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16 Jul 2007

Volume 91, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 91, 033106 (2007); http://dx.doi.org/10.1063/1.2757609 (3 pages)

S. Ingole, P. Aella, Sean J. Hearne, and S. T. Picraux
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Electron detrapping characteristics in positive bias temperature stressed n-channel metal-oxide-semiconductor field-effect transistors with ultrathin HfSiON gate dielectrics

Shiyang Zhu and Anri Nakajima

Appl. Phys. Lett. 91, 033501 (2007); http://dx.doi.org/10.1063/1.2754640 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2007

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Electrons trapped in the HfSiON gate dielectrics of n-channel metal-oxide-semiconductor field-effect transistors induced by positive bias temperature stress start to decay when the stress is interrupted or an opposite (recovery) voltage is applied. The decay begins with a quick detrapping within tens of nanoseconds followed by a slow detrapping. The quick detrapping depends on the recovery voltage and the trapping history, whereas the slow detrapping obeys approximately a logarithmic dependence on time with an almost identical slope before saturation. The observed detrapping behavior can be explained by a spatial and/or energetic distribution of trapped electrons in the HfSiON film. The device degradation under various dynamic stresses is found to be almost independent of frequency ranging from 0.001 to 1 MHz, while it is slightly enhanced at 10 MHz, probably due to insufficient recovery at the recovering half cycle.
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85.30.Tv Field effect devices

Charge characterization in metal-gate/high-κ layers: Effect of post-deposition annealing and gate electrode

B. J. O’Sullivan, G. Pourtois, V. S. Kaushik, T. Schram, J. A. Kittl, L. Pantisano, S. De Gendt, and M. Heyns

Appl. Phys. Lett. 91, 033502 (2007); http://dx.doi.org/10.1063/1.2754647 (3 pages) | Cited 2 times

Online Publication Date: 16 July 2007

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The effect of varying interfacial SiO2 and high-κ thickness on charge density within the gate stack are examined. It is demonstrated that there is a significant effect of the gate electrode on the charge density levels within the stack, with one order of magnitude lower charge in the case of Ni3Si2 electrodes, than in the case of tantalum-rich metal electrodes. The effect of post-deposition annealing on high-κ HfSixOy(Nz) stacks is less significant that that of the electrode. The reasons behind these findings are discussed.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Ns Metal-nonmetal contacts

Observation of a two dimensional electron gas formed in a polarization doped C-face 3C/4H SiC heteropolytype junction

M. V. S. Chandrashekhar, C. I. Thomas, Jie Lu, and Michael. G. Spencer

Appl. Phys. Lett. 91, 033503 (2007); http://dx.doi.org/10.1063/1.2754650 (3 pages) | Cited 5 times

Online Publication Date: 17 July 2007

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A two dimensional electron gas (2DEG) was observed in a C-face 3C/4H SiC heteropolytype junction. Sheet carrier concentrations of ∼ 3×1013 cm−2 and Hall mobility of ∼ 314 cm2/V s were measured at 77 K. The temperature dependences of mobility and carrier concentration clearly demonstrate the presence of the 2DEG. Comparison with theory indicates that the carriers originate from both spontaneous polarization and unintentional degenerate nitrogen doping of 3C-SiC, suggesting a 77 K 2DEG mobility ∼ 700 cm2/V s in parallel with bulk hopping conduction. Mobility at high temperatures was phonon limited, indicating a Debye temperature of 1600 K. Transmission line measurements yielded similar mobilities, with saturation currents of ∼ 3 A/mm, suggesting the utility of SiC heteropolytypes in microwave devices.
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73.21.Ac Multilayers
72.20.Ee Mobility edges; hopping transport
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.up Other materials
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.50.Dn Low-field transport and mobility; piezoresistance

Direct insertion of oxygen atoms into the backbonds of subsurface Si atoms using translational energies of oxygen atom beams

Masahito Tagawa, Kumiko Yokota, Shinnosuke Tsumamoto, Chie Sogo, Akitaka Yoshigoe, and Yuden Teraoka

Appl. Phys. Lett. 91, 033504 (2007); http://dx.doi.org/10.1063/1.2759262 (3 pages) | Cited 1 time

Online Publication Date: 18 July 2007

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A direct oxidation reaction of Si atoms on a Si(001) surface was studied by ellipsometry and synchrotron radiation photoemission spectroscopy. In situ ellipsometry measurements when exposed to 2.7–5.0 eV O atom beams indicated that oxide growth follows a linear relationship with an O atom fluence up to an oxide thickness of 0.6–0.7 nm. In contrast, the limit of linear growth was 0.3 nm in the case of the 1.8 eV beam. These results suggest that the backbonds of Si atoms in the first layer are directly oxidized by O atom with a translational energy between 2.7 and 5.0 eV.
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81.65.Mq Oxidation
82.40.-g Chemical kinetics and reactions: special regimes and techniques
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Experimental determination of the effective minority carrier lifetime in the operation of a quantum-well n-p-n heterojunction bipolar light-emitting transistor of varying base quantum-well design and doping

H. W. Then, M. Feng, N. Holonyak, Jr., and C. H. Wu

Appl. Phys. Lett. 91, 033505 (2007); http://dx.doi.org/10.1063/1.2759263 (3 pages) | Cited 7 times

Online Publication Date: 18 July 2007

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The authors show that the electrical characteristics of an n-p-n transistor structure can be used to determine experimentally, under dynamical operating conditions, the effective carrier lifetime of injected minority carriers in the quantum-well (QW) base region of a heterojunction bipolar light-emitting transistor. The carrier lifetime is progressively reduced from 134 ps (no base QW) to ∼ 35 ps by inserting single or double QWs of increasing width to enhance the effective capture cross section for injected carriers (electrons), and is further reduced to ∼ 10 ps by increasing the p-type doping from 5×1018 to 4×1019 cm−3.
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85.30.Pq Bipolar transistors
85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Rubrene polycrystalline transistor channel achieved through in situ vacuum annealing

Se-W. Park, S. H. Jeong, Jeong-M. Choi, Jung Min Hwang, Jae Hoon Kim, and Seongil Im

Appl. Phys. Lett. 91, 033506 (2007); http://dx.doi.org/10.1063/1.2756379 (3 pages) | Cited 16 times

Online Publication Date: 18 July 2007

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The authors report on the rubrene polycrystalline film growth for its thin film transistor (TFT) applications. Amorphous rubrene thin film was initially obtained on 200-nm-thick SiO2/Si substrate at 40 °C in a vacuum chamber by thermal evaporation but in situ long time postannealing at the elevated temperatures of 60–80 °C transformed the amorphous phase into crystalline. Based on an optimum condition to cover the whole channel area with polycrystalline film, the authors have fabricated a rubrene TFT with a relatively high field effect mobility of 0.002 cm2/V s, an on/off ratio of ∼ 104, and a low threshold voltage of −9 V.
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68.55.A- Nucleation and growth
73.61.Ph Polymers; organic compounds
81.40.Gh Other heat and thermomechanical treatments
85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.10.Bk Growth from vapor

Low frequency noise in highly sensitive magnetic tunnel junctions with (001) MgO tunnel barrier

Dipanjan Mazumdar, Xiaoyong Liu, B. D. Schrag, Matthew Carter, Weifeng Shen, and Gang Xiao

Appl. Phys. Lett. 91, 033507 (2007); http://dx.doi.org/10.1063/1.2754352 (3 pages) | Cited 8 times

Online Publication Date: 18 July 2007

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Low frequency voltage noise was measured in highly sensitive magnetic tunnel junctions with MgO tunnel barrier. The voltage noise is observed to scale linearly with the magnetic field sensitivity. Fluctuations in noise, possibly due to local domain nucleation or annihilation inside the free layer, are also observed. Results indicate that an external hard-axis bias field can significantly suppress the magnetization fluctuations of the free layer and lower the magnetic field noise.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials
75.60.Ch Domain walls and domain structure

Fabrication and characterization of metal-molecule-silicon devices

Adina Scott, David B. Janes, Chad Risko, and Mark A. Ratner

Appl. Phys. Lett. 91, 033508 (2007); http://dx.doi.org/10.1063/1.2750516 (3 pages) | Cited 18 times

Online Publication Date: 18 July 2007

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Metal-molecule-silicon (MMSi) devices have been fabricated, electrically characterized, and analyzed. Molecular layers were grafted to n and p+ silicon by electrochemical reduction of para-substituted aryl-diazonium salts and characterized using standard surface analysis techniques; MMSi devices were then fabricated using traditional silicon (Si) processing methods combined with this surface modification. The measured current-voltage characteristics were strongly dependent on both substrate type and molecular head group. The device behavior was analyzed using a qualitative model considering semiconductor depletion effects and molecular dipole moments and frontier orbital energies.
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85.65.+h Molecular electronic devices
85.30.De Semiconductor-device characterization, design, and modeling

Direct x-ray detection with conjugated polymer devices

F. A. Boroumand, M. Zhu, A. B. Dalton, J. L. Keddie, P. J. Sellin, and J. J. Gutierrez

Appl. Phys. Lett. 91, 033509 (2007); http://dx.doi.org/10.1063/1.2748337 (3 pages) | Cited 12 times

Online Publication Date: 18 July 2007

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The authors report the first direct detection of x-ray induced photocurrents in thick films (up to 20 μm) of conjugated polymers. Schottky-based “sandwich” structures were fabricated from layers of either poly[1-methoxy-4-(2-ethylhexyloxy)-phenylenevinylene] (MEH-PPV) or poly(9,9-dioctylfluorene) (PFO) on indium tin oxide substrates using a top contact of aluminum. Good rectification was achieved from the Al-polymer contact, with a reverse bias leakage current density as low as 4 nA/cm2 at an electric field strength of 25 kV/cm. Irradiation with x-rays from a 50 kV x-ray tube produced a linear increase in photocurrent over a dose rate range from 4 to 18 mGy/s. The observed x-ray sensitivities of 240 nC/mGy/cm3 for MEH-PPV and 480 nC/mGy/cm3 for PFO structures are comparable to that reported for Si devices. A response time of <150 ms to pulsed x-ray irradiation was measured with no evidence of long-lived current transients. Conjugated polymers offer the advantage of easy coatability over large areas and on curved surfaces. Their low average atomic number provides tissue-equivalent dosimetric response, with many potential applications including medical x-ray and synchrotron photon detection.
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72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ph Polymers; organic compounds
73.40.Ei Rectification
61.80.Cb X-ray effects
73.30.+y Surface double layers, Schottky barriers, and work functions

Mesoscopic structures and two-dimensional hole systems in fully field effect controlled heterostructures

R. L. Willett, M. J. Manfra, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 91, 033510 (2007); http://dx.doi.org/10.1063/1.2757128 (3 pages) | Cited 2 times

Online Publication Date: 18 July 2007

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Two fundamental extensions to the function of previously described fully field effect two-dimensional (2D) electron heterostructures are presented. First, using the same basic heterostructure design of lithographically defined contacts overlain by both an insulating layer and top gate employed for electron systems, appropriate contact material allows a high mobility 2D hole layer to be populated. Second, a simple method for producing mesoscopic structures in these devices is presented, in which small-scale metallic patterns are placed on the heterostructure under the insulating and global gate layers which allows local carrier density tuning via the overlapping gate arrays. Example devices using these generally applicable methods are demonstrated.
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85.30.Tv Field effect devices

Effects of metal gate-induced strain on the performance of metal-oxide-semiconductor field effect transistors with titanium nitride gate electrode and hafnium oxide dielectric

Chang Yong Kang, Rino Choi, M. M. Hussain, Jinguo Wang, Young Jun Suh, H. C. Floresca, Moon J. Kim, Jiyoung Kim, Byoung Hun Lee, and Raj Jammy

Appl. Phys. Lett. 91, 033511 (2007); http://dx.doi.org/10.1063/1.2766667 (3 pages) | Cited 8 times

Online Publication Date: 19 July 2007

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In this letter, the authors investigate the strain induced by titanium nitride (TiN) electrode and effective work function (EWF) tuning for metal-oxide-semiconductor field effect transistors (MOSFETs). Scaling of TiN thickness was found to be effective both in increasing tensile stress on Si substrates and in lowering the EWF of metal gate n-MOSFETs. The device with 3 nm TiN as a gate electrode showed favorable threshold voltage (Vth) for n-MOSFETs as well as higher channel electron mobility by 17% compared to the device with 20 nm TiN film.
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85.30.Tv Field effect devices

Improved thermal stability of ruthenium oxide metal gate electrode on hafnium oxide gate dielectric

Musarrat Hasan, Hokyung Park, Joon-myong Lee, and Hyunsang Hwang

Appl. Phys. Lett. 91, 033512 (2007); http://dx.doi.org/10.1063/1.2766654 (3 pages) | Cited 2 times

Online Publication Date: 20 July 2007

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This study focused on the detailed understanding of the thermal stability of ruthenium oxide metal gate electrode for hafnium oxide gate dielectric. A sample with ruthenium oxide electrode shows reduction of capacitance and flatband voltage shift after high temperature annealing. The degradation of device parameter can be explained by the reduction of amorphous ruthenium oxide phase into ruthenium metallic phase and oxygen. With the introduction of an additional ruthenium metal layer between ruthenium oxide and hafnium oxide, the authors can minimize oxygen diffusion from ruthenium oxide electrode toward silicon/hafnium oxide interface which in turn improves the thermal stability of hafnium oxide devices.
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81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
68.60.Dv Thermal stability; thermal effects
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