bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth and Fabrication of High Reverse Breakdown Heterojunction n-Gan: p-6H-Sic Diodes
Authors: Sampath A. V. , Bhattacharyya A. , Singh R. , Eddy C. R. , Lamarre P. , Stacey W. F. , Morris R. S. , Moustakas T. D. 
Published: April 2011

ABSTRACTWide band gap semiconductors are attractive for developing high power switching devices because of their ability to operate at both higher temperatures as well as higher frequencies than conventional Si. In this paper we report on the growth and fabrication of GaN/SiC np heterojunction diodes by depositing Si doped n-GaN films by plasma-assisted molecular beam epitaxy directly on SiC without the use of GaN or AlN buffers.Careful ex-situ and in-situ preparation of the Si terminated 6H- SiC surface was necessary to produce high quality diodes. Vertical circular diodes were fabricated with sizes varying from 200 microns to 1mm in diameter. Mesas were formed by ICP etching of the MBE deposited n-GaN layer using Cl2. A Ti/Al/Ni/Au metal stack was employed as an n-ohmic contact to the GaN layer and an Al/Ti/Au metal stack was employed as a backside p-ohmic contact to the 6H- SiC layer. The diodes were characterized by I-V and C-V measurements. The 1 mm diameter diodes exhibited almost ideal behavior under forward bias with an ideality factor of 1.6, and a reverse saturation current of 10–19 A/cm2. Under reverse bias, these devices were driven up to 1000 V with a measured leakage current of 5×10–7 A. and a dynamic resistance varying from 1010 to 109 ohms with increasing reverse bias. The built-in potential in these n-p heterojunctions was determined from C-V measurements to be 2.25 V. From these values we determined that the heterojunction is of Type II with conduction and valence bands offsets calculated to be 0.65 and 1.1 eV respectively.
Segregation effects and bandgap engineering in InGaN quantum-well heterostructures
Authors: Bulashevich Kirill A. , Karpov Sergey Yu. , Talalaev Roman A. , Evstratov Igor Yu. , Makarov Yuri N. 
Published: April 2011

ABSTRACTThe analysis of In surface segregation and its impact on the composition profile and light emission spectra of the InGaN single quantum well heterostructures grown by Metalorganic Vapor Phase Epitaxy (MOVPE) is carried out by coupled solution of the Poisson and Schrödinger equations. Effective methods of controlling the composition profile, indium predeposition and temperature ramping during the cap layer growth are considered in terms of surface segregation model. General trends in spectra transformation upon the forward bias variation and their correlations with the quantum well electronic structure are discussed.
AlGaN/GaN Metal-Oxide-Semiconductor Heterostructure Field-Effect Transistors (MOSHFETs) with the Delta-Doped Barrier Layer
Authors: Fan Z. Y. , Li J. , Lin J. Y. , Jiang H. X. , Liu Y. , Bardwell J. A. , Webb J. B. , Tang H. 
Published: April 2011

ABSTRACTThe fabrication and characterization of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with the δ-doped barrier are reported. The incorporation of the SiO2 insulated-gate and the δ-doped barrier into HFET structures reduces the gate leakage and improves the 2D channel carrier mobility. The device has a high drain-current-driving and gate-control capabilities as well as a very high gate-drain breakdown voltage of 200 V, a cutoff frequency of 15 GHz and a maximum frequency of oscillation of 34 GHz for a gate length of 1 μm. These characteristics indicate a great potential of this structure for high-power-microwave applications.
AlGaN/GaN Heterostructure Field-Effect Transistors with Back-Doping Design for High-Power Applications: High Current Density with High Transconductance Characteristics
Authors: Maeda Narihiko , Tsubaki Kotaro , Saitoh Tadashi , Tawara Takehiko , Kobayashi Naoki 
Published: April 2011

ABSTRACTElectron transport properties and DC device characteristics have been examined in the AlGaN/GaN heterostructure field-effect transistors (HFETs) with back-doping design that makes it possible to obtain high two-dimensional electron gas (2DEG) densities even for the devices with thin AlGaN barrier layers. In the back-doping design, an asymmetric double-heterostructure is employed, and donor atoms are doped not only in the surface-side AlGaN layer but also in the underlying AlGaN layer. In this structure, electrons are efficiently supplied also from the back-doped AlGaN barrier layer to the GaN channel and merged into a single 2DEG layer, with the help of the negative polarization charges at the heterointerface between the GaN channel and the underlying AlGaN barrier layer. By using back-doping design, very high 2DEG densities around 3×1013 cm−2 has been achieved in the Al0.3Ga0.7N/GaN HFET whose barrier layer (Al0.3Ga0.7N) is designed to be as thin as 120 Å. An HFET with the gate-length of 1.5 μm has exhibited a high current density of 1.2 A/mm and a high transconductance of 200 mS/mm, which is ascribed to high 2DEG densities and thin barrier layers in these devices. HFETs with the back-doping design are thus promising for high-power applications.
Effect of Al-content and Post Deposition Annealing on the Electrical Properties of Ultra-thin HfAlxOy Layers
Authors: Carter R. J. , Tsai W. , Young E. , Caymax M. , Maes J. W. , Chen P. J. , Delabie A. , Zhao C. , DeGendt S. , Heyns M. 
Published: April 2011

ABSTRACTScaled HfAlxOy/SiO2 stacks down to 1.5 nm EOT have been achieved. Although the addition of Al to the HfO2 matrix can be beneficial, it is observed that the benefit of using a Hf-aluminate is compromised if the film has a high Al-content. This is observed in terms of a dielectric constant close to that of pure Al2O3 (∼ 9) and a large amount of negative fixed charge in the film (∼ 1012 cm-2). Using oxygen post deposition anneals we have been able to reduce flatband voltage shifts associated with fixed charge as well as CV hysteresis. In terms of scaling, the benefit of using a high-k material is compromised if a SiO2 layer is also present in the gate stack. Therefore, it is necessary to perform an O2 PDA at moderate temperatures or in low O2 partial pressures in order to control the thickness of the interfacial oxide layer.
2D Dopant Profiling for Advanced Process Control
Authors: Wang Xiang-Dong , Xie Qianghua , Hooker Joe , Lu Shifeng , Lee J. J. , Tobin Phil , Liu Wei , Cross Linda 
Published: April 2011

ABSTRACTAs the CMOS device dimensions continue to shrink, it is more and more critical to control the process parameters during mass production of advanced VLSI chips in order to achieve high yield and profitability. 2D dopant characterization is one of the critical techniques to resolve manufacturing excursions. A quick access to dopant distribution, especially precise delineation of p-n junction would readily provide critical information for many manufacturing issues, as well as device design and process development. Here we present our approaches to some of those issues with available techniques. The main techniques we used are dopant selective etching (DSE) and scanning probe microscopy based electrical measurements including scanning capacitance microscopy (SCM) and scanning spread resistance microscopy (SSRM). These techniques provided complementary results and showed strengths in solving different issues. We have successfully delineated junction of CMOS devices with 0.13 μm technology with source/drain extensions. Other applications, including diode leakage, well-well isolation, and buried layer delineation with the combination of these methods are presented.
SiGe pMOSFETs Fabricated on Limited Area SiGe Virtual Substrates
Authors: Waite Andrew , Straube Urs , Lloyd Neil , Croucher Sally , Teng Tang Yue , Rong Bifeng , Evans Alan , Grasby Tim , Whall Terry , Parker Evan 
Published: April 2011

ABSTRACTSilicon germanium pMOSFETs with channel lengths down to 0.4m have been fabricated on limited area silicon germanium virtual substrates. The devices have a 5nm thick Si0.3Ge0.7 active layer grown by MBE on top of relaxed Si0.7Ge0.3 virtual substrate. Virtual substrates were grown on top of 10μm square silicon pillars defined by etching trenches around their perimeter into the original silicon substrate. This limits the area of the growth zone, which in turn promotes the relaxation of the virtual substrate. Electrical measurements on 2μm long channel devices show that the maximum mobility in the strained SiGe devices is 211cm2V-1cm-1, compared to 104cm2V-1cm-1 for silicon reference devices. This increase in hole mobility increases the current drive of 0.4m devices measured at Vgt=-2V, Vds=-2.5V from 154μA/m to 192μA/μm.
Effect of Nature of the Precursor on Crystallinity and Microstructure of MOCVD-Grown ZrO2 Thin Films
Authors: Dharmaprakash M. S. , Shivashankar S. A. 
Published: April 2011

ABSTRACTIn the present work, we report the deposition of zirconia thin films on Si(100) at various substrate temperatures by low-pressure metalorganic chemical vapor deposition (MOCVD). Three different zirconium complexes, viz., tetrakis(2,4-pentadionato)zirconium(IV), [Zr(pd)4], tetrakis(2,2,6,6-tetramethyl-3,5-heptadionato)zirconium(IV), [Zr(thd)4], and tetrakis(t-butyl-3-oxo-butanoato)zirconium(IV), [Zr(tbob)4] are used as precursors. The relationship between the molecular structures of the precursors and their thermal properties, as examined by TG/DTA is presented. The films deposited using these precursors have distinctly different morphology, though all of them are of the cubic phase. The films grown from Zr(thd)4 are well crystallized, showing faceted growth at 575°C, whereas the films grown from Zr(pd)4 and Zr(tbob)4 are not well crystallized, and display cracks. These differences in the observed microstructure may be attributed to the different chemical decomposition pathways of the precursors during the film growth, which influence the nucleation and the growth processes. This is also evidenced by the different kinetics of growth from these three precursors under otherwise identical CVD conditions. The details of thin film deposition, and film microstructure analysis by XRD and SEM is presented. The dielectric behavior of the films deposited from different precursors, as studied by C-V measurements, are compared.
Growth and Physical Properties of MOCVD-Deposited Hafnium Oxide Films and Their Properties on Silicon
Authors: Van Elshocht S. , Caymax M. , De Gendt S. , Conard T. , Pétry J. , Claes M. , Witters T. , Zhao C. , Brijs B. , Richard O. , Bender H. , Vandervorst W. , Carter R. , Kluth J. , Daté L. , Pique D. , Heyns M. M. 
Published: April 2011

ABSTRACTThis paper discusses metal organic chemical vapor deposited (MOCVD) HfO2 layers using tetrakis(diethylamido)hafnium (TDEAH) as precursor. We have studied the influence of the starting surface and deposition temperature on the growth kinetics and physical properties of the HfO2 layers. Important characteristics such as crystalline state, density, and organic contamination in the layers were found to be dependent on these parameters.Typical for this deposition process is the formation of an interfacial layer underneath the high-k layer. Its composition and thickness, affecting scaling of the equivalent oxide thickness, are shown to be closely related to the HfO2 process parameters mentioned above.Finally, we will show electrical results for HfO2/polySi gate stacks indicating the effect for deposition temperature.
Effectiveness of Plasma Nitrided Silicon Oxynitride as a Barrier Layer between High k Materials and Si Substrates
Authors: Lai Yi-Sheng , Chen J. S. 
Published: April 2011

ABSTRACTIn this work, low temperature (300 – 450°C) plasma nitridation was conducted using N2O and NH3 atmosphere to produce an ultrathin SiOxNy layer. The bonding structure, distribution, and quantity of nitrogen and their effects on the growth kinetic of SiOxNy layers are studied by X-ray photoelectron spectroscopy (XPS). It is found that nitrogen atoms pile at the SiOxNy/Si interface at the very beginning of plasma N2O and NH3 nitridation. Due to the lack of additional Si source and low diffusivity of O or N atoms at low temperature, plasma nitridation will form a self-limited growth of SiOxNy layer. Thermal stability of the interlayer between ultrathin Ta2O5 films on bare Si, plasma N2O nitrided Si, and plasma NH3 nitrided Si is also studied.
Physical-Chemical Evolution upon Thermal Treatments of Al2O3, HfO2 and Al/Hf Composite Materials Deposited by ALCVD™
Authors: Crivelli B. , Alessandri M. , Alberici S. , Cazzaniga F. , Dekadjevi D. , Maes J. W. , Ottaviani G. , Pavia G. , Queirolo G. , Santucci S. , Zanderigo F. 
Published: April 2011

ABSTRACTThis paper presents a systematic investigation of thermal stability of high-k materials deposited on RCA cleaned wafers by ALCVD™ in an ASM Pulsar™ 2000 reactor. Physical-chemical evolution of Al2O3, HfO2 and Al/Hf composite materials (nanolaminate and aluminates) was studied considering two types of thermal treatments: quenched vacuum anneals from 300°C to 900°C and furnace atmospheric processes in N2 or O2 at 850°C and 900°C. Material crystallization and changes in film structure were studied by means of TEM, XRD, XRR, XRF, RBS and TOF-SIMS. Non-contact electrical measurements were used to detect modification in EOT and fixed charge. Al2O3 was found still amorphous at 900°C. Not so for HfO2 that crystallized in monoclinic phase at a temperature between 300–400°C. Crystallization temperature and possible phase separation of Al/Hf composite materials were found to be a function of Al2O3 content and film type. In most of these samples, however, a chemical evolution was detected in addition to the above reported crystallization phenomena. All the achieved results demonstrate that depending on thermal treatment conditions, ALCVD™ high-k stability does not only concern phase transition effects but also a transformation of the “SiO2/high-k” system into “doped-SiO2/silicate” stack.
Influence of Substrate Temperature During Sputter Deposition on the Subsequent Formation of Titanium Disilicide
Authors: Özcan A. S. , Ludwig K. F. , Cabral C. , Lavoie C. , Harper J. M. E. 
Published: April 2011

ABSTRACTWe examine how the substrate temperature during Ti film sputter deposition influences the subsequent texture formation in TiSi2 thin films. Titanium films of 32 nm thickness were sputtered onto Si(001) at elevated substrate temperatures varying between 100 °C and 900 °C. After the depositions, in situ x-ray diffraction (XRD) measurements were performed to study the thin film reactions in real time, as the samples were annealed. The XRD results show that the substrate temperature significantly influences the texture of the initial Ti film as well as the texture of the resulting C54-phase TiSi2. The preferred Ti orientation gradually changes from (002) to (101) fiber texture as the deposition temperature increases up to 500 °C. Films deposited at 600 °C transformed into the C49 phase during deposition while films deposited at 700 °C and higher temperatures transformed into the C54 phase during deposition. The series of deposited films was annealed up to 1000 °C in He to complete the C54 phase formation while monitoring the texture evolution in situ using a position sensitive x-ray detector. The XRD results show that the final C54 phase texture changes from a dominant (311) orientation normal to the substrate to a (010) orientation for substrate temperatures between 600 °C and 700 °C. The C49-C54 phase transformation temperature is also lowered for these deposition temperatures. Ex situ pole figure analysis of the film deposited at 700 °C confirms the dominant C54 (010) texture and shows an in-plane orientation with C54 [001] ∥ Si [110]. For substrate temperatures between 800 °C and 900 °C, the C54 texture changes dramatically. In this case, θ - 2 θ scans do not show a preferred C54 orientation, but pole figure analysis indicates weak inplane orientations.
First-principles Study of Electronic and Dielectric Properties of ZrO2 and HfO2
Authors: Zhao Xinyuan , Vanderbilt David 
Published: April 2011

ABSTRACTUsing density-functional theory with ultrasoft pseudopotentials, we previously investigated the structural and electronic properties of the low-pressure (cubic, tetragonal, and monoclinic) phases of ZrO2 and HfO2, in order to elucidate phonon modes, Born effective charge tensors, and especially the lattice dielectric response in these phases. We now extend this previous work by carrying out similar calculations on the two high-pressure orthorhombic phases, and by providing density-of-states and band-gap information on all polymorphs. Our results show that the electronic structures and dielectric responses are strongly phase-dependent. In particular, the monoclinic phases of ZrO2 and HfO2 are found to have a strongly anisotropic dielectric tensor and a rather small orientational average () compared to the two other low-pressure phases. Our calculations show that is even smaller in the orthorhombic phases.
Structural Quality And Electrical Behavior Of Epitaxial High-κ Y2O3 / Si(001)
Authors: Vellianitis G. , Apostolopoulos G. , Dimoulas A. , Argyropoulos K. , Mereu B. , Scholz R. , Alexe M. , Hooker J. C. 
Published: April 2011

ABSTRACTY2O3 thin films were grown directly on Si (001) by MBE and annealed in-situ under UHV at various annealing temperatures. The samples were investigated in-situ by RHEED and ex-situ by HRTEM. A 7 to 15 Å thick non-uniform interfacial amorphous layer is observed in the as-grown sample. After annealing at 490°C under UHV for 30 minutes the amorphous layer is reduced and a sharp Y2O3/Si interface is obtained. At higher annealing temperatures, YSi2 islands start to form at the Y2O3/Si interface. I-V measurements performed on generic MIS structures show that the annealed samples exhibit higher leakage current density than the as-grown sample, due to reduction of the wide band gap interfacial layer. Leakage current densities in annealed samples remain below 1A/cm2, which is acceptable for future high-κ transistor fabrication.
Electro-optic Mach-Zehnder modulators with polycrystalline BaTiO3 thin films on MgO
Authors: Petraru A. , Schubert J. , Schmid M. , Trithaveesak O. , Buchal Ch. 
Published: April 2011

ABSTRACTThe optical and electro-optical properties of epitaxially grown thin films of ferroelectric BaTiO3 on MgO substrates have been established and high quality Mach-Zehnder waveguide modulators have been demonstrated. As a next step towards the integration of ferroelectric thin films on different substrates, we have modified the growth conditions by lowering the growth temperature to study polycrystalline, but still highly transparent BaTiO3 (BTO) films. Polycrystalline BTO on MgO substrates has been grown by pulsed laser deposition (PLD). The growth temperature was reduced from 800 °C to 400 °C at an oxygen pressure of 2×10-3 mbar. Although polycrystalline, the BTO is still birefringent with no= 2.32 and ne = 2.30. Ridge waveguides have been formed by ion beam etching. The estimated waveguide propagation loss is 4 dB/cm at 633 nm. Electro-optic Mach-Zehnder modulators have been realized. Using 3 mm long electrodes with a spacing of 10 μm, a Vπ voltage of 14 V was obtained at 633 nm wavelength. This is half of the observed effective electro-optic coefficient measured at epitaxial BTO films. At 1.5 μm wavelength similar results were observed.
Fabrication and Characterization of Lead Silicate Doped PZT Thin Films
Authors: Karasawa Junichi , Hamada Yasuaki , Ohashi Koji , Kijima Takeshi , Natori Eiji , Shimoda Tatsuya 
Published: April 2011

ABSTRACTThe crystal structure, surface morphology and electrical properties of PbSiOx (PSO) doped Pb(Zr,Ti)O3 (PZT) thin films were systematically investigated. The starting solutions of PSO-doped PZT were prepared by mixing sol-gel solutions of PZT and PSO. RTA-calcined thin films were crystallized by means of an oxygen partial pressure controlled post-annealing process. After the calcining process, lightly doped PZT thin films containing an amount of PSO dopant less than 1.0 at.% exhibit (111)-preferred orientation, and fine grains having a diameter of 50 nm and column-like structure. As the amount of PSO dopant is increased to 5.0 at.%, the (111) peaks becomes obscure and the (100) peaks together with the minor (110) peaks becomes dominant. The column-like structure changes into a plate-like structure having coarse grains whose diameter exceeds 500 nm. Further increasing the level of PSO dopant to 20.0 at.% causes the appearance of a pyrochlore phase having an extremely smooth surface without apparent grains. On the other hand, after the post-annealing process, the pyrochlore phase seen in the heavily doped PZT remarkably disappears, replaced by a perovskite phase together with PSO. The remnant polarization (Pr) gradually decreases as the amount of PSO dopant increases. The break down voltage, fatigue, imprint and other reliability parameters are improved within the proper doping range.
Growth of Zr Substituted Barium Titanate Thin Films from the Vapor Phase
Authors: Ganster R. , Hoffmann-Eifert S. , Waser R. 
Published: April 2011

ABSTRACTWe report on the growth of Ba(Ti1-xZrx)O3 thin films on Pt(111) / TiO2 / SiO2 / Si substrates by means of metal-organic chemical vapor deposition (MOCVD) using liquid precursors. The MOCVD system consists of an AIXTRON AIX-200 horizontal reactor with a TriJet® vaporizer. In the multi-source injection system the different single element precursor solutions were introduced separately in a pulse mode. The focus of our investigations lies on the correlation between processing conditions, growth rate, and film properties, namely stoichiometry, crystal structure, and surface morphology. Dense, polycrystalline Ba(Ti0.63Zr0.37)O3 films were successfully grown on platinum coated silicon substrates at temperatures around 630°C.
Parametric Optimization of a Sol-Gel Process for the Synthesis of Highly-Oriented (Pb, Ba)TiO3 Thin Films
Authors: Yang Wein-Duo , Pillai Suresh C. , Boland Stacey W. , Haile Sossina M. 
Published: April 2011

ABSTRACTA sol-gel process incorporating lead acetate trihydrate, barium acetate and titanium isopropoxide as precursors, acetylacetone as a chelating agent, and ethylene glycol as a solvent was used to prepare solid solution (Pb0.5,Ba0.5)TiO3. Water content, annealing temperature and heating rate were varied and the resulting effects on material properties were studied using TGA/DSC, FTIR, FESEM and X-ray diffraction. Crystallization of the perovskite structure occurred at a temperature as low as 450°C. Thin films were prepared by spin coating on (100) MgO using the optimized precursor sol. Pyrolysis and anneal temperatures were varied and the resultant film properties investigated. The pyrolysis temperature used to dry the film was found to strongly affect orientation. Under optimized conditions, highly oriented films were obtained at a crystallization temperature of 600°C.
Development of Improved Precursors for the MOCVD of Bismuth Titanate
Authors: Williams Paul A. , Jones Anthony C. , Tobin Neil L. , Marshall Paul A. , Chalker Paul R. , Davies Hywel O. , Smith Lesley M. 
Published: April 2011

ABSTRACTBismuth titanate thin films have been grown by liquid injection MOCVD using Bi(mmp)3 in combination with the new Ti precursors Ti(OPri)2(mmp)2 and Ti(mmp)4 (mmp = OCMe2CH2OMe). Films were grown on Si(100) substrates over the temperature range 300 – 600°C, and were shown to consist predominantly of the Bi4Ti3O12 phase at substrate temperatures > 500°C.