Nanotwinning and structural phase transition in CdS quantum dots

Nanotwin structures are observed in high-resolution transmission electron microscopy studies of cubic phase CdS quantum dots in powder form by chemical co-precipitation method. The deposition of thin films of nanocrystalline CdS is carried out on silicon, glass, and TEM grids keeping the substrates at room temperature (RT) and 200°C by pulsed laser ablation. These films are then subjected to thermal annealing at different temperatures. Glancing angle X-ray diffraction results confirm structural phase transitions after thermal annealing of films deposited at RT and 200°C. The variation of average particle size and ratio of intensities in Raman peaks I_2LO/I_1LO with annealing temperature are studied. It is found that electron-phonon interaction is a function of temperature and particle size and is independent of the structure. Besides Raman modes LO, 2LO and 3LO of CdS at approximately 302, 603, and 903 cm⁻¹ respectively, two extra Raman modes at approximately 390 and 690 cm⁻¹ are studied for the first time. The green and orange emissions observed in photoluminescence are correlated with phase transition.     

Si-rich Al2O3 films grown by RF magnetron sputtering: structural and photoluminescence properties versus annealing treatment

Silicon-rich Al₂O₃ films (Si_x(Al₂O₃)_1−x) were co-sputtered from two separate silicon and alumina targets onto a long silicon oxide substrate. The effects of different annealing treatments on the structure and light emission of the films versus x were investigated by means of spectroscopic ellipsometry, X-ray diffraction, micro-Raman scattering, and micro-photoluminescence (PL) methods. The formation of amorphous Si clusters upon the deposition process was found for the films with x ≥ 0.38. The annealing treatment of the films at 1,050°C to 1,150°C results in formation of Si nanocrystallites (Si-ncs). It was observed that their size depends on the type of this treatment. The conventional annealing at 1,150°C for 30 min of the samples with x = 0.5 to 0.68 leads to the formation of Si-ncs with the mean size of about 14 nm, whereas rapid thermal annealing of similar samples at 1,050°C for 1 min showed the presence of Si-ncs with sizes of about 5 nm. Two main broad PL bands were observed in the 500- to 900-nm spectral range with peak positions at 575 to 600 nm and 700 to 750 nm accompanied by near-infrared tail. The low-temperature measurement revealed that the intensity of the main PL band did not change with cooling contrary to the behavior expected for quantum confined Si-ncs. Based on the analysis of PL spectrum, it is supposed that the near-infrared PL component originates from the exciton recombination in the Si-ncs. However, the most intense emission in the visible spectral range is due to either defects in matrix or electron states at the Si-nc/matrix interface.     

Preparation strategy for low-stress and uniform SiC-on-diamond wafer: A silicon nitride dielectric layer

Reducing the self-heating of SiC- and GaN/SiC-based high-powered devices by integrating diamond films offers promising performance enhancement of these devices. However, such a reduction strategy faces serious problems, such as diamond nucleation on SiC and stress accumulation greater than 10 GPa. In this work, a SiN_x dielectric layer (～50 nm) was coated onto the C polar face of a 4H–SiC wafer using microwave plasma chemical vapor deposition (MPCVD) to improve direct dense diamond nucleation and growth, significantly reduce the stress, and build Si–C(SiC)?Si?C(diamond) bond bridges. This SiN_x thin layer, prepared by activating Si ions under Ar/N plasma during magnetron sputtering, gave rise to local Si₃N₄ crystal features and a low effective work function (EWF) for promoting surface dipoles with electronegative carbon-containing groups. In the H plasma environment during diamond growth, the local Si₃N₄ crystal was amorphized, and the N atoms escaped as a result of atomic H and the high temperature. At the same time, C atoms diffused into the SiN_x and formed C–Si bonds (49.7% of the total C bonds) by replacing N–Si and Si–Si, thus increasing the direct nucleation density of the diamond grains. The diamond thin film grew rapidly and uniformly, with a grain size of approximately 2 μm in mixed orientation, and the stress of the 2-inch SiC-on-diamond wafer was extremely low (to ～0.1–0.2 GPa). In comparison, partially connected diamond grains (>10 μm) on the bare SiC in the preferential (110) orientation resulted in a film with twin-grain features and significant stress, which was associated with the hexagonal lattice interface of 4H–SiC. These results are considered the material and surface/interface bases for actively controlling wafer fabrication and enhancing the heat dissipation of SiC and GaN/SiC electronics.     

Mechanical and field emission properties of CGed Si(C,N) films synthesized by PECVD from HMDS precursor

Compositionally graded (CGed) Si(C,N) films were prepared by Ar/H₂/N₂ plasma enhanced chemical vapor deposition from liquid injected hexamethyldisiloxane precursor. The films were characterized by scanning/transmission electron microscopy (SEM/TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Monolithic crystalline SiC and amorphous SiN_x films were produced from Ar/H₂ and Ar/H₂/N₂ thermal plasma, respectively. The CGed SiC–SiN_x film was obtained by changing N₂ flow rate from 2 L/min to zero in Ar/H₂/N₂ during the deposition process, and it was composed of an uppermost crystalline SiC layer, a thin intermediate layer containing nanocomposite c-SiC/a-SiN_x and an innermost layer of amorphous SiN_x. The CGed SiN_x–SiC film, in which SiN_x acts as a top layer with a SiC layer underneath, was fabricated by an inverse change of the plasma gas supply from initial Ar/H₂ to Ar/H₂/N₂. Microhardness increase and promising field emission properties were obtained from these CGed films in comparison with monolithic SiC and SiN_x films.     

Passivation mechanism of thermal atomic layer-deposited Al2O3 films on silicon at different annealing temperatures

Thermal atomic layer-deposited (ALD) aluminum oxide (Al₂O₃) acquires high negative fixed charge density (Q_f) and sufficiently low interface trap density after annealing, which enables excellent surface passivation for crystalline silicon. Q_f can be controlled by varying the annealing temperatures. In this study, the effect of the annealing temperature of thermal ALD Al₂O₃ films on p-type Czochralski silicon wafers was investigated. Corona charging measurements revealed that the Q_f obtained at 300°C did not significantly affect passivation. The interface-trapping density markedly increased at high annealing temperature (>600°C) and degraded the surface passivation even at a high Q_f. Negatively charged or neutral vacancies were found in the samples annealed at 300°C, 500°C, and 750°C using positron annihilation techniques. The Al defect density in the bulk film and the vacancy density near the SiO_x/Si interface region decreased with increased temperature. Measurement results of Q_f proved that the Al vacancy of the bulk film may not be related to Q_f. The defect density in the SiO_x region affected the chemical passivation, but other factors may dominantly influence chemical passivation at 750°C.     

Effect of the post-heating temperatures on the microstructure,mechanical and electrical properties of silicon nitride thin films

Silicon nitride (SiN_x) thin film is a potential candidate for the fabrication of the insulating layer of thin-film thermocouples, which can be utilised to measure cutting temperatures, owing to its excellent insulation properties and hardness and a thermal expansion coefficient similar to that of carbide tool. Thus, it is necessary to investigate the stability of the SiN_x microstructure and its mechanical and electrical properties at high temperatures. In this study, SiN_x thin films were deposited using reactive magnetron sputtering, followed by post-heating in an air atmosphere at 200–600 °C. The microstructure, adhesion, and sheet resistance were investigated using atomic force microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scratch tests, and four-probe resistance tests. The results showed that the SiN_x film had a typical amorphous structure. During the heating process, the grain size increased, as did the content of columnar structures. When the temperature was increased from room temperature to 200 °C, the SiN_x film was oxidised to SiN_xO_y. The oxidative product (SiO₂) and escaping nitrogen gas were not observed until the film was heated above 400 °C, revealing the different oxidation reactions and products induced by the elevated temperature. The adhesive strength of the SiN_x film increased monotonically with increasing temperature but was severely weakened when the film was heated to temperatures above 400 °C. Oxygen could not completely invade the deeper layers of the film until the temperature reached 600 °C. The sheet resistance of the SiN_x film improved at 200 °C, but reduced severely when the temperature exceeded 400 °C.     

Fabrication of Si heterojunction solar cells using P-doped Si nanocrystals embedded in SiNx films as emitters

Si heterojunction solar cells were fabricated on p-type single-crystal Si (sc-Si) substrates using phosphorus-doped Si nanocrystals (Si-NCs) embedded in SiN_x (Si-NCs/SiN_x) films as emitters. The Si-NCs were formed by post-annealing of silicon-rich silicon nitride films deposited by electron cyclotron resonance chemical vapor deposition. We investigate the influence of the N/Si ratio in the Si-NCs/SiN_x films on their electrical and optical properties, as well as the photovoltaic properties of the fabricated heterojunction devices. Increasing the nitrogen content enhances the optical gap E₀₄ while deteriorating the electrical conductivity of the Si-NCs/SiN_x film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device. These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiN_x film as a mixture of a high-transparency SiN_x phase and a low-resistivity Si-NC phase. A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell.     

New understanding of hardening mechanism of TiN/SiNx-based nanocomposite films

In order to clarify the controversies of hardening mechanism for TiN/SiN_x-based nanocomposite films, the microstructure and hardness for TiN/SiN_x and TiAlN/SiN_x nanocomposite films with different Si content were studied. With the increase of Si content, the crystallization degree for two series of films firstly increases and then decreases. The microstructural observations suggest that when SiN_x interfacial phase reaches to a proper thickness, it can be crystallized between adjacent TiN or TiAlN nanocrystallites, which can coordinate misorientations between nanocrystallites and grow coherently with them, resulting in blocking of the dislocation motions and hardening of the film. The microstructure of TiN/SiN_x-based nanocomposite film can be characterized as the nanocomposite structure with TiN-based nanocrystallites surrounded by crystallized SiN_x interfacial phase, which can be denoted by nc-TiN/c-SiN_x model (''c’ before SiN_x means crystallized) and well explain the coexistence between nanocomposite structure and columnar growth structure within the TiN/SiN_x-based film.     

Bismuth-induced effects on optical,lattice vibrational,and structural properties of bulk GaAsBi alloys

Bulk GaAs_{1 - x}Bi_x/GaAs alloys with various bismuth compositions are studied using power- and temperature-dependent photoluminescence (PL), Raman scattering, and atomic force microscopy (AFM). PL measurements exhibit that the bandgap of the alloy decreases with increasing bismuth composition. Moreover, PL peak energy and PL characteristic are found to be excitation intensity dependent. The PL signal is detectable below 150 K at low excitation intensities, but quenches at higher temperatures. As excitation intensity is increased, PL can be observable at room temperature and PL peak energy blueshifts. The quenching temperature of the PL signal tends to shift to higher temperatures with increasing bismuth composition, giving rise to an increase in Bi-related localization energy of disorders. The composition dependence of the PL is also found to be power dependent, changing from about 63 to 87 meV/Bi% as excitation intensity is increased. In addition, S-shaped temperature dependence at low excitation intensities is observed, a well-known signature of localized levels above valence band. Applying Varshni’s law to the temperature dependence of the PL peak energy, the concentration dependence of Debye temperature (β) and thermal expansion coefficient (α) are determined. AFM observations show that bismuth islands are randomly distributed on the surface and the diameter of the islands tends to increase with increasing bismuth composition. Raman scattering spectra show that incorporation of Bi into GaAs causes a new feature at around 185 cm^-1 with slightly increasing Raman intensity as the Bi concentration increases. A broad feature located between 210 and 250 cm^-1 is also observed and its intensity increases with increasing Bi content. Furthermore, the forbidden transverse optical (TO) mode becomes more pronounced for the samples with higher bismuth composition, which can be attributed to the effect of Bi-induced disorders on crystal symmetry.

PACS

78.55Cr 78.55-m 78.20-e 78.30-j     

Effect of the Nd content on the structural and photoluminescence properties of silicon-rich silicon dioxide thin films

In this article, the microstructure and photoluminescence (PL) properties of Nd-doped silicon-rich silicon oxide (SRSO) are reported as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates by reactive magnetron co-sputtering, contain the same Si excess as determined by Rutherford backscattering spectrometry. Fourier transform infrared (FTIR) spectra show that a phase separation occurs during the annealing because of the condensation of the Si excess resulting in the formation of silicon nanoparticles (Si-np) as detected by high-resolution transmission electron microscopy and X-ray diffraction (XRD) measurements. Under non-resonant excitation at 488 nm, our Nd-doped SRSO films simultaneously exhibited PL from Si-np and Nd³⁺ demonstrating the efficient energy transfer between Si-np and Nd³⁺ and the sensitizing effect of Si-np. Upon increasing the Nd concentration from 0.08 to 4.9 at.%, our samples revealed a progressive quenching of the Nd³⁺ PL which can be correlated with the concomitant increase of disorder within the host matrix as shown by FTIR experiments. Moreover, the presence of Nd-oxide nanocrystals in the highest Nd-doped sample was established by XRD. It is, therefore, suggested that the Nd clustering, as well as disorder, are responsible for the concentration quenching of the PL of Nd³⁺.     

Compositional and optical properties of SiO x films and (SiO x /SiO y ) junctions deposited by HFCVD

In this work, non-stoichiometric silicon oxide (SiO _x ) films and (SiO _x /SiO _y ) junctions, as-grown and after further annealing, are characterized by different techniques. The SiO _x films and (SiO _x /SiO _y ) junctions are obtained by hot filament chemical vapor deposition technique in the range of temperatures from 900°C to 1,150°C. Transmittance spectra of the SiO _x films showed a wavelength shift of the absorption edge thus indicating an increase in the optical energy band gap, when the growth temperature decreases; a similar behavior is observed in the (SiO _x /SiO _y ) structures, which in turn indicates a decrease in the Si excess, as Fourier transform infrared spectroscopy (FTIR) reveals, so that, the film and junction composition changes with the growth temperature. The analysis of the photoluminescence (PL) results using the quantum confinement model suggests the presence of silicon nanocrystal (Si-nc) embedded in a SiO _x matrix. For the case of the as-grown SiO _x films, the absorption and emission properties are correlated with quantum effects in Si-nc and defects. For the case of the as-grown (SiO _x /SiO _y ) junctions, only the emission mechanism related to some kinds of defects was considered, but silicon nanocrystal embedded in a SiO _x matrix is present. After thermal annealing, a phase separation into Si and SiO₂ occurs, as the FTIR spectra illustrates, which has repercussions in the absorption and emission properties of the films and junctions, as shown by the change in the A and B band positions on the PL spectra. These results lead to good possibilities for proposed novel applications in optoelectronic devices.

PACS

61.05.-a; 68.37.Og; 61.05.cp; 78.55.-m; 68.37.Ps; 81.15.Gh     

Raman characterization and photoluminescence properties of La1-xTbxPO4·nH2O and La1-xTbxPO4 phosphor nanorods prepared by microwave-assisted hydrothermal synthesis

The effect of the Tb³⁺–doping content (in the range 0–100 mol%) on the structure (using Raman spectroscopy) and photoluminescence (PL) properties of both rhabdophane-type La_1-xTb_xPO₄·nH₂O and monazite-type La_1-xTb_xPO₄ single-crystal nanorods was investigated. La_1-xTb_xPO₄·nH₂O was directly obtained by microwave-assisted hydrothermal synthesis and La_1-xTb_xPO₄ by calcination of La_1-xTb_xPO₄·nH₂O at 700 °C in air for 2 h. It was found that the characteristic Raman bands shift to higher wavenumbers and become broader with increasing Tb³⁺ concentration, which is attributed to attendant unit-cell volume reduction. The PL due to the Tb³⁺ f-f transitions has been studied with continuous and pulsed excitations. The PL intensity increases with doping and is maximum for La_0.80Tb_0.20PO₄·nH₂O and La_0.85Tb_0.15PO₄, i.e., for rhabdophane and monazite-type structures, respectively. A quenching effect is detected for concentrations below x=0.05, but constant efficiency is obtained at higher doping. The calcination increases the efficiency by a factor around 2 due to the combined effects of water molecules and defect elimination. The PL decay curves reveal a long lifetime attributable to single Tb³⁺ ions which is almost independent of doping for monazite nanorods (5–4.5 ms), and a shorter one around 0.2 ms most likely due to Tb³⁺ dimmers.     

Initial stage growth of GexSi1?x layers and Ge quantum dot formation on GexSi1?x surface by MBE

Critical thicknesses of two-dimensional to three-dimensional growth in Ge_xSi_1−x layers were measured as a function of composition for different growth temperatures. In addition to the (2 × 1) superstructure for a Ge film grown on Si(100), the Ge_xSi_1−x layers are characterized by the formation of (2 × n) reconstruction. We measured n for all layers of Ge/Ge_xSi_1−x/Ge heterosystem using our software with respect to the video recording of reflection high-energy electron diffraction (RHEED) pattern during growth. The n reaches a minimum value of about 8 for clear Ge layer, whereas for Ge_xSi_1−x films, n is increased from 8 to 14. The presence of a thin strained film of the Ge_xSi_1−x caused not only the changes in critical thicknesses of the transitions, but also affected the properties of the germanium nanocluster array for the top Ge layer. Based on the RHEED data, the hut-like island form, which has not been previously observed by us between the hut and dome islands, has been detected. Data on the growth of Ge/Ge_xSi_1−x/Ge heterostructures with the uniform array of islands in the second layer of the Ge film have been received.     

Enhanced resistive switching phenomena using low-positive-voltage format and self-compliance IrOx/GdOx/W cross-point memories

Enhanced resistive switching phenomena of IrO_x/GdO_x/W cross-point memory devices have been observed as compared to the via-hole devices. The as-deposited Gd₂O₃ films with a thickness of approximately 15 nm show polycrystalline that is observed using high-resolution transmission electron microscope. Via-hole memory device shows bipolar resistive switching phenomena with a large formation voltage of -6.4 V and high operation current of >1 mA, while the cross-point memory device shows also bipolar resistive switching with low-voltage format of +2 V and self-compliance operation current of <300 μA. Switching mechanism is based on the formation and rupture of conducting filament at the IrO_x/GdO_x interface, owing to oxygen ion migration. The oxygen-rich GdO_x layer formation at the IrO_x/GdO_x interface will also help control the resistive switching characteristics. This cross-point memory device has also Repeatable 100 DC switching cycles, narrow distribution of LRS/HRS, excellent pulse endurance of >10,000 in every cycle, and good data retention of >10⁴ s. This memory device has great potential for future nanoscale high-density non-volatile memory applications.     

Evolution of TiOx-SiOx nano-composite during annealing of ultrathin titanium oxide films on Si substrate

This paper discusses the formation of the TiO_x-SiO_x nano-composite phase during annealing of ultrathin titanium oxide films (~27 nm). The amorphous titanium oxide films are deposited on silicon substrates by sputtering. These films are important for high-k dielectrics and sensing applications. Annealing of these films at 750 °C in the O₂ environment (for 15–60 min) resulted in the polycrystalline rutile phase. The films exhibit Raman peaks at 150 cm⁻¹ (B_1g), 435 cm⁻¹ (E_g), and 615 cm⁻¹ (A_1g) confirming the rutile phase. The signature TO (1078 cm⁻¹) and LO (1259 cm⁻¹) infrared active vibrational modes of Si–O–Si bond confirms the presence of silicon-oxide. The X-ray photoelectron spectra of the TiO_x films show multiple peaks corresponding to Ti metal (453.8 eV); Ti⁴⁺ state (458.3 eV (Ti 2p_3/2) and 464 eV (Ti 2p_1/2)); and Ti³⁺ state (456.4 eV (Ti 2p_3/2) and 460.8 eV (Ti 2p_1/2)). The O1s XPS spectra peaks at 530–533 eV can be attributed to Ti–O and Si–O bonds of the TiO_x-SiO_x nano-composite phase in the annealed films. The depth profiling XPS study shows that the top surface of the annealed film is mainly TiO_x and the amount of SiO_x increases with the depth.     

Selective area epitaxy of ultra-high density InGaN quantum dots by diblock copolymer lithography

Highly uniform InGaN-based quantum dots (QDs) grown on a nanopatterned dielectric layer defined by self-assembled diblock copolymer were performed by metal-organic chemical vapor deposition. The cylindrical-shaped nanopatterns were created on SiN _x layers deposited on a GaN template, which provided the nanopatterning for the epitaxy of ultra-high density QD with uniform size and distribution. Scanning electron microscopy and atomic force microscopy measurements were conducted to investigate the QDs morphology. The InGaN/GaN QDs with density up to 8 × 10¹⁰ cm^-2 are realized, which represents ultra-high dot density for highly uniform and well-controlled, nitride-based QDs, with QD diameter of approximately 22-25 nm. The photoluminescence (PL) studies indicated the importance of NH₃ annealing and GaN spacer layer growth for improving the PL intensity of the SiN _x -treated GaN surface, to achieve high optical-quality QDs applicable for photonics devices.     

Enhanced resistive switching memory characteristics and mechanism using a Ti nanolayer at the W/TaOx interface

Enhanced resistive memory characteristics with 10,000 consecutive direct current switching cycles, long read pulse endurance of >10⁵ cycles, and good data retention of >10⁴ s with a good resistance ratio of >10² at 85°C are obtained using a Ti nanolayer to form a W/TiO_x/TaO_x/W structure under a low current operation of 80 μA, while few switching cycles are observed for W/TaO_x/W structure under a higher current compliance >300 μA. The low resistance state decreases with increasing current compliances from 10 to 100 μA, and the device could be operated at a low RESET current of 23 μA. A small device size of 150 × 150 nm² is observed by transmission electron microscopy. The presence of oxygen-deficient TaO_x nanofilament in a W/TiO_x/TaO_x/W structure after switching is investigated by Auger electron spectroscopy. Oxygen ion (negative charge) migration is found to lead to filament formation/rupture, and it is controlled by Ti nanolayer at the W/TaO_x interface. Conducting nanofilament diameter is estimated to be 3 nm by a new method, indicating a high memory density of approximately equal to 100 Tbit/in.².     

Recrystallization behavior,oxygen vacancy and photoluminescence performance of sputter-deposited Ga2O3 films via high-vacuum in situ annealing

Ga₂O₃ films were deposited on Si substrates through radio-frequency magnetron sputtering at room temperature and were annealed in situ in a high-vacuum environment. The as-deposited Ga₂O₃ film exhibited an island-like surface morphology and had an amorphous microstructure, with a few nanocrystalline grains embedded in it. After high-temperature in situ annealing, the films recrystallized and exhibited coalesced surfaces. Because of the thermally driven diffusion of Ga, the interfacial layer between Si and Ga₂O₃ was composed of SiGaO_x. Compared with ex situ annealing in air, in situ annealing in high vacuum is more advantageous because it enhances surface mobility and improves the crystallinity of the Ga₂O₃ films. The higher oxygen vacancy concentration of in situ annealed films revealed that oxygen atoms were easily released from the Ga₂O₃ lattice during high-vacuum annealing. Photoluminescence (PL) spectra exhibited four emission peaks centered in ultraviolet, blue, and green regions, and the peak intensities were significantly enhanced by thermal annealing at >600 °C. This work elucidates the effect of the in situ annealing treatment on the recrystallization behavior, interfacial microstructure, oxygen vacancy concentration, and PL performance of the Ga₂O₃ films, making it significant and instructional for the further development of Ga₂O₃-based devices.     

Resistive switching memory characteristics of Ge/GeOx nanowires and evidence of oxygen ion migration

The resistive switching memory of Ge nanowires (NWs) in an IrO_x/Al₂O₃/Ge NWs/SiO₂/p-Si structure is investigated. Ge NWs with an average diameter of approximately 100 nm are grown by the vapor–liquid-solid technique. The core-shell structure of the Ge/GeO_x NWs is confirmed by both scanning electron microscopy and high-resolution transmission electron microscopy. Defects in the Ge/GeO_x NWs are observed by X-ray photoelectron spectroscopy. Broad photoluminescence spectra from 10 to 300 K are observed because of defects in the Ge/GeO_x NWs, which are also useful for nanoscale resistive switching memory. The resistive switching mechanism in an IrO_x/GeO_x/W structure involves migration of oxygen ions under external bias, which is also confirmed by real-time observation of the surface of the device. The porous IrO_x top electrode readily allows the evolved O₂ gas to escape from the device. The annealed device has a low operating voltage (<4 V), low RESET current (approximately 22 μA), large resistance ratio (>10³), long pulse read endurance of >10⁵ cycles, and good data retention of >10⁴ s. Its performance is better than that of the as-deposited device because the GeO_x film in the annealed device contains more oxygen vacancies. Under SET operation, Ge/GeO_x nanofilaments (or NWs) form in the GeO_x film. The diameter of the conducting nanofilament is approximately 40 nm, which is calculated using a new method.     

Time-resolved photoluminescence studies of annealed 1.3-μm GaInNAsSb quantum wells

Time-resolved photoluminescence (PL) was applied to study the dynamics of carrier recombination in GaInNAsSb quantum wells (QWs) emitting near 1.3 μm and annealed at various temperatures. It was observed that the annealing temperature has a strong influence on the PL decay time, and hence, it influences the optical quality of GaInNAsSb QWs. At low temperatures, the PL decay time exhibits energy dependence (i.e., the decay times change for different energies of emitted photons), which can be explained by the presence of localized states. This energy dependence of PL decay times was fitted by a phenomenological formula, and the average value of E₀, which describes the energy distribution of localized states, was extracted from this fit and found to be smallest (E₀ = 6 meV) for the QW annealed at 700°C. In addition, the value of PL decay time at the peak energy was compared for all samples. The longest PL decay time (600 ps) was observed for the sample annealed at 700°C. It means that based on the PL dynamics, the optimal annealing temperature for this QW is approximately 700°C.