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16 Apr 2012

Volume 100, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 100, 164101 (2012); http://dx.doi.org/10.1063/1.3702579 (4 pages)

Cheol-Ho Yun, Leslie Y. Yeo, James R. Friend, and Bernard Yan
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Metal–semiconductor transition in ultrathin cobalt-phthalocyanine films grown on SrTiO3 single crystal substrates

S. Samanta, Arvind Kumar, A. Singh, A. K. Debnath, P. Veerender, S. Basu, R. Prasad, D. K. Aswal, and S. K. Gupta

Appl. Phys. Lett. 100, 162101 (2012); http://dx.doi.org/10.1063/1.4704141 (4 pages)

Online Publication Date: 17 April 2012

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We have investigated the low temperature charge transport properties of ultrathin cobalt-phthalocyanine films grown on (100) SrTiO3 single crystal substrates. The temperature dependence of resistivity shows an anomalous behavior, i.e., a transition from semiconducting to metallic behavior at around 110 K. We demonstrated that metallic behavior in these films is triggered by compressive strains of the SrTiO3 substrate due to its cubic to tetragonal structural phase transition at 110 K.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations

Two-dimensional electron gas mobility limited by barrier and quantum well thickness fluctuations scattering in AlxGa1−xN/GaN multi-quantum wells

Guipeng Liu, Ju Wu, Yanwu Lu, Guijuan Zhao, Chengyan Gu, Changbo Liu, Ling Sang, Shaoyan Yang, Xianglin Liu, Qinsheng Zhu, and Zhanguo Wang

Appl. Phys. Lett. 100, 162102 (2012); http://dx.doi.org/10.1063/1.4704142 (4 pages) | Cited 1 time

Online Publication Date: 17 April 2012

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We calculate the electron mobility limited by the AlxGa1−xN barrier and the GaN well thickness fluctuations scattering of the two-dimensional electron gas (2DEG) at AlxGa1−xN/GaN multi-quantum wells (MQWs) with a triangle potential well. For this potential well, the ground subband energy is governed by the spontaneous and piezoelectric polarization fields and the fields are determined by the barrier and well thicknesses in undoped AlxGa1−xN/GaN MQWs. Thus, the thickness fluctuations of AlxGa1−xN barrier and GaN well will cause a local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.
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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.Fr Low-field transport and mobility; piezoresistance
77.22.Ej Polarization and depolarization

Red-green luminescence in indium gallium nitride alloys investigated by high pressure optical spectroscopy

Marius Millot, Zachary M. Geballe, Kin M. Yu, Wladek Walukiewicz, and Raymond Jeanloz

Appl. Phys. Lett. 100, 162103 (2012); http://dx.doi.org/10.1063/1.4704367 (4 pages) | Cited 2 times

Online Publication Date: 17 April 2012

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We performed optical absorption and photoluminescence experiments under high pressure up to 10 GPa on two good quality InGaN epilayers with ∼ 40% indium. The pressure coefficient of about 30 meV/GPa for the absorption edge is close to the bandgap pressure coefficients of InN and GaN, indicating similar pressure dependence of the fundamental band gap in the whole composition range. In contrast, the pressure coefficient of the photoluminescence peak energy shows much weaker pressure dependence which we attribute to an increasing role of highly localized defects when the conduction band approaches the Fermi level stabilization energy at higher indium contents.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
62.50.-p High-pressure effects in solids and liquids
71.20.Nr Semiconductor compounds
61.72.J- Point defects and defect clusters

Unusual photoresponse of indium doped ZnO/organic thin film heterojunction

Sesha Vempati, Saraswathi Chirakkara, J. Mitra, Paul Dawson, Karuna Kar Nanda, and S. B. Krupanidhi

Appl. Phys. Lett. 100, 162104 (2012); http://dx.doi.org/10.1063/1.4704655 (4 pages) | Cited 3 times

Online Publication Date: 17 April 2012

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Photoresponse of n-type indium-doped ZnO and a p-type polymer (PEDOT:PSS) heterojunction devices are studied, juxtaposed with the photoluminescence of the In-ZnO samples. In addition to the expected photoresponse in the ultraviolet, the heterojunctions exhibit significant photoresponse to the visible (532 nm). However, neither the doped ZnO nor PEDOT:PSS individually show any photoresponse to visible light. The sub-bandgap photoresponse of the heterojunction originates from visible photon mediated e-h generation between the In-ZnO valence band and localized states lying within the band gap. Though increased doping of In-ZnO has limited effect on the photoluminescence, it significantly diminishes the photoresponse. The study indicates that optimally doped devices are promising for the detection of wavelengths in selected windows in the visible.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Composition dependent bilayer atomic ordering in AlxGa1−xN films examined by polarization-dependent extended x-ray absorption fine structure

J. C. Woicik, K. F. Ludwig, Jr., and T. D. Moustakas

Appl. Phys. Lett. 100, 162105 (2012); http://dx.doi.org/10.1063/1.4704678 (4 pages)

Online Publication Date: 17 April 2012

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Extended x-ray absorption fine structure has been used to study the local structure of ordered AlxGa1−xN films with nominal concentrations of x = 0.20 and x = 0.45. Strong cation ordering is found in alternating (0001) planes for both samples, with the 20% sample exhibiting nearly ideal local order compared to the 45% sample. Significant distortions in the nearest-neighbor Ga-N distances compared to the virtual crystal approximation are observed, although these distortions are found to be smaller than for disordered films. This result is counter to current theoretical predictions.
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68.55.Nq Composition and phase identification
78.70.Dm X-ray absorption spectra

Laser energy tuning of carrier effective mass and thermopower in epitaxial oxide thin films

A. I. Abutaha, S. R. Sarath Kumar, and H. N. Alshareef

Appl. Phys. Lett. 100, 162106 (2012); http://dx.doi.org/10.1063/1.4704183 (4 pages) | Cited 1 time

Online Publication Date: 18 April 2012

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The effect of the laser fluence on high temperature thermoelectric properties of the La doped SrTiO3 (SLTO) thin films epitaxially grown on LaAlO3 〈100〉 substrates by pulsed laser deposition is clarified. It is shown that oxygen vacancies that influence the effective mass of carriers in SLTO films can be tuned by varying the laser energy. The highest power factor of 0.433 W K−1 m−1 has been achieved at 636 K for a film deposited using the highest laser fluence of 7 J cm−2 pulse−1.
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81.15.Fg Pulsed laser ablation deposition
61.72.jd Vacancies
68.55.ag Semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Semipolar {nmath01} InGaN/GaN ridge quantum wells (n = 1−3) fabricated by a regrowth technique

Mitsuru Funato, Teruhisa Kotani, Takeshi Kondou, and Yoichi Kawakami

Appl. Phys. Lett. 100, 162107 (2012); http://dx.doi.org/10.1063/1.4704779 (4 pages) | Cited 1 time

Online Publication Date: 19 April 2012

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Semipolar {nmath01} InGaN/GaN quantum wells (QWs) (n = 1−3) are fabricated on top of GaN microstructures, which consist of semipolar {1math01} facets. Semipolar planes are obtained via regrowth of three-dimensional structures on (0001) GaN templates under controlled growth conditions. Compared to QWs on {1math01} facets, {nmath01} ridge QWs show an intense emission at ∼ 440 nm. Time resolved photoluminescence reveals that the radiative lifetime of excitons in {nmath01} InGaN ridge QWs at 13 K is 310 ps, which is comparable to that in {1math01} QWs. The estimated internal quantum efficiency at room temperature is as high as 57%.
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81.07.St Quantum wells
78.47.jd Time resolved luminescence
71.35.-y Excitons and related phenomena
73.21.Fg Quantum wells
78.55.Cr III-V semiconductors
78.67.De Quantum wells

Improvement in the device performance of tin-doped indium oxide transistor by oxygen high pressure annealing at 150 °C

Se Yeob Park, Kwang Hwan Ji, Hong Yoon Jung, Ji-In Kim, Rino Choi, Kyoung Seok Son, Myung Kwan Ryu, Sangyoon Lee, and Jae Kyeong Jeong

Appl. Phys. Lett. 100, 162108 (2012); http://dx.doi.org/10.1063/1.4704926 (4 pages) | Cited 4 times

Online Publication Date: 19 April 2012

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This study examined the effect of oxygen (O2) high pressure annealing (HPA) on tin-doped indium oxide (ITO) thin film transistors (TFTs). The HPA-treated TFT at 150 °C exhibited a high saturation mobility (μSAT), low subthreshold gate swing (SS), threshold voltage, and Ion/off of 25.8 cm2/Vs, 0.14 V/decade, 0.6 V, and 2 × 108, respectively. In contrast, the ambient-annealed device suffered from a lower μSAT and high SS value of 5.2 cm2/Vs and 0.58 V/decade, respectively. This improvement can be attributed to the decreased concentration of oxygen vacancy defects in the ITO channel layer during the effective O2 HPA treatment, which also resulted in smaller hysteresis and less degradation of the drain current under positive bias stress conditions.
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85.30.Tv Field effect devices

Spatially modulated photoluminescence properties in dynamically strained GaAs/AlAs quantum wells by surface acoustic wave

Tetsuomi Sogawa, Haruki Sanada, Hideki Gotoh, Hiroshi Yamaguchi, and Paulo V. Santos

Appl. Phys. Lett. 100, 162109 (2012); http://dx.doi.org/10.1063/1.3703309 (4 pages) | Cited 3 times

Online Publication Date: 20 April 2012

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Spatially resolved photoluminescence (PL) spectra and polarization anisotropy were investigated in GaAs/AlAs dynamic wires, which were formed by applying a surface acoustic wave (SAW) on GaAs/AlAs quantum wells along the [110] or [1-10] direction. A synchronized excitation method clearly demonstrates that the band gap energies are spatially modulated by the travelling-SAW-induced strain. It is found that both the spatial PL modulation and anisotropic polarization properties depend on the SAW direction. The spatial modulation of the polarization anisotropies and their dependence on the strain-induced valence band mixing are also discussed theoretically.
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78.55.Cr III-V semiconductors
78.67.De Quantum wells
68.65.Fg Quantum wells

Structural and electrical properties of epitaxial Bi2Se3 thin films grown by hybrid physical-chemical vapor deposition

Joseph E. Brom, Yue Ke, Renzhong Du, Dongjin Won, Xiaojun Weng, Kalissa Andre, Jarod C. Gagnon, Suzanne E. Mohney, Qi Li, Ke Chen, X. X. Xi, and Joan M. Redwing

Appl. Phys. Lett. 100, 162110 (2012); http://dx.doi.org/10.1063/1.4704680 (4 pages) | Cited 1 time

Online Publication Date: 20 April 2012

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We report the epitaxial growth of Bi2Se3 thin films on (0001) Al2O3 substrates by hybrid physical-chemical vapor deposition (HPCVD). The HPCVD technique combines the thermal decomposition of trimethylbismuth with the thermal evaporation of Se and leads to a high Se partial pressure in the growth ambient. The Bi2Se3 films are highly c-axis oriented on sapphire but contain planar defects including stacking faults and twin boundaries. Variable-temperature Hall-effect measurements demonstrate a carrier concentration of 5.8 × 1018 cm−3 and a mobility of 900 cm2/Vs at 4.2 K. These results demonstrate the potential of HPCVD for producing high quality Bi2Se3 films for topological insulator studies.
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68.55.ag Semiconductors
61.72.Nn Stacking faults and other planar or extended defects
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
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