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13 Nov 2006

Volume 89, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 89, 202101 (2006); http://dx.doi.org/10.1063/1.2388049 (3 pages)

J. H. Lee, Zh. M. Wang, N. W. Strom, Yu. I. Mazur, and G. J. Salamo
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InGaAs quantum dot molecules around self-assembled GaAs nanomound templates

J. H. Lee, Zh. M. Wang, N. W. Strom, Yu. I. Mazur, and G. J. Salamo

Appl. Phys. Lett. 89, 202101 (2006); http://dx.doi.org/10.1063/1.2388049 (3 pages) | Cited 61 times

Online Publication Date: 13 November 2006

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Several distinctive self-assembled InGaAs quantum dot molecules (QDMs) are studied. The QDMs self-assemble around nanoscale-sized GaAs moundlike templates fabricated by droplet homoepitaxy. Depending on the specific InAs monolayer coverage, the number of QDs per GaAs mound ranges from two to six (bi-QDMs to hexa-QDMs). The Ga contribution from the mounds is analyzed in determining the morphologies of the QDMs, with respect to the InAs coverages ranging between 0.8 and 2.4 ML. Optical characterization shows that the resulting nanostructures are high-quality nanocrystals.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
61.46.Hk Nanocrystals

p-type Zn1−xMgxO films with Sb doping by radio-frequency magnetron sputtering

Peng Wang, Nuofu Chen, Zhigang Yin, Ruixuan Dai, and Yiming Bai

Appl. Phys. Lett. 89, 202102 (2006); http://dx.doi.org/10.1063/1.2388254 (3 pages) | Cited 24 times

Online Publication Date: 13 November 2006

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Sb-doped Zn1−xMgxO films were grown on c-plane sapphire substrates by radio-frequency magnetron sputtering. The p-type conduction of the films (0.05 ⩽ x ⩽ 0.13) was confirmed by Hall measurements, revealing a hole concentration of 1015–1016 cm−3 and a mobility of 0.6–4.5 cm2/V s. A p-n homojunction comprising an undoped ZnO layer and an Sb-doped Zn0.95Mg0.05O layer shows a typical rectifying characteristic. Sb-doped p-type Zn1−xMgxO films also exhibit a changeable wider band gap as a function of x, implying that they can probably be used for fabrication of ZnO-based quantum wells and ultraviolet optoelectronic devices.
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81.05.Dz II-VI semiconductors
73.61.Ga II-VI semiconductors
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Mechanism analysis of periodicity and weakening surge of GaAs photoconductive semiconductor switches

Wei Shi and Liqiang Tian

Appl. Phys. Lett. 89, 202103 (2006); http://dx.doi.org/10.1063/1.2387120 (3 pages) | Cited 11 times

Online Publication Date: 13 November 2006

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The authors analyze the periodicity and weakening surge of semi-insulating GaAs photoconductive semiconductor switches. It is shown that the periodicity and weakening surge of the output current wave form is caused by the self-excitation of the circuit. The electric field threshold ET and the sustaining electric field Es (the minimum electric field required to support the domain) are modulated by the ac electric field; the output wave form becomes two main modes of transelectron oscillator, namely, delayed domain mode and quenched domain mode.
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85.60.-q Optoelectronic devices

Realization of high hole concentrations in Mg doped semipolar (10mathmath) GaN

J. F. Kaeding, H. Asamizu, H. Sato, M. Iza, T. E. Mates, S. P. DenBaars, J. S. Speck, and S. Nakamura

Appl. Phys. Lett. 89, 202104 (2006); http://dx.doi.org/10.1063/1.2378486 (3 pages) | Cited 9 times

Online Publication Date: 13 November 2006

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The authors report on the growth of Mg doped semipolar (10mathmath) GaN layers on vicinal (100) MgAl2O4 substrates miscut in the ⟨011⟩ direction by metal-organic chemical vapor deposition. A maximum hole concentration of 2.4×1018 cm−3 and a maximum mobility of 8 cm2 V−1 s−1, respectively, were achieved following a postgrowth thermal annealing step. Although the hole concentration decreased for Mg concentrations greater than 3.3×1019 cm−3, significant hole concentrations, combined with the reduction in internal polarization fields, make semipolar GaN layers suitable for the fabrication of high brightness optoelectronic devices.
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81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
72.20.Fr Low-field transport and mobility; piezoresistance
61.72.Cc Kinetics of defect formation and annealing

Temperature dependence of the GaAsN conduction band structure

A. Grau, T. Passow, and M. Hetterich

Appl. Phys. Lett. 89, 202105 (2006); http://dx.doi.org/10.1063/1.2387973 (3 pages) | Cited 5 times

Online Publication Date: 13 November 2006

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In this contribution the authors investigate the temperature-dependent conduction band structure of GaAs1−xNx for different nitrogen contents. An analysis of their experimental photoreflectance data based on the two-band version of the band anticrossing model shows that with decreasing temperature the energy of the effective nitrogen level EN in GaAsN epilayers shifts significantly to higher energies. Simultaneously, the coupling parameter CNM between the nitrogen states and the host conduction band also rises to higher values.
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71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
78.20.-e Optical properties of bulk materials and thin films
61.72.S- Impurities in crystals

Magnetic field dependence of valley splitting in realistic Si/SiGe quantum wells

Mark Friesen, M. A. Eriksson, and S. N. Coppersmith

Appl. Phys. Lett. 89, 202106 (2006); http://dx.doi.org/10.1063/1.2387975 (3 pages) | Cited 16 times

Online Publication Date: 13 November 2006

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The authors investigate the magnetic field dependence of the energy splitting between low-lying valley states for electrons in a Si/SiGe quantum well tilted with respect to the crystallographic axis. The presence of atomic steps at the quantum well interface may explain the unexpected, strong suppression of the valley splitting observed in recent experiments. The authors find that the suppression is caused by an interference effect associated with multiple steps, and that the magnetic field dependence arises from the lateral confinement of the electronic wave function. Using numerical simulations, the authors clarify the role of step disorder, obtaining quantitative agreement with the experiments.
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73.21.Fg Quantum wells
73.20.At Surface states, band structure, electron density of states
68.65.Fg Quantum wells

Energy-band alignments at LaAlO3 and Ge interfaces

Y. Y. Mi, S. J. Wang, J. W. Chai, J. S. Pan, A. C. H. Huan, M. Ning, and C. K. Ong

Appl. Phys. Lett. 89, 202107 (2006); http://dx.doi.org/10.1063/1.2387986 (3 pages) | Cited 13 times

Online Publication Date: 13 November 2006

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The energy-band alignments for LaAlO3 films on p-Ge(001) with and without GeOxNy interfacial layer have been studied using photoemission spectroscopy. The valence-band offsets at LaAlO3/GeOxNy/Ge and LaAlO3/Ge interfaces were measured to be 2.70 and 3.06 eV, respectively. The effect of interfacial GeOxNy layer on the band alignments is attributed to the modification of interface dipoles. The conduction-band offsets at LaAlO3/Si(001) and LaAlO3/Ge interfaces are found to have the same value of 2.25±0.05 eV, where the shift of valence-band top accounts for the difference in the energy-band alignment at two interfaces.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces

High-performance microscale single-crystal transistors by lithography on an elastomer dielectric

Colin Reese, Wook-Jin Chung, Mang-mang Ling, Mark Roberts, and Zhenan Bao

Appl. Phys. Lett. 89, 202108 (2006); http://dx.doi.org/10.1063/1.2388151 (3 pages) | Cited 48 times

Online Publication Date: 14 November 2006

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Organic single crystals have emerged as powerful tools for the exploration of the intrinsic charge transport properties of organic materials. To date, however, the limited number of fabrication techniques has forced a steep compromise between performance, reproducibility, range of feature sizes, gentle treatment of the single crystal, and facility of construction. Here the authors present a materials-general technique for the fabrication of single-crystal field-effect transistors with the use of a spin-coated elastomer gate dielectric and photolithographically defined source and drain electrodes. This allows the production of feature sizes and patterns previously impossible with reported elastomeric techniques yet yields devices with performance far superior to those fabricated on nonconformal dielectrics. The authors measure saturation-regime mobilities of 19.0 and 1.9 cm2/V s for the semiconductors rubrene and pentacene, comparable to the best published values, and 2.4 cm2/V s for tetracene, nearly double that previously reported. Device characteristics are indicative of good contact, with negligible hysteresis and exceptionally low normalized subthreshold swings.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

p-type semiconducting dendrimers bearing thiophenyl peripheral moieties for organic field effect transistors

Kyung Hwan Kim, Zhenguo Chi, Min Ju Cho, Dong Hoon Choi, Han Saem Kang, Mi Yeon Cho, and Jin-Soo Joo

Appl. Phys. Lett. 89, 202109 (2006); http://dx.doi.org/10.1063/1.2388244 (3 pages) | Cited 3 times

Online Publication Date: 14 November 2006

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First generation thiophene-labeled conjugated dendrimers have been synthesized through the Heck coupling reaction between the 5-hexyl-5-propenyl thiophene derivative and 1, 2, 4, 5-tetrabromo-benzene as the core. They display a p-type semiconducting behavior and a considerably better solubility than the linear conjugated oligothiophene. Two crystalline dendrimers such as 4(HPBT)-benzene and 4(HPTT)-benzene showed carrier mobilities as high as 6.2×10−3 and 2.4×10−4 cm2 V−1 s−1, respectively.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
85.30.Tv Field effect devices
64.75.-g Phase equilibria
72.20.Fr Low-field transport and mobility; piezoresistance

Transition from electron accumulation to depletion at InGaN surfaces

T. D. Veal, P. H. Jefferson, L. F. J. Piper, C. F. McConville, T. B. Joyce, P. R. Chalker, L. Considine, Hai Lu, and W. J. Schaff

Appl. Phys. Lett. 89, 202110 (2006); http://dx.doi.org/10.1063/1.2387976 (3 pages) | Cited 27 times

Online Publication Date: 14 November 2006

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The composition dependence of the Fermi-level pinning at the oxidized (0001) surfaces of n-type InxGa1−xN films (0 ⩽ x ⩽ 1) is investigated using x-ray photoemission spectroscopy. The surface Fermi-level position varies from high above the conduction band minimum (CBM) at InN surfaces to significantly below the CBM at GaN surfaces, with the transition from electron accumulation to depletion occurring at approximately x = 0.3. The results are consistent with the composition dependence of the band edges with respect to the charge neutrality level.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Gate-controlled nuclear magnetic resonance in an AlGaAs/GaAs quantum Hall device

S. Masubuchi, K. Hamaya, and T. Machida

Appl. Phys. Lett. 89, 202111 (2006); http://dx.doi.org/10.1063/1.2387895 (3 pages)

Online Publication Date: 15 November 2006

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The authors study the resistively detected nuclear magnetic resonance (NMR) in an AlGaAs/GaAs quantum Hall device with a side gate. The strength of the hyperfine interaction between electron and nuclear spins is modulated by tuning a position of the two-dimensional electron systems with respect to the polarized nuclear spins using the side-gate voltages. The NMR frequency is systematically controlled by the gate-tuned technique in a semiconductor device.
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85.30.-z Semiconductor devices

Effect of hydrogenation on the memory properties of Si nanocrystals obtained by inductively coupled plasma chemical vapor deposition

Young-Kwan Cha, Sangjin Park, Youngsoo Park, In-Kyeong Yoo, Daigil Cha, Jung H. Shin, and Suk-Ho Choi

Appl. Phys. Lett. 89, 202112 (2006); http://dx.doi.org/10.1063/1.2388144 (3 pages) | Cited 2 times

Online Publication Date: 15 November 2006

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Effect of hydrogenation on memory properties has been studied for metal-oxide-semiconductor (MOS) structures with Si nanocrystals fabricated using inductively coupled plasma chemical vapor deposition and subsequent annealing. Hydrogenation induces a drastic increase of a dip in the quasistatic capacitance-voltage (C-V) curve of the MOS capacitor, caused by the reduction of the interface states due to hydrogen passivation. This is consistent with high-frequency C-V measurements showing more well-defined curves with less distortion in hydrogenated samples. After hydrogenation, the MOS device shows a significantly larger decrease of flatband voltage shift in electron charging than in hole charging, indicating more effective passivation of the defect states related to the electron charging. A longer retention time is found for electron charging after hydrogenation, but almost no change of charge loss rate for hole charging. These results suggest that an asymmetry exists in the effect of hydrogenation between electron and hole storage.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors

Measurement of the GaSb surface band bending potential from the magnetotransport characteristics of GaSb–InAs–AlSb quantum wells

P. A. Folkes, Godfrey Gumbs, Wen Xu, and M. Taysing-Lara

Appl. Phys. Lett. 89, 202113 (2006); http://dx.doi.org/10.1063/1.2388147 (3 pages) | Cited 12 times

Online Publication Date: 16 November 2006

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Low-temperature magnetotransport measurements on GaSb/InAs/AlSb coupled quantum well structures with a GaSb cap layer and self-consistent calculations of their electronic structure have led to the determination of the Fermi level at the surface, EFS, of undoped molecular-beam-epitaxy-grown GaSb. EFS is pinned around 0.2 eV above the top of the GaSb valence band when the GaSb cap layer width is greater than around 900 Å. For smaller GaSb cap widths, EFS decreases with the GaSb width. The undoped GaSb/InAs/AlSb heterostructure’s Fermi level is determined by bulk donor defects in the AlSb layer adjacent to the InAs quantum well.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects

Deep level transient spectroscopy study of Pd and Pt sputtering damage in n-type germanium

E. Simoen, K. Opsomer, C. Claeys, K. Maex, C. Detavernier, R. L. Van Meirhaeghe, and P. Clauws

Appl. Phys. Lett. 89, 202114 (2006); http://dx.doi.org/10.1063/1.2388869 (3 pages) | Cited 4 times

Online Publication Date: 16 November 2006

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Defect formation during Pd and Pt germanidation of n-type germanium, using rapid thermal annealing in the range of 300–500 °C, is investigated by deep level transient spectroscopy. Small concentrations of an electron trap at ∼ EC−0.385 eV are found, which is believed to be associated with vacancy-related sputtering damage. This is supported by the observation of much higher concentrations of vacancy-related deep levels on as-deposited Pt and Pd Schottky barriers. A steep concentration profile rising towards the surface confirms the assignment to Ar ion-related damage. The applied thermal budget points out that the defects observed in the germanide samples are more stable than simple vacancy-related point defects and could correspond to vacancy clusters formed during the deposition and/or the annealing step.
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71.55.Cn Elemental semiconductors
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
73.30.+y Surface double layers, Schottky barriers, and work functions

Extended microtunnels in GaN prepared by wet chemical etch

Hsin-Hsiung Huang, Hung-Yu Zeng, Chi-Ling Lee, Shih-Chang Lee, and Wei-I Lee

Appl. Phys. Lett. 89, 202115 (2006); http://dx.doi.org/10.1063/1.2374841 (3 pages) | Cited 10 times

Online Publication Date: 16 November 2006

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It is demonstrated in GaN that microtunnels extended beyond hundreds of microns can be easily achieved using wet chemical etch. To obtain this result, specially designed structures of GaN layers are first grown on sapphire substrates with metal-organic chemical vapor deposition and subsequently with hydride vapor phase epitaxy techniques. The prepared samples are then chemically etched in molten KOH. With the designed structure of GaN layers, extended microtunnels with triangular cross sections are formed. The crystallographic planes of the triangular bevels belong to the {11math2} family. The etch rate of the tunnel can be as high as 10 μm/min at proper etching conditions.
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81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.47.Fg Semiconductor surfaces
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Intermolecular and interlayer interactions in copper phthalocyanine films as measured with microspot photoemission spectroscopy

Takeharu Sugiyama, Toshihide Sasaki, Satoshi Kera, Nobuo Ueno, and Toshiaki Munakata

Appl. Phys. Lett. 89, 202116 (2006); http://dx.doi.org/10.1063/1.2388922 (3 pages) | Cited 11 times

Online Publication Date: 16 November 2006

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The authors have applied photoemission microspectroscopy to copper phthalocyanine films grown on a graphite surface with a lateral resolution of 0.3 μm and an energy resolution of 30 meV. The photoemission peak due to the highest occupied molecular orbital was found to be at binding energies of 1.13, 1.23, 1.38, and 1.5 eV, depending on film thickness. From the thickness and light-polarization dependence, the peaks were assigned to originate from isolated molecules, the first layer, the second layer, and multilayer, respectively. They demonstrate the capability of photoemission microspectroscopy to resolve electronic states modified by fine differences of molecular environments.
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71.20.Rv Polymers and organic compounds
73.21.Ac Multilayers
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.15.Nc Total energy and cohesive energy calculations

Hot phonons in Si-doped GaN

J. Liberis, M. Ramonas, O. Kiprijanovic, A. Matulionis, N. Goel, J. Simon, K. Wang, H. Xing, and D. Jena

Appl. Phys. Lett. 89, 202117 (2006); http://dx.doi.org/10.1063/1.2388866 (3 pages) | Cited 7 times

Online Publication Date: 17 November 2006

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Microwave noise and electron transport are studied in silicon-doped GaN channels grown by molecular beam epitaxy and subjected to a high electric field. The drift velocity of 2.8×107 cm/s is reached at 290 kV/cm for n ∼ 1×1018 cm−3 channel. No negative differential resistance is observed. The noise temperature exceeds ∼ 5000 K at ∼ 110 kV/cm for n ∼ 3×1017 cm−3 channel. The hot-phonon effect on power dissipation in GaN:Si is 3–4 times weaker as compared with the effect in an undoped AlGaN/GaN two-dimensional channel. Monte Carlo simulation shows a weak effect of hot phonons on hot-electron energy distribution.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
72.70.+m Noise processes and phenomena
73.61.Ey III-V semiconductors
72.20.Ht High-field and nonlinear effects

Critical thickness of heavily boron-doped silicon-germanium alloys

Saurabh Chopra, Mehmet C. Ozturk, Veena Misra, Kris McGuire, and L. E. McNeil

Appl. Phys. Lett. 89, 202118 (2006); http://dx.doi.org/10.1063/1.2374870 (3 pages) | Cited 1 time

Online Publication Date: 17 November 2006

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In this work, the effect of boron concentration on the critical thickness of heavily boron doped Si1−xGex alloys (Si1−x−yGexBy) has been studied using Raman spectroscopy. The experimental results indicate that while boron decreases the stored strain energy, it can substantially increase the critical thickness for a given Ge concentration. The Si1−x−yGexBy critical thickness was calculated using two different models based on energy balance and kinetic considerations. The results show that the kinetic model provides a good estimate for the Si1−x−yGexBy critical thickness.
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78.30.Hv Other nonmetallic inorganics
61.72.up Other materials
61.72.S- Impurities in crystals
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