Rutile TiO2 Substrates by ECR-MBE
Authors: Araki T. , Mamiya H. , Kitamura K. , Nanishi Y.
Published: April 2011

GaN layers were grown on a (001) rutile TiO2 substrate by electron cyclotron resonance plasma-excited molecular beam epitaxy. For the first time, c-GaN with a preferential growth orientation was obtained. Based on the results from electron diffraction and X-ray diffraction analysis, we found that c-GaN with the growth direction of [110] was grown on the TiO2 substrate. The formation of c-GaN was also confirmed by cathodoluminescence, in which a luminescence peak was observed at 3.24eV.
Aluminum Nitride Crystal Growth by Halide Vapor Transport Epitaxy
Authors: Tassev V. L. , Bliss D. F. , Weyburne D. , Bailey J. S. , Wang S.-Q.
Published: April 2011

Halide vapor transport epitaxy (HVTE) is demonstrated for growth of AlN layers with thickness up to 50 μm at deposition rates up to 60 μm/h. The HVTE process uses an aluminum chloride amine adduct as the aluminum source of both aluminum and nitrogen. This new technique eliminates the main difficulties of the conventional hydride VPE growth, where aluminum oxidation and the strong reactivity of aluminum chloride with fused silica create the potential for oxygen contamination. This study shows the effect of temperature, gas flow velocities, and reactor pressure on the growth rate and layer quality. It is found that the growth rate and the layer quality strongly depend on the gas ratio. The species of carrier gas, the flow rates and partial pressures can be used as tools to optimize growth rate and to avoid any etching effects resulting from reverse chemical reactions. The crystalline layer quality as determined by x-ray rocking curve measurement shows FWHM of 300–900 and 500–1300 arc-sec for (002) and (102) planes, respectively.

PACS: 81.05.Ea; 81.15.Kk; 68.55.Jk.
Low-Electron-Energy Cathodoluminescence Study Of Polishing And Etching Effects On The Optical Properties Of Bulk Single-Crystal Gallium Nitride
Authors: Robins Lawrence H. , Steiner Bruce , Sanford Norman A. , Menoni Carmen
Published: April 2011

Low electron energy cathodoluminescence (LEECL) was used to examine polishing-induced damage in a bulk high-pressure grown GaN single-crystal platelet. The Ga-polarity face of the platelet was mechanically polished; chemically-assisted ion-beam etching (CAIBE) to a depth of 200 nm was performed on a portion of this face. Low-temperature (15 K) CL spectra of the polished-only and polished+CAIBE regions of the Ga-face were taken at 2.8 kV, 5.4 kV, and 10.6 kV (corresponding to average electron penetration depths of 19 nm, 56 nm, and 170 nm). The low-temperature CL spectrum of the unpolished, N-polarity face was taken at 10.6 kV. In the near-band-edge region, all the CL spectra from the Ga-polarity face show a narrow peak near 3.47 eV, ascribed to donor-bound exciton recombination, and several overlapping peaks at lower energy (3.1 eV to 3.4 eV), ascribed to defect-related levels or to donor-acceptor pair recombination. Functional curve-fitting analysis enabled deconvolution of the spectra into the sum of an asymmetric peak (the donor-bound exciton) and several symmetric Gaussian peaks (the lower energy, defect-related or donor-acceptor peaks). The linewidth of the donor-bound exciton peak decreased with increasing penetration depth, and also decreased on going from the polished-only to the polished+CAIBE region. The relative intensity of a defect-related peak at ≈3.325 eV showed a similar decreasing trend with increasing penetration depth or with CAIBE treatment. The LEECL results suggest that the thickness of the polishing damage layer is approximately 400 nm; the 200 nm CAIBE step is thus insufficient to completely remove the damage.
Photoreflectance Probing of Below Gap States in Gan/Algan High Electron Mobility Transitor Structures
Authors: Gaskill D. K. , Glembocki O. J. , Peres B. , Henry R. , Koleske D. , Wickenden A.
Published: April 2011

Optical Impedence Spectroscopy of GaN/AlGaN high electron mobility transistor structures (HEMTs) using photoreflectance exhibit a photoreflectance lags – the component of the modulated reflectance out of phase with the chopper – ranging from 0.1 to 0.5. Photoreflectance was performed using below gap pumping on various samples. Samples that do exhibit appreciable photoreflectance lag for above gap pumping show significantly enhanced photoreflectance signals for below gap pumping. Yet, samples that do not exhibit appreciable photoreflectance lag for above gap pumping do not exhibit a signal for below gap pumping. This implies that the photoreflectance phase lag is due to mid-gap trap states. At least 2 types of traps are found, above and below about 2.5 eV. This result means that that photoreflectance can be used as a probe of HEMT device quality.
Compositional Fluctuations in AlxGa1-xN Layers grown on 6H-SiC (0001) by Metal Organic Vapor Phase Epitaxy
Authors: Kröger R. , Einfeldt S. , Reitmeier Z. J. , Chierchia R. , Ryder P. , Hommel D. , Davis R. F.
Published: April 2011

The microstructural evolution of AlxGa1-xN films grown by metalorganic vapor phase epitaxy on 6H-SiC (0001) was studied by means of X-ray diffraction, atomic force microscopy and transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy. A significant spatial variation of composition was found in 100 nm thick layers the nature of which could be traced back to the initial stage of film formation. Upon nucleation two phases are formed: a wetting layer and isolated islands of high and low aluminum content, respectively. The observed results are discussed in terms of strain and growth rates.
Photoreflectance Characterization and Control of Defects in Gan by Etching with an Inductively Coupled Plasma
Authors: Glembocki O. J. , Gaskill D. K. , Prokes S. M. , Pearton S. W.
Published: April 2011

Photoreflectance (PR) is used to detect and characterize the electronic effects etch-induced defects in GaN that is exposed to an Ar or Ar/Cl inductively coupled plasma (ICP). Because of the sensitivity of PR we can follow the formation of etch-induced defects as a function of ion energies and densities. We show that at low RF powers, below 100W, the surface improves in electronic quality, but as the power is increased beyond 200W, etch-induced defects, are formed. The use of an Ar/Cl mixture plays a critical role in control of etch-induced defects.
Optical Characterization of High Quality GaN Produced by High Rate Magnetron Sputter Epitaxy
Authors: Park Minseo , Carlson E. , Chang Y. C , Muth J. F. , Bumgarner J. , Kolbas R. M. , Cuomo J. J. , Nemanich R. J.
Published: April 2011

The thick films of GaN were investigated using X-ray diffraction, micro-Raman spectroscopy and photoluminescence spectroscopy. The thick films of GaN were prepared on (0001) sapphire using high rate magnetron sputter epitaxy with growth rates as high as 10–60 m/min. The width of the X-ray rocking curve ((0002) reflection) for the sample produced by this method is ∼300 arc-sec. Only the allowed modes were observed in the polarized Raman spectra. The background electron concentration is lower than 3×1016 cm−3, which was determined from the Raman spectra. The phonon lifetime determined from Raman E2(2) mode was 1.6 ps, which is comparable to that of bulk single crystal GaN grown by sublimation (1.4 ps). The full-width-at-half-maximum of the near band-edge photoluminescence peak obtained at 77K is ∼100 meV.
Subpicosecond Luminescence Studies of Carrier Dynamics in Nitride Semiconductors Grown Homoepitaxially By MBE On GaN Templates
Authors: Garrett G. A. , Sampath A. V. , Collins C. J. , Semendy F. , Aliberti K. , Shen H. , Wraback M. , Fedyunin Y. , Moustakas T. D.
Published: April 2011

A new technique is presented that employs luminescence downconversion using an ultrashort gating pulse to enable the characterization of UV light emission from III-nitride semiconductors with subpicosecond temporal resolution. This technique also allows one to measure PL rise times and fast components of multiple decays in the subsequent time evolution of the PL intensity. Comparison of luminescence emission intensity and lifetime in GaN and AlGaN with ∼0.1 Al content grown homoepitaxially on GaN templates with the same quantities measured in heteroepitaxial layers grown on sapphire indicate significant improvement in the homoepitaxial layers due to reduction in dislocation density. Fast (<15 ps) initial decays in the AlGaN are attributed to localization associated with alloy fluctuations and subsequent recombination through gap states.
Lattice Location and Cathodoluminescence Studies of Ytterbium/Thulium Implanted 2H-Aluminium Nitride
Authors: Vetter U. , Reid M. F. , Hofsäss H. , Ronning C. , Zenneck J. , Dietrich M.
Published: April 2011

Lattice location studies of radioactive 169Yb ions, implanted at an energy of 60 keV into 2H-AlN at the on-line isotope separator ISOLDE at CERN, were performed using the emission channeling technique. The measurements, which yield a substitutional Al lattice site for the implanted ions, were recorded for annealing temperatures ranging from 293 K to 1273 K. After complete decay of 169Yb to 169Tm cathodoluminescence measurements were performed in the range 12 K – 300 K. The samples show a strong visible luminescence at 460 - 470 nm at room temperature, which is attributed to the 1D2−3F4 intra-4f electron transition of Tm3+. At 12 K the luminescence is dominated by transitions starting from the 1H6 multiplet. Time resolved as well as temperature dependent cathodoluminescence measurements are presented and discussed.

The lattice location as well as the time resolved cathodoluminescence measurements suggest that there is only one pronounced site of the implanted ions in the AlN lattice and that this is the substitutional aluminium site.
Molecular Beam Epitaxial Growth of AlN/GaN Multiple Quantum Wells
Authors: Wu Hong , Schaff William J. , Koley Goutam , Furis Madalina , Cartwright A. N. , Mkhoyan Karen A. , Silcox John , Henderson Walter , Alan Doolittle W. , Osinsky A. V.
Published: April 2011

AlN/GaN multiple quantum wells (MQWs) were grown on sapphire substrates by plasmaassisted molecular beam epitaxy. Growth temperature, III/V ratio, growth rate, and other growth parameters were optimized for the buffer layer and the MQWs, separately. The growth of AlN buffer was kept as Al-rich as possible while the formation of Al droplets was avoided. A GaN buffer layer was also tried but proved to be inferior to AlN buffer probably due to its larger surface roughness, higher dislocation density, and larger lattice mismatch with the AlN barrier layers in the MQWs. Very flat surfaces with a RMS roughness of 0.7nm were observed by atomic force microscopy (AFM) on the samples with both AlN buffer layer and 20 MQWs deposited under the optimized growth conditions. Abrupt interfaces and excellent periodicities of the MQWs were confirmed by X-ray diffraction (XRD) and reflectivity measurements with MQWs' satellite peaks clearly visible up to the 10th order. Room-temperature intense ultraviolet (UV) photoluminescence (PL) emission with wavelength in the range of 320–350nm was also observed from the MQWs with well width ranging from 1.0 to 1.5nm. These MQW structures can potentially be used for UV light emitters and quantum cascade lasers.
Growth and Characterization of Deep UV Emitter Structures Grown on Single Crystal Bulk AlN Substrates
Authors: Hu X. , Gaska R. , Chen C. , Yang J. , Kuokstis E. , Khan A. , Tamulaitis G. , Yilmaz I. , Shur M. S. , Rojo J. C. , Schowalter L. J.
Published: April 2011

We report on high Al-content AlGaN-based deep UV emitter structures grown over single crystal, slightly off c-axis (5.8 degrees) bulk AlN substrates. AlN/AlGaN multiple quantum well (MQW) structures with up to 50% of Al in the well material were grown by using low-pressure MOCVD and characterized by using X-ray, AFM, SEM and photoluminescence techniques. Two light sources, one at 213 nm wavelength for selective excitation of quantum well layers and another one at 193 nm to excite both wells and barriers, were exploited. A weak temperature dependence (from 8 K to 300 K) of the luminescence intensity and the absence of blue-shift of the luminescence peak with increasing excitation intensity pointed to a low density of localized states, in a good agreement with the X-ray data, which indicated very high quality of these MQW structures.

The most striking result was observation of stimulated emission at wavelength as short as 258 nm in Al0.5Ga0.5N/AlN MQWs grown on bulk AlN single crystals.
Properties of Surface Acoustic Waves in AlN And GaN
Authors: Deng Jianyu , Ciplys Daumantas , Bu Gang , Shur Michael , Gaska Remis
Published: April 2011

The surface acoustic wave velocities, electromechanical coupling coefficients, and the spatial distributions of both elastic displacement and electric potential have been calculated for various configurations of gallium nitride and aluminum nitride. The electromechanical coupling coefficient values of 0.13 % in GaN and 0.29 % in AlN have been predicted. The maximum electromechanical coupling coefficient values of 0.24 % at Euler angles (0, 54°, 90°) in GaN and 1.08 % at (0, 53°, 90°) in AlN have been found. For GaN layer-on- sapphire substrate structures, the SAW velocity and electromechanical coupling coefficient have been calculated as functions of layer thickness and acoustic wavelength. The experimentally measured values of the surface acoustic wave velocity and electromechanical coupling coefficient are in satisfactory agreement with the calculation results.
Indium distribution inside quantum wells: The effect of growth interruption in MBE
Authors: Sanchez A. M. , Ruterana P. , Kret S. , Dłużewski P. , Maciejewski G. , Grandjean N. , Damilano B.
Published: April 2011

Quantitative analysis of high resolution electron microscopy image has been carried out to measure the indium distribution inside InGaN/GaN quantum well. The analyzed samples were nominally grown with 15% indium composition by molecular beam epitaxy with interruptions during the InxGa1-xN layer growth. The strain distribution is not homogeneous inside the quantum wells, and indium rich clusters can be observed. Areas with almost no indium concentration were observed corresponding to the growth interruption. A comparison with samples grown by metalorganic chemical vapor deposition is attempted.
New UV Light Emitter Based on AlGaN Heterostructures with Graded Electron and Hole Injectors
Authors: Johnson M.A.L. , Long J.P. , Schetzina J. F.
Published: April 2011

New ultraviolet (UV) light emitting device structures address the problems of small carrier concentrations and large band-offsets in wide bandgap Aluminum Gallium Nitride (AlGaN) heterostructures through the use of graded epilayers for electron and hole injection. For light emission at 280–290 nm, a multiple-quantum-well separate confinement heterostructure (MQWSCH) employs a graded AlGaN structure for the injection of majority carriers from the metal-semiconductor contact layers into the spacecharge region of the pn-junction with a higher bandgap energy. Sample LED mesa devices were fabricated and have shown light emission of 289 nm under a forward bias of 12V (20mA). These results provide a ‘proof-of-concept’ for this new graded device structure which can be employed for the development of both UV-LEDs and laser diodes.
High Performance HFET Devices on Sapphire and SiC: Passivation with AlN
Authors: Bardwell Jennifer A. , Liu Ying , Webb James B. , Tang Haipeng , Rolfe Stephen J. , Lapointe Jean
Published: April 2011

AlGaN/GaN two dimensional electron gas (2DEG) heterostructures were grown by ammonia-MBE on sapphire and SiC substrates. Devices fabricated from these optimized HFET layers, with optically defined gates showed excellent characteristics, e.g. a maximum drain current density of 1.3 A/mm, maximum transconductance of 220 mS/mm, fT of 15.6 GHz and fMAX of 58.1 GHz was measured for devices with 0.9 μm gate length and 40 μm gate width. Shorter gate length devices exhibited higher frequency responses: fT of 68 GHz and fMAX of 125 GHz for 0.25 μm gate length and fT of 103 GHz and fMAX of 170 GHz for 0.15 μm gate length. However, these devices showed “current collapse” when subjected to load pull measurements. Current collapse was also observed in sequentially repeated DC measurements in the dark, both on sapphire and SiC substrates, although the degree of collapse varied greatly from one wafer to another. One method of reducing the current collapse was to apply a thin (100 - 6000 Å) magnetron sputtered AlN passivation layer (over the gates) or a 500 Å layer under the gates so that MISFET devices were obtained. The electrical characteristics of the passivated and unpassivated devices are discussed.
Physcial characterization of ultrathin high k dielectrics
Authors: Vandervorst W. , Brijs B. , Bender H. , Conard O. T. , Petry J. , Richard O. , Van Elshocht S. , Delabie A. , Caymax M. , De Gendt S.
Published: April 2011

Targeting very thin equivalent oxides (<1 nm) requires the deposition of (very) thin dielectrica onto silicon surfaces with minimal interfacial oxide. Typically, high-k dielectric layers are deposited using ALD or MOCVD with, at present, a prime emphasis on Hf-based high-k dielectrics, either as pure HfO2, as silicate or mixed with Al2O3. In some cases nitrogen is added to improve the high-temperature stability. Depending on the deposition conditions ALD as well as MOCVD show serious deficiencies in terms of film closure and material density for ultra thin (<3 nm) films. Various surface preparation methods and deposition conditions are used to improve the film quality. Detailed studies on the film growth and its evolution requires the use of many analytical methods such as Rutherford Backscattering Spectrometry, Low Energy Ion Scattering, Time-of-flight SIMS, (spectroscopic) ellipsometry and X-ray photoelectron spectroscopy. When trying to correlate the results in terms of film thickness, apparent discrepancies can be observed which relate to non-homogeneous growth and reduced material density.
In Situ Spectroscopic Approach to Atomic Layer Deposition
Authors: Frank Martin M. , Chabal Yves J. , Wilk Glen D.
Published: April 2011

There is great need for a mechanistic understanding of growth chemistry during atomic layer deposition (ALD) of films for electronic applications. Since commercial ALD reactors are presently not equipped for in situ spectroscopy, we have constructed a model reactor that enables single-pass transmission infrared spectroscopy to be performed in situ on a layer-by-layer basis. We demonstrate the viability of this approach for the study of aluminum oxide growth on silicon surfaces, motivated by alternative gate oxide applications. Thanks to submonolayer dielectric and adsorbate sensitivity, we can quantify oxide thicknesses and hydroxyl areal densities on thermal and chemical SiO2/Si(100) substrates. Methyl formation and hydroxyl consumption upon initial trimethylaluminum (TMA) reaction can also be followed. We verify that in situ grown Al2O3 films are compatible in structure to films grown in a commercial ALD reactor.
Characterization of Ruthenium and Ruthenium Oxide Thin Films deposited by Chemical Vapor Deposition for CMOS Gate Electrode Applications
Authors: Papadatos Filippos , Skordas Spyridon , Consiglio Steve , Kaloyeros Alain E. , Eisenbraun Eric
Published: April 2011

This study describes work carried out to date involving evaluation of the chemical, structural, and electrical performance of ruthenium (Ru) and ruthenium oxide (RuO2) films grown on SiO2 substrates employing metal organic chemical vapor deposition (MOCVD). Diethyl ruthenocene and oxygen were employed as reactant gases for this work, which was carried out using a 200mm wafer cluster tool. The films were characterized using cross-sectional scanning electron microscopy (CS-SEM), four-point resistance probe, x-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), x-ray diffraction (XRD), and energy dispersive spectrometry (EDS). Capacitance-voltage (C-V) measurements were also carried out to assess the work function of the deposited films. It was determined that both Ru and RuO2 phases possess near-bulk resistivity and low contamination levels. Importantly, it was observed that the film stoichiometry could be modulated by controlled changes of the processing conditions, and that pure Ru and RuO2 films can be deposited in an oxygen ambient. In order to assess thermal stability, the films were subsequently annealed in forming gas and oxygen ambients, and it was found that the film stability is dependent upon both the deposited phase and the annealing ambient. Results of PMOS gate electrode performance testing of CVD Ru films, has been carried out, and the results are similar to those previously reported for ruthenium-based films.
The Effect of SiGe Barriers on the Thermal Stability of Highly B-Doped Si Surface Layers
Authors: Thompson Phillip E. , Bennett Joe , Crosby Robert , Twigg Mark E.
Published: April 2011

We have investigated the use of low-temperature (320 °C) molecular-beam epitaxy (MBE) to form highly conductive, p+, ultra-shallow layers in Si. Although the as-grown B-doped Si is electrically active, in a practical application the doped layers may be exposed to high temperature during post-growth device processing. To minimize the B diffusion, we investigated the use of SiGe diffusion barrier layers. In this work we demonstrate there is less B redistribution with the SiGe diffusion barriers. The use of SiGe diffusion barriers may prove to be critical in the activation of B implants for the formation of ultra-shallow junctions.
Strained-Si-on-Insulator (SSOI) and SiGe-on-Insulator (SGOI): Fabrication Obstacles and Solutions
Authors: Taraschi Gianni , Pitera Arthur J. , McGill Lisa M. , Cheng Zhi-Yuan , Lee Minjoo L. , Langdo Thomas A. , Fitzgerald Eugene A.
Published: April 2011

Advanced CMOS substrates composed of ultra-thin strained-Si and SiGe-on-insulator were fabricated, combining both the benefits of high-mobility strained-Si and SOI. Our pioneering method employed wafer bonding of SiGe virtual substrates (with strained-Si layers) to oxidized handle wafers. Layer transfer onto insulating handle wafers can be accomplished using grind-etchback or delamination via implantation. Both methods were found to produce a rough transferred layer, but polishing is unacceptable due to non-uniform material removal across the wafer and the lack of precise control over the final layer thickness. To solve these problems, a strained-Si stop layer was incorporated into the bonding structure. After layer transfer, excess SiGe was removed using a selective etch process, stopping on the strained-Si. Within the context of ultra-thin SSOI and SGOI fabrication, this paper describes recent improvements including metastable stop layers, low temperature wafer bonding, and improved selective SiGe removal.
Electrical and Structural Characterization of HfO2 MIM Capacitors
Authors: Yang Fan , Kotecki David E.
Published: April 2011

Hafnium oxide is a promising dielectric for future microelectronic applications. HfO2 thin films (10–75nm) were deposited on Pt/SiO2/Si and quartz substrates by Pulsed DC magnetron reactive sputtering. Top electrodes of Pt were formed by e-beam evaporation through an aperture mask on the HfO2/Pt/SiO2/Si samples to create MIM capacitors. Various process conditions (Ar/O2 ratio, DC power, and deposition rate) and post-deposition annealing conditions (time and temperature) were investigated. The structure of the HfO2 films was characterized by X-ray diffraction (XRD) and the roughness was measured by a profilometer. The electrical properties were characterized in terms of their relative permittivity (εr(T) and εr(f)), and leakage behavior (I-V and I-t). The electrical measurements were performed over a temperature range from –5 to 200°C. For the best samples, the relative permittivity of HfO2 was found to be ∼27 after anneal and increased by 0.027%/°C with increasing temperature over the measured temperature range. At 25°C, leakage current density was below 10-8 A/cm2 at 1 volt. The optical bandgap was measured to be 5.4eV after anneal.
Oriented Growth of Thin Films of Samarium Oxide by MOCVD
Authors: Shalini K. , Shivashankar S. A.
Published: April 2011

Thin films of samarium oxide, Sm2O3, have been grown on Si(100) and fused quartz by low-pressure MOCVD using an adducted β-diketonate precursor developed in house. It is found that the nature of the film grown is strongly dependent on substrate temperature. As examined by X-ray diffraction, the films of Sm2O3 grown at lower temperatures (∼550°C) on fused quartz are cubic and display a random grain orientation, while they become highly oriented in the (111) direction as the growth temperature is increased (to 625°C). On Si(100), highly oriented films of cubic Sm2O3 are obtained at a substrate temperature of 625°C. When the growth temperature is raised, the phase changes to monoclinic. The morphology of the films grown on both quartz and Si(100) substrates has been studied by scanning electron microscopy and atomic force microscopy. The growth of strongly oriented Sm2O3 on the disordered surface of fused quartz may be interpreted as being driven by the minimization of surface energy.
Physical and Electrical Characterization of Hafnium Silicate Thin Films
Authors: Lysaght Patrick S. , Foran Brendan , Bersuker Gennadi , Larson Larry , Murto Robert W. , Huff Howard R.
Published: April 2011

Evaluation of physically thicker gate insulator materials with significantly higher dielectric constants (k = 10 – 25) as potential replacements for silicon dioxide, SiO2 (k = 3.9), and silicon oxynitride continues to be a focus of the semiconductor industry. The challenge is to provide a film with lower leakage current and with capacitance equivalent to < 1.0 nm SiO2 [1–4]. One such candidate material; metal-organic chemical vapor deposited (MOCVD) hafnium silicate, has been physically characterized by high resolution transmission electron microscopy (HRTEM) in plan view, as a blanket, uncapped film and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) in cross section following integration into capacitors and complementary metal oxide semiconductor (CMOS) transistors. Changes in the material microstructure associated with phase segregation and crystallization as a function of Hf silicate composition and rapid thermal anneal (RTA) temperature have been observed and a discussion of the segregation mechanisms is presented [5–8]. Also, various methods of incorporating nitrogen into bulk hafnium silicate films have been investigated and resultant transistor electrical performance data has been correlated with physical characterization for NH3 post deposition anneal (PDA) treatments at various temperatures.
Hrtem Investigation of Effect of Various Rare Earth Oxide Dopants on Epitaxial Zirconia High-K Gate Dielectrics
Authors: Kiguchi Takanori , Wakiya Naoki , Shinozaki Kazuo , Mzutani Nobuyasu
Published: April 2011

The effects of several rare earth oxide on the capacitance-voltage (C-V) characteristics and the SiO2 interlayer growth of ZrO2 based gate dielectrics were examined. The width of the hysteresis window of La2O3 stabilized ZrO2 (LaSZ) gate dielectric was only 0.2V, on the other hands, that of Sc2O3 stabilized ZrO2 (ScSZ) gate dielectric was 1.4V HRTEM analysis indicated that the growth of SiO2 interlayer of RSZ (R=Sm,Nd,La) gate dielectric was about 1nm, which was less than half of the ScSZ one. These results indicate the advantage of the ZrO2 gate dielectric doped with rare earth oxide composed of larger ionic radius cation.
Study of poly-Si/TaSiN/Pt structure for stacked capacitors
Authors: Letendu F. , Hugon M. C. , Voldoire O. , Agius B. , Vickridge I. , Berthier C. , Lameille J. M.
Published: April 2011

Due to its high oxidation resistance, TaSiN is a promising candidate as an electrically conductive barrier layer for integration of high permittivity oxides in advanced memory devices. In this work, we report on the properties of TaSiN thin films deposited by reactive magnetron sputtering of a TaSi2 target. We have mainly studied the influence of deposition pressure and power density on film properties (composition, density, resistivity). The oxidation resistance of TaSiN films has been investigated at typical conditions for crystallization of perovskite dielectrics. The as-deposited and annealed samples were characterized using Rutherford backscattering spectroscopy and nuclear reaction analysis for atomic composition and XPS for chemical bonding. To study oxidation resistance, films have been processed in 18O2. The concentration depth profiles of 18O was measured after thermal treatments via the narrow resonances of 18O(p,α)15N at 151 keV (fwhm=100eV). The different results suggest that a pressure of 0.5 Pa, a power density of 2.63W/cm2 and a gas flow ratio N2/Ar of 5% allow to perform TaSiN films with high density, low resistivity and good oxidation resistance.
Ferroelectric Oxide Single-Crystalline Layers by Wafer Bonding and Hydrogen/Helium Implantation
Authors: Radu Ionut , Szafraniak Izabela , Scholz Roland , Alexe Marin , Gösele Ulrich
Published: April 2011

Layer splitting by helium and/or hydrogen and wafer bonding was applied for the transfer of thin single-crystalline ferroelectric oxide layers onto different substrates. The optimum conditions for achieving blistering/splitting after post-implantation annealing were experimentally obtained for LiNbO3, LaAlO3, SrTiO3 single crystals and transparent PLZT ceramic. Under certain implantation conditions large area exfoliation instead of blistering occurs after annealing of as-implanted oxides. Small area single-crystal oxide layer transfer was successfully achieved.
Dielectric Studies of laser ablated Ca doped BaTiO3 thin films.
Authors: Victor P. , Ranjith, Asis Sarkar R. , Vinayak R. , Saha S. , Krupanidhi S. B.
Published: April 2011

Recently, there has been growing interest in Ca modified BaTiO3 structures due to their larger electro-optic coefficients for their use in optical storage of information over conventional BaTiO3 crystals. Barium Calcium Titanate (BCT) shows promising applications in advanced laser systems, optical interconnects and optical storage devices. BaTiO3 thin films of varied Ca (3 at. % - 15 at. %) doping were deposited using pulsed laser ablation (KrF excimer laser) technique over Pt/Si substrates. The stoichiometric and the compositional analysis were carried out using EDAX and SIMS. The dielectric studies were done at the frequency regime of 40 Hz to 100 kHz at different ambient temperatures from 200 K to 600 K. The BCT thin films exhibited diffuse phase transition, which was of a typical non lead relaxor behavior and had high dielectric constant and low dielectric loss. The phase transition for the different compositions of BCT thin films was near the room temperature, showing a marked departure from the bulk phase transition. The C - V and the hysteresis behavior confirmed the ferroelectric nature below the phase transition and paraelectric at the room temperature.
Hysteresis Offset in Stress Induced Polarization-Graded Ferroelectrics
Authors: Mantese J. V. , Schubring N. W. , Micheli A. L. , Thompson M. P. , Naik R. , Auner G. W. , Misirlioglu I. B. , Ban Z.-G. , Alpay S. P.
Published: April 2011

Polarization-graded ferroelectrics and their electrically active counterparts, graded ferroelectric devices (GFDs) and transpacitors has been achieved in a number ways, including a variation in the composition of the material, or impressing a temperature gradients across the structure. In this article, we report how these same devices can be formed from homogeneous ferroelectric films of lead strontium titanate by imposing stress gradients on the materials normal to their electrode surfaces. A qualitative description of asymmetric hysteresis behavior based on a modified Landau potential is provided.
Piezoelectric property investigation for sol-gel derived Bi4Ti3O12 thick films
Authors: Matsuda Hirofumi , Ito Sachiko , Iijima Takashi
Published: April 2011

Strongly (117)-oriented Bi4Ti3O12 (BIT) thin (300 nm in thickness) and thick (900 nm in thickness) films were successfully synthesized from chemical solution and the piezoelectric and ferrelectric properties were studied. The chemical solution of Bi-acetate and Ti-iso-propoxide dissolved in 2-methoxyethanol was spin-coated on Pt(111)/Ti/SiO2/Si(001) substrate, pyrolysed at 450–600 °C and annealed at 600 °C. On 300-nm-thick BIT thin film, Pt top electrodes were deposited through a metal mask by RF-sputtering. For longitudinal piezoelectric displacement measurement in partially unconstraint, 900-nm-thick BIT thick film, an array of disk-shape BIT capacitor cells with Pt top electrode layers standing on the Pt bottom electrode were fabricated by photolithography with the diameter of 80, 50, 30, 20 μm. To recover from plasma damage, post deposition annealing of 300-nm-thick BIT film and post lithograph annealing of 900-nm-thick BIT film were performed, respectively. Longitudinal piezoelectric displacement was measured directly from the Z-feedback and Z-error signals of an AFM piezoscanner head with application of ac electric field at 5 Hz and 1 kHz, respectively between the conductive cantilever tip contacted to the top Pt electrode and the bottom Pt electrode. By the removal of sidewalls of BIT, positive piezoelectric displacement response was measured. The maximum strain was about 0.1 % under bipolar drive (amplitude of 400 kV/cm or 4Ec). From the unipolar driven piezoelectric displacement, piezoelectric coefficient AFM-d33 was measured. The value of AFM-d33 increased to decreasing cell diameter and approached to a somewhat constant value of 12–13 pC/N. Considering the crystalline orientation, this value well corresponds to that of 20 pC/N which were reported previously in single crystal. The result of ferroelectric property measurement was rather contradictory. The values of remanent and saturated polarization Pr=20 and Psat=28 μC/cm2, respectively measured in 300-nm-thick BIT thin film were in good agreement with reported spontaneous polarization Ps=50 μC/cm2 along a-axis with the consideration of measured inclination angle of Ψ=58° between (200) and (117). In 900-nm-thick BIT thick film, on the other hand, measured values of Pr=6–7 μC/cm2 were much poorer than those of the thin film even with the consideration that measurement frequencies were 1 kHz in the thick film and 50 Hz in the thin film, although the films showed (117)-orientation. Measured piezoelectric response may reflect a specific single grain with favorable orientation in a cell, on the other hand, average value of ferroelectric property throughout a cell in the 900-nm-thick BIT thick film having mixed orientation of (117) and (020).
Novel Candidate of c-axis-oriented BLSF Thin Films for High-Capacitance Condenser
Authors: Kojima Takashi , Sakashita Yukio , Watanabe Takayuki , Kato Kazumi , Funakubo Hiroshi
Published: April 2011

c-axis-oriented SrBi2Ta2O9 thin films with various thickness ranging from 20–170 nm were epitaxially grown on (100)SrRuO3 (SrRuO3 is give for the pseudo-cubic unit cell)//(100)SrTiO3 substrates by metalorganic chemical vapor deposition (MOCVD). The relative dielectric constants of these films kept a constant value of about 55 with decreasing film thickness down to 20 nm. The capacitances of these films were almost independent of the applied electric field; change of capacitance for these films on applied electric field from 0 kV/cm to 100 kV/cm was within 0.017 % and tano value was within 1.3 %. The leakage current densities were constant against the film thickness on the order of 10-8 A/cm2 at 150 kV/cm. Surface flatness of these films were also almost the same irrespective of the film thickness. These characteristics are very attractive for high-capacitance condenser application. Therefore, c-axis-oriented BLSF thin films are novel candidates for high-capacitance condenser application having both bias-free and thickness independent characteristics together with the good surface smoothness.
Tuning the Tunability in Epitaxial Barium Strontium Titanate Film via Internal Stresses
Authors: Ban Z.-G. , Alpay S. P.
Published: April 2011

The tunability of epitaxial barium strontium titanate films is analyzed theoretically for the first time using a modified phenomenological Landau-Devonshire approach taking into account the formation of unusual ferroelectric phases that cannot form in bulk and single-crystal ceramics. It is shown that enhanced tunability can be achieved by adjusting the misfit strain especially in the vicinity of a structural phase transformation. The internal stresses in epitaxial films as characterized by the misfit strain can be controlled by changing the substrate material and/or varying the film thickness. The latter is due to the possibility of stress relaxation by formation of misfit dislocations that relieve epitaxial stresses at film growth temperature. Based on the thermodynamic model, we provide quantitative estimations of tunability of (001) Ba0.5Sr0.5TiO3 films on (001) LaAlO3 (LAO) and SrTiO3 (STO) as a function of film thickness. The analysis indicates that films on STO substrates should be as thick as possible in order to achieve optimum tunability. To obtain maximum tunability on LAO substrates, the thickness of films should be as close as possible to a critical film thickness (∼120 nm).
Long-Range Lattice Matching between (100)/(010) Bismuth-Layered Perovskite Structure and (101) Rutile Structure
Authors: Watanabe Takayuki , Saito Keisuke , Osada Minoru , Suzuki Toshimasa , Fujimoto Masayuki , Yoshimoto Mamoru , Sasaki Atsushi , Liu Jin , Kakihana Masato , Funakubo Hiroshi
Published: April 2011

a-/b-axis-oriented epitaxial bismuth layer-structured ferroelectric thin films were epitaxially grown on (101)-oriented oxide with rutile structure. The long-range lattice matching between the ferroelectric layer and the bottom rutile layer, particularly the number of rutile units facing one ferroelectric unit and the surface orientation, were discussed for (100)(010)Bi4Ti3O12//(101)TiO2 structure. Cross sectional transmission electron microscope analysis suggests that seven rutile units lie under one a-/b-axis-oriented Bi4Ti3O12 unit with lower misfit dislocation density comparing to eight rutile units by one Bi4Ti3O12 model. Based on this result, the surface orientation at the interface was simulated to give us an appropriate ion alignment model. The titanium layer in the (101)TiO2 structure is most likely to match with the oxygen layer in the a-/b-axis-oriented Bi4Ti3O12 film.
Seed Layers of the titania - lead oxide system
Authors: Muralt Paul , Hiboux Stephane , Cantoni Marco
Published: April 2011

Seed layers of (TiO2)x(PbO)y for the growth Pb(Z,Ti)O3 (PZT) thin films have been studied as a function of thickness and composition. The seed layers have been deposited by reactive in-situ sputter deposition at 530°C from two metal targets in a dynamic sputtering mode. The compositional variation was achieved by varying the relative fluxes. The PZT process was run with a limited lead excess resulting in pyrochlore nucleation on bare Pt electrodes. When the electrode was covered with a dense seed layer, perovskite was obtained everywhere. Ti rich seed layers yielded (111)-textured PZT even for very thin seed layers. Pb rich seed layers nucleated as PbTiO3{100} and gave rise to (100)-textured PZT. In an intermediate zone, the major perovskite orientations (100), (110) and (111) have been found together with pyrochlore for a small seed layer thickness. In this zone, the seed layer nucleates in islands leaving bare Pt spots. The intermediate region is a transition region between (111) seeds and (100) seeds. The latter exhibit diverging critical sizes at a given critical flux ratio, leading to large nuclei and bare Pt. Small perovskite(111) seed grains in the 10 to 100 nm range are found at equal lead oxide and titania flux.
Ferroelectric Properties of 15–20nm-Thick PZT Ultrathin Films Prepared by MOCVD
Authors: Nonomura H. , Fujisawa H. , Shimizu M. , Niu H. , Honda K.
Published: April 2011

We investigated ferroelectric properties of 20nm-thick epitaxial Pb(Zr,Ti)O3 (PZT) ultrathin films prepared on SrRuO3 (SRO)/SrTiO3 (STO) by metalorganic chemical vapor deposition (MOCVD). When SRO with terrace ledges was used as a bottom electrode, 20nm-thick PZT ultrathin films with ferroelectricity were successfully obtained. These PZT films exhibited saturated hysteresis loops with remanent polarizations (Pr) of 29–33 μC/cm2 and coercive electric fields (Ec) of 340–370 kV/cm. On the other hand, when PZT films were grown on SRO without terrace ledges, PZT films showed no saturated hysteresis loops because of large leakage current. The 15nm-thick PZT ultrathin film exhibiting unsaturated hysteresis loop was also obtained.