G. Pozina | Linköping University (original) (raw)

Papers by G. Pozina

GaN layers doped by Mg show a metastable behavior of the near-band-gap luminescence caused by ele... more GaN layers doped by Mg show a metastable behavior of the near-band-gap luminescence caused by electron irradiation or UV excitation. At low temperatures < 30 K the changes in luminescence are permanent. Heating to room temperature recovers the initial low temperature spectrum shape completely. Two acceptors are involved in the recombination process as confirmed by transient PL. In as-grown samples a possible candidate for the metastable acceptor is C N , while after annealing a second more stable acceptor related to Mg became active.

Journal of Vacuum Science & Technology B, 1998

Annealing effects on the crystal structure of GaInNAs quantum wells with large In and N content g... more Annealing effects on the crystal structure of GaInNAs quantum wells with large In and N content grown by molecular beam epitaxy

COMMAD 2000 Proceedings. Conference on Optoelectronic and Microelectronic Materials and Devices, 2000

We review o " ur recent results from studies of electronic properties of GaNAs/GaAs structures wi... more We review o " ur recent results from studies of electronic properties of GaNAs/GaAs structures with low nitrogen content, by photoluminescence (PL), PL excitation, time-resolved PL spectroscopies as well as optically detected magnetic resonance (ODMR) and cyclotron resonance (ODCR) studies. The issues to be addressed include key material-related properties and fundamental electronic parameters of the GaNAs aHoy, relevant to device applications, such as identiication of the dominant recombination processes in the alloy, compositional dependence of the electron efective mass and band alignment in the GaNAs/GaAs heterostructures.

Scripta Materialia, 2009

Cathodoluminescence (CL) properties were studied for metastable c-and j-Al 2 O 3 coatings for cut... more Cathodoluminescence (CL) properties were studied for metastable c-and j-Al 2 O 3 coatings for cutting tool inserts. The alumina films demonstrate a strong CL, with peak energies depending on the Al 2 O 3 polymorphs. The phase transformation caused by heat treatment is shown to correlate with strong CL modification in the annealed coatings. Spatially resolved CL is found to be a powerful nondestructive technique for identification of different alumina phases on the microscopic level. The corresponding optical properties of c-and j-Al 2 O 3 are discussed.

physica status solidi (b), 2004

The effects of the Si doping level on the recombination dynamics and carrier (exciton) localizati... more The effects of the Si doping level on the recombination dynamics and carrier (exciton) localization in modulation doped GaN/Al 0.07 Ga 0.93 N multiple-quantum-well (MQW) structures were studied by means of photoluminescence (PL) and time-resolved PL measurements. All samples with different doping levels show a QW emission which is blue shifted with respect to the 3.48 eV PL peak from the GaN buffer layer. The decay time at the peak position remains nearly constant in the range of 320-420 ps at 2 K for all doping levels. For the undoped and low-doped samples (3 × 10 18 cm -3 ), which have less free electrons in the QWs, a non-exponential PL decay behaviour at 2 K is attributed to localized exciton recombination. The more highly doped samples (5 × 10 18 cm -3 to 10 20 cm -3 ) show almost exponential decay curves at 2 K, suggesting the recombination of free electrons and localized holes. This localization effect appears even at high electron concentrations to cancel the expected lowering of the radiative lifetime with doping at 2 K; such a lowering is clearly observed at elevated temperatures for the highly doped samples, however. The internal polarization-induced fields of the medium and highly-doped samples are partly screened by the electrons originating from the doping in the barriers. Only the PL peak of the undoped and low-doped samples shows a redshift with time delay, related to the photogenerated carriers.

Physica Scripta, 1999

An ultrathin, 1-6 monolayers (MLs) thick, Si d-layer, is embedded in bulk GaAs. The normally obse... more An ultrathin, 1-6 monolayers (MLs) thick, Si d-layer, is embedded in bulk GaAs. The normally observed self-assembling with resulting phase separation can be avoided up to d-layer thicknesses of 4 MLs, which opens the possibility to study two-dimensional (2D) properties of this III-V/IV heterostructure. Optical, electrical, transport and structural characterization of the Si d-layer has been carried out. In luminescence, two novel emission bands are observed, which are blue-shifted as the width of the Si d-layer is reduced, indicating pronounced 2D properties. The derived results on transition energies and electronic structure are compared with theoretical predictions obtained by a self-consistent approach.

Physica E: Low-dimensional Systems and Nanostructures, 2001

We report on cw and time-resolved photoluminescence (PL) studies of Cd(Mn)Se=Zn(Mn)Se diluted mag... more We report on cw and time-resolved photoluminescence (PL) studies of Cd(Mn)Se=Zn(Mn)Se diluted magnetic semiconductor nanostructures grown by molecular beam epitaxy. Excitonic PL intensity, decay time and Zeeman splitting have been studied systematically as a function of Cd(Mn)Se nominal thickness, Mn concentration and sample design. Wave function mapping has been performed, evidencing the formation of semi-magnetic quantum disk islands in the samples with thick enough Cd(Mn)Se insertions.

Journal of Crystal Growth, 2000

We report for the "rst time on MBE growth, structural and optical properties of single layers, qu... more We report for the "rst time on MBE growth, structural and optical properties of single layers, quantum well structures and short-period superlattices based on Be V Cd \V Se ternary alloys on GaAs. Both the conventional MBE growth mode and the sub-monolayer digital alloying technique (SDA) have been employed for the fabrication of the structures. Compositional boundaries of an instability region 0.03(x(0.38, calculated in a regular solution approximation for the completely coherent system, agree well with available experimental data. A suppression of the phase separation in BeCdSe by elastic stress in the layer, accompanied by a strong reduction of the Cd incorporation coe$cient has been found. Ultrathin 2.8 ML BeCdSe SDA QWs with x&0.15 demonstrate about an order of magnitude increase in the PL intensity with respect to the pure CdSe one, probably resulting from an enhanced carrier localization e$ciency. E as a function of the Be content reveals a strong bowing in optical data, which allows one to consider BeCdSe alloys with compositions nearly lattice-matched to GaAs as potential materials for the active region of blue-green lasers.

Journal of Crystal Growth, 2001

We report on studies of an In 0.12 Ga 0.88 N/GaN structure with three 35 ( A thick quantum wells ... more We report on studies of an In 0.12 Ga 0.88 N/GaN structure with three 35 ( A thick quantum wells (QWs) grown by metalorganic vapor phase epitaxy with employment of mass transport. The mass-transport regions demonstrate a threading dislocation density less than 10 7 cm À2 . The photoluminescence (PL) spectrum is dominated by a 40 meV}narrow line centered at 2.97 eV at 2 K. This emission has a typical PL decay time of about 5 ns at 2 K within the PL contour. An additional line with longer decay time (about 200 ns) is observed at an energy about 2.85 eV. The position of this line shifts towards higher energies with increasing excitation power. The data are consistent with a model, where the PL originates from at least two nonequivalent QWs, which could be realized due to a potential gradient across the layers. #

Journal of Applied Physics, 2011

GaN films were grown on Si(111) substrates under various beam equivalent pressure (BEP) ratios by... more GaN films were grown on Si(111) substrates under various beam equivalent pressure (BEP) ratios by plasma-assisted molecular beam epitaxy. The optical properties for the grown samples were studied over a wide spectral range from 200 to 3300 nm using the reflectance spectrum only. It was found that increasing the N/Ga BEP ratio from 17.9 to 46.1 increases the refractive index (n) from 2.05 to 2.38 at wavelength 630 nm (for example), while the optical energy gap (Eg) were found to be in the range between 3.325 to 3.35 eV with no specific trend. The structural properties for the grown films were studied through two types of rocking curve measurements; normal rocking curve (omega-scan) and triple axis rocking curve (omega/2theta-scan). It was found that with decreasing the N/Ga ratio from 46.1 to 17.9 the full width at half maximum decreases from 0.62° to 0.58° for omega-scan and from 0.022° to 0.021° for omega/2theta-scan. Thus, our results showed a clear correlation between the optical-structural parameters and the BEP ratios of N and Ga.

IEEE Electron Device Letters, 2000

Currently, up to 50% of the channel temperature in AlGaN/GaN electronic devices is due to the the... more Currently, up to 50% of the channel temperature in AlGaN/GaN electronic devices is due to the thermal-boundary resistance (TBR) associated with the nucleation layer (NL) needed between GaN and SiC substrates for high-quality heteroepitaxy. Using 3-D time-resolved Raman thermography, it is shown that modifying the NL used for GaN on SiC epitaxy from the metalorganic chemical vapor deposition (MOCVD)-grown standard AlN-NL to a hot-wall MOCVD-grown AlN-NL reduces NL TBR by 25%, resulting in ∼10% reduction of the operating temperature of AlGaN/GaN HEMTs. Considering the exponential relationship between device lifetime and temperature, lower TBR NLs open new opportunities for improving the reliability of AlGaN/ GaN devices.