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1 Acta Physica Polonica A

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Electrostatic Gates for GaN/AlGaN Quantum Point Contacts

100%

Czapkiewicz M. , Cywiński G. , Dybko K. , Siekacz M. , Wolny P. , Gierałtowska S. , Guziewicz E. , Skierbiszewski C. , Wróbel J.

nr 6

1026-1028

We report on AlGaN/GaN quantum point contacts fabricated by using e-beam lithography and dry ion etching. The tunable nano-constrictions are defined by the integration of side and top gates in a single device. In this configuration, the planar gates are located on the both sides of a quantum channel and the metallic top gates, which cover the active region, are separated from the substrate by an insulating and passivating layers of HfO_2 or Al_2O_3/HfO_2 composite. The properties of devices have been tested at T = 4.2 K. For side gates we have obtained a very small surface leakage current I_g< 10^{-11} A at gate voltages |V_g| < 2 V, however, it is not enough to close the quantum channel. With top gates we have been able to reach the pinch-off voltage at V_g = - 3.5 V at a cost of I_g ≈ 10^{-6} A, which has been identified as a bulk leakage current.

Magnetoplasmons in a High Electron Mobility GaAs/AlGaAs Heterostructure

100%

Białek M. , Karpierz K. , Piętka B. , Grynberg M. , Łusakowski J. , Czapkiewicz M. , Fronc K. , Wróbel J. , Umansky V.

nr 6

1096-1098

We have observed a multimode spectrum of magnetoplasmons in the Hall bars processed on a high electron mobility GaAs/AlGaAs heterostructure. We have found that the dispersion relation of these excitation follows square root dependence. Calculated wavelength of the fundamental magnetoplasmon mode fits to the width of sample.

Terahertz Response of a Point Contact Based on CdTe/CdMgTe Quantum Well in Magnetic Field

80%

Grigelionis I. , Białek M. , Grynberg M. , Czapkiewicz M. , Kolkovskiy V. , Wiater M. , Wojciechowski T. , Wróbel J. , Wojtowicz T. , But D. , Knap W. , Łusakowski J.

nr 6

1069-1072

A photoresponse at THz frequencies of a quantum point contact fabricated on a CdTe/CdMgTe quantum well was studied at low temperatures as a function of magnetic field. The spectra show a structure which was interpreted as resulting from the cyclotron resonance and magnetoplasmon excitations. The wavelength of the fundamental magnetoplasmon mode was found to be about 2 μm which coincides with one of dimensions of the point contact. We also discuss the possibility of coupling of magnetoplasmon modes to shallow impurity transitions in the quantum well.

Photoluminescence Properties of ZnO Nanowires Grown on Ni Substrate

80%

Zaleszczyk W. , Fronc K. , Przeździecka E. , Janik E. , Czapkiewicz M. , Wróbel J. , Paszkowicz W. , Kłopotowski Ł. , Karczewski G. , Wojtowicz T. , Presz A.

nr 5

1451-1456

Photoluminescence studies of zinc oxide nanowires produced by a carbo-thermal method on a nickel foil substrate are reported. Two types of as-grown samples: the first - containing only buffer film, and the second - containing both zinc oxide nanowires and buffer film grown in the same technological process, were investigated by means of the temperature-dependent photoluminescence. X-ray diffraction measurements of buffer film show that it is polycrystalline and is composed from wurtzite-type ZnO (main phase) and includes minority phases: rock salt type (Ni,Zn)O and hexagonal C₃N₄. The shape of the apparently monocrystalline nanowires is characterized by hexagonal section matching with the expectations of the hexagonal ZnO structure. The presence of LO-phonon replicas in photoluminescence spectra for the second sample is used as an argument for confirmation that ZnO nanowires are single crystalline. The method of growth of ZnO nanowires on nickel oxide opens perspectives to produce Zn_{1-x}Ni_{x}O diluted magnetic semiconductor nanowires.