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27 Mar 2006

Volume 88, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 133105 (2006); http://dx.doi.org/10.1063/1.2189203 (3 pages)

Premila Mohan, Junichi Motohisa, and Takashi Fukui
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Discovery of the deep level related to hydrogen in anatase TiO2

Takahira Miyagi, Masayuki Kamei, Takefumi Mitsuhashi, and Atsushi Yamazaki

Appl. Phys. Lett. 88, 132101 (2006); http://dx.doi.org/10.1063/1.2191090 (3 pages)

Online Publication Date: 27 March 2006

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Deep level transient spectroscopy was carried out to investigate the origin of the deep levels in the band gap of anatase TiO2. The epitaxial anatase-TiO2 film grown by metal-organic chemical vapor deposition possessed a deep level whose activation energy was 0.52 eV. In contrast, this deep level at 0.5 eV was not observed in the films grown by sputtering. However, by adding CH4 or H2 to the sputtering gas, the deep level at 0.5 eV was observed in the sputter-grown films. Furthermore, the density of this deep level increased with increasing hydrogen gas, suggesting that this deep level originated from hydrogen doping.
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71.55.Ht Other nonmetals
71.20.Nr Semiconductor compounds
61.72.up Other materials

Room-temperature electroluminescence of AlSb/InAsSb single quantum wells grown by metal organic vapor phase epitaxy

K. D. Moiseev, E. V. Ivanov, G. G. Zegrya, M. P. Mikhailova, Yu. P. Yakovlev, E. Hulicius, A. Hospodková, J. Pangrác, K. Melichar, and T. Šimeček

Appl. Phys. Lett. 88, 132102 (2006); http://dx.doi.org/10.1063/1.2189572 (3 pages) | Cited 2 times

Online Publication Date: 27 March 2006

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Intense mid-infrared (λ ∼ 2 μm) room temperature electroluminescence from metal organic vapor phase epitaxy (MOVPE) grown type-I single AlSb/InAsSb/AlSb quantum wells (QWs) is reported. The spectral position of the electroluminescent peaks is in good agreement with k∙p envelope function calculation in the frame of four-band Kane’s model taking into account the intermixing of s and p states in the deep quantum well. A four times increase of the emission intensity with temperature increasing from 77 to 300 K can be explained by highly efficient radiative recombination of the electrons injected into the narrow AlSb/InAsSb/AlSb QW due to its specific design, leading to Auger process suppression.
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73.21.Fg Quantum wells
78.60.Fi Electroluminescence
78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Si and SiO2 layer transfer induced by mechanical residual stress

V. Loryuenyong and N. W. Cheung

Appl. Phys. Lett. 88, 132103 (2006); http://dx.doi.org/10.1063/1.2189669 (3 pages) | Cited 1 time

Online Publication Date: 27 March 2006

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Using the polymer SU-8 as a bonding and stress-inducing layer, we have demonstrated that Si and SiO2 layers can be transferred by mechanical cleavage to SU-8/glass substrates without ion implantation of the donor wafers. Cracks tend to propagate under mode II criterion (KII = 0) at a characteristic depth defined by the residual stress and elastic properties of the Si/SU-8/glass matrix. An analytical model is developed and verified for the dependence of the measured characteristic crack depth on the elastic modulus of substrate materials.
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68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Current transport studies of ZnO/p-Si heterostructures grown by plasma immersion ion implantation and deposition

X. D. Chen, C. C. Ling, S. Fung, C. D. Beling, Y. F. Mei, Ricky K. Y. Fu, G. G. Siu, and Paul. K. Chu

Appl. Phys. Lett. 88, 132104 (2006); http://dx.doi.org/10.1063/1.2190444 (3 pages) | Cited 25 times

Online Publication Date: 27 March 2006

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Rectifying undoped and nitrogen-doped ZnO/p-Si heterojunctions were fabricated by plasma immersion ion implantation and deposition. The undoped and nitrogen-doped ZnO films were n type (n ∼ 1019 cm−3) and highly resistive (resistivity ∼ 105 Ω cm), respectively. While forward biasing the undoped-ZnO/p-Si, the current follows Ohmic behavior if the applied bias Vforward is larger than ∼ 0.4 V. However, for the nitrogen-doped-ZnO/p-Si sample, the current is Ohmic for Vforward<1.0 V and then transits to J ∼ V2 for Vforward>2.5 V. The transport properties of the undoped-ZnO/p-Si and the N-doped-ZnO/p-Si diodes were explained in terms of the Anderson model and the space charge limited current model, respectively.
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81.05.Dz II-VI semiconductors
81.05.Cy Elemental semiconductors
81.15.Jj Ion and electron beam-assisted deposition; ion plating
52.77.Dq Plasma-based ion implantation and deposition
61.72.uf Ge and Si
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Behavior of antimony in ZnSe grown by a closed Bridgman method

J. F. Wang and M. Isshiki

Appl. Phys. Lett. 88, 132105 (2006); http://dx.doi.org/10.1063/1.2190271 (3 pages)

Online Publication Date: 28 March 2006

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High-quality and large-size p-ZnSe single crystals doped with antimony (Sb) have been grown by a Bridgman method using a closed double crucible. Photoluminescence spectra at low temperatures indicate that Sb works as both a shallow acceptor and a deep complex donor. By studying the temperature and excitation intensity dependences of the free-to-acceptor and donor-acceptor pair emissions, we estimated that the ionization energy of Sb as a shallow acceptor in ZnSe is (112–114) meV above the valence band, and that of the deep complex donor related to Sb is 37 ±1 meV below the conduction band.
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71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
81.10.Fq Growth from melts; zone melting and refining
61.72.uj III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors

Controlling field-effect mobility in pentacene-based transistors by supersonic molecular-beam deposition

T. Toccoli, A. Pallaoro, N. Coppedè, S. Iannotta, F. De Angelis, L. Mariucci, and G. Fortunato

Appl. Phys. Lett. 88, 132106 (2006); http://dx.doi.org/10.1063/1.2187494 (3 pages) | Cited 16 times

Online Publication Date: 28 March 2006

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We show that pentacene field-effect transistors, fabricated by supersonic molecular beams, have a performance strongly depending on the precursor’s kinetic energy (KE). The major role played by KE is in achieving highly ordered and flat films. In the range KE ≈ 3.5–6.5 eV, the organic field effect transistor linear mobility increases of a factor ∼ 5. The highest value (1.0 cm2 V−1 s−1) corresponds to very uniform and flat films (layer-by-layer type growth). The temperature dependence of mobility for films grown at KE>6 eV recalls that of single crystals (bandlike) and shows an opposite trend for films grown at KE ⩽ 5.5 eV.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Subnanometer-equivalent-oxide-thickness germanium p-metal-oxide-semiconductor field effect transistors fabricated using molecular-beam-deposited high-k/metal gate stack

A. Ritenour, A. Khakifirooz, D. A. Antoniadis, R. Z. Lei, W. Tsai, A. Dimoulas, G. Mavrou, and Y. Panayiotatos

Appl. Phys. Lett. 88, 132107 (2006); http://dx.doi.org/10.1063/1.2189456 (3 pages) | Cited 36 times

Online Publication Date: 28 March 2006

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Metal-oxide-semiconductor field effect transistors (MOSFET) with a thin high-k dielectric were fabricated on bulk n-type germanium substrates. Surface oxides were thermally desorbed in situ by heating the substrates under ultrahigh vacuum conditions. First an ultrathin passivating layer was formed by evaporating germanium in the presence of atomic oxygen and nitrogen supplied from a remote radio frequency plasma source. Subsequently, the HfO2 dielectric was deposited by evaporating hafnium in the presence of atomic oxygen. An in situ TaN metal gate was similarly deposited. Long channel devices were fabricated using a standard process flow. These devices exhibited a low equivalent oxide thickness (EOT) of 0.7 nm with gate leakage less than 15 mA/cm2 at VFB+1 V. Device mobility was extracted from Is-Vg and split C-V characteristics. Results indicate a 2× mobility enhancement in Ge p-MOSFET devices compared to Si control devices. The demonstration of subnanometer EOT suggests that high-k gate dielectrics on germanium are scalable to low EOT and suitable for use in ultrascaled MOSFET devices.
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85.30.Tv Field effect devices

Molecular beam epitaxy growth of In0.52Al0.48As/In0.53Ga0.47As metamorphic high electron mobility transistor employing growth interruption and in situ rapid thermal annealing

Soo-Ghang Ihn, Seong June Jo, and Jong-In Song

Appl. Phys. Lett. 88, 132108 (2006); http://dx.doi.org/10.1063/1.2189607 (3 pages) | Cited 1 time

Online Publication Date: 28 March 2006

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We investigated the effects of high temperature ( ∼ 700 °C) in situ rapid thermal annealing (RTA) carried out during growth interruption between spacer and δ-doping layers of an In0.52Al0.48As/In0.53Ga0.47As metamorphic high electron mobility transistor (MHEMT) grown on a compositionally graded InGaAlAs buffer layer. The in situ RTA improved optical and structural properties of the MHEMT without degradation of transport property, while postgrowth RTA improved the structural property of the MHEMT but significantly degraded mobility due to the defect-assisted Si diffusion. The results indicate the potential of the in situ RTA for use in the growth of high-quality metamorphic epitaxial layers for optoelectronic applications requiring improved optical and electrical properties.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Thermally stimulated current studies on neutron irradiation induced defects in GaN

K. Kuriyama, M. Ooi, A. Onoue, K. Kushida, M. Okada, and Q. Xu

Appl. Phys. Lett. 88, 132109 (2006); http://dx.doi.org/10.1063/1.2190446 (3 pages) | Cited 5 times

Online Publication Date: 28 March 2006

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The evaluation of the neutron irradiation induced defects in GaN is studied using a thermally stimulated current (TSC) method with excitation above (below) the energy band gap using ultraviolet (blue, green, red, and infrared) emitting diodes. Annealing at 1000 °C, a broad TSC spectrum for excitation by the ultraviolet light is resolved by five traps, P1 (ionization energy is 200 meV), P2 (270 meV), P3 (380 meV), P4 (490 meV), and P5 (595 meV). Infrared illumination shows a remarkable reduction in TSC for the P2 and P3 traps, indicating the photoquenching behavior. The possible origins of the observed five traps are discussed.
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73.61.Ey III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Eq III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

HgCdTe superlattices for solid-state cryogenic refrigeration

Daryoosh Vashaee and Ali Shakouri

Appl. Phys. Lett. 88, 132110 (2006); http://dx.doi.org/10.1063/1.2191094 (3 pages) | Cited 2 times

Online Publication Date: 29 March 2006

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A tall barrier superlattice structure based on mercury cadmium telluride material system is proposed that can achieve a large effective thermoelectric figure of merit (ZTmax ∼ 3) at cryogenic temperatures. Calculations based on the Boltzmann transport equation taking into account the quantum mechanical electron transmission show that the Seebeck coefficient can be increased significantly at low temperatures with the use of nonplanar barriers as the thermal spreading of the electron density is tightened around the Fermi level. This provides a better asymmetric differential conductivity around the Fermi level close to the top of the barrier. Consequently, a high thermoelectric power factor is produced resulting in a large ZT.
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72.20.Pa Thermoelectric and thermomagnetic effects
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Electron energy band alignment at interfaces of (100)Ge with rare-earth oxide insulators

V. V. Afanas’ev, S. Shamuilia, A. Stesmans, A. Dimoulas, Y. Panayiotatos, A. Sotiropoulos, M. Houssa, and D. P. Brunco

Appl. Phys. Lett. 88, 132111 (2006); http://dx.doi.org/10.1063/1.2191736 (3 pages) | Cited 22 times

Online Publication Date: 31 March 2006

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Energy diagrams of interfaces between (100)Ge and several rare-earth oxide insulators deposited from a molecular beam are determined using a combination of internal photoemission and photoconductivity measurements. For the wide band gap (5.9 eV) oxides Gd2O3 and LaHfOx, the band alignment at the interface is found to be close to that of HfO2 and is characterized by conduction/valence band offsets of ∼ 2/ ∼ 3 eV. In contrast, CeO2 which has a much narrower band gap (3.3 eV) does not provide a band alignment diagram corresponding to sufficient insulation.
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73.20.-r Electron states at surfaces and interfaces
79.60.Jv Interfaces; heterostructures; nanostructures
72.40.+w Photoconduction and photovoltaic effects

Analytical model for incomplete signal generation in semiconductor detectors

Ho Kyung Kim

Appl. Phys. Lett. 88, 132112 (2006); http://dx.doi.org/10.1063/1.2191742 (3 pages) | Cited 3 times

Online Publication Date: 31 March 2006

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Signal generation from semiconductor detectors has been modeled considering incomplete charge signal due to the charge trapping within a detector as well as to the ballistic deficit caused by insufficient charge collection time. The analytical formalism was experimentally confirmed with the charge collection efficiency of a planar mercuric iodide (HgI2) detector. The developed model is useful for the characterization of detector material properties such as the mobility and the lifetime, as well as the optimization of operation conditions such as the applied bias and the charge collection time.
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85.60.-q Optoelectronic devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Ultrafast spectroscopy of impact ionization and avalanche multiplication in GaAs

S. Trumm, M. Betz, F. Sotier, A. Leitenstorfer, A. Schwanhäußer, M. Eckardt, O. Schmidt, S. Malzer, G. H. Döhler, M. Hanson, D. Driscoll, and A. C. Gossard

Appl. Phys. Lett. 88, 132113 (2006); http://dx.doi.org/10.1063/1.2191880 (3 pages) | Cited 3 times

Online Publication Date: 31 March 2006

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Femtosecond carrier dynamics in biased AlxGa1−xAs heterostructure diodes is investigated tracing transient modifications of the Franz-Keldysh absorption spectrum. The nonlinear optical response is sensitive to the number of electron-hole pairs in the high-field region of the sample. As a result, the dynamical buildup of a nonequilibrium carrier avalanche due to impact ionization for electric fields F ≥ 350 kV/cm is directly analyzed in the time domain. The time scale of the carrier multiplication is found to be in the order of 10 ps depending on the number of photoinjected carriers. Monte Carlo simulations in a simplified band structure agree well with the experiment.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Ht High-field and nonlinear effects
78.47.-p Spectroscopy of solid state dynamics
85.30.Kk Junction diodes

Control of p- and n-type conductivities in P doped ZnO thin films by using radio-frequency sputtering

Zhi Gen Yu, Ping Wu, and Hao Gong

Appl. Phys. Lett. 88, 132114 (2006); http://dx.doi.org/10.1063/1.2192089 (3 pages) | Cited 23 times

Online Publication Date: 31 March 2006

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The conduction type of P doped ZnO thin films using Zn3P2 dopant source can be controlled by adjusting the oxygen partial pressure by means of radio-frequency sputtering. Under an optimal oxygen partial pressure of 5%, p-type ZnO thin films were obtained with a hole concentration of 1.93×1016–3.84×1019 cm−3. Under a growth condition of extremely low oxygen partial pressure, P doped ZnO thin films exhibit n-type conduction with a hole concentration of 8.34×1017–3.1×1019 cm−3. This research not only achieved significant technical advance in the fabrication of p-type ZnO but also gained critical advance in fundamental understanding of the governing mechanism of p-type ZnO.
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81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
73.61.Ga II-VI semiconductors
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