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29 Oct 2012

Volume 101, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 183101 (2012); http://dx.doi.org/10.1063/1.4761935 (4 pages)

S. J. Kim, J. J. Lee, H. J. Kang, J. B. Choi, Y.-S. Yu, Y. Takahashi, and D. G. Hasko
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Topological phase transition and unexpected mass acquisition of Dirac fermion in TlBi(S1−xSex)2

Chengwang Niu, Ying Dai, Yingtao Zhu, Jibao Lu, Yandong Ma, and Baibiao Huang

Appl. Phys. Lett. 101, 182101 (2012); http://dx.doi.org/10.1063/1.4764946 (5 pages)

Online Publication Date: 29 October 2012

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Based on first-principles calculations and effective Hamiltonian analysis, we predict a topological phase transition from normal to topological insulators and the opening of a gap without breaking the time-reversal symmetry in TlBi(S1−xSex)2. The transition can be driven by modulating the Se concentration, and the rescaled spin-orbit coupling and lattice parameters are the key ingredients for the transition. For topological surface states, the Dirac cone evolves differently as the explicit breaking of inversion symmetry and the energy band can be opened under asymmetry surface. Our results present theoretical evidence for experimental observations [Xu et al., Science 332, 560 (2011); Sato et al., Nat. Phys. 7, 840 (2011)].
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
61.66.Fn Inorganic compounds
71.20.Ps Other inorganic compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.20.At Surface states, band structure, electron density of states

A 2 nm low temperature GaN spacer to improve the transport properties of two-dimensional electron gas in AlGaN/InAlN/AlN/GaN heterostructures

Jieqin Ding, Xiaoliang Wang, Hongling Xiao, Cuimei Wang, Hong Chen, Yang Bi, Qinwen Deng, Jingwen Zhang, and Xun Hou

Appl. Phys. Lett. 101, 182102 (2012); http://dx.doi.org/10.1063/1.4765086 (4 pages)

Online Publication Date: 29 October 2012

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AlGaN layers were grown on InAlN/AlN/GaN heterostructure with various temperatures. The two-dimensional electron gas density and mobility in heterostructure with high temperature AlGaN were deteriorated which is attributed to the reverse polarization field of AlGaN and the degradation of InAlN structural quality and surface morphology. A 2 nm low temperature GaN spacer was inserted to reduce the risk of InAlN degradation. The improved structures demonstrated an increase of two-dimensional electron gas density and mobility compared to the heterostructures without the GaN spacer, which results in the reduction of sheet resistance. Particularly, at 855 °C, an enhancement of mobility in the improved structure indicates that the heterostructure is relatively stable at this temperature. At higher temperature of 920 °C, significant increase of sheet resistance indicates a sharp degradation of InAlN quality.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.-r Electron states at surfaces and interfaces

Polarization spectroscopy of N-polar AlGaN/GaN multi quantum wells grown on vicinal (000math) GaN

S. Keller, N. Pfaff, S. P. DenBaars, and U. K. Mishra

Appl. Phys. Lett. 101, 182103 (2012); http://dx.doi.org/10.1063/1.4764070 (3 pages)

Online Publication Date: 29 October 2012

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Pronounced polarized light emission was observed from N-polar AlGaN/GaN multi quantum wells grown on (000math) GaN with a misorientation of 4° toward the m-direction grown by metal organic chemical vapor deposition. The misoriented (Al,Ga,In)N layers exhibited a high density of surface steps parallel to the 〈11math0〉 direction with step heights between 1 and 2 nm. The corrugated surfaces led to the formation of self organized quantum wire arrays in samples with 2.5 and 3.5 nm thick wells, revealed by a degree of polarization of 0.19 and 0.14, respectively, for light emission at 10 K.
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78.67.De Quantum wells
81.07.St Quantum wells
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors

Tuning hole mobility in InP nanowires

M. Rebello Sousa Dias, A. Picinin, V. Lopez-Richard, S. E. Ulloa, L. K. Castelano, J. P. Rino, and G. E. Marques

Appl. Phys. Lett. 101, 182104 (2012); http://dx.doi.org/10.1063/1.4764902 (4 pages)

Online Publication Date: 1 November 2012

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Transport properties of holes in InP nanowires (NWs) were calculated considering electron-phonon interaction via deformation potentials, the effect of temperature, and strain fields. Using molecular dynamics, we simulate NW structures, the longitudinal optical phonon (LO-phonon) energy renormalization, and lifetime. The valence band ground state changes between light- and heavy-hole character, as the strain fields and the NW size vary. Drastic changes in the mobility arise with the onset of resonance between the LO-phonons and the separation between valence subbands.
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73.61.Ey III-V semiconductors
63.20.kd Phonon-electron interactions
63.22.Gh Nanotubes and nanowires
71.38.-k Polarons and electron-phonon interactions
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance

Fermi-level unpinning and low resistivity in contacts to n-type Ge with a thin ZnO interfacial layer

Prashanth Paramahans Manik, Ravi Kesh Mishra, V. Pavan Kishore, Prasenjit Ray, Aneesh Nainani, Yi-Chiau Huang, Mathew C. Abraham, Udayan Ganguly, and Saurabh Lodha

Appl. Phys. Lett. 101, 182105 (2012); http://dx.doi.org/10.1063/1.4764909 (5 pages)

Online Publication Date: 1 November 2012

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We report low resistance Ohmic contacts on n-Ge using a thin ZnO interfacial layer (IL) capped with Ti. A 350°C post metallization anneal is used to create oxygen vacancies that dope ZnO heavily n-type (n+). Rectifying Ti/n-Ge contacts become Ohmic with 1000× higher reverse current density after insertion of n+-ZnO IL. Specific resistivity of ∼ 1.4×10−7 Ω cm2 is demonstrated on epitaxial n+-Ge (2.5×1019 cm−3) layers. Low resistance with ZnO IL can be attributed to (a) low barrier height from Fermi-level unpinning, (b) good conduction band alignment between ZnO and Ge, and (c) thin tunneling barrier due to the n+ doping.
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73.40.Ns Metal-nonmetal contacts
61.72.jd Vacancies
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
73.40.Ei Rectification
73.40.Gk Tunneling

Indicators of mobility extraction error in bottom gate CdS metal-oxide-semiconductor field-effect transistors

Ukjin Jung, Young Gon Lee, Jin Ju Kim, Sang Kyung Lee, I. Mejia, A. Salas-Villasenor, Manuel Quevedo-Lopez, and Byoung Hun Lee

Appl. Phys. Lett. 101, 182106 (2012); http://dx.doi.org/10.1063/1.4765067 (3 pages)

Online Publication Date: 1 November 2012

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Widely varying mobility values of CdS metal-oxide-semiconductor field-effect transistors have been reported in the literature (μ = 1–48 cm2/Vs). Sulfide vacancies in CdS channel generated by an incomplete post deposition anneal are found to be the origin of scattered mobility values. The presence of sulfide vacancies can be easily diagnosed by simple electrical measurements checking a strong channel length dependence of mobility and an abrupt drain current increase due to the carrier ionization at sulfur vacancies.
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85.30.Tv Field effect devices
61.72.jd Vacancies
72.80.Ey III-V and II-VI semiconductors
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