Sh. U. Yuldashev

Optical and magnetic measurements of p-type GaN epilayers implanted with Mn+ ions

The p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently Mn+ ions implanted. The properties of Mn+ ions-implanted GaN epilayers were investigated by optical and magnetic measurements. The results of photoluminescence measurement show that optical transitions related to Mn apparently appear at 2.5 eV and around 3.0 eV. It is confirmed that the photoluminescence peak at 2.5 eV is a donor–Mn acceptor transition. Ferromagnetic hysteresis loop was observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting up to ∼270 K.

Effect of additional nonmagnetic acceptor doping on the resistivity peak and the Curie temperature of Ga1-xMnxAs epitaxial layers

We have investigated the effect of additional doping by Be on the properties of Ga1−xMnxAs (x=0.03). For this relatively low value of x, the Curie temperature is observed to increase with increasing Be concentration. We show that the temperature dependence of the resistivity at zero magnetic field, including the resistivity maximum near the Curie temperature, can be successfully described by the magnetoimpurity scattering model proposed by Nagaev [Phys. Rep. 346, 387 (2001)] in both the paramagnetic and the ferromagnetic temperature regions. Quantitative analysis of the data in terms of this model yields the value of the p–d exchange energy |N0β|≈1.6 eV for Ga0.97Mn0.03As.

Enhanced positive magnetoresistance effect in GaAs with nanoscale magnetic clusters

The enhanced positive magnetoresistance effect has been observed in GaAs containing nanoscale magnetic clusters. The ferromagnetic metallic clusters were embedded into GaAs by Mn ion implantation and rapid thermal annealing. Positive magnetoresistance in these structures has been observed and attributed to the enhanced geometric magnetoresistance effect in inhomogeneous semiconductors with metallic inclusions. The additional enhancement of positive magnetoresistance under light illumination is due to the higher mobility of photoexcited electrons in comparison with the mobility of holes in p-type GaAs prepared by Mn ion implantation.

Ferromagnetic behavior of p-type GaN epilayer implanted with Fe+ ions

p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently implanted with Fe+ ions. The properties of Fe+ implanted GaN epilayers were investigated by various measurements. The results of photoluminescence measurement show that optical transitions related to Fe appear at 2.5 eV and around 3.1 eV. It was confirmed that the photoluminescence peak at 2.5 eV is a donor-Fe acceptor transition and the photoluminescence peak around 3.1 eV is a conduction band-Fe acceptor transition. Apparent ferromagnetic hysteresis loops measured at 10 and 300 K were observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting above 350 K.

Electrical and optical properties of ZnO thin films grown on Si substrates

Undoped and nitrogen doped ZnO films were deposited on Si substrates by ultrasonic spray pyrolysis at ambient atmosphere. The p type of conductivity for the nitrogen doped ZnO films has been observed. The concentration of free holes in ZnO films has been found to depend strongly on the resistivity of Si substrate. With decreasing of the substrate resistivity the concentration of free holes in ZnO films increases. The hole concentration of 1.1×1018cm−3 and the hole mobility of 24cm2V−1s−1 were observed in the ZnO films grown on the Si substrates with the resistivity of 0.001Ωcm.

Highly efficient CNT functionalized cotton fabrics for flexible/wearable heating applications

In this work, a highly efficient, flexible electro thermal heater based on highly conductive carbon nanotube functionalized cotton fabrics has been studied. Cotton fabrics were functionalized with single walled carbon nanotubes through a simple dip coating method. To explore their potential as heaters, electrothermal performances of the devices were studied in terms of applied voltage, heating rate and input power density. The highly flexible heater is constructed based on uniformly interconnected CNT networks, which yields an effective and rapid heating of the heater at low input power. The investigation results suggest promising applications of these devices in wearable electronics and beyond and they could also be woven into textile materials.

Surface passivation by sulfur treatment of undoped p-CdTe(100)

The effect of surface passivation of undoped p-CdTe(100) by (NH4)2Sx treatment was investigated by using photoluminescence (PL), photoconductivity (PC), and x-ray photoelectron spectroscopy (XPS). After sulfur treatment for 2 min, the acceptor bound exciton (A0, X) peak increases greatly in the PL spectrum, and the minority-carrier lifetime of CdTe becomes the longest value in the PC measurement. The XPS spectrum for untreated CdTe shows the additional peaks on the right side of two main Te peaks corresponding to the Te 3d core levels, and these additional peaks are related to TeO3 with binding energies of 576.2 and 586.5 eV. After sulfur treatment, while the intensities of the Te 3d core levels decreased gradually, those of the TeO3 peaks disappear. In addition, the S 2p core-level spectra for sulfur-treated CdTe show the peaks at the 161.7 and 162.8 eV, which are attributed to a CdS formation at the surface of CdTe. These results indicate the sulfur effectively dissociates the native oxides from and neu...

Study of the photoluminescence emission line at 3.33 eV in ZnO films

We study properties of the line at 3.33 eV observed in photoluminescence (PL) emission spectra of various ZnO films prepared using pulsed laser deposition method. The influence of deposition parameters, such as oxygen pressure, laser fluence, post-annealing, and electric field exposure on intensity of this luminescence band has been investigated. The recombination characteristics are probed by temperature and excitation dependent PL spectroscopy. The obtained experimental data suggest that the 3.33 eV luminescence line in ZnO depends strongly on surface band bending and originates from recombination of bound excitons (BEs) complex located near the surface and grain boundaries. The anomalously small thermal activation energy of BE in comparison with the localization energy is explained by decreasing of the interface barrier. Possible nature of defects that bind free excitons and cause the 3.33 eV emission line in ZnO is proposed.

Deep level emission of ZnO nanoparticles deposited inside UV opal

Abstract The temperature-dependent photoluminescence spectra of zinc oxide (ZnO) nanocrystals deposited inside the ultraviolet (UV) opal were studied. ZnO was grown in the voids between FCC packed SiO 2 spheres using spray pyrolysis under ultrasonic vibration in the solution containing a zinc nitrate precursor. The ZnO nanoparticles inside opal matrix with UV photonic band-gap exhibit suppression of the excitonic emission and enhancement of the deep level emission. Suppression of the excitonic lines is due to the inhibition of spontaneous emission, while enhancement and broadening of the DL emission in the green spectral region is due to Purcell effect. The infiltration of ZnO nanoparticles inside the photonic crystal may be a useful technique to increase its emission efficiency in the selected spectral region.

Diluted magnetic semiconductor of p-type GaN epilayers implanted with Mn+ ions

The study of diluted magnetic semiconductor based on GaN was performed employing a variety of various measurement techniques. p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and were subsequently implanted with Mn+ ions. The properties of Mn+ ion-implanted GaN epilayers were investigated with optical and magnetic measurements. The results of photoluminescence (PL) measurement show that optical transitions related to Mn apparently appear at 2.5 and around 3.0 eV. It is confirmed that the PL peak at 2.5 eV is a donor-Mn acceptor transition and the PL peak around 3.0 eV is a conduction band-Mn acceptor transition. Ferromagnetic hysteresis loop was observed, and the temperature dependent-magnetization displayed a ferromagnetic behavior persisting up to ∼270 K.The study of diluted magnetic semiconductor based on GaN was performed employing a variety of various measurement techniques. p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and were subsequently implanted with Mn+ ions. The properties of Mn+ ion-implanted GaN epilayers were investigated with optical and magnetic measurements. The results of photoluminescence (PL) measurement show that optical transitions related to Mn apparently appear at 2.5 and around 3.0 eV. It is confirmed that the PL peak at 2.5 eV is a donor-Mn acceptor transition and the PL peak around 3.0 eV is a conduction band-Mn acceptor transition. Ferromagnetic hysteresis loop was observed, and the temperature dependent-magnetization displayed a ferromagnetic behavior persisting up to ∼270 K.