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6 Feb 2006

Volume 88, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 88, 063509 (2006); http://dx.doi.org/10.1063/1.2171834 (3 pages)

M. Feng, N. Holonyak, R. Chan, A. James, and G. Walter
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Propagation of stacking faults from surface damage in SiC PiN diodes

Z. Zhang, S. I. Maximenko, A. Shrivastava, P. Sadagopan, Y. Gao, and T. S. Sudarshan

Appl. Phys. Lett. 88, 062101 (2006); http://dx.doi.org/10.1063/1.2172015 (3 pages) | Cited 3 times

Online Publication Date: 6 February 2006

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The propagation of stacking faults (SF) in SiC PiN diodes under forward bias was studied by the electron beam induced current mode of scanning electron microscopy. The primary SF nucleation sites were confirmed to be pre-existing basal plane dislocations (BPD). Damage to the diode surface can also cause SF propagation in the device. Hence, in addition to the elimination of BPDs in the active layer of the diode, avoidance of surface damage by paying careful attention to device processing and testing is also important for fabricating stable SiC PiN diodes.
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61.72.−y
61.72.Nn Stacking faults and other planar or extended defects
61.72.Lk Linear defects: dislocations, disclinations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Studies of charge carrier trapping and recombination processes in Si/SiO2/MgO structures using second-harmonic generation

Y. V. White, X. Lu, R. Pasternak, N. H. Tolk, A. Chatterjee, R. D. Schrimpf, D. M. Fleetwood, A. Ueda, and R. Mu

Appl. Phys. Lett. 88, 062102 (2006); http://dx.doi.org/10.1063/1.2172008 (3 pages) | Cited 5 times

Online Publication Date: 6 February 2006

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Effects of MgO deposition on Si/SiO2 system and charge carrier trapping and recombination in Si/SiO2/MgO structures are studied using second-harmonic generation (SHG). An ultrafast 800 nm laser was used both for multi-photon induced electron injection through the SiO2 into a potential well in the MgO, and for monitoring the time-dependent SHG signal, which is sensitive to the electric field at the Si/SiO2 interface. Our results indicate that the MgO deposition introduces new trap states, and electrons trapped in the MgO transport more readily through the SiO2 than those in traps on the surface of SiO2. We attribute this to differences in trap energy levels and/or differences in process damage-induced defect densities in the SiO2.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Exciton localization in AlGaN alloys

N. Nepal, J. Li, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 88, 062103 (2006); http://dx.doi.org/10.1063/1.2172728 (3 pages) | Cited 24 times

Online Publication Date: 6 February 2006

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Deep ultraviolet (UV) photoluminescence emission spectroscopy has been employed to study the exciton localization effect in AlGaN alloys. The temperature dependence of the exciton emission peak energy in AlxGa1−xN alloys (0 ⩽ x ⩽ 1) was measured from 10 to 800 K and fitted by the Varshni equation. Deviations of the measured data from the Varshni equation at low temperatures directly provide the exciton localization energies, ELoc. It was found that ELoc increases with x for x ⩽ 0.7, and decreases with x for x ≥ 0.8. Our experimental results revealed that for AlGaN alloys, ELoc obtained by the above method has simple linear relations with the localized exciton thermal activation energy and the emission linewidth, thereby established three parallel methods for directly measuring the exciton localization energies in AlGaN alloys. The consequence of strong carrier and exciton localization in AlGaN alloys on the applications of nitride deep UV optoelectronic devices is also discussed.
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78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
78.40.Fy Semiconductors
73.61.Ey III-V semiconductors

Investigation of a polythiophene interface using photoemission spectroscopy in combination with electrospray thin-film deposition

A. J. Cascio, J. E. Lyon, M. M. Beerbom, R. Schlaf, Y. Zhu, and S. A. Jenekhe

Appl. Phys. Lett. 88, 062104 (2006); http://dx.doi.org/10.1063/1.2172069 (3 pages) | Cited 24 times

Online Publication Date: 9 February 2006

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The conjugated polymer poly(3-hexylthiophene) (P3HT) was deposited in several steps onto a highly oriented pyrolytic graphite (HOPG) substrate directly from solution in high vacuum, using an electrospray thin-film deposition system. The deposition system was attached to a photoemission spectroscopy setup via in situ sample transfer, allowing characterization in between deposition steps with x-ray and ultraviolet photoemission spectroscopy. The resultant series of spectra enabled the determination of the ionization energy, work function, and highest occupied molecular orbital binding energy of the P3HT overlayer, while giving detailed insight into the orbital alignment and dipole formation at the P3HT/HOPG contact.
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78.66.Qn Polymers; organic compounds
81.15.Pq Electrodeposition, electroplating
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.55.-a Thin film structure and morphology
73.30.+y Surface double layers, Schottky barriers, and work functions

Electrical spin injection from ZnMnSe into InGaAs quantum wells and quantum dots

W. Löffler, D. Tröndle, J. Fallert, H. Kalt, D. Litvinov, D. Gerthsen, J. Lupaca-Schomber, T. Passow, B. Daniel, J. Kvietkova, M. Grün, C. Klingshirn, and M. Hetterich

Appl. Phys. Lett. 88, 062105 (2006); http://dx.doi.org/10.1063/1.2172221 (3 pages) | Cited 26 times

Online Publication Date: 9 February 2006

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We report on efficient injection of electron spins into InGaAs-based nanostructures. The spin light-emitting diodes incorporate an InGaAs quantum well or quantum dots, respectively, as well as a semimagnetic ZnMnSe spin-aligner layer. We show a circular polarization degree of up to 35% for the electroluminescence from InGaAs quantum wells and up to 21% for InGaAs quantum dots. We can clearly attribute the polarization of the emitted photons to the spin alignment in the semimagnetic layer by comparison to results from reference devices (where the ZnMnSe is replaced by ZnSe) and from all-optical measurements.
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73.63.Kv Quantum dots
73.63.Hs Quantum wells
72.25.Dc Spin polarized transport in semiconductors
78.67.Hc Quantum dots
78.67.De Quantum wells
75.50.Pp Magnetic semiconductors

Effects of hydrogen on majority carrier transport and minority carrier lifetimes in long wavelength infrared HgCdTe on Si

P. Boieriu, C. H. Grein, S. Velicu, J. Garland, C. Fulk, S. Sivananthan, A. Stoltz, L. Bubulac, and J. H. Dinan

Appl. Phys. Lett. 88, 062106 (2006); http://dx.doi.org/10.1063/1.2172295 (3 pages) | Cited 6 times

Online Publication Date: 9 February 2006

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We present the results of using an electron cyclotron resonance (ECR) plasma to incorporate hydrogen into long wavelength infrared HgCdTe layers grown by molecular beam epitaxy. Both as-grown and annealed layers doped in situ with indium were hydrogenated. Secondary ion mass spectroscopy confirmed the incorporation of hydrogen. Hall and photoconductive lifetime measurements were used to assess the effects of the hydrogenation. Increases in the electron mobilities and minority carrier lifetimes were observed for almost all ECR conditions.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Ga II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
76.40.+b Diamagnetic and cyclotron resonances
52.77.-j Plasma applications
72.40.+w Photoconduction and photovoltaic effects

Dopant source choice for formation of p-type ZnO: Li acceptor

Y. J. Zeng, Z. Z. Ye, W. Z. Xu, D. Y. Li, J. G. Lu, L. P. Zhu, and B. H. Zhao

Appl. Phys. Lett. 88, 062107 (2006); http://dx.doi.org/10.1063/1.2172743 (3 pages) | Cited 82 times

Online Publication Date: 10 February 2006

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Li-doped, p-type ZnO thin films have been realized via dc reactive magnetron sputtering. An optimized result with a resistivity of 16.4 Ω cm, Hall mobility of 2.65 cm2/V s, and hole concentration of 1.44×1017 cm−3 was achieved, and electrically stable over a month. Hall-effect measurements supported by secondary ion mass spectroscopy indicated that the substrate temperature played a key role in optimizing the p-type conduction of Li-doped ZnO thin films. Furthermore, ZnO-based p-n homojunction was fabricated by deposition of a Li-doped p-type ZnO layer on an Al-doped n-type ZnO layer.
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61.72.uj III-V and II-VI semiconductors
73.61.Ga II-VI semiconductors
71.55.Gs II-VI semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

InAsP/InGaAs composite quantum well for separate TE and TM gain

R. Prasanth, J. E. M. Haverkort, and J. H. Wolter

Appl. Phys. Lett. 88, 062108 (2006); http://dx.doi.org/10.1063/1.2172709 (3 pages)

Online Publication Date: 10 February 2006

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Composite InAsP/InGaAs quantum wells are a promising candidate for realizing polarization-independent semiconductor optical amplifiers at 1.55 μm. We investigated the possibility of 8 nm tensile-strained InGaAs well surrounded by two compressively-strained InAsP layers, for achieving separate gain for TE and TM polarized light. The InAsP layers provide strain compensation while simultaneously shifting the band gap to 1.55 μm. The edge photoluminescence spectra shows that the gain for TE and TM polarized light is in the order of (3:1).
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42.70.Hj Laser materials
78.67.De Quantum wells
78.55.Cr III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes
73.21.Fg Quantum wells
71.20.Nr Semiconductor compounds

Mesoscopic electrical conduction in nanocrystalline SrTiO3

P. Balaya, J. Jamnik, J. Fleig, and J. Maier

Appl. Phys. Lett. 88, 062109 (2006); http://dx.doi.org/10.1063/1.2171798 (3 pages) | Cited 29 times

Online Publication Date: 10 February 2006

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Detailed impedance analysis of dense nanocrystalline SrTiO3 ceramics in comparison to microcrystalline samples gives direct and unambiguous evidence of a space charge overlap as a characteristic size effect. Owing to the significant extension of depletion zones for the holes, the bulk impedance signal disappears at about 100 nm grain boundary spacing. In accordance with the increased homogeneity of this mesoscopic situation the remaining signal is characterized by a frequency dispersion of the circuit parameters that is low compared with the microcrystalline samples. Space charge potentials for various sizes are extracted. The conclusions are corroborated by numerical calculations.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
73.23.-b Electronic transport in mesoscopic systems
73.63.Bd Nanocrystalline materials
61.46.-w Structure of nanoscale materials
77.22.Jp Dielectric breakdown and space-charge effects
61.72.Mm Grain and twin boundaries

Comparison of valence band x-ray photoelectron spectrum between Al–N-codoped and N-doped ZnO films

G. W. Cong, W. Q. Peng, H. Y. Wei, X. X. Han, J. J. Wu, X. L. Liu, Q. S. Zhu, Z. G. Wang, J. G. Lu, Z. Z. Ye, L. P. Zhu, H. J. Qian, R. Su, C. H. Hong, J. Zhong, et al.

Appl. Phys. Lett. 88, 062110 (2006); http://dx.doi.org/10.1063/1.2171804 (3 pages) | Cited 17 times

Online Publication Date: 10 February 2006

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The valence band structures of Al–N-codoped [ZnO:(Al, N)] and N-doped (ZnO:N) ZnO films were studied by normal and soft x-ray photoelectron spectroscopy. The valence-band maximum of ZnO:(Al, N) shifts up to Fermi energy level by about 300 meV compared with that of ZnO:N. Such a shift can be attributed to the existence of a kind of Al–N in ZnO:(Al, N), as supported by core level XPS spectra and comparison of modified Auger parameters. Al–N increased the relative quantity of Zn–N in ZnO:(Al, N), while N–N decreased that of Zn–N in ZnO:N.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Enhanced conductivity in graphene layers and at their edges

S. Banerjee, M. Sardar, N. Gayathri, A. K. Tyagi, and Baldev Raj

Appl. Phys. Lett. 88, 062111 (2006); http://dx.doi.org/10.1063/1.2166697 (3 pages) | Cited 21 times

Online Publication Date: 10 February 2006

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We have observed that the conductivity of graphene sheets is higher whenever they are loosely bound to the underlying bulk graphite. We also observe that certain edges of the graphene layers show sharp rise in current when biased, indicating enhanced electronic density of states spatially localized near those edges. In certain edges, we do not observe this phenomenon. These two observations, i.e., enhancement of conductivity of loosely bound layers and sharp rise in current at the edges are discussed with possible reasons and invoking recent theoretical predictions.
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72.80.Rj Fullerenes and related materials
72.20.Fr Low-field transport and mobility; piezoresistance
73.22.-f Electronic structure of nanoscale materials and related systems
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.20.Tx Fullerenes and related materials; intercalation compounds

Electron paramagnetic resonance of a donor in aluminum nitride crystals

S. M. Evans, N. C. Giles, L. E. Halliburton, G. A. Slack, S. B. Schujman, and L. J. Schowalter

Appl. Phys. Lett. 88, 062112 (2006); http://dx.doi.org/10.1063/1.2173237 (3 pages) | Cited 9 times

Online Publication Date: 10 February 2006

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Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectra are obtained from a donor in aluminum nitride (AlN) crystals. Although observed in as-grown crystals, exposure to x rays significantly increases the concentration of this center. ENDOR identifies a strong hyperfine interaction with one aluminum neighbor along the c axis and weaker equivalent hyperfine interactions with three additional aluminum neighbors in the basal plane. These aluminum interactions indicate that the responsible center is a deep donor at a nitrogen site. The observed paramagnetic defect is either a neutral oxygen substituting for nitrogen (ON0) or a neutral nitrogen vacancy (VN0).
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76.70.Dx Electron-nuclear double resonance (ENDOR), electron double resonance (ELDOR)
76.30.Mi Color centers and other defects
71.55.Eq III-V semiconductors
61.72.J- Point defects and defect clusters

Thermal stability improvement by using Pd/NiO/Al/Ti/Au reflective ohmic contacts to p-GaN for flip-chip ultraviolet light-emitting diodes

Chang-Chi Pan, Guan-Ting Chen, Wen-Jay Hsu, Chih-Wei Lin, and Jen-Inn Chyi

Appl. Phys. Lett. 88, 062113 (2006); http://dx.doi.org/10.1063/1.2173245 (3 pages) | Cited 1 time

Online Publication Date: 10 February 2006

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The thermal stability, optical reflectivity, and contact resistivity of Pd/NiO/Al/Ti/Au ohmic contacts to p-type GaN were investigated. In contrast to Pd/Ni/Al/Ti/Au counterparts, the ohmic contacts Pd/NiO/Al/Ti/Au retained their specific contact resistivity (<3.3×10−2 Ω cm2) and high reflectivity (>75% @ 370 nm) after a long thermal aging at 200 °C for 100 h in nitrogen ambient. According to the results of the secondary ion mass spectroscopy in-depth profiles study, it is found that the NiO layer is more transparent and a better diffusion barrier than Ni to prevent the penetration of upper metals into p-type GaN during thermal treatment.
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73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
81.40.Gh Other heat and thermomechanical treatments
66.30.Ny Chemical interdiffusion; diffusion barriers
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