Growth and fabrication of AlGaN/GaN HEMT based on Si(1 1 1) substrates by MOCVD

AlGaN/GaN high electron mobility transistor (HEMT) hetero-structures were grown on the 2-in Si (1 1 1) substrate using metal-organic chemical vapor deposition (MOCVD). Low-temperature (LT) AlN layers were inserted to relieve the tension stress during the growth of GaN epilayers. The grown AlGaN/GaN HEMT samples exhibited a maximum crack-free area of 8 mm×5 mm, XRD GaN (0 0 0 2) full-width at half-maximum (FWHM) of 661 arcsec and surface roughness of 0.377 nm. The device with a gate length of 1.4 μm and a gate width of 60 μm demonstrated maximum drain current density of 304 mA/mm, transconductance of 124 mS/mm and reverse gate leakage current of 0.76 μA/mm at the gate voltage of −10 V.     

Crystalline orientation dependence of electrical properties of Mn Germanide/Ge(1 1 1) and (0 0 1) Schottky contacts

We have investigated the crystalline orientation dependence of the electrical properties of Mn germanide/Ge(1 1 1) and (0 0 1) Schottky contacts. We prepared epitaxial and polycrystalline Mn₅Ge₃ layers on Ge(1 1 1) and (0 0 1) substrates, respectively. The Schottky barrier height (SBH) estimated from the current density-voltage characteristics for epitaxial Mn₅Ge₃/Ge(1 1 1) is as low as 0.30 eV, while the SBH of polycrystalline Mn₅Ge₃/Ge(0 0 1) is higher than 0.56 eV. On the other hand, the SBH estimated from capacitance-voltage characteristics are higher than 0.6 eV for both samples. The difference of these SBHs can be explained by the local carrier conduction through the small area with the low SBH regions in the epitaxial Mn₅Ge₃/Ge(1 1 1) contact. This result suggests the possibility that the lowering SBH takes place due to Fermi level depinning in epitaxial germanide/Ge(1 1 1) contacts.     

Solid phase epitaxial growth of Dy-germanide films on Ge(0 0 1) substrates

Dy thin films are grown on Ge(0 0 1) substrates by molecular beam deposition at room temperature. Subsequently, the Dy film is annealed at different temperatures for the growth of a Dy-germanide film. Structural, morphological and electrical properties of the Dy-germanide film are investigated by in situ reflection high-energy electron diffraction, and ex situ X-ray diffraction, atomic force microscopy and resistivity measurements. Reflection high-energy electron diffraction patterns and X-ray diffraction spectra show that the room temperature growth of the Dy film is disordered and there is a transition at a temperature of 300-330 °C from a disordered to an epitaxial growth of a Dy-germanide film by solid phase epitaxy. The high quality Dy₃Ge₅ film crystalline structure is formed and identified as an orthorhombic phase with smooth surface in the annealing temperature range of 330-550 °C. But at a temperature of 600 °C, the smooth surface of the Dy₃Ge₅ film changes to a rough surface with a lot of pits due to the reactions further.     

Performance enhancement in Ge pMOSFETs with <1 0 0> orientation fabricated with a Si-compatible process flow

The electrical characterization of Ge pMOSFETs having <1 1 0> and <1 0 0> orientations with gate lengths of 3 μm have been demonstrated with a Si-compatible process flow. Employment of <1 0 0> orientation in Ge pMOSFETs without incorporation of strain provided ∼10% enhancement in effective hole mobility and drive current when compared to <1 1 0> oriented regular transistors. In this fabrication technology, the effective hole mobility improves from 190 cm²/V s for <1 1 0> devices to 210 cm²/V s for the <1 0 0> oriented Ge devices at room temperature, which is ∼2 times the hole mobility of Si pFET devices. This study also presents first time investigation of post metallization anneal (PMA) at 350 °C in H₂ ambient for <1 0 0> Ge pMOSFETs. The overall performance of the devices has been enhanced by 15% after performing PMA. It is likely attributed to a strong decrease of D_it, improving the transistor performance. These results indicate that the <1 0 0> Ge pMOSFETs could be a viable candidate for future low voltage high speed CMOS applications.     

PAMBE growth of (1 1 2¯ 2)-oriented GaN/AlN nanostructures on m-sapphire

We report on the plasma-assisted molecular-beam epitaxial growth of (1 1 2¯ 2)-oriented GaN/AlN nanostructures on (1 1¯ 0 0) m-plane sapphire. Moderate N-rich conditions enable to synthesize AlN(1 1  2) directly on m-sapphire, with in-plane epitaxial relationships [1 1 2¯ 3¯]_AlN∥[0 0 0 1]_sapphire and [1  0 0]_AlN∥[1 1 2¯ 0]_sapphire. In the case of GaN, a Ga-excess of one monolayer is necessary to achieve two-dimensional growth of GaN(1 1 2¯ 2). Applying these growth conditions, we demonstrate the synthesis of (1 1 2¯ 2)-oriented GaN/AlN quantum well structures, showing a strong reduction of the internal electric field. By interrupting the growth under vacuum after the deposition of few monolayers of GaN under slightly Ga-rich conditions, we also demonstrate the feasibility of quantum dot structures with this orientation.     

H2S molecular beam passivation of Ge(0 0 1)

A fundamental issue regarding the introduction of high-mobility Ge channels in CMOS circuits is the electrical passivation of the interface with the high-k gate dielectric. In this paper, we investigate the passivation of p-Ge(0 0 1) using molecular H₂S. The modification of the semiconductor surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. MOS capacitors are fabricated to extract interface state density, and finally we demonstrate the efficiency of the passivation scheme using a combination with an ultra thin Al interlayer.     

Formation speed of atomically flat surface on Si (1 0 0) in ultra-pure argon

The flattening speed of the low temperature atomically flattening technology is evaluated in order to apply atomically flat surface of (1 0 0) orientation on large-diameter silicon wafers to the LSI manufacturing. The atomically flatness of the whole surface of wafers with the diameter of 200 mm can be obtained after annealing at 800 °C or above. The process time required to obtain the atomically flatness for the whole wafer surface can be shortened by increasing the annealing temperature as well as by increasing the gas flow rate. With the off angle of 0.50° or below, it was found that only mono-atomic steps appear on the surfaces and the flattening speed is independent of the off angle. These indicate that the process speed is independent of the migration speed of Si atoms on the surface, but depends on the gas replacement efficiency near the Si surface in this technique.     

Yttrium silicide formation and its contact properties on Si(1 0 0)

Yttrium silicide formation and its contact properties on Si(1 0 0) have been studied in this paper. By evaporating a yttrium metal layer onto Si(1 0 0) wafer in conventional vacuum condition and rapid thermal annealing, we found that YSi_2-x begins to form at 350 °C, and is stable to 950 °C. Atomic force microscopy characterization shows the pinholes formation in the formed YSi_2-x film. By current-voltage measurement, the Schottky barrier height (SBH) of YSi_2-x diode on p-type Si(1 0 0) was shown to be between 0.63 and 0.69 eV for annealing temperature from 500 to 900 °C. By low temperature current-voltage measurement, the SBH of YSi_2-x diode on n-type Si(1 0 0) was directly measured and shown to be 0.46, 0.37, 0.32 eV for annealing temperature of 500, 600, and 900 °C, respectively, and possibly even lower for annealing at 700 or 800 °C.     

In situ atomic layer deposition and synchrotron-radiation photoemission study of Al2O3 on pristine n-GaAs(0 0 1)-4 × 6 surface

This work presents the in situ reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM) and synchrotron-radiation photoemission studies for the morphological and interfacial chemical characterization of in situ atomic layer deposited (ALD) Al₂O₃ on pristine molecular beam epitaxy (MBE) grown Ga-rich n-GaAs (1 0 0)-4 × 6 surface. Both the RHEED pattern and STM image demonstrated that the first cycle of ALD-Al₂O₃ process reacted immediately with the GaAs surface. As revealed by in situ synchrotron-radiation photoemission studies, two types of surface As atoms that have excess in charge in the clean surface served as reaction sites with TMA. Two oxidized states were then induced in the As 3d core-level spectra with chemical shifts of +660 meV and +1.03 eV, respectively.     

Epitaxial growth of Dy2O3 thin films on epitaxial Dy-germanide films on Ge(0 0 1) substrates

Ultra-thin films of Dy are grown on Ge(0 0 1) substrates by molecular beam deposition near room temperature and immediately annealed for solid phase epitaxy at higher temperatures, leading to the formation of DyGe_x films. Thin films of Dy₂O₃ are grown on the DyGe_x film on Ge(0 0 1) substrates by molecular beam epitaxy. Streaky reflection high energy electron diffraction (RHEED) patterns reveal that epitaxial DyGe_x films grow on Ge(0 0 1) substrates with flat surfaces. X-ray diffraction (XRD) spectrum suggests the growth of an orthorhombic phase of DyGe_x films with (0 0 1) orientations. After the growth of Dy₂O₃ films, there is a change in RHEED patterns to spotty features, revealing the growth of 3D crystalline islands. XRD spectrum shows the presence of a cubic phase with (1 0 0) and (1 1 1) orientations. Atomic force microscopy image shows that the surface morphology of Dy₂O₃ films is smooth with a root mean square roughness of 10 Å.     

Behavior of (1 1 1) grains during the thermal treatment of copper film studied in situ by electron back-scatter diffraction

An annealed Cu blanket film was investigated in situ at high temperature using electron back-scatter diffraction (EBSD). The primary aim of the experiment was to study the changes in the (1 1 1) texture in the Cu film where the microstructure was already stabilized by previous annealing treatment. Two separate investigations were carried out at the same location of the film for better statistical reliability of data. It was found that the (1 1 1) planes got increasingly inclined to the specimen surface with increasing temperature. Additionally, a change in the strength of {1 1 1}〈1 1 0〉 and {1 1 1}〈1 1 2〉 texture components was observed with increasing temperature. Absence of these phenomena in freestanding Cu film indicates the impact of substrate on the behavior of (1 1 1) grains. The effect of substrate on the peculiar behavior of the (1 1 1) grains has been explained by a model which describes the contribution of both dislocations and diffusion to the observed phenomenon. The tilting of the (1 1 1) grains is discussed with reference to the recently reported Bauschinger effect in the Cu films.     

Study of Ni/Si(1 0 0) solid-state reaction with Y addition

The characteristics of Ni/Si(1 0 0) solid-state reaction with yttrium (Y) addition are studied in this paper. Film stacks of Ti(20 nm)/TiN(40 nm)/Ni(8 nm)/Y(4 nm)/Ni(8 nm)/Si(1 0 0) and Ti(20 nm)/TiN(40 nm)/Ni(7 nm)/Y(6 nm)/Ni(7 nm)/Si(1 0 0) were prepared by physical vapor deposition. After solid-state reaction between metal films and Si was performed by rapid thermal annealing, various material analyses show that NiSi forms even with the addition of Y, and Ni silicidation is accompanied with Y diffusion in Ni film toward its top surface. The electrical characteristic measurements reveal that no significant Schottky barrier height modulation with the addition of Y occurs.     

Growth and structural properties of crystalline LaAlO3 on Si (0 0 1)

Crystalline LaAlO₃ was grown by oxide molecular beam epitaxy (MBE) on Si (0 0 1) surfaces utilizing a 2 ML SrTiO₃ buffer layer. This SrTiO₃ buffer layer, also grown by oxide MBE, formed an abrupt interface with the silicon. No SiO₂ layer was detectable at the oxide-silicon interface when studied by cross-sectional transmission electron microscopy. The crystalline quality of the LaAlO₃ was assessed during and after growth by reflection high energy electron diffraction, indicating epitaxial growth with the LaAlO₃ unit cell rotated 45° relative to the silicon unit cell. X-ray diffraction indicates a (0 0 1) oriented single-crystalline LaAlO₃ film with a rocking curve of 0.15° and no secondary phases. The use of SrTiO₃ buffer layers on silicon allows perovskite oxides which otherwise would be incompatible with silicon to be integrated onto a silicon platform.     

Study of GaAsBi MOVPE growth on (1 0 0) GaAs substrate under high Bi flow rate by high resolution X-ray diffraction

GaAsBi alloy was grown on (1 0 0) GaAs substrate by metalorganic vapour phase epitaxy. GaAsBi film was elaborated with V/III ratio of 9.5, trimethyl bismuth molar flow rate of about 3 μmol/min and a growth temperature of 420 °C. The surface morphology of GaAsBi alloy was investigated by means of scanning electron microscopy and atomic force microscopy. Results show surface Bi droplets formation. High-resolution X-ray diffraction (HRXRD) curves present more diffraction peaks other than that of GaAs substrate. Detailed HRXRD characterization shows that diffraction peaks splitting do not represent a crystallographic tilting with respect to GaAs substrate. Diffraction patterns also show a remarkable stability of the alloy against thermal annealing.     

In0.53Ga0.47As(1 0 0) native oxide removal by liquid and gas phase HF/H2O chemistries

The native oxide removal, surface termination, and stoichiometry of InGaAs(1 0 0) surfaces using liquid and gas phase HF/H₂O etching were studied using X-ray photoelectron spectroscopy. Oxide removal in liquid phase HF stopped at the As layer, producing either elemental or H-terminated As. The surface oxidized upon air exposure, forming a 4.8 Å As₂O₃ layer on an As rich InGaAs sub-surface (17% In, 16% Ga, 66% As). A sub atmospheric gas phase HF/H₂O process (100 Torr, 29 °C, 0.5 min) completely removed As₂O₃ and produced mainly In and Ga fluorides, since As fluoride is volatile at these experimental conditions. Once enough F accumulated on the surface, the water sticking probability decreased and the etching reaction proceeded at a much lower rate. The highest oxide removal (4.2 Å residual oxide) was achieved after 5 min of etching. As₂O₃ and As₂O₅ were completely removed and considerably more InF₃ and GaF₃ were produced. The surface contained a group III-fluoride rich overlayer (34% In, 36% Ga) on a slightly As rich bulk (21% In, 21% Ga, and 58% As). The As rich InGaAs sub-surface produced with both liquid and the longer gas phase HF treatments is intrinsic to HF-InGaAs chemistry, although the oxide removal mechanism is likely different.     

Epitaxial growth of Fe/MgO/Ge(0 0 1) heterostructures

We report on the growth of epitaxial Fe/MgO heterostructures on Ge(0 0 1) by Molecular Beam Epitaxy. The better crystal quality and interfacial chemical sharpness at the oxide-semiconductor interface have been obtained by growing MgO at room temperature, followed by a post-annealing at 773 K, on top of a p(2 × 1)-Ge(0 0 1) clean surface. The growth of Fe at room temperature followed by annealing at 473 K gives the best epitaxial structure with optimized crystallinity of each layer compatible with limited chemical interdiffusion. Tunneling devices based on the epitaxial Fe/MgO/Ge heterostructure have been micro-fabricated and tested in order to probe the electrical properties of the MgO barrier. The current-voltage characteristics clearly show that tunneling is the dominant phenomenon, thus indicating that this system is very promising for practical applications in electronics and spintronics.     

A 1.0 V power supply, 9.3 GB/s write speed, Single-Cell Self-Boost program scheme for high performance ferroelectric NAND flash SSD

A Single-Cell Self-Boost (SCSB) program scheme is proposed to achieve a 1.0 V power supply operation in Ferroelectric (Fe-) NAND flash memories. The proposed SCSB scheme only self-boosts the channel voltage of the cell to which the program voltage V_PGM is applied in the program-inhibit NAND string. The program disturb is well suppressed at the 1.0 V power supply voltage in the proposed program scheme. The power consumption of the Fe-NAND at V_CC = 1.0 V decreases by 86% compared with the conventional floating gate (FG-) NAND at V_CC = 1.8 V without the degradation of the write speed. The number of NAND chips written simultaneously in Solid-State Drives (SSD) increases by 6.7 times and the 9.3 GB/s write throughput of the Fe-NAND SSD is achieved for an enterprise application.     

Origin of electron mobility enhancement in (1 1 1)-oriented InGaAs channel metal-insulator-semiconductor field-effect-transistors

Electrical and physical characteristics of the Al₂O₃/InGaAs interfaces with (1 1 1)A and (1 0 0) orientations were investigated in an attempt to understand the origin of electron mobility enhancement in the (1 1 1)A-channel metal-insulator-semiconductor field-effect-transistor. The (1 1 1)A interface has less As atoms of high oxidation states as probed by X-ray photoelectron spectroscopy. The electrical measurements showed that energy distribution of the interface traps for the (1 1 1)A interface is shifted toward the conduction band as compared to that for the (1 0 0) interface. Laterally-compressed cross-section transmission electron microscopy images showed that the characteristic lengths of the interface roughness are different between the (1 1 1)A and (1 0 0) interfaces. The contributions of the Coulomb and roughness scattering mechanisms are discussed based on the experimental results.