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23 Jul 2012

Volume 101, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 101, 043101 (2012); http://dx.doi.org/10.1063/1.4737152 (4 pages)

Toshiaki Tanigaki, Yoshikatsu Inada, Shinji Aizawa, Takahiro Suzuki, Hyun Soon Park, Tsuyoshi Matsuda, Akira Taniyama, Daisuke Shindo, and Akira Tonomura
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Self-heating enhanced charge trapping effect for InGaZnO thin film transistor

Te-Chih Chen, Ting-Chang Chang, Tien-Yu Hsieh, Ming-Yen Tsai, Yu-Te Chen, Yi-Chen Chung, Hung-Che Ting, and Chia-Yu Chen

Appl. Phys. Lett. 101, 042101 (2012); http://dx.doi.org/10.1063/1.4733617 (4 pages) | Cited 1 time

Online Publication Date: 23 July 2012

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This paper investigates the degradation mechanism under self-heating stress for InGaZnO thin film transistor. The apparent positive threshold voltage (Vt) shift and on-current degradation indicate that the combination of trap states generation and electron trapping effect occur during stress. Furthermore, the asymmetric degradation behavior in the Id-Vg saturation measurement demonstrates that the trap states location is near the source side since the relative vertical electrical field is higher than drain side. Moreover, the Joule heating generated by self-heating operation can enhance electron trapping effect and cause larger Vt shift in comparison with the gate-bias stress.
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85.30.Tv Field effect devices

In-situ transmission electron microscopy of partial-dislocation glide in 4H-SiC under electron radiation

Yutaka Ohno, Ichiro Yonenaga, Kotaro Miyao, Koji Maeda, and Hidekazu Tsuchida

Appl. Phys. Lett. 101, 042102 (2012); http://dx.doi.org/10.1063/1.4737938 (3 pages) | Cited 1 time

Online Publication Date: 23 July 2012

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Electron-radiation-enhanced glide of 30°-Si(g) partial dislocations bringing about an expansion/shrinkage of Shockley-type stacking faults in 4H-SiC was observed in-situ by transmission electron microscopy. Geometrical kinks on 30°-Si(g) partials did not migrate in the dark, indicating that the kink migration is enhanced by electron irradiation. The direction of the enhanced glide was reversible depending on the irradiation intensity, which can be interpreted in terms of a sign reversal of the driving force originating in the effective stacking fault energy variable with the irradiation intensity.
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61.80.Fe Electron and positron radiation effects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Nn Stacking faults and other planar or extended defects

Optical polarization in c-plane Al-rich AlN/AlxGa1-xN single quantum wells

T. M. Al tahtamouni, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 101, 042103 (2012); http://dx.doi.org/10.1063/1.4737941 (3 pages) | Cited 1 time

Online Publication Date: 23 July 2012

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The optical polarization of AlN/AlxGa1-xN single quantum wells (x = 0.65) has been studied by means of photoluminescence (PL) spectroscopy. The predominant polarization component of the band-edge PL switched from E ∥ c to E ⊥ c at a well width around 2 nm. The emission intensity with polarization of E ⊥ c and the degree of polarization were found to decrease with increasing well width. The emission intensity with polarization of E ∥ c was found to increase with increasing well width.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Impact of surface morphology above threading dislocations on leakage current in 4H-SiC diodes

Hirokazu Fujiwara, Hideki Naruoka, Masaki Konishi, Kimimori Hamada, Takashi Katsuno, Tsuyoshi Ishikawa, Yukihiko Watanabe, and Takeshi Endo

Appl. Phys. Lett. 101, 042104 (2012); http://dx.doi.org/10.1063/1.4738886 (4 pages)

Online Publication Date: 24 July 2012

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The nano-scale pits above the threading dislocations were found to be in the same location as the leakage current points in Schottky barrier diodes and junction barrier Schottky diodes. This study compared the leakage current of 1.2 kV, 200 A diodes with and without nano-scale pits. The leakage current in diodes without nano-scale pits was lower than those in diodes with pits. In the diodes without nano-scale pits, the leakage currents were generated at step-bunching area and the leakage current at the threading dislocations was not observed.
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85.30.Hi Surface barrier, boundary, and point contact devices
68.35.bg Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Dielectric covered hairpin probe for its application in reactive plasmas

G. S. Gogna, C. Gaman, S. K. Karkari, and M. M. Turner

Appl. Phys. Lett. 101, 042105 (2012); http://dx.doi.org/10.1063/1.4738888 (4 pages)

Online Publication Date: 24 July 2012

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The hairpin probe is a well known technique for measuring local electron density in low temperature plasmas. In reactive plasmas, the probe characteristics are affected by surface sputtering, contamination, and secondary electron emission. At higher densities, the plasma absorbs the entire electromagnetic energy of hairpin and hence limits the density measurements. These issues can be resolved by covering the hairpin surface with a thin layer of dielectric. In this letter, the dielectric contribution to the probe characteristics is incorporated in a theory which is experimentally verified. The dielectric covering improves the performance of probe and also allows the hairpin tip to survive in reactive plasma where classical electrical probes are easily damaged.
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52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties

Mg doping in wurtzite ZnO coupled with native point defects: A mechanism for enhanced n-type conductivity and photoluminescence

Rajkrishna Dutta and Nibir Mandal

Appl. Phys. Lett. 101, 042106 (2012); http://dx.doi.org/10.1063/1.4738990 (4 pages) | Cited 2 times

Online Publication Date: 24 July 2012

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From first-principles calculations, we show that Mg energetically prefers to substitute Zn atoms rather than occupying interstitial octahedral or tetrahedral sites in ZnO structure. The Mg substitutions significantly reduce the formation energies of Zn/O vacancy and Zn interstitial defects, which consequently promotes the n-type conductivity and photoluminescence in ZnO. The defects form complexes with moderate binding energies, as supported by the shorter Mg-O bonds relative to Zn-O bonds. In agreement with available experimental data, Mg substitutions result in contraction along c-axis and extension along a-axis in wurtzite ZnO.
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61.72.uj III-V and II-VI semiconductors
61.66.Fn Inorganic compounds
71.20.Nr Semiconductor compounds
72.80.Ey III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors

Heavy p-type doping of ZnSe thin films using Cu2Se in pulsed laser deposition

Xiaojun Zhang, Kin Man Yu, Coleman X. Kronawitter, Zhixun Ma, Peter Y. Yu, and Samuel S. Mao

Appl. Phys. Lett. 101, 042107 (2012); http://dx.doi.org/10.1063/1.4739083 (3 pages)

Online Publication Date: 25 July 2012

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Undoped, Cu-doped, Se-enriched, and Cu2Se-doped ZnSe films have been grown on fused quartz substrates by pulsed laser deposition. While the other films are highly resistive, Cu2Se-doped ZnSe films are p-type conducting with hole concentrations of ∼1.1 × 1019 cm−3 and resistivities of ∼0.098 Ω cm (compared with previous reports of ∼1×1018 cm−3 and ∼0.75 Ω cm). The exceptional heavy p-type doping of ZnSe films can be attributed to substitution of Zn atoms with Cu while limiting selenium-vacancy-associated compensating defects with additional selenium. This work is of importance to solve doping difficulties and contact problems of wide-bandgap semiconductors.
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68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition

A unified model for insulator selection to form ultra-low resistivity metal-insulator-semiconductor contacts to n-Si, n-Ge, and n-InGaAs

Ashish Agrawal, Nikhil Shukla, Khaled Ahmed, and Suman Datta

Appl. Phys. Lett. 101, 042108 (2012); http://dx.doi.org/10.1063/1.4739784 (4 pages) | Cited 3 times

Online Publication Date: 26 July 2012

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A comprehensive, physics-based unified model is developed for study of low resistivity metal-insulator-semiconductor (M-I-S) ohmic contact. Reduction in metal-induced gap state density and Fermi unpinning in semiconductor as a function of insulator thickness is coupled with electron transport including tunnel resistance through the metal-insulator-semiconductor (M-I-S) system to calculate specific contact resistivity at each insulator thickness for n-Si, n-Ge, and n-InGaAs. Low conduction band offset results in ∼ 1×10−9 Ω−cm2 contact resistivity with TiO2 insulator on n-Si, ∼ 7×10−9 Ω−cm2 can be achieved using TiO2 and ZnO on n-Ge, and ∼ 6×10−9 Ω−cm2 can be achieved with CdO insulator on n-InGaAs, which meet the sub-22nm CMOS requirements.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling
73.40.Ns Metal-nonmetal contacts

Relationship between dielectric coefficient and Urbach tail width of hydrogenated amorphous germanium carbon alloy films

C. Q. Hu, F. F. Meng, M. Wen, Z. Q. Gu, J. Y. Wang, X. F. Fan, and W. T. Zheng

Appl. Phys. Lett. 101, 042109 (2012); http://dx.doi.org/10.1063/1.4739788 (5 pages)

Online Publication Date: 26 July 2012

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It is found in hydrogenated amorphous germanium carbon alloy films that the dielectric coefficient (ε) plays an important role in Urbach tail width (E0), besides the degree of structural disorder that has previously proved to be an important factor contributing to E0 in amorphous semiconductor alloy films. The quantitative relationship between E0 and ε has been well explored by means of hydrogen-like atom model of energy levels in defective crystalline semiconductors. It is shown that E0 is proportional to the variation in 1/ε2 if the degree of structural disorder remains constant, which agrees well with the existing experimental findings.
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77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
61.43.Dq Amorphous semiconductors, metals, and alloys
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.55.Jv Disordered structures; amorphous and glassy solids

Dependence of internal quantum efficiency on doping region and Si concentration in Al-rich AlGaN quantum wells

Hideaki Murotani, Daiki Akase, Koji Anai, Yoichi Yamada, Hideto Miyake, and Kazumasa Hiramatsu

Appl. Phys. Lett. 101, 042110 (2012); http://dx.doi.org/10.1063/1.4739431 (4 pages)

Online Publication Date: 26 July 2012

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The internal quantum efficiency (IQE) of Si-doped AlGaN quantum wells has been studied by means of photoluminescence spectroscopy. Analysis of the IQE as a function of doping region revealed that the IQE increased from 19% to 40% with doping of the well layers. This increase was attributed to an improvement in the interface quality between well and barrier layers as well as a reduction in point defect density. Moreover, the IQE increased to a maximum of 50% and then decreased with increasing Si concentration of the well layers. This indicated the existence of an optimum Si concentration for IQE improvement.
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61.72.uj III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.67.De Quantum wells
61.72.J- Point defects and defect clusters
61.72.sd Impurity concentration
61.72.uf Ge and Si

Mobility enhancement of strained Si by optimized SiGe/Si/SiGe structures

S.-H. Huang, T.-M. Lu, S.-C. Lu, C.-H. Lee, C. W. Liu, and D. C. Tsui

Appl. Phys. Lett. 101, 042111 (2012); http://dx.doi.org/10.1063/1.4739513 (3 pages)

Online Publication Date: 26 July 2012

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An un-doped SiGe/strained Si/SiGe quantum well was fabricated on p-type Si at 550 °C by hot-wall ultrahigh vacuum chemical vapor deposition. To induce a two-dimensional electron gas (2DEG) in the strained Si channel, a gate structure with Al2O3 and Cr/Au metal was deposited and biased at positive bias. The 2DEG mobility reaches 2 × 106 cm2/V s, a record value, at 0.3 K for 15 nm Si well with a 526 nm Si0.86Ge0.14 barrier layer. The dominant factors that limit the mobility are Coulomb scattering of background charges and interface roughness scattering. In addition, the threading dislocation scattering also plays a role to determine the peak mobility. Reduction of Ge concentration in the SiGe barrier layer and the relaxed buffer layer decreases the threading dislocation density and the roughness, effectively enhancing the mobility of the 2DEG in the Si channel.
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73.63.Hs Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.35.Ct Interface structure and roughness
73.21.Fg Quantum wells

Optimization of sample-chip design for stub-matched radio-frequency reflectometry measurements

S. Hellmüller, M. Pikulski, T. Müller, B. Küng, G. Puebla-Hellmann, A. Wallraff, M. Beck, K. Ensslin, and T. Ihn

Appl. Phys. Lett. 101, 042112 (2012); http://dx.doi.org/10.1063/1.4739248 (4 pages) | Cited 2 times

Online Publication Date: 27 July 2012

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A radio-frequency (rf) matching circuit with an in situ tunable varactor diode used for rf reflectometry measurements in semiconductor nanostructures is investigated and used to optimize the sample-specific chip design. The samples are integrated in a 2–4 GHz stub-matching circuit consisting of a waveguide stub shunted to the terminated coplanar waveguide. Several quantum point contacts fabricated on a GaAs/AlGaAs heterostructure with different chip designs are compared. We show that the change of the reflection coefficient for a fixed change in the quantum point contact conductance can be enhanced by a factor of 3 compared to conventional designs by a suitable electrode geometry.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
84.32.Tt Capacitors
84.40.Dc Microwave circuits
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Kk Junction diodes

Copper centers in copper-diffused n-type silicon measured by photoluminescence and deep-level transient spectroscopy

Minoru Nakamura, Susumu Murakami, and Haruhiko Udono

Appl. Phys. Lett. 101, 042113 (2012); http://dx.doi.org/10.1063/1.4739470 (4 pages)

Online Publication Date: 27 July 2012

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While photoluminescence observed the continuous change of the 1.014-eV copper center (CuPL center) intensity with diffusion temperature, deep-level transient spectroscopy (DLTS) measured a considerable number of independent copper-related peaks in silicon samples copper-diffused at different temperatures. There was no DLTS peak whose intensity showed the same diffusion-temperature dependence as that of the CuPL center intensity, which led the conclusion that the CuPL center has no electrically active energy level in the upper-half of the band-gap in silicon. All the DLTS peaks observed were attributed to originate from the variety of copper clusters or small copper precipitates.
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78.55.Ap Elemental semiconductors
66.30.J- Diffusion of impurities
68.35.Fx Diffusion; interface formation
68.47.Fg Semiconductor surfaces
71.20.Mq Elemental semiconductors
71.55.Cn Elemental semiconductors

Room temperature fabrication of p-channel Cu2O thin-film transistors on flexible polyethylene terephthalate substrates

Z. Q. Yao, S. L. Liu, L. Zhang, B. He, A. Kumar, X. Jiang, W. J. Zhang, and G. Shao

Appl. Phys. Lett. 101, 042114 (2012); http://dx.doi.org/10.1063/1.4739524 (4 pages) | Cited 4 times

Online Publication Date: 27 July 2012

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The effects of growth temperature on the microstructure evolution and electrical transport properties of Cu2O films were investigated. Nanocrystalline Cu2O films with modest p-type semiconducting properties (Hall mobilities ∼20 cm2/Vs, hole concentrations ∼1016 cm−3) were successfully prepared at room temperature without post-annealing. Bottom gate and top contact p-channel Cu2O thin-film transistors (TFTs) were constructed on flexible polyethylene terephthalate substrates at room temperature, which shows superior transfer performance (field effect mobility ∼2.40 cm2/Vs and current on/off ratio ∼3.96 × 104). The low processing temperature and the good electrical performance of the p-type Cu2O TFTs suggest their good potential for applications in high-throughput and low-cost electronics.
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85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
72.20.Ee Mobility edges; hopping transport
73.63.Bd Nanocrystalline materials
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