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8 Sep 2008

Volume 93, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 101905 (2008); http://dx.doi.org/10.1063/1.2977760 (3 pages)

Mei Wang, Yinwei Li, Tian Cui, Yanming Ma, and Guangtian Zou
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Kinetic Monte Carlo study of metal organic chemical vapor deposition growth mechanism of GaSb quantum dots

K. Fu and Y. Fu

Appl. Phys. Lett. 93, 101906 (2008); http://dx.doi.org/10.1063/1.2981515 (3 pages) | Cited 3 times

Online Publication Date: 9 September 2008

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The growth dynamics of self-assembled GaSb quantum dots (QDs) on GaAs substrate in the strain-induced Stranski–Krastanov mode was investigated using kinetic Monte Carlo method. The strain induced by the lattice mismatch between the epitaxial material and the substrate was shown to be directly responsible for the QD formation and the transition of growth mode from two dimensional to three dimensional.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Bond strength and interface energy between Pd membranes and TiAl supports

H. R. Gong, Y. H. He, and B. Y. Huang

Appl. Phys. Lett. 93, 101907 (2008); http://dx.doi.org/10.1063/1.2970966 (3 pages) | Cited 9 times

Online Publication Date: 10 September 2008

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Intermetallic TiAl alloy is proposed as a promising support for Pd membranes. First principles calculations reveal that coherent Pd/TiAl interfaces possess high values of bond strengths. Calculations also show that Ti-terminated (100) Pd/(100) TiAl and (110) Pd/(110) TiAl interfaces are energetically favorable with negative interface energies of about −3.1 J/m2, and that the bond strengths of Pd–Ti are bigger than those of Pd–Al. In addition, densities of states calculations suggest that a stronger chemical bonding is formed in the Pd/TiAl interface than corresponding Pd or TiAl bulks, which agrees well with similar experimental observations in literature.
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73.20.At Surface states, band structure, electron density of states
71.20.Be Transition metals and alloys
71.15.-m Methods of electronic structure calculations

Site-controlled growth and luminescence of InAs quantum dots using in situ Ga-assisted deoxidation of patterned substrates

P. Atkinson, S. Kiravittaya, M. Benyoucef, A. Rastelli, and O. G. Schmidt

Appl. Phys. Lett. 93, 101908 (2008); http://dx.doi.org/10.1063/1.2980445 (3 pages) | Cited 33 times

Online Publication Date: 10 September 2008

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Site-controlled growth of single and pairs of InAs quantum dots is demonstrated on ex situ electron-beam patterned (001) GaAs substrates using in situ Ga-assisted deoxidation prior to overgrowth. 6–8 ML of gallium deposited at a substrate temperature of 460 °C in the absence of arsenic followed by a brief anneal under arsenic is used to remove the surface oxide without damaging a pattern consisting of ∼ 100 nm wide, ∼ 20 nm deep holes. Single dot luminescence is shown from a dilute array (10 μm spacing) of such site-controlled dots, located only 8 nm from the regrowth interface.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
61.72.Cc Kinetics of defect formation and annealing
78.55.Cr III-V semiconductors

Plasmon resonances and electron phase shifts near Au nanospheres

T. C. Petersen, M. Bosman, V. J. Keast, and G. R. Anstis

Appl. Phys. Lett. 93, 101909 (2008); http://dx.doi.org/10.1063/1.2980505 (3 pages) | Cited 5 times

Online Publication Date: 10 September 2008

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Quantitative phase maps from Au and polystyrene nanospheres were obtained using the transport of intensity equation approach for phase retrieval in the electron microscope. These were compared to surface plasmon maps, as generated by electron energy loss spectroscopy. Large phase excursions were observed in the vacuum regions surrounding the Au nanospheres, yet not near adjacent polystyrene nanospheres. It is proposed that these phase excursions are associated with surface plasmon excitation. These results suggest that phase retrieval offers an alternative means for sensing and interpreting the optical response of nanostructured metals.
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73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
79.20.Uv Electron energy loss spectroscopy

Germanium substrate loss during low temperature annealing and its influence on ion-implanted phosphorous dose loss

N. Ioannou, D. Skarlatos, C. Tsamis, C. A. Krontiras, S. N. Georga, A. Christofi, and D. S. McPhail

Appl. Phys. Lett. 93, 101910 (2008); http://dx.doi.org/10.1063/1.2981522 (3 pages) | Cited 10 times

Online Publication Date: 10 September 2008

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In this work we demonstrate germanium loss from uncapped substrates during low temperature drive-in annealing in inert ambient. An Arrhenius law with an activation energy of 2.03 eV describes the measured loss rate of germanium as a function of temperature. Accurate simulations of implanted phosphorous profiles in nonpassivated substrates have been performed considering the extracted germanium loss rate. A capping layer on the germanium surface reduces phosphorous dose loss, with Si3N4 being more efficient than SiO2. The capping layer material also affects the extent of dopant concentration-dependent diffusion for high dose phosphorous implantation.
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61.72.sd Impurity concentration
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
77.55.-g Dielectric thin films
66.30.J- Diffusion of impurities

Nature of heterointerfaces in GaAs/InAs and InAs/GaAs axial nanowire heterostructures

Mohanchand Paladugu, Jin Zou, Ya-Nan Guo, Xin Zhang, Yong Kim, Hannah J. Joyce, Qiang Gao, H. Hoe Tan, and C. Jagadish

Appl. Phys. Lett. 93, 101911 (2008); http://dx.doi.org/10.1063/1.2978959 (3 pages) | Cited 20 times

Online Publication Date: 11 September 2008

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The structural and compositional characteristics of heterointerfaces of Au-catalyzed GaAs/InAs and InAs/GaAs axial nanowire heterostructures were comprehensively investigated by transmission electron microscopy. It has been found that the GaAs/InAs interface is not sharp and contains an InGaAs transition segment, and in contrast, the InAs/GaAs interface is atomically sharp. This difference in the nature of heterointerfaces can be attributed to the difference in the affinity of the group III elements with the catalyst material.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
68.37.Og High-resolution transmission electron microscopy (HRTEM)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.65.La Quantum wires (patterned in quantum wells)

Fourth-order shear elastic constant assessment in quasi-incompressible soft solids

Mathieu Rénier, Jean-Luc Gennisson, Christophe Barrière, Daniel Royer, and Mathias Fink.

Appl. Phys. Lett. 93, 101912 (2008); http://dx.doi.org/10.1063/1.2979875 (3 pages) | Cited 10 times

Online Publication Date: 11 September 2008

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In isotropic quasi-incompressible media, an expression of the elastic energy density has been developed as a function of the second-, third-, and fourth-order elastic constants (respectively μ, A, D). Thus the shear nonlinearity parameter βS depends only on these coefficients. In this letter βS is measured using finite amplitude plane shear waves in agar-gelatin based phantoms. Combining the results with recently published measurements of μ and A on the same phantoms, the fourth-order shear elastic constant D is found to be of the order of 10 kPa and thus of the same order of magnitude as μ and A.
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87.63.D- Ultrasonography
87.19.R- Mechanical and electrical properties of tissues and organs

Atomic structure of the interface between SrTiO3 thin films and Si(001) substrates

Shao-Bo Mi, Chun-Lin Jia, Venu Vaithyanathan, Lothar Houben, Jürgen Schubert, Darrell G. Schlom, and Knut Urban

Appl. Phys. Lett. 93, 101913 (2008); http://dx.doi.org/10.1063/1.2981524 (3 pages) | Cited 11 times

Online Publication Date: 11 September 2008

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The structure of the SrTiO3/Si interface is determined by high-angle annular dark field imaging in combination with a recently developed technique based on aberration-corrected high-resolution transmission electron microscopy. At the interface, a monolayer of SrO faces the terminating plane of silicon. In this monolayer, the strontium atoms lie above the face-center of four silicon atoms in the terminating plane, and the oxygen atoms are located directly above the terminating silicon atoms. This structure, which is the dominant type of interface structure observed in this system, agrees with one of the interface structures predicted by first-principles calculations.
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68.35.Ct Interface structure and roughness
68.37.Og High-resolution transmission electron microscopy (HRTEM)

Quantification of porosity and deposition rate of nanoporous films grown by oblique-angle deposition

D. J. Poxson, F. W. Mont, M. F. Schubert, J. K. Kim, and E. F. Schubert

Appl. Phys. Lett. 93, 101914 (2008); http://dx.doi.org/10.1063/1.2981690 (3 pages) | Cited 24 times

Online Publication Date: 11 September 2008

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We propose an analytic model that accurately predicts the porosity and deposition rate of nanoporous films grown by oblique-angle deposition. The model employs a single fitting parameter and takes into account geometrical factors as well as surface diffusion. We have determined the porosity and deposition rate from the measured refractive index and thickness of SiO2 and indium tin oxide nanoporous films deposited at various incident angles. Comparison of experimental data with the model reveals excellent agreement. The theoretical model allows for the predictive control of refractive index, porosity, and deposition rate for a wide range of deposition angles and materials.
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81.05.Rm Porous materials; granular materials
78.66.Nk Insulators
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.aj Insulators
68.35.Fx Diffusion; interface formation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Plastic deformation and optical behavior of high-purity synthetic diamond crystal subjected to high stress load at room temperature

H. Sumiya, Y. Nakamoto, K. Shimizu, and H. Kanda

Appl. Phys. Lett. 93, 101915 (2008); http://dx.doi.org/10.1063/1.2978070 (3 pages) | Cited 2 times

Online Publication Date: 12 September 2008

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The optical behavior around the culet of a diamond anvil made of high-purity and defect-free synthetic diamond crystal, which was plastically deformed at room temperature, was investigated by cathodoluminescence spectroscopy. It was found that the free exciton peaks weaken while the A-band and 2BD bands appear at the culet center where plastic deformation occurred. It was demonstrated that the free exciton peaks near the edge of the culet shift to the long wavelength side, indicating that the band structure of the peripheral areas of the culet changes because of residual strain caused by the plastic deformation in the culet center.
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81.40.Lm Deformation, plasticity, and creep
61.72.Bb Theories and models of crystal defects
78.60.Hk Cathodoluminescence, ionoluminescence
71.35.-y Excitons and related phenomena
78.20.-e Optical properties of bulk materials and thin films
62.20.fq Plasticity and superplasticity

Size-dependent mechanical properties of molybdenum nanopillars

Ju-Young Kim and Julia R. Greer

Appl. Phys. Lett. 93, 101916 (2008); http://dx.doi.org/10.1063/1.2979684 (3 pages) | Cited 26 times

Online Publication Date: 12 September 2008

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We report the deformation behavior of single crystalline molybdenum nanopillars in uniaxial compression, which exhibits a strong size effect called the “smaller is stronger” phenomenon. We show that higher strengths arise from the increase in the yield strength rather than through postyield strain hardening. We find the yield strength at nanoscale to depend strongly on sample size and not on the initial dislocation density, a finding strikingly different from that of the bulk metal.
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62.25.-g Mechanical properties of nanoscale systems
81.07.Bc Nanocrystalline materials
81.40.Lm Deformation, plasticity, and creep
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
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Strain dependence of indirect band gap for strained silicon on insulator wafers

J. Munguía, G. Bremond, J. M. Bluet, J. M. Hartmann, and M. Mermoux

Appl. Phys. Lett. 93, 102101 (2008); http://dx.doi.org/10.1063/1.2978241 (3 pages) | Cited 5 times

Online Publication Date: 8 September 2008

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We have used low temperature photoluminescence measurements in order to quantify the impact of strain effect on the Si indirect band gap in 9 nm thick tensely strained silicon on insulator layers. A redshift of the transverse optical phonon excitonic recombination in the strained silicon layer was evidenced as the strain in the layer is increased. Band gap shrinkages in the Δ direction equal to 130±3 meV, 184±3 meV, and 239±3 meV were obtained for 0.87±0.03%, 1.22±0.05%, and 1.54±0.06% strain values. These measured indirect transitions are in good agreement with the calculated strained silicon indirect band gap values.
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71.20.Mq Elemental semiconductors
71.35.-y Excitons and related phenomena
63.20.kk Phonon interactions with other quasiparticles
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors

Ti-based nonalloyed Ohmic contacts for Al0.15Ga0.85N/GaN high electron mobility transistors using regrown n+-GaN by plasma assisted molecular beam epitaxy

Hui-Chan Seo, Patrick Chapman, Hyun-Ick Cho, Jung-Hee Lee, and Kyekyoon (Kevin) Kim

Appl. Phys. Lett. 93, 102102 (2008); http://dx.doi.org/10.1063/1.2979702 (3 pages) | Cited 4 times

Online Publication Date: 8 September 2008

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A technique for regrowing n+-GaN layers has been developed to realize nonalloyed Ohmic contacts using plasma assisted molecular beam epitaxy. The contact resistance and device performance were measured of a recessed-gate with the regrowth and of recessed-source/drain AlGaN/GaN high electron mobility transistors (HEMTs). With the regrown n+-GaN layers and recessed drain/source, a low contact resistance of 0.6 Ω mm was obtained for Ti/Au contacts to AlGaN. The peak drain current (IDS,max) and maximum transconductance (gm,max) of the AlGaN/GaN HEMTs with nonalloyed Ohmic contacts were 573 mA/mm and 60 mS/mm, respectively. These results demonstrate that the regrowth of highly doped GaN layers is crucial in achieving low-resistance nonalloyed Ohmic contacts for the HEMT structures.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors

Ultrafast carrier dynamics and terahertz conductivity of photoexcited GaAs under electric field

Qing-li Zhou, Yulei Shi, Bin Jin, and Cunlin Zhang

Appl. Phys. Lett. 93, 102103 (2008); http://dx.doi.org/10.1063/1.2980026 (3 pages) | Cited 11 times

Online Publication Date: 8 September 2008

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The ultrafast carrier dynamics and terahertz conductivity in semi-insulating GaAs have been investigated under electric field (E) by using optical pump-terahertz probe technique. The measurements indicate that the terahertz transmission change induced by the pump pulses at high E is smaller than that without E. We attribute this phenomenon to carrier scattering into the L valley, which leads to a drop in carrier mobility. The calculated transient photoconductivities fit well with the Drude–Smith model, being consistent with our intervalley scattering model.
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72.20.Ee Mobility edges; hopping transport
72.40.+w Photoconduction and photovoltaic effects

Dynamic carrier lifetime imaging of silicon wafers using an infrared-camera-based approach

K. Ramspeck, S. Reissenweber, J. Schmidt, K. Bothe, and R. Brendel

Appl. Phys. Lett. 93, 102104 (2008); http://dx.doi.org/10.1063/1.2972122 (3 pages) | Cited 16 times

Online Publication Date: 9 September 2008

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We present a calibration-free dynamic infrared carrier lifetime mapping technique, yielding images of the carrier lifetime of multicrystalline silicon wafers within seconds. Images of the infrared emission of the sample under test are taken directly after switching on a monochromatic illumination source and after steady-state conditions have been established in the sample. Making use of the proportionality between the infrared emission and the free carrier density inside the sample, the carrier lifetime is calculated from the signal ratio of these two images by an analytical method. We achieve an excellent agreement when comparing our results with carrier lifetime mappings obtained by the microwave-detected photoconductance decay technique.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Adsorption-controlled growth of EuO by molecular-beam epitaxy

R. W. Ulbricht, A. Schmehl, T. Heeg, J. Schubert, and D. G. Schlom

Appl. Phys. Lett. 93, 102105 (2008); http://dx.doi.org/10.1063/1.2973180 (3 pages) | Cited 15 times

Online Publication Date: 10 September 2008

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Using molecular-beam epitaxy, we demonstrate the adsorption-controlled growth of epitaxial EuO films on single crystalline (110) YAlO3 substrates. Four-circle x-ray diffraction (XRD) reveals phase-pure, epitaxial, (001)-oriented films with rocking curve full width at half maxima as narrow as 34 arc sec (0.0097°). The critical thickness for the onset of relaxation of (001) EuO on (110) YAlO3 ( ∼ 2% lattice mismatch) was determined from XRD measurements to be 382±25 Å. A saturation magnetization of 6.96±0.07μB/Eu, a value close to the theoretical limit of 7μB/Eu, is observed.
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68.55.at Other materials
68.43.Mn Adsorption kinetics
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Photoresponse of the Schottky junction Au/SrTiO3:Nb in different resistive states

D. S. Shang, J. R. Sun, L. Shi, and B. G. Shen

Appl. Phys. Lett. 93, 102106 (2008); http://dx.doi.org/10.1063/1.2978240 (3 pages) | Cited 17 times

Online Publication Date: 10 September 2008

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A systematic study on photovoltaic effects has been performed for the Schottky junction Au/SrTiO3:0.05 wt %Nb, the resistance of which can be tuned, by applied electric pulses, between ∼ 1 and ∼ 200 MΩ. It is found that, despite the great change in junction resistance, the photocurrent across the junction is constant when the power and wavelength of incident light are fixed. The corresponding Schottky barrier, deduced from the photoresponse data is ∼ 1.5 eV, independent of junction resistance. This result suggests the invariance of the interfacial barrier during resistance switching and the occurrence of filamentary conduction channels.
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73.30.+y Surface double layers, Schottky barriers, and work functions
72.40.+w Photoconduction and photovoltaic effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Electrochemical fabrication of ultralow noise metallic nanowires with hcp crystalline lattice

Amrita Singh, T. Phanindra Sai, and Arindam Ghosh

Appl. Phys. Lett. 93, 102107 (2008); http://dx.doi.org/10.1063/1.2979709 (3 pages) | Cited 2 times

Online Publication Date: 10 September 2008

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We experimentally demonstrate that low-frequency electrical noise in silver nanowires is heavily suppressed when the crystal structure of the nanowires is hexagonal closed pack (hcp) rather than face centered cubic (fcc). Using a low-potential electrochemical method we have grown single crystalline silver nanowires with hcp crystal structure, in which the noise at room temperature is two to six orders of magnitude lower than that in the conventional fcc nanowires of the same diameter. We suggest that motion of dislocations is probably the primary source of electrical noise in metallic nanowires, which is strongly diminished in hcp crystals.
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81.07.Bc Nanocrystalline materials
82.45.Yz Nanostructured materials in electrochemistry
61.66.-f Structure of specific crystalline solids
87.80.Kc Electrochemical techniques

Improved contact for thermal and electrical transport in carbon nanofiber interconnects

Tsutomu Saito, Toshishige Yamada, Drazen Fabris, Hirohiko Kitsuki, Patrick Wilhite, Makoto Suzuki, and Cary Y. Yang

Appl. Phys. Lett. 93, 102108 (2008); http://dx.doi.org/10.1063/1.2979710 (3 pages) | Cited 8 times

Online Publication Date: 10 September 2008

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We study the performance and reliability of carbon nanofiber (CNF) interconnects under high-current stress by examining CNF breakdown for four test configurations, suspended/supported with/without tungsten deposition. The use of W is to improve the CNF-electrode contact. The supported cases show a larger current density just before breakdown than the suspended ones, suggesting an effective heat dissipation to the substrate. The W-deposited contacts reduce the initial total resistance from megaohm range without W to kilo-ohms. High-current stress does not change the total resistance of the test structures with W unlike those without W deposition.
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85.40.Ls Metallization, contacts, interconnects; device isolation

High figures of merit and natural nanostructures in Mg2Si0.4Sn0.6 based thermoelectric materials

Q. Zhang, J. He, T. J. Zhu, S. N. Zhang, X. B. Zhao, and T. M. Tritt

Appl. Phys. Lett. 93, 102109 (2008); http://dx.doi.org/10.1063/1.2981516 (3 pages) | Cited 39 times

Online Publication Date: 10 September 2008

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Mg2(Si,Sn) compounds have shown great promise for thermoelectric applications due to good thermoelectric properties, nontoxicity, and abundantly available constituent elements. Herein we report on the thermoelectric properties and microstructure of high performance Mg2Si0.4−xSn0.6Sbx (0 ⩽ x ⩽ 0.015) alloys. The state-of-the-art ZT value of ∼ 1.1 has been attained in the samples with x = 0.0075  due to the relatively low thermal conductivity. In light of the simple cubic structure and mostly light constituent elements, the reduction in lattice thermal conductivity has been discussed in connection with a fairly large amount of in situ formed nanostructures in these samples.
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72.15.Jf Thermoelectric and thermomagnetic effects
73.63.-b Electronic transport in nanoscale materials and structures
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Small scale lateral superlattices in two-dimensional electron gases prepared by diblock copolymer masks

S. Hugger, T. Heinzel, and T. Thurn-Albrecht

Appl. Phys. Lett. 93, 102110 (2008); http://dx.doi.org/10.1063/1.2981567 (3 pages) | Cited 1 time

Online Publication Date: 10 September 2008

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A poly(styrene-block-methylmethacrylate) diblock copolymer in the hexagonal cylindrical phase has been used as a mask for preparing a periodic gate on top of a GaAs/AlxGa1−xAs heterostructure. A superlattice period of 43 nm could be imposed on the two-dimensional electron gas. Transport measurements show a characteristic positive magnetoresistance around zero magnetic field, which we interpret as a signature of electron motion guided by the superlattice potential.
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73.21.Cd Superlattices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects

Polar face dependence of the ultrafast UV reflectivity of ZnO single crystal

J. R. Schneck, E. Bellotti, P. Lamarre, and L. D. Ziegler

Appl. Phys. Lett. 93, 102111 (2008); http://dx.doi.org/10.1063/1.2968717 (3 pages) | Cited 1 time

Online Publication Date: 11 September 2008

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The transient reflectivity of an ∼ 40 fs, 340 nm pulse incident on each face of a ZnO single crystal is reported as a function of carrier density. Three exponentially damped carrier relaxation components can be identified in these responses. Only the Zn face reflectivity reveals a subpicosecond decay (200–300 fs) due to electron scattering. In contrast, the O face reflectivity exhibits an ∼ 2 ps absorptive decay attributed to the trapping of carriers by O-surface defects at the earliest times. The other decay components are consistent with electron cooling via acoustic phonons and exciton recombination for both faces.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.J- Ultrafast spectroscopy (<1 psec)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
63.20.-e Phonons in crystal lattices
71.35.-y Excitons and related phenomena

Enhanced electroluminescence intensity of InGaN/GaN multi-quantum-wells based on Mg-doped GaN annealed in O2

Ping Ma, Yanqin Gai, Junxi Wang, Fuhua Yang, Yiping Zeng, Jinmin Li, and Jingbo Li

Appl. Phys. Lett. 93, 102112 (2008); http://dx.doi.org/10.1063/1.2980032 (3 pages) | Cited 4 times

Online Publication Date: 11 September 2008

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InGaN/GaN multi-quantum-well blue (461±4 nm) light emitting diodes with higher electroluminescence intensity are obtained by postgrowth thermal annealing at 720 °C in O2-ambient. Based on our first-principle total-energy calculations, we conclude that besides dissociating the Mg–H complex by forming H2O, annealing in O2 has another positive effect on the activation of acceptor Mg in GaN. Mg can be further activated by the formation of an impurity band above the valence band maximum of host GaN from the passivated MgGa–ON complex. Our calculated ionization energy for acceptor Mg in the passivated system is about 30 meV shallower than that in pure GaN, in good agreement with previous experimental measurement. Our model can explain that the enhanced electroluminescence intensity of InGaN/GaN MQWs based on Mg-doped p-type GaN is due to a decrease in the ionization energy of Mg acceptor with the presence of oxygen.
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78.60.Fi Electroluminescence
78.67.De Quantum wells
61.72.Cc Kinetics of defect formation and annealing

Strain engineered Si/SiGe resonant interband tunneling diodes with outside barriers grown on Si0.8Ge0.2 virtual substrates

R. Anisha, Niu Jin, Sung-Yong Chung, Ronghua Yu, Paul R. Berger, and Phillip E. Thompson

Appl. Phys. Lett. 93, 102113 (2008); http://dx.doi.org/10.1063/1.2981211 (3 pages)

Online Publication Date: 11 September 2008

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Si-based resonant interband tunneling diodes (RITDs) grown on commercially available Si0.8Ge0.2 virtual substrates were studied. Peak-to-valley current ratios (PVCRs) were improved by utilizing strain induced band offsets to 3.5 with a peak current density (Jp) of 161 A/cm2. More specifically, a tensilely strained Si layer on the p-side and a compressively strained Si0.5Ge0.5 layer on the n-side were added to the design to form enhanced potential barriers away from the tunneling junction. The outside barriers deepen the respective hole and electron quantum wells and also block nonresonant tunneling current, which improved the PVCR significantly. However, due to the large surface roughness of the SiGe virtual substrates used in this study, the RITDs grown on Si0.8Ge0.2 substrates exhibit a smaller PVCR overall than RITDs optimized on standard Si substrates. Better performance is expected by using higher quality SiGe substrates with smaller surface roughness.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Electrical spectroscopy of high resistivity ion-implanted layers by current-voltage measurements

Tiziana Cesca, Andrea Gasparotto, and Beatrice Fraboni

Appl. Phys. Lett. 93, 102114 (2008); http://dx.doi.org/10.1063/1.2975372 (3 pages) | Cited 3 times

Online Publication Date: 12 September 2008

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We report on a spectroscopic characterization of electrically compensated high resistivity Fe-implanted InP and GaInP by room temperature space-charge-limited-current measurements. This method results to be a reliable and powerful tool to obtain a quantification of the degree of compensation and the free carrier concentration in the samples, together with the activation energy and density of states distribution of the dominant majority carrier traps. Moreover, by correlating these results with temperature dependent electrical spectroscopy analyses, it is possible to obtain information on material parameters, such as the carrier mobility, not always easily accessible by direct measurements.
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73.61.Ey III-V semiconductors
73.50.Fq High-field and nonlinear effects
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.55.-a Thin film structure and morphology
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