Interface traps effect on the charge transport mechanisms in metal oxide semiconductor structures based on silicon nanocrystals

The transport phenomena in Metal-Oxide-Semiconductor (MOS) structures having silicon nanocrystals (Si-NCs) inside the dielectric layer has been investigated by high frequency Capacitance-Voltage (C-V) method and the Deep-Level Transient Spectroscopy (DLTS). For the reference samples without Si-NCs, we observe a slow electron trap for a large temperature range, which is probably a response of a series electron traps having a very close energy levels. A clear series of electron traps are evidenced in DLTS spectrum for MOS samples with Si-NCs. Their activation energies are comprised between 0.28 eV and 0.45 eV. Moreover, we observe in this DLTS spectrum, a single peak that appears at low temperature which we attributed to Si-NCs response. In MOS structure without Si-NCs, the conduction mechanism is dominated by the thermionic fast emission/capture of charge carriers from the highly doped polysilicon layer to Si-substrate through interface trap-states. However, at low temperature, the tunneling of charge carriers from highly Poly-Si to Si-substrate trough the trapping/detrapping mechanism in the Si-NCs contributed to the conduction mechanism for MOS with Si-NCs. These results are helpful to understand the principle of charge transport of MOS structures having a Si-NCs in the SiO_x = 1.5 oxide matrix.     

Investigation of deep level defects in copper irradiated bipolar junction transistor

Commercial bipolar junction transistor (2N 2219A, npn) irradiated with 150 MeV Cu¹¹⁺-ions with fluence of the order 10¹² ions cm^?2, is studied for radiation induced gain degradation and deep level defects. I–V measurements are made to study the gain degradation as a function of ion fluence. The properties such as activation energy, trap concentration and capture cross-section of deep levels are studied by deep level transient spectroscopy (DLTS). Minority carrier trap levels with energies ranging from E_C ? 0.164 eV to E_C ? 0.695 eV are observed in the base–collector junction of the transistor. Majority carrier trap levels are also observed with energies ranging from E_V + 0.203 eV to E_V + 0.526 eV. The irradiated transistor is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 350 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for transistor gain degradation.     

Electrical characterization and DLTS analysis of a gold/n-type gallium nitride Schottky diode

This work describes a comparison of current density–voltage (J–V) and capacitance–voltage (C–V) properties measured as a function of temperature; deep trap properties are measured by deep level transient spectroscopy (DLTS) of Schottky diodes fabricated on n-type gallium nitride (GaN grown by metal organic vapor phase epitaxy (MOVPE). Unexpected behavior in the standard Richardson plot was observed in the temperature range 165–480 K, reflecting a range of Schottky barrier heights and a variation of ideality factor. This was explained by applying a Gaussian spatial distribution of barrier heights across the Schottky diode. C–V measurements were carried out in the temperature range 165–480 K to compare the temperature dependence of the barrier height with those obtained by the Gaussian distribution method. DLTS and high-resolution Laplace DLTS (LDLTS) show a majority carrier peak centered at 450 K.     

Electrical characterization of defects introduced during electron beam deposition of W Schottky contacts on n-type 4H-SiC

We have studied the defects introduced in n-type 4H-SiC during electron beam deposition (EBD) of tungsten by deep-level transient spectroscopy (DLTS). The results from current-voltage and capacitance-voltage measurements showed deviations from ideality due to damage, but were still well suited to a DLTS study. We compared the electrical properties of six electrically active defects observed in EBD Schottky barrier diodes with those introduced in resistively evaporated material on the same material, as-grown, as well as after high energy electron irradiation (HEEI). We observed that EBD introduced two electrically active defects with energies E_C – 0.42 and E_C – 0.70 eV in the 4H-SiC at and near the interface with the tungsten. The defects introduced by EBD had properties similar to defect attributed to the silicon or carbon vacancy, introduced during HEEI of 4H-SiC. EBD was also responsible for the increase in concentration of a defect attributed to nitrogen impurities (E_C – 0.10) as well as a defect linked to the carbon vacancy (E_C – 0.67). Annealing at 400 °C in Ar ambient removed these two defects introduced during the EBD.     

Spirobifluorene/sulfone hybrid: Highly efficient solution-processable material for UV–violet electrofluorescence,blue and green phosphorescent OLEDs

A high efficient UV–violet emission type material bis[4-(9,9′-spirobifluorene-2-yl)phenyl] sulfone (SF-DPSO) has been synthesized by incorporating electron deficient sulfone and morphologically stable spirobifluorene into one molecule. The steric and bulky compound SF-DPSO exhibits an excellent solid state photoluminescence quantum yield (Φ_PL = 92%), high glass transition temperature (T_g = 211 °C) and high triplet energy (E_T = 2.85 eV). In addition, the uniform amorphous thin film could be formed by spin-coating from its solution. These promising physical properties of the material made it suitable for using as UV–violet emitter in non-doped device and appropriate host in phosphorescent OLEDs. With SF-DPSO as an emitter, the non-doped solution processed device achieved an efficient UV–violet emission with the EL peak around 400 nm. By using SF-DPSO as a host, solution processed blue and green phosphorescent organic light emitting diodes showed a high luminous efficiency of 13.7 and 30.2 cd A⁻¹, respectively.     

The use of hydrogen passivation to fabricate Schottky diodes for DLTS measurements of heavily-doped p+ Si

Schottky diodes were successfully fabricated on p⁺ Si for deep-level transient spectroscopy (DLTS) measurements by the use of hydrogen passivation of boron. Atomic hydrogen was introduced into the near-surface region of boron-doped (1 0 0) CZ Si crystals, which had a resistivity of about 0.01 Ω cm, at temperatures between room temperature and 300°C by exposure to a hydrogen plasma. Rectifying characteristics were obtained for fabricated Schottky contacts on hydrogenated samples. This was due to the carrier concentration decrease in the near-surface region by hydrogen passivation of boron. As the hydrogenation temperatures were increased, the decrease in carrier concentration was significant. Some results of DLTS measurements were given for fabricated diodes.     

Spectroscopic differentiation between O-atom vacancy and divacancy defects,respectively, in TiO2 and HfO2 by X-ray absorption spectroscopy

Defect state features have been detected in second derivative O K edge spectra for thin films of nano-crystalline TiO₂ and HfO₂. Based on soft X-ray photoelectron band edge spectra, and the occurrence of occupied band edge 4f states in Gd(Sc,Ti)O₃, complementary spectroscopic features have been confirmed in the pre-edge (<530 eV) and vacuum continuum (>545 eV) regimes of O K edge spectra. Qualitatively similar spectral features have been obtained for thin films of HfO₂ and TiO₂, and these have been assigned to defect states associated with vacancies. The two electrons/removed O-atom are not distributed uniformly over the TM atoms defining the vacancy geometry, but instead are localized in equivalent d-states: a d² state for a Ti monovacancy and a d⁴ state for a Hf divacancy. This new model for electronic structure provides an unambiguous way to differentiate between monovacancy and divacancy arrangements, as well as immobile (or fixed) and mobile vacancies.     

Realizing high breakdown voltage for a novel interface charges islands structure based on partial-SOI substrate

A novel interface charge islands partial-SOI (ICI PSOI) high voltage device with a silicon window under the source and its mechanism are studied in this paper. ICI PSOI is characterized by a series of equidistant high concentration n⁺-regions on the bottom interface of top silicon layer. On the condition of high-voltage blocking state, inversion holes located in the spacing of two n⁺-regions effectively enhance the electric field of the buried oxide layer (E_I) and reduce the electric field of the silicon layer (E_S), resulting in a high breakdown voltage (V_B). It is shown by the simulations that the enhanced field ΔE_I and reduced field ΔE_S by the accumulated holes reach to 449 V/μm and 24 V/μm, respectively, which makes V_B of ICI PSOI increase to 663 V from 266 V of the conventional PSOI on 5 μm silicon layer and 1 μm buried oxide layer with the same silicon window length. On-resistance of ICI PSOI is lower than that of the conventional PSOI. Moreover, self-heating-effect is alleviated by the silicon window in comparison with the conventional SOI at the same power of 1 mW/μm.     

Structure,charge-transfer and luminescent properties of bis(2-(2-hydroxyphenyl)benzothiazolate)beryllium

A luminescent Be(II) complex of aromatic N, O-chelate ligand, namely Be(BTZ)₂ (BTZ = 2-(2-hydroxyphenyl)benzothiazolate), has been synthesized and characterized by X-ray crystallography. Its charge-transfer and luminescent properties were studied. The results indicated that the single crystal of Be(BTZ)₂ is monoclinic, space group C2/c. With larger the electron-transfer rate than hole-transfer rate, Be(BTZ)₂ may serve as candidate for electron-transport material. The highest occupied molecular orbital energy level (E_HOMO) and the lowest unoccupied molecular orbital energy level (E_LUMO) are −5.79 eV and −2.98 eV, respectively. Be(BTZ)₂displays strong photoluminescence (PL) in the blue region at 456 nm, and the electroluminescent (EL) peak wavelength is located at 460 nm, CIE coordinates are X = 0.1525, Y = 0.1803.     

Growth and characterization of silicon oxide films formed in the presence of Si,SiC, and Si3N4

In order to comparatively study the growth and characterization of silicon oxide films on Si-based substrates, top-cut solar grade silicon (SOG-Si) containing Si₃N₄ rods and SiC lumps were used as raw materials and respectively heated at 1773 K and 1873 K under Ar gas. The samples were investigated by Focus Ion Beam/Scanning Electron Microscope (FIB/SEM) and Energy Dispersive Spectroscopy (EDS). Results indicated that silicon oxides with different morphologies successfully grew on the substrates via various mechanisms. Passive oxidation was evident in the formation of a dense SiO₂ surface layer on the base material at 1773 K, while active oxidation was evident in the formation of SiO₂ with particle, rod, and nanowire-like morphologies, which was the re-oxidation product of SiO at 1873 K under the active-to-passive transition. Si, SiC, and Si₃N₄ have the similar oxidation tendency to form silicon oxides under either passive or active regimes.     

Extremely low driving voltage electrophosphorescent green organic light-emitting diodes based on a host material with small singlet–triplet exchange energy without p- or n-doping layer

In order to achieve low driving voltage, electrophosphorescent green organic light-emitting diodes (OLEDs) based on a host material with small energy gap between the lowest excited singlet state and the lowest excited triplet state (ΔE_ST) have been fabricated. 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)- 1,3,5-triazine (PIC–TRZ) with ΔE_ST of only 0.11 eV has been found to be bipolar and used as the host for green OLEDs based on tris(2-phenylpyridinato) iridium(III) (Ir(ppy)₃). A very low onset voltage of 2.19 V is achieved in devices without p- or n-doping. Maximum current and power efficiencies are 68 cd/A and 60 lm/W, respectively, and no significant roll-off of current efficiency (58 cd/A at 1000 cd/m² and 62 cd/A at 10,000 cd/m²) have been observed. The small roll-off is due to the improved charge balance and the wide charge recombination zone in the emissive layer.     

Elimination of impurities from the surface of silicon using hydrochloric and nitric acid

Acid leaching of silicon is insufficient in order to achieve solar grade silicon. Leaching of silicon previously purified by the copper gathering method can significantly reduce amount of impurities congregated in the Cu–Si intermetallic phase during solidification process. Two samples of 50 wt% Cu–50 wt% Si alloy were solidified at 0.5 and 1.0 °C/min cooling rate. They were treated with 10 vol% HNO₃ and 5 vol% HCl and 7 vol% HNO₃. The inductively Coupled Plasma Mass Spectrometry technique was employed to measure traces of impurities before and after the treatment. It was determined that the overall impurity level in purified silicon was reduced from 5277 ppm_wt to 225.5 ppm_wt. The samples cooled at 0.5 °C/min achieved lower impurities levels in all instances while the sample leached with 10% HNO₃ produced the greatest reduction in impurity level. Scanning electron microscopy and Energy Dispersive X-Ray Spectroscopy analysis showed that the traces of Cu–Si intermetallic together with gathered impurities can be found only in the large silicon particles after the acid leaching treatment. In all instances, the surface of the silicon particles was free of impurities while Si yield was preserved at above 97%.     

Silicon/organic hybrid heterojunction infrared photodetector operating in the telecom regime

The authors report on the fabrication of a silicon/organic heterojunction based IR photodetector. It is demonstrated that an Al/p-Si/perylene-derivative/Al heterostructure exhibits a photovoltaic effect up to 2.7 μm (0.46 eV), a value significantly lower than the bandgap of either material. Although the devices are not optimized, at room temperature a rise time of 300 ns, a responsivity of ≈0.2 mA/W with a specific detectivity of D¹ ≈ 7 × 10⁷ Jones at 1.55 μm is found. The achieved responsivity is two orders of magnitude higher compared to our previous efforts [1], [2]. It will be outlined that the photocurrent originates from an absorption mechanism involving excitation of an electron from the Si valence band into the extended LUMO state in the perylene-derivative, with possible participation of intermediate localized surface state in the organic material.The non-invasive deposition of the organic interlayer onto the Si results in compatibility with the CMOS process, making the presented approach a potential alternative to all inorganic device concepts.     

High-efficiency fluorescent white organic light-emitting device with double emissive layers

The authors demonstrate a fluorescent white organic light-emitting device (WOLED) with double emissive layers. The yellow and blue dyes, 5,6,11,12-tetraphenylnaphthacene and N-(4-((E)-2-(6-((E)-4-(diphenylamino)styryl)naphthalen-2-yl)vinyl)phenyl)-N-phenylbenzenamine, are doping into the same conductive host material, N,N′-dicarbazolyl-4-4′-biphenyl). The maximum luminance and power efficiency of the WOLED are 14.6 cd/A and 9.5 lm/W at 0.01 mA/cm², with the maximum brightness of 20 100 cd/m² at 17.8 V. The Commission International de L’Éclairage coordinates change slightly from (0.27, 0.37) to (0.28, 0.36), as the applied voltage increases from 6 V to 16 V. The high efficiencies can be attributed to the balance between holes and electrons.     

Frequency and voltage dependency of interface states and series resistance in Al/SiO2/p-Si MOS structure

The capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics of Al/SiO₂/p-Si metal-oxide-semiconductor (MOS) Schottky diodes have been measured in the voltage range from ?3 to +3 V and frequency range from 5 KHz to 1 MHz at room temperature. It is found that both C and G/ω of the MOS capacitor are very sensitive to frequency. The fairly large frequency dispersion of C–V and G/ω–V characteristics can be interpreted in terms of the particular distribution of interface states at SiO₂/Si interface and the effect of series resistance. At relatively low frequencies, the interface states can follow an alternating current (AC) signal that contributes to excess capacitance and conductance. This leads to an anomalous peak of C–V curve in the depletion and accumulation regions. In addition, a peak at approximately ?0.2 V appears in the R_s–V profiles at low frequency. The peak values of the capacitance and conductance decrease with increasing frequency. The density distribution profile of interface state density (N_ss) obtained from C_HF–C_LF capacitance measurement also shows a peak in the depletion region.     

Multiple exciton generation regions in phosphorescent white organic light emitting devices

We demonstrate a white electrophosphorescent organic light emitting device (WOLED) with a three-section emission layer (EML) where excitons are formed in the multiple emission regions. The EML consists of a stepped progression of highest occupied and lowest unoccupied molecular orbital energies of the ambipolar hosts. Analysis shows that (36 ± 6)% of the excitons form in the blue emitting region, while (64 ± 6)% form in the green emitting region at 100 mA/cm². The doping of the red, green and blue phosphors, each in its own host, allows for efficient utilization of excitons formed in these multiple regions. Based on this architecture, the WOLED has an internal quantum efficiency close to unity. The WOLED has total external quantum and power efficiencies of η_ext,t = (26 ± 1)% and η_p,t = (63 ± 3) lm/W at 12 cd/m², decreasing to η_ext,t = (23 ± 1)% and η_p,t = (37 ± 2) lm/W at 500 cd/m². When an undoped electron transport layer is used, the peak efficiency is η_ext,t = (28 ± 1)%. Due to the distributed exciton formation in the EML, the WOLED exhibits higher total efficiency than monochromatic devices employing the same red, green and blue dopant–host combinations.     

Reliability challenges for barrier/liner system in high aspect ratio through silicon vias

The reliability results for barrier/liner systems in different high aspect ratio (5 × 50 μm) through silicon vias (TSV) are presented. Quite a few factors can influence the TSV barrier/liner reliability performance, including the TSV trench etch process, the oxide liner material/thickness, etc. The challenges for more advanced TSV technology nodes (e.g. 3 × 40 μm) are also discussed and possible solutions are proposed.     

New hole blocking material for green-emitting phosphorescent organic electroluminescent devices

The new amorphous molecular material, 2,5-bis(4-triphenylsilanyl-phenyl)-[1,3,4]oxadiazole, that functions as good hole blocker as well as electron transporting layer in the phosphorescent devices. The obtained material forms homogeneous and stable amorphous film. The new synthesized showed the reversible cathodic reduction for hole blocking material and the low reduction potential for electron transporting material in organic electroluminescent (EL) devices. The fabricated devices exhibited high performance with high current efficiency and power efficiency of 45 cd/A and 17.7 lm/W in 10 mA/cm², which is superior to the result of the device using BAlq (current efficiency: 31.5 cd/A and power efficiency: 13.5 lm/W in 10 mA/cm²) as well-known hole blocker. The ITO/DNTPD/α-NPD/6% Ir(ppy)₃ doped CBP/2,5-bis(4-triphenylsilanyl-phenyl)-[1,3,4]oxadiazole as both hole blocking and electron transporting layer/Al device showed efficiency of 45 cd/A and maximum brightness of 3000 cd/m² in 10 mA/cm².     

Effect of interface traps for ultra-thin high-k gate dielectric based MIS devices on the capacitance-voltage characteristics

The impact of states at the Al₂O₃/Si interface on the capacitance-voltage C-V characteristics of a metal/insulator/semiconductor heterostructure (MIS) capacitor was studied by a numerical simulation, by solving Schrodinger-Poisson equations and taking the electron emission rate from the interface state into account. Efficient computation and accurate physics based capacitance model of MOS devices with advanced ultra-thin equivalent oxide thickness (EOT) (down to 2.5 nm clearly considered here) were introduced for the near future integrated circuit IC technology nodes. Due to the importance of the interface state density for a low dimension and very low oxide thickness, a high frequency C-V model has been developed to interpret the effect of interface state density traps which communicate with the Al₂O₃/Si and their influence on the C-V characteristics. We found that these states are manifested by jumping capacity in the inversion zone, for a density of interface, higher than 1 × 10¹¹ cm^− 2 eV^− 1 during a p-doping of 1 × 10¹⁸ cm^− 3. This behavior has been investigated with various doping, temperature, frequency and energy levels on the C-V curves, and compared with the MIS structure that contains a standard SiO₂ insulator.     

A blue light emitting perylene derivative with improved solubility and aggregation control: Synthesis,characterisation and optical limiting properties

We report the synthesis and characterisation of 3,4,9,10-tetra-(12-alkoxycarbonyl)-perylene, a blue emitting organic material with controlled aggregation and improved solubility. The dye has a UV–Vis maximum absorption peak at 472 nm. Room temperature photoluminescence reveal a blue emission peak at 489 nm. Thermo gravimetric analysis (TGA) performed in air show the product to be thermally stable up to 300 °C. Dynamic scanning calorimetry (DSC) did not show a liquid crystalline phase normally present in 3,4,9,10-tetra-(n-alkoxycarbonyl)-perylenes for 2 ? n ? 9 where n is the number of carbon atoms in the alkyl chain. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were employed for aggregation studies of the dye showing that molecular stacking is not favoured. The Tauc relation applied to the UV–Vis absorbance cut-off wavelength at 500 nm was used to evaluate the optical band gap of the material as 3.81 eV and an exciton binding energy of 1.2 eV. Open-aperture Z-scan proved the molecule to be nonlinear optically active with an optical limiting extinction coefficient of 3.0 × 10^?10 cm W^?1. Experimental evidence shows that the optical limiting ability is attributed to nonlinear scattering.