In this paper, the photoluminescence spectra of excitons in ZnO/ZnMgO/ZnO double asymmetric quantum wells grown on a–plane Al2O3 substrates with internal electric-field bands structures were studied. ...In these structures, the electron and the hole in the exciton are spatially separated between neighbouring quantum wells, by a ZnMgO barrier with different thickness. The existence of an internal electric field generates a linear potential and, as a result, lowers the energy of quantum states in the well. For the wide wells, the electrons are spatially separated from the holes and can create indirect exciton. To help the understanding of the photoluminescence spectra, for single particle states the 8 k·p for wurtzite structure is employed. Using these states, the exciton in the self-consistent model with 2D hydrogenic 1s–like wave function is calculated.
The article presents a systematic study of Sb-doped Zn1−xMgxO layers, with various concentrations of Mg, that were successfully grown by plasma-assisted MBE on polar a- and c-oriented and non-polar ...r-oriented sapphire substrates. X-ray diffraction confirmed the polar c-orientation of alloys grown on c-and a-oriented sapphire and non-polar structures grown on r-oriented substrates. A uniform depth distribution of the Sb dopant at level of 2 × 1020 cm−3 was determined by SIMS measurements. Raman spectroscopy revealed the presence of Sb-related modes in all samples. It also showed that Mg alloying reduces the compressive strain associated with Sb doping in ZnO. XPS analysis indicates that the chemical state of Sb atoms in ZnMgO is 3+, suggesting a substitutional position of SbZn, probably associated with two VZn vacancies. Luminescence and transmission spectra were measured to determine the band gaps of the Zn1−xMgxO layers. The band gap energies extracted from the transmittance measurements differ slightly for the a, c, and r substrate orientations, and the differences increase with increasing Mg content, despite identical growth conditions. The differences between the energy gaps, determined from transmission and PL peaks, are closely correlated with the Stokes shift and increase with the Mg content in the analyzed series of ZnMgO layers.
In this work, luminescence properties of Europium doped ZnO and ZnMgO thin films grown on a-oriented (11–20) sapphire substrates by oxygen plasma assisted Molecular Beam Epitaxy method are studied. ...The concentrations and distributions of Eu atoms in the respective hosts were analysed using Secondary Ion Mass Spectrometry, which confirmed successful doping around the level of ∼1%. Optical properties of the samples were investigated by room temperature photoluminescence (PL) and Photoluminescence excitation (PLE) measurements. The PL data suggest the co-existence of 2+ and 3+ ionic states of Eu in the as-grown samples. It has been observed that alloying Mg with ZnO increases the intensity of the 5D0→7FJ intra-4f-shell emission of Eu3+ ions by an order of magnitude even in as-grown samples. The samples were also annealed at 800 °C in oxygen flux and re-measured to see changes in the PL. After annealing, all the emission lines due to the 5D0→7FJ intra-4f-shell transitions of Eu3+ were strongly enhanced, whereas the bands attributed to Eu2+ were found to diminish or disappear completely. The results of PLE measurements point to efficient host to dopant energy transfer in the studied films.
•Europium (Eu) doping into ZnO and ZnMgO thin films by Molecular Beam Epitaxy.•Comparison of Europium luminescence from ZnO and ZnMgO hosts before and after annealing.•PL and PLE measurements confirmed energy transfer from ZnO and ZnMgO hosts to the Eu ion centres.•PL evidence for coexistence of divalent and trivalent Europium ions in ZnO and ZnMgO hosts.•PL studies confirmed ZnMgO to be a better oxide host material for Europium luminescence.
Herein, the properties of ZnO:N/n‐SiC heterojunctions (HJs) and light‐emitting diodes based on them are studied. The HJs are grown by molecular beam epitaxy. Active nitrogen generated by a radio ...frequency plasma source is used for p‐type doping. The location of the space charge area on the ZnO:N/n‐SiC interface is revealed by electron‐beam‐induced current (EBIC) scans. The diffusion lengths of holes and electrons are calculated. This article presents the characterization of ZnO:N/n‐SiC HJs and reveals the presence of tunneling‐related current transport in them as well as the contribution of exponentially distributed traps at large voltage bias. Electroluminescence (EL) is measured at ambient pressure by a standard EL system and also at 77 K in vacuum by a system utilizing EBIC in a scanning electron microscope. Analysis of the light output power at higher current level indicates the limited effect of nonradiative defects in this structure. EL results are compared with cathodoluminescence spectra. Color temperature for HJs based on the EL spectra is also calculated.
The properties of ZnO:N/n‐SiC heterojunctions are analyzed by current–voltage and electron‐beam‐induced current (EBIC) measurements. Electroluminescence (EL) is measured at ambient pressure by a standard EL system and in the vacuum by a system utilizing EBIC in a scanning electron microscope. Analysis of the light output power indicates a limited effect of nonradiative defects in this structure.
Control of nanostructure growth is a prerequisite for the development of electronic and optoelectronic devices. This paper reports the growth conditions and structural properties of ZnMgO nanowalls ...grown on the Si face of 4H‐SiC substrates by molecular beam epitaxy without catalysts and buffer layers. Images from scanning electron microscopy revealed that the ZnMgO nanowalls are arranged in parallel rows following the stripe morphology of the SiC surface, and their thickness is around 15 nm. The crystal quality of the structures was evaluated by X‐ray diffraction measurements.
The crystal quality of ZnMgO nanowalls grown on 4H‐SiC substrates has been investigated by X‐ray diffraction.
The article presents a systematic study of Sb-doped Zn
Mg
O layers, with various concentrations of Mg, that were successfully grown by plasma-assisted MBE on polar
- and
-oriented and non-polar
...-oriented sapphire substrates. X-ray diffraction confirmed the polar
-orientation of alloys grown on
-and
-oriented sapphire and non-polar structures grown on
-oriented substrates. A uniform depth distribution of the Sb dopant at level of 2 × 10
cm
was determined by SIMS measurements. Raman spectroscopy revealed the presence of Sb-related modes in all samples. It also showed that Mg alloying reduces the compressive strain associated with Sb doping in ZnO. XPS analysis indicates that the chemical state of Sb atoms in ZnMgO is 3+, suggesting a substitutional position of Sb
, probably associated with two V
vacancies. Luminescence and transmission spectra were measured to determine the band gaps of the Zn
Mg
O layers. The band gap energies extracted from the transmittance measurements differ slightly for the
,
, and
substrate orientations, and the differences increase with increasing Mg content, despite identical growth conditions. The differences between the energy gaps, determined from transmission and PL peaks, are closely correlated with the Stokes shift and increase with the Mg content in the analyzed series of ZnMgO layers.
The article presents a systematic study of Sb-doped Znsub.1−xMgsub.xO layers, with various concentrations of Mg, that were successfully grown by plasma-assisted MBE on polar a- and c-oriented and ...non-polar r-oriented sapphire substrates. X-ray diffraction confirmed the polar c-orientation of alloys grown on c-and a-oriented sapphire and non-polar structures grown on r-oriented substrates. A uniform depth distribution of the Sb dopant at level of 2 × 10sup.20 cmsup.−3 was determined by SIMS measurements. Raman spectroscopy revealed the presence of Sb-related modes in all samples. It also showed that Mg alloying reduces the compressive strain associated with Sb doping in ZnO. XPS analysis indicates that the chemical state of Sb atoms in ZnMgO is 3+, suggesting a substitutional position of Sbsub.Zn, probably associated with two Vsub.Zn vacancies. Luminescence and transmission spectra were measured to determine the band gaps of the Znsub.1−xMgsub.xO layers. The band gap energies extracted from the transmittance measurements differ slightly for the a, c, and r substrate orientations, and the differences increase with increasing Mg content, despite identical growth conditions. The differences between the energy gaps, determined from transmission and PL peaks, are closely correlated with the Stokes shift and increase with the Mg content in the analyzed series of ZnMgO layers.
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