E. Kamińska

In-plane uniaxial anisotropy rotations in (Ga,Mn)As thin films

We show, by superconducting quantum interference device magnetometry, that in (Ga,Mn)As films the in-plane uniaxial magnetic easy axis is consistently associated with particular crystallographic directions and that it can be rotated from the

Interband optical absorption in free standing layer of Ga0.96In0.04As0.99N0.01

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Fundamental and practical aspects of alloying encapsulated gold-based contacts to GaAs

direction to the [110] direction by low-temperature annealing. We show that this behavior is hole-density dependent and does not originate from surface anisotropy. The presence of uniaxial anisotropy as well its dependence on the hole concentration and temperature can be explained in terms of the

Photoluminescence study and structural characterization of p-type ZnO doped by N and/or As acceptors

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Ohmic Contact to n-GaN with TiN Diffusion Barrier

Zener model of the ferromagnetism assuming a small trigonal distortion.

Optical characterizations of ZnO, SnO 2 , and TiO 2 thin films for butane detection

We have measured the interband optical absorption of a free-standing sample of Ga0.96In0.04As0.99N0.01 in a wide energy range from 1 to 2.5 eV. We found that the fundamental absorption edge is shifted by 150 meV towards lower energies, and the absorption coefficient measured at higher energies exhibits substantial reduction comparing to that of GaAs. By removing the GaAs substrate, we were able to get an experimental insight into the interband optical transitions and the density of state in this material. The changes can be understood within the band anticrossing model predicting the conduction band splitting. New absorption edges associated with optical transitions from the spin-orbit split off band to the lower conduction subband (1.55 eV) and from the top of the valence band to the upper subband (1.85 eV) are observed.

Photonic structures with grating couplers based on ZnO

Abstract Au/GaAs and Au(Zn)/GaAs protected with either SiO 2 or Al 2 O 3 overlayers were alloyed at temperatures of 400–500°C. Rutherford backscattering spectrometry, secondary ion mass spectrometry, scanning electron microscopy and X-ray diffraction show that the extent of interaction expressed in terms of the amount of gallium in the metal or the total volume of decomposed GaAs is reduced by a factor of 20 or more compared with unprotected contacts. A lower specific resistance of (SiO 2 )Au/Zn/Au ohmic contacts to p-GaAs is obtained over a wider range of processing temperatures. Also, the morphology of both the surface and the interface of the contact is significantly improved. The observed effects of encapsulation made it possible to formulate a revised model of interaction between gold and GaAs when annealed in the conventional open-system configuration. It is postulated that gold does not react directly with GaAs. The primary process responsible for decomposition of the semiconductor is the enhanced evaporation of arsenic through the metallic layer. Rapid reaction of the released gallium with gold is a secondary process which can be substantially limited by preventing the loss of arsenic.

Interaction of Au/Zn/Au sandwich contact layers with AIIIBV compound semiconductors

ZnO doped with N and/or As layers was fabricated by thermal oxidation of ZnTe films grown by MBE on different substrates. Hall effect measurements demonstrated p-type conductivity with a hole concentration of ~5 × 1019 cm−3 for ZnO:As and ZnO:As:N on GaAs substrates and ~6 × 1017 cm−3 for ZnO:N on ZnTe substrates. The concentration of N and As atoms in ZnO is estimated to be ~1020 cm−3. This suggested that simple substitutional N atoms form acceptor impurities with a smaller efficiency than an As-related complex, probably AsZn–2VZn. In particular, we were able to distinguish between nitrogen and arsenic acceptor-related luminescence. Optical studies showed meaningful differences of the PL features in samples with different acceptors, grown on different substrates.

Gold-based ohmic contacts on III–V compounds: Thermally induced reactions between metallization and the semiconductor compound☆

The formation of n-GaN/Ti ohmic contacts with TiN diffusion barriers has been investigated by electrical measurements, x-ray diffraction and SIMS. It has been shown that the onset of the ohmic behaviour is associated with the thermally induced phase transformation of Ti into TiN at the GaN/Ti interface. It is suggested that the process is accompanied by an increase in the doping level in the semiconductor subcontact region. The presence of a TiN barrier is found to inhibit excessive decomposition of GaN and to confine the reaction between n-GaN and Ti.

Disorder suppression and precise conductance quantization in constrictions of PbTe quantum wells

The optogeometric properties of various sensitive thin films involved in gas sensing applications are investigated by using the m-line technique and atomic force microscopy. Variations of these optical properties are studied under butane and ozone exposure.