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21 Jan 2008

Volume 92, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 92, 033101 (2008); http://dx.doi.org/10.1063/1.2830979 (3 pages)

Koichiro Zaitsu, Yosuke Kitamura, Keiji Ono, and Seigo Tarucha
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Frequency dispersion in capacitance-voltage characteristics of AlGaN/GaN heterostructures

James R. Shealy and Richard J. Brown

Appl. Phys. Lett. 92, 032101 (2008); http://dx.doi.org/10.1063/1.2835708 (3 pages) | Cited 5 times

Online Publication Date: 22 January 2008

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Capacitance-voltage (CV) characterization of AlGaN/GaN heterostructures is a widely used method for determining the depletion characteristics of the two-dimensional electron gas at the heterointerface. In combination with the Hg probe, these measurements are considered nondestructive. The technique can provide accurate determination of the sheet electron density, the concentration profile, the AlGaN barrier thickness, and the pinch off voltage. If the measurement conditions are not chosen properly, significant errors result from the effects of the series resistance, the backside Hg contact, and the electron generation lifetime. The best conditions (bias and frequency) for CV data acquisition are identified.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Observation of delayed fluorescence in CdSxSe1−x nanobelts by femtosecond time-resolved fluorescence spectroscopy

Xiao-Feng Han, Yu-Xiang Weng, Anlian Pan, Bingsuo Zou, and Jing-Yuan Zhang

Appl. Phys. Lett. 92, 032102 (2008); http://dx.doi.org/10.1063/1.2836080 (3 pages) | Cited 5 times

Online Publication Date: 22 January 2008

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The time-resolved fluorescence spectra as well as the decay kinetics for CdSxSe1−x single crystal nanobelts without and with the presence of structural disorders have been investigated by femtosecond time-resolved fluorescence spectrometer based on optical parametric fluorescence amplifier technique. The structural disorders in the crystal give rise to an inhomogeneous broadening of the steady-state fluorescence spectra and also to a distinct time-dependent redshift in the transient photoluminescence spectra, due to the carrier relaxation from the conduction band to the trapped states. The delayed fluorescence was observed and it can be attributed to several mechanisms including the electron-phonon interaction and the Auger effect.
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78.55.Hx Other solid inorganic materials
71.38.-k Polarons and electron-phonon interactions
79.20.Fv Electron impact: Auger emission

Migration and luminescence enhancement effects of deuterium in ZnO/ZnCdO quantum wells

W. Lim, D. P. Norton, S. J. Pearton, X. J. Wang, W. M. Chen, I. A. Buyanova, A. Osinsky, J. W. Dong, B. Hertog, A. V. Thompson, W. V. Schoenfeld, Y. L. Wang, and F. Ren

Appl. Phys. Lett. 92, 032103 (2008); http://dx.doi.org/10.1063/1.2836946 (3 pages) | Cited 7 times

Online Publication Date: 22 January 2008

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ZnO/ZnCdO/ZnO multiple quantum well samples grown on sapphire substrates by molecular beam epitaxy and annealed in situ were exposed to D2 plasmas at 150 °C. The deuterium showed migration depths of ∼ 0.8 μm for 30 min plasma exposures, with accumulation of 2H in the ZnCdO wells. The photoluminescence (PL) intensity from the samples was increased by factors of 5 at 5 K and ∼ 20 at 300 K as a result of the deuteration, most likely due to passivation of competing nonradiative centers. Annealing up to 300 °C led to increased migration of 2H toward the substrate but no loss of deuterium from the sample and little change in the PL intensity. The initial PL intensities were restored by annealing at ≥ 400 °C as 2H was evolved from the sample ( ∼ 90% loss by 500 °C). By contrast, samples without in situ annealing showed a decrease in PL intensity with deuteration. This suggests that even moderate annealing temperatures lead to degradation of ZnCdO quantum wells.
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78.67.De Quantum wells
78.55.Et II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.65.Rv Passivation
52.77.-j Plasma applications

Sources of unintentional conductivity in InN

Anderson Janotti and Chris G. Van de Walle

Appl. Phys. Lett. 92, 032104 (2008); http://dx.doi.org/10.1063/1.2832369 (3 pages) | Cited 40 times

Online Publication Date: 23 January 2008

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Using first-principles methods, we investigate the effects of monatomic hydrogen in InN. We find that hydrogen can occupy interstitial and substitutional sites. Interstitial hydrogen is stable in the bond-center configuration and acts exclusively as a shallow donor, with a H–N stretching vibration at 3050 cm−1. Hydrogen can also substitute for nitrogen in InN, bonding equally to the four In nearest neighbors in a multicenter-bond configuration. Substitutional hydrogen has low formation energy and, counterintuitively, is a double donor. Our results suggest that monatomic hydrogen is a plausible cause of the unintentional n-type conductivity that is often observed in as-grown InN.
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78.66.Fd III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Ge 3d core-level shifts at (100)Ge/Ge(Hf)O2 interfaces: A first-principles investigation

G. Pourtois, M. Houssa, A. Delabie, T. Conard, M. Caymax, M. Meuris, and M. M. Heyns

Appl. Phys. Lett. 92, 032105 (2008); http://dx.doi.org/10.1063/1.2833696 (3 pages) | Cited 23 times

Online Publication Date: 23 January 2008

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First-principles calculations of Ge 3d core-level shifts on (100)Ge/Ge(Hf)O2 interface models, presenting a GeOx transition region that samples different possible oxidation states for Ge atoms near the interface are reported. The fractional densities of these different oxidation states present in the modeled structures are consistent with those inferred from x-ray photoelectron spectroscopy data on thermally oxidized (100)Ge surfaces. The computed relative Ge 3d core-level shifts are in overall fair agreement with the experimental values reported in the literature, especially for the Ge–O–Hf bonds that are likely formed at the GeO2/HfO2 interface. The computed core-level shifts increase linearly with the partial atomic charges on the Ge atoms, consistently with a classical charge-transfer model usually used for the interpretation of experimental data on (100)Ge/Ge(Hf)O2 interfaces.
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73.20.-r Electron states at surfaces and interfaces

Time-resolved photoluminescence of type-II quantum dots and isoelectronic centers in Zn–Se–Te superlattice structures

M. C.-K. Cheung, A. N. Cartwright, I. R. Sellers, B. D. McCombe, and I. L. Kuskovsky

Appl. Phys. Lett. 92, 032106 (2008); http://dx.doi.org/10.1063/1.2835699 (3 pages) | Cited 9 times

Online Publication Date: 23 January 2008

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Spectrally and time-resolved photoluminescence of a ZnTe/ZnSe superlattice reveals a smooth transition of the photoluminescence (PL) lifetime from ∼ 100 ns at 2.35 eV to less than a few nanoseconds at 2.8 eV. The significant increase of the lifetime in the low energy region is strong evidence to support the formation of type-II quantum dots (QDs), since in these nanostructures the spatial separation of carriers is increased. The shorter lived emission above 2.5 eV is attributed to excitons bound to Te isoelectronic centers in the ZnSe matrix. The smooth transition of the PL lifetime confirms that clusters of these Te atoms evolve into type-II ZnTe/ZnSe QDs.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Et II-VI semiconductors
78.47.D- Time resolved spectroscopy (>1 psec)
71.35.-y Excitons and related phenomena

Band alignment between amorphous Ge2Sb2Te5 and prevalent complementary-metal-oxide-semiconductor materials

Lina Wei-Wei Fang, Ji-Sheng Pan, Rong Zhao, Luping Shi, Tow-Chong Chong, Ganesh Samudra, and Yee-Chia Yeo

Appl. Phys. Lett. 92, 032107 (2008); http://dx.doi.org/10.1063/1.2837189 (3 pages) | Cited 3 times

Online Publication Date: 23 January 2008

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Band alignment of amorphous Ge2Sb2Te5 and various substrates was obtained using high-resolution x-ray photoelectron spectroscopy. The valence band offset of Ge2Sb2Te5 on various complementary-metal-oxide-semiconductor (CMOS) materials, i.e., Si, SiO2, HfO2, Si3N4 and NiSi, were investigated with the aid of the core level, valence band, and energy loss spectra. Energy band lineups of Ge2Sb2Te5 on these materials were thus determined which can be used as for phase change memory device engineering and integration with CMOS technology.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Investigation of Zr–Si–N/Zr bilayered film as diffusion barrier for Cu ultralarge scale integration metallization

Ying Wang, Fei Cao, Yun-tao Liu, and Ming-Hui Ding

Appl. Phys. Lett. 92, 032108 (2008); http://dx.doi.org/10.1063/1.2837190 (3 pages) | Cited 12 times

Online Publication Date: 23 January 2008

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The effectiveness of ZrSiN/Zr bilayered films to serve as diffusion barriers in Cu/Si contacts has been investigated. Annealing studies for Cu/ZrSiN/Zr/Si contact systems were carried out in N2/H2(10%) ambient. X-ray diffraction data suggest that Cu film has preferential (111) crystal orientation and Cu silicide cannot be observed up to 700 °C. Scanning electron microscopy micrographs show that the Cu film was integrated and free from agglomeration after annealing at 700 °C. Auger electron spectroscopy depth profiles of the Cu/ZrSiN(10 nm)/Zr(20 nm)/Si samples have no noticeable change except Zr silicide grows with annealing temperature up to 700 °C. The results indicate excellent barrier property for ZrSiN(10 nm)/Zr(20 nm) bilayer structure for Cu metallization.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.40.Ls Metallization, contacts, interconnects; device isolation
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Observation of SrTiO3 in-gap states by depletion mode field effect

Keisuke Shibuya, Tsuyoshi Ohnishi, Takayuki Uozumi, Taisuke Sato, Kazunori Nishio, and Mikk Lippmaa

Appl. Phys. Lett. 92, 032109 (2008); http://dx.doi.org/10.1063/1.2837627 (3 pages) | Cited 3 times

Online Publication Date: 25 January 2008

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We have fabricated SrTiO3 (100) single crystal field-effect transistors with epitaxial and amorphous DyScO3 gate insulator layers. The devices showed an on-off ratio of 107 with a field-effect mobility of over 100 cm2/V s at 50 K. The residual oxygen vacancy concentration in the transistor channel was adjusted so that the off-state current was high at room temperature but dropped sharply upon cooling. The temperature dependence of the channel current under a carrier-depleting gate bias was used to show that oxygen vacancies form an in-gap impurity state at about 0.24 eV below the SrTiO3 mobility edge.
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85.30.Tv Field effect devices
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