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10 May 2004

Volume 84, Issue 19, pp. 3723-3937

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Appl. Phys. Lett. 84, 3933 (2004); http://dx.doi.org/10.1063/1.1745103 (3 pages)

A. Cassinese, G. M. De Luca, A. Prigiobbo, M. Salluzzo, and R. Vaglio
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Field-effect transistor based on KTaO3 perovskite

K. Ueno, I. H. Inoue, T. Yamada, H. Akoh, Y. Tokura, and H. Takagi

Appl. Phys. Lett. 84, 3726 (2004); http://dx.doi.org/10.1063/1.1703841 (3 pages) | Cited 22 times

Online Publication Date: 29 April 2004

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An n-channel accumulation-type field-effect transistor (FET) has been fabricated utilizing a KTaO3 single crystal as an active element and a sputtered amorphous Al2O3 film as a gate insulator. The device demonstrated an ON/OFF ratio of 104 and a field-effect mobility of 0.4 cm2/V s at room temperature, both of which are much better than those of the SrTiO3 FETs reported previously. The field-effect mobility was almost temperature independent down to 200 K. Our results indicate that the Al2O3/KTaO3 interface is worthy of further investigations as an alternative system of future oxide electronics. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
85.30.De Semiconductor-device characterization, design, and modeling
72.80.Jc Other crystalline inorganic semiconductors

Highly resistive p-PbTe films with carrier concentration as low as 1014 cm−3

V. Sandomirsky, A. V. Butenko, I. G. Kolobov, A. Ronen, Y. Schlesinger, A. Yu. Sipatov, and V. V. Volubuev

Appl. Phys. Lett. 84, 3732 (2004); http://dx.doi.org/10.1063/1.1728319 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2004

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We propose here a model according to which a high density of semiconductor–insulator interface states can deplete practically the whole film volume, provided that the film thickness is of the order of Debye screening length. We demonstrated this experimentally by showing that thin p-PbTe films, thermally deposited on mica substrate, have an unusually low concentration of free holes, as low as 1014 cm−3 at 100 K, resulting in a very high value of resistance, Hall constant, and Seebeck coefficient, respectively. Such low concentration of free carriers allows an investigation of a whole series of phenomena in AIVBVI semiconductors, such as injection currents, injection electroluminescence, electronic memory phenomena, electric field effect control of thermopower, and more. © 2004 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Le Other inorganic semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects
78.66.Li Other semiconductors
78.60.Fi Electroluminescence

Radiative efficiency limits of solar cells with lateral band-gap fluctuations

U. Rau and J. H. Werner

Appl. Phys. Lett. 84, 3735 (2004); http://dx.doi.org/10.1063/1.1737071 (3 pages) | Cited 23 times

Online Publication Date: 29 April 2004

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The radiative recombination limit of photovoltaic power conversion under one sun terrestrial illumination is calculated for solar cells with lateral fluctuations of the band-gap energy. A simple analytical model quantifies the fluctuations by the standard deviation σEg from the mean band gap. The calculated maximum efficiency decreases by 1.7% (absolute) for σEg = 50 meV and by 6.1% for σEg = 100 meV with respect to a uniform band gap. © 2004 American Institute of Physics.
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84.60.Jt Photoelectric conversion
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Synthesis and characterization of two-layer-structured ZnO p-n homojunctions by ultrasonic spray pyrolysis

J. M. Bian, X. M. Li, C. Y. Zhang, L. D. Chen, and Q. Yao

Appl. Phys. Lett. 84, 3783 (2004); http://dx.doi.org/10.1063/1.1739280 (3 pages) | Cited 36 times

Online Publication Date: 29 April 2004

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The two-layer-structured ZnO p-n homojunctions were prepared on single-crystal Si (100) substrate by depositing undoped n-type ZnO film on N–In codoped p-type ZnO film using ultrasonic spray pyrolysis. The crystal structure and morphology of the obtained ZnO homojunctions were examined by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The two-layer structure was confirmed by secondary ion mass spectroscopy depth profile analysis. The current–voltage (I–V) characteristics derived from the undoped ZnO/N–In codoped ZnO two-layer structure clearly show the rectifying characteristics of typical p-n junctions. © 2004 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Rs Spray coating techniques
68.55.-a Thin film structure and morphology

A hybrid Al0.10Ga0.90As/AlAs bilayer electron system with tunable g-factor

E. P. De Poortere and M. Shayegan

Appl. Phys. Lett. 84, 3837 (2004); http://dx.doi.org/10.1063/1.1745111 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2004

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We have fabricated a device composed of two closely coupled two-dimensional electron systems, one of which resides within an AlAs quantum well at the X point of the Brillouin zone, while the other is contained at the Γ point in the alloy Al0.10Ga0.90As, grown directly below the AlAs. The electronic properties of these two systems are strongly asymmetric: the respective cyclotron masses in the AlAs and the Al0.10Ga0.90As layers, measured in units of the free electron mass, are ∼ 0.5 and 0.07, while the effective electron g-factors are approximately 7 and 0. With the help of front and back gates, we can confine mobile carriers to either or both of the two quantum wells, as confirmed by magnetotransport measurements. © 2004 American Institute of Physics.
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73.21.Fg Quantum wells
68.65.Fg Quantum wells
72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Type-II interband transition of ZnS0.78Te0.22/ZnTe single quantum wells

Jae Ho Bahng, S. J. Moon, K. H. Lee, J. C. Choi, K. Jeong, and H. L. Park

Appl. Phys. Lett. 84, 3870 (2004); http://dx.doi.org/10.1063/1.1728306 (3 pages) | Cited 8 times

Online Publication Date: 29 April 2004

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Optical properties of ZnS0.78Te0.22/ZnTe single quantum wells grown on GaAs (100) substrates by hot wall epitaxy technique with varying the ZnS0.78Te0.22 well width from 0.3 to 1.8 nm were investigated by photoluminescence (PL) measurements at low temperature and by temperature-dependent PL measurements. PL results show the evidence of type-II transition and their peak energy shifts to higher energies as the ZnS0.78Te0.22 well width decreases. In addition, temperature-dependent PL measurements show the increase of the activation energy as the well thickness decreases, indicating the increase of confinement effect. This study makes it possible to introduce proper band diagram for this structure, and can give very useful information on their device applications. © 2004 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.21.Fg Quantum wells
78.67.De Quantum wells
68.55.A- Nucleation and growth
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.07.St Quantum wells
81.05.Dz II-VI semiconductors
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Observation of a Be-correlated donor state in GaN

F. Albrecht, U. Reislöhner, G. Pasold, C. Hülsen, W. Witthuhn, J. Grillenberger, and M. Dietrich

Appl. Phys. Lett. 84, 3876 (2004); http://dx.doi.org/10.1063/1.1738181 (3 pages)

Online Publication Date: 29 April 2004

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A Be-related donor level was identified in the band gap of GaN. Thermal admittance spectroscopy (TAS) was combined with the radiotracer principle by applying the radioactive isotope 7Be which was implanted into n-type and p-type GaN. TAS spectra of n-type GaN recorded, repeatedly, during the elemental transmutation of 7Be to 7Li reveal one shallow donor level undergoing concentration changes correlated to the radioactive decay (7Be→7Li;T1/2 = 53.3d). From this, a relation is deduced between Be and this level at 390 meV below the conduction band edge of GaN. Furthermore, the implantation of 7Be was observed to enhance the hole concentration significantly in Mg-doped p-type GaN. A Be-correlated acceptor state was not detected. © 2004 American Institute of Physics.
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71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
61.72.uj III-V and II-VI semiconductors
73.20.At Surface states, band structure, electron density of states

Influence of buffer layers on the performance of polymer solar cells

F. L. Zhang, A. Gadisa, O. Inganäs, M. Svensson, and M. R. Andersson

Appl. Phys. Lett. 84, 3906 (2004); http://dx.doi.org/10.1063/1.1739279 (3 pages) | Cited 49 times

Online Publication Date: 29 April 2004

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The influence of different anode buffer layers on the performance of solar cells based on blends of polyfluorene copolymer poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (DiO-PFDTBT), acting as electron donor, and [6,6]-phenyl-C61-butyric acid methylester (PCBM), acting as electron acceptor was studied. The buffer layers were constructed from different forms of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)(PEDOT-PSS). Variations in open-circuit voltage, short-circuit current, and fill factor were observed. These were attributed to the slight rearrangement of the insulating layer PSS on top of PEDOT, which altered the charge injection at the interface between anode and photoactive layer. © 2004 American Institute of Physics.
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84.60.Jt Photoelectric conversion
82.45.Fk Electrodes
71.55.Jv Disordered structures; amorphous and glassy solids
72.20.Fr Low-field transport and mobility; piezoresistance

Semiconductor–superlattice frequency multiplier for generation of submillimeter waves

F. Klappenberger, K. F. Renk, P. Renk, B. Rieder, Yu. I. Koshurinov, D. G. Pavelev, V. Ustinov, A. Zhukov, N. Maleev, and A. Vasilyev

Appl. Phys. Lett. 84, 3924 (2004); http://dx.doi.org/10.1063/1.1741037 (3 pages) | Cited 8 times

Online Publication Date: 29 April 2004

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We report on a semiconductor–superlattice frequency multiplier for the generation of submillimeter waves. A monochromatic microwave-pump field (frequency near 100 GHz) periodically excited a superlattice into states of negative differential conductivity giving rise to space-charge domain creation and annihilation joint with a nonsinusoidal high-frequency current and radiation at harmonics of the pump field. A highly doped GaAs/AlAs superlattice allowed the conversion of pump to third-harmonic radiation at 300 GHz with an efficiency of about 1% (power∼30 μW). © 2004 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
84.30.-r Electronic circuits
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