A. Kanjilal

Structural and electrical properties of silicon dioxide layers with embedded germanium nanocrystals grown by molecular beam epitaxy

A sheet of spherical, well-separated, crystalline Ge nanodots embedded in SiO2 on top of a p-(001)Si wafer was fabricated by molecular beam epitaxy (MBE) combined with rapid thermal processing and characterized structurally and electrically. The average size of the Ge nanodots was estimated to be 4.5 nm with an average aerial density of 3×1011 cm−2, situated at 4.4 nm in average away from the Si/SiO2 interface. Significant charge storage effects were observed through capacitance–voltage measurements of metal–oxide–semiconductor capacitors.

Solution grown PbS nanoparticle films

Lead sulfide (PbS) nanoparticle films were chemically grown on glass, quartz and silicon substrates. Structure and size of PbS nanoparticles were characterized by X-ray diffraction and transmission electron microscopy (TEM), respectively. Large optical band gap has been observed in these films. The decreases in dc-conductivity, Hall mobility and carrier concentration with reducing grain size were also examined. Heterojunctions of p-PbS/n-Si were fabricated and photovoltaic effect was observed in these self-assembled heterojunctions.

Size dependence of optical properties in solution-grown Pb1?xFexS nanoparticle films

The optical band gap (Eg) of Pb1−xFexS solution-grown nanoparticle films was varied from 2.65 to 2.22 eV with an increase in iron concentration 0.25 ≤ x ≤ 0.75 in films grown at fixed pH and temperature by the chemical bath deposition method. The presence of excitonic structure in the ternary Pb1−xFexS for x ≥ 0.50 suggests increasing binding energy with increase in iron concentration in the films. A shift of excitonic peak towards higher energy with an increase in iron concentration is also observed.

Structure and optical anisotropy of vertically correlated submonolayer InAs/GaAs quantum dots

A vertically correlated submonolayer (VCSML) InAs/GaAs quantum-dot (QD) heterostructure was studied using transmission electron microscopy, high-resolution x-ray diffraction (HRXRD) and polarization-dependent photoluminescence. The HRXRD (004) rocking curve was simulated using the Tagaki–Taupin equations. Excellent agreement between the experimental curve and the simulation is achieved assuming that indium-rich VCSML QDs are embedded in a quantum well (QW) with lower indium content and an observed QD coverage of 10%. In the VCSML QDs, the vertical lattice mismatch of the InAs monolayer with respect to GaAs is around 1.4%, while the lattice mismatch in the QW is negligible. The photoluminescence is transverse magnetic—polarized in the edge geometry.

Blue and red electroluminescence of Europium-implanted metal-oxide-semiconductor structures as a probe for the dynamics of microstructure

The strong blue and red electroluminescence from Eu-implanted SiO2 layers were investigated as a function of implantation and annealing conditions. It is shown that the red electroluminescence assigned to Eu3+ ions is favored by low Eu concentrations, low annealing temperatures, and short annealing times. Based on a more quantitative analysis of the electroluminescence spectra this preference is explained by a shorter supply of oxygen for higher Eu concentrations and the growth of Europium or Europium oxide clusters with increasing annealing temperatures and annealing times. The correlation between electroluminescence and microstructure is supported by transmission electron microscopy investigations and demonstrates that the electroluminescence of Eu-implanted SiO2 layers can serve as a probe for the microstructural development in the active layer of the light emitter.

Implantation-assisted Co-doped CdS thin films: Structural, optical, and vibrational properties

This paper reports on structural, optical, vibrational, and morphological properties of cobalt-doped CdS thin films, prepared by 90 keV Co+ implantation at room temperature. In this work, we have used cobalt concentration in the range of 0.34–10.8 at. %. Cobalt doping does not lead to the formation of any secondary phase, either in the form of metallic clusters or impurity complexes. However, with increasing cobalt concentration a decrease in the optical band gap, from 2.39 to 2.26 eV, is observed. This reduction is addressed on the basis of band tailing due to the creation of localized energy states in association with Urbach energy calculations. In addition, implantation gives rise to grain growth and increase in the surface roughness. Size and shape fluctuations of individual CdS grains, at higher fluences, give rise to inhomogeneity in strain. The results are discussed in the light of ion-matter interaction in the keV regime.

Structural and optical properties of Mn-doped CdS thin films prepared by ion implantation

We report on structural and optical properties of Mn-doped CdS thin films prepared by 190 keV Mn-ion implantation at different temperatures. Mn-ion implantation in the fluence range of 1×1013–1×1016 ions cm−2 does not lead to the formation of any secondary phase. However, it induces structural disorder, causing a decrease in the optical band gap. This is addressed on the basis of band tailing due to creation of localized energy states and Urbach energy calculations. Mn-doped samples exhibit a new band in their photoluminescence spectra at 2.22 eV, which originates from the d-d (T41→A61) transition of tetrahedrally coordinated Mn2+ ions.

Effect of grain-boundaries on electrical properties of n-ZnO:Al/p-Si heterojunction diodes

We report on room temperature diode characteristics of ZnO:Al (AZO)/Si heterostructures by current-voltage measurements. In this study, with increasing AZO film thickness, systematic reduction in the turn-on potential (from 3.16 to 1.80 V) and the film stress are observed. Complementary capacitance-voltage studies reveal a decreasing trend in barrier height at the junction with increasing AZO film thickness. A gradual decrease in resistivity takes place with increasing AZO film thickness. Above observations are explained in the framework of AZO thickness dependent variation in grain size and in turn trap density at the grain boundaries influencing carrier transport across the adjacent grains.

Correlation between the microstructure and electroluminescence properties of Er-doped metal-oxide semiconductor structures

Optical response of a rare earth (RE)-doped SiO2 layer is known to deteriorate markedly at room temperature due to RE clustering. The key challenge is therefore to probe the ongoing processes at the microscopic level and the subsequent impact on the luminescence properties with increasing RE concentration. Here, we report how the Er electroluminescence in a metal-oxide-semiconductor structure has been affected by increasing Er content. Our results indicate that the Er oxide clustering is anticipated by the formation of Si-based oxygen-deficiency centers during postimplantation annealing and leads to a strong quenching of the short-wavelength (350–500 nm) Er electroluminescence.

Influence of annealing on the Er luminescence in Si-rich SiO2 layers coimplanted with Er ions

The impact of rapid thermal annealing (RTA) in producing samples by sequential implantation of Si and Er ions into a 200 nm SiO2 layer combined with different annealing cycles as well as the corresponding room-temperature visible and infrared photoluminescence (PL) have been studied. The Er-related PL intensity at 1533 nm for the samples prepared by implanting Si with subsequent annealing, followed by Er implantation, and final annealing (type I) was found to be stronger than the one produced similarly but without the first annealing step (type II). In fact, the 1533 nm peak intensity in the optimized RTA processed sample is comparable to the PL yield of the furnace-annealed sample. Moreover, the excitation wavelength (405 nm) was found to be suitable for exciting the Si=O related point defects in the SiO2 layer and can provide a PL band with a maximum at ∼580 nm. While this band was further intensified in the presence of Si nanocrystals (Si NCs), it became weaker by introducing additional Er3+ ions with ...