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15 Jul 2010

Volume 108, Issue 2, Articles (02xxxx)

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back to top Device Physics

Universality of Zener tunneling in homojunction p-n diodes

Amlan Majumdar, Isaac Lauer, and Terrance O’Regan

J. Appl. Phys. 108, 024501 (2010); http://dx.doi.org/10.1063/1.3267148 (4 pages) | Cited 2 times

Online Publication Date: 19 July 2010

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We show that in homojunction p-n diodes made of semiconductors with unequal electron and hole effective masses, Zener tunneling is approximately universal, but not perfectly universal, as a function of effective tunneling width, where the effective tunneling width takes the effects of band curvature into account. We find that the curvature correction (CC), which is applied to obtain the approximate universality of tunneling, is by itself not universal but show that (1−CC)/N2 is universal as a function of the tunneling width for a given material, where N is the doping density.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Demonstration of homojunction ZnTe solar cells

Tooru Tanaka, Kin M. Yu, Peter R. Stone, Jeffrey W. Beeman, Oscar D. Dubon, Lothar A. Reichertz, Vincent M. Kao, Mitsuhiro Nishio, and Wladek Walukiewicz

J. Appl. Phys. 108, 024502 (2010); http://dx.doi.org/10.1063/1.3463421 (3 pages) | Cited 8 times

Online Publication Date: 19 July 2010

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We report on the proof of photovoltaic activity of homojunction ZnTe solar cells in which n-ZnTe layers are fabricated by thermal diffusion of Al into p-ZnTe at several diffusion times to control the junction depth. An open circuit voltage of approximately 0.9 V was obtained under 1× sun AM1.5G condition in all solar cells, independent of diffusion times, while a short circuit current dropped down with increasing the diffusion time due to an increased light absorption in heavily defective Al-diffused layer. These fundamental results provide a basis for future development of intermediate band solar cells based on ZnTe materials.
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88.40.jm Thin film III-V and II-VI based solar cells
84.60.Jt Photoelectric conversion

Analysis of electron traps at the 4H–SiC/SiO2 interface; influence by nitrogen implantation prior to wet oxidation

I. Pintilie, C. M. Teodorescu, F. Moscatelli, R. Nipoti, A. Poggi, S. Solmi, L. S. Løvlie, and B. G. Svensson

J. Appl. Phys. 108, 024503 (2010); http://dx.doi.org/10.1063/1.3457906 (9 pages) | Cited 6 times

Online Publication Date: 19 July 2010

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Electron states at the SiO2/4H–SiC interface have been investigated using capacitor structures and especially, the influence of excess nitrogen, introduced by ion implantation, at the interface is studied in detail. Implanted and nonimplanted n-type samples with an interfacial concentration of nitrogen of ∼ 1019 cm−3 and 1016 cm−3, respectively, were analyzed by capacitance-voltage (C-V) measurements, performed at different temperatures and probe frequencies, and thermal dielectric relaxation current (TDRC) measurements performed in the temperature range of 35–295 K. Three main categories of electron states are disclosed, true interface states (Dit), fast near interface states (NIToxfast) and slow near interface states (NIToxslow). The density versus energy distributions of Dit and NIToxfast have been deduced from the TDRC data and they are shown to give a close quantitative agreement with the shape and frequency dependence of the C-V curves. Further, the amount of NIToxslow extracted from TDRC is demonstrated to be responsible for the parallel shifts and hysterezis effects occurring in the C-V characteristics. All three categories of electron states are reduced in concentration in the implanted samples. This holds particularly for NIToxfast with a peak at ∼ 0.1 eV below the conduction band edge of 4H–SiC that is suppressed by at least two orders of magnitude relative to the nonimplanted samples. The decrease for Dit is also substantial (a factor of ∼ 10) while the loss for NIToxslow is considerably smaller (only ∼ 30%). The results provide firm evidence that NIToxfast and NIToxslow do not originate from the same kind of defect center.
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71.55.Ht Other nonmetals
73.20.At Surface states, band structure, electron density of states
61.72.U- Doping and impurity implantation
77.22.Gm Dielectric loss and relaxation
77.80.Dj Domain structure; hysteresis
84.32.Tt Capacitors

Fluctuations in induced charge introduced by Te inclusions within CdZnTe radiation detectors

Derek S. Bale

J. Appl. Phys. 108, 024504 (2010); http://dx.doi.org/10.1063/1.3448234 (8 pages) | Cited 2 times

Online Publication Date: 21 July 2010

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Recently, homogenization theory based on a multiple-scale perturbation of the electron transport equation has been used to derive a mathematical framework for modeling the excess charge lost to Te inclusions within radiation detectors based on semi-insulating cadmium zinc telluride (CdZnTe). In that theory, the heterogeneous material is mathematically replaced by a homogenized CdZnTe crystal whose effective electron attenuation length incorporates the additional uniform electron trapping caused by the inclusions. In this paper, the homogenization theory is extended to incorporate fluctuations in the induced charge (i.e., charge collection nonuniformities) introduced by the random position and size distributions of a noncorrelated population of small (i.e, <20 μm) Te inclusions. Analysis of the effective parameters derived within the homogenized framework is used to develop a probability distribution of effective electron attenuation lengths, and therefore effective mobility-lifetime products, as a function of both the position and size distribution of Te inclusions. Example distributions are detailed for the case of an exponential size distribution at various number densities. Further, it is demonstrated that the inclusion-induced material nonuniformities derived in this paper can be numerically sampled efficiently, making them applicable to Monte Carlo device simulation of realistic CdZnTe detectors. Simulated charge induction maps and pulse-height spectra are presented and compared to recently published measurements.
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29.40.Wk Solid-state detectors

Demonstration of a Meissner-effect transition edge sensor

S. I. Woods, S. M. Carr, T. M. Jung, A. C. Carter, and R. U. Datla

J. Appl. Phys. 108, 024505 (2010); http://dx.doi.org/10.1063/1.3456539 (5 pages)

Online Publication Date: 26 July 2010

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We have built and tested a transition edge sensor which monitors temperature change by measuring magnetic flux expulsion from a superconducting element. Flux change is sensed by a dc superconducting quantum interference device coupled to the element using a flux transformer in a gradiometer arrangement. The operating temperature of the sensor can be varied by application of moderate magnetic fields to the superconducting core, using an integrated solenoid. With a Sn core at 3.58 K, the thermometer has demonstrated a noise level of 2.25 nK/Hz1/2. We estimate that such a sensor will allow femtowatt sensitivity of an absolute cryogenic radiometer presently under development.
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07.20.Dt Thermometers
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.55.Ge Magnetometers for magnetic field measurements

Amorphous-to-crystalline phase transition of (InTe)x(GeTe) thin films

Ki-Ho Song, Seung-Cheol Beak, and Hyun-Yong Lee

J. Appl. Phys. 108, 024506 (2010); http://dx.doi.org/10.1063/1.3457868 (6 pages) | Cited 5 times

Online Publication Date: 27 July 2010

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The crystallization speed (v) of the amorphous (InTe)x(GeTe) (x = 0.1, 0.3, and 0.5) films and their thermal, optical, and electrical behaviors were investigated by using a nanopulse scanner (wavelength = 658 nm, laser beam diameter <2 μm), x-ray diffraction, a four-point probe, and a UV-vis-IR spectrophotometer. These results were compared to the results for a Ge2Sb2Te5 (GST) film, which was comprehensively utilized for phase-change random access memory (PRAM). Both the v—value and the thermal stability of the (InTe)0.1(GeTe) and (InTe)0.3(GeTe) films were enhanced in comparison to the GST film. Contrarily, the v—value of the (InTe)0.5(GeTe) film was so drastically deteriorated that it could not be quantitatively evaluated. This deterioration occurred because the amorphous (InTe)0.5(GeTe) film had relatively high reflectance, resulting in the absorption being too low to cause the crystallization. Conclusively, proper compositional (InTe)x(GeTe) films (e.g., x<0.3) could be good candidates for PRAM application with both high crystallization speed and thermal stability.
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64.70.kg Semiconductors
68.55.-a Thin film structure and morphology
78.66.Jg Amorphous semiconductors; glasses
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics
78.35.+c Brillouin and Rayleigh scattering; other light scattering

High-resolution soft x-ray spectroscopic study on amorphous gallium indium zinc oxide thin films

Mi Ji Lee, Se Jun Kang, Jae Yoon Baik, Ki-jeong Kim, Hyeong-Do Kim, Hyun-Joon Shin, JaeGwan Chung, Jaecheol Lee, and JaeHak Lee

J. Appl. Phys. 108, 024507 (2010); http://dx.doi.org/10.1063/1.3457782 (6 pages) | Cited 6 times

Online Publication Date: 28 July 2010

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Amorphous gallium indium zinc oxide (a-GIZO) thin films of different compositions (Ga2O3:In2O3:ZnO = 1:1:1,2:2:1,3:2:1,4:2:1) on Si substrates were investigated by high-resolution x-ray photoelectron spectroscopy and x-ray absorption spectroscopy (XAS) using synchrotron radiation. The O 1s, Ga 3d, In 4d, Zn 3d core, and shallow-core levels as well as the valence band maxima and O K-edge XAS were investigated. Each O 1s spectrum could be deconvoluted by a main component (O1 in the text) representing the Ga–In–Zn–O quaternary system along with two other higher-binding energy (BE) components (O2 and O3 in the text). The O2+O3 intensity increased as the Ga2O3 content increased. For the as-prepared samples, the spectral peak separations between the Ga 3d ( ∼ 20 eV) and Zn 3d ( ∼ 11 eV) orbitals and between the In 4d ( ∼ 18 eV) and Zn 3d orbitals became larger, respectively, as the Ga2O3 content increased. For the surface-cleaned samples, this trend was the same but with smaller increases in their separations. The sputter-cleaning effectively reduced the Zn 3d intensity by ∼ 30% relative to those of Ga 3d and In 4d. The valence band maximum shifted toward higher BE, up to ∼ 0.5 eV for the as-prepared samples and ∼ 0.25 eV for the cleaned samples, and the conduction band minimum (measured at the O K-edge) was measured at photon energies ranging upwards to ∼ 0.2 eV as the Ga2O3 content increased, demonstrating that the band gap can be tailored by increasing the Ga2O3 content. The effects of increasing Ga2O3 contents on the local chemical states and the corresponding electrical conduction are discussed in this paper.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Jc Amorphous semiconductors; glasses
71.15.Nc Total energy and cohesive energy calculations
81.65.Cf Surface cleaning, etching, patterning
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Effect of forward current stress on low frequency noise in 4H–SiC p-n junctions

S. L. Rumyantsev, M. E. Levinshtein, M. S. Shur, J. W. Palmour, A. K. Agarwal, and M. K. Das

J. Appl. Phys. 108, 024508 (2010); http://dx.doi.org/10.1063/1.3457789 (5 pages)

Online Publication Date: 28 July 2010

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We report on the effect of forward current stress on the low frequency noise in the 4H–SiC rectifier p+-n diodes rated at 20 and 10 kV. The 4H–SiC diodes with 20 kV blocking voltage were the most sensitive to the forward current stress. Even the stress by the current density j = 13 A/cm2 for 30 min led to a noticeable increase in the forward voltage drop and changes in the noise spectra. The stress decreased the level of the 1/f noise but led to the appearance of the burst noise. Stress at higher current densities (50 A/cm2) led to the disappearance of the burst noise and to a further increase in the forward voltage drop. Diodes with 10 kV blocking capability were more resistant to the forward current stress. However, they also demonstrated a decrease in the 1/f noise as a result of the 60 min stress at j = 100 A/cm2.
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85.30.Kk Junction diodes

Multitone harmonic-balance simulations of an x-ray transition-edge sensor characterized at BESSY II

K. Rostem, D. J. Goldie, S. Withington, H. F. C. Hoevers, L. Gottardi, and J. van der Kuur

J. Appl. Phys. 108, 024509 (2010); http://dx.doi.org/10.1063/1.3466795 (4 pages)

Online Publication Date: 29 July 2010

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We present multitone harmonic-balance (MTHB) simulations of a Ti–Au x-ray transition-edge sensor (TES) microcalorimeter in a 5×5 pixel spectrometer array. The dynamic response of the TES microcalorimeter under simulation has been extremely well characterized at the BESSY II Synchrotron Radiation Facility in Berlin. We compare our simulated results directly with these measurements, and show that the MTHB algorithm is able to simulate to great accuracy the dynamic behavior of the TES, even when saturated by 6 keV photons. In this paper, we provide a detailed account of the MTHB simulations, and discuss the impact of this work on future missions such as the International X-ray Observatory.
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78.70.-g Interactions of particles and radiation with matter
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.20.Fw Calorimeters
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Direct hole injection in to 4,4′-N,N′-dicarbazole-biphenyl: A simple pathway to achieve efficient organic light emitting diodes

Z. B. Wang, M. G. Helander, J. Qiu, Z. W. Liu, M. T. Greiner, and Z. H. Lu

J. Appl. Phys. 108, 024510 (2010); http://dx.doi.org/10.1063/1.3456513 (4 pages) | Cited 14 times

Online Publication Date: 29 July 2010

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The conventional carrier-blocking design of the exciton formation zone used in nearly all organic light emitting diodes is shown to be problematic, due to exciton quenching from accumulated radical cations. To reduce exciton quenching, a single layer of 4,4′-N,N′-dicarbazole-biphenyl (CBP) is used as hole transport layer, resulting in a dramatically improved device efficiency even at high luminance (e.g., 20.5 cd/A at 100 000 cd/m2 for fluorescent green). Various high work function transition metal oxides (WO3, V2O5, and MoO3) coated on indium tin oxide anodes have been shown to enable direct hole injection into the deep highest occupied molecular orbital of CBP (6.1 eV).
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85.60.Jb Light-emitting devices
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.60.Fi Electroluminescence
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