Admittance of metal–insulator–semiconductor structures based on graded-gap HgCdTe grown by molecular-beam epitaxy on GaAs substrates

Metal–insulator–semiconductor structures based on n-Hg_1−xCd_xTe (x = 0.19–0.25) were grown by molecular-beam epitaxy on the GaAs (0 1 3) substrates. Near-surface graded-gap layers with high CdTe content were formed on both sides of the epitaxial HgCdTe. Admittance of these structures was studied experimentally in a wide temperature range (8–150) K. It is shown that an increase in the composition of the working layer and a decrease in temperature lead to a decrease in the frequency of transition to high-frequency behavior of the capacitance–voltage characteristics. The differential resistance of space charge region in the strong inversion increases with the composition of the working layer and for x = 0.22 and 0.25, the differential resistance is limited by the Shockley-Read generation. The values of the differential resistance of space charge region at different frequencies and temperatures were found.     

The effect of series resistance and interface states on the frequency dependent C–V and G/w–V characteristics of Al/perylene/p-Si MPS type Schottky barrier diodes

The capacitance–voltage–frequency (C–V–f) and conductance–voltage–frequency (G/w–V–f) characteristics of Al/perylene/p-Si Schottky barrier diodes (SBDs) fabricated with spin coating system have been investigated in the frequency range of 30 kHz–2 MHz at room temperature. In order to elucidate the electrical characteristics of SBDs with perylene interface, the voltage and frequency dependent series resistance (R_s), frequency dependent density distribution profile of interface state (N_ss) were obtained. The measurements of C and G/w were found to be strongly dependent on bias voltage and frequency for Al/perylene/p-Si SBDs. For each frequency, the R_s–V plot gives a peak, decreasing with increasing frequencies. Also, it has been shown that the interface states density exponentially decreases with increasing frequency. The C–V–f and G/w–V–f characteristics confirm that the N_ss and R_s of the diode are important parameters that strongly influence the electric parameters in metal/polymer/semiconductor (MPS) structure.     

Analysis of surface and guided wave plasmon polariton modes in insulator–metal–insulator planar plasmonic waveguides

Theoretical and experimental study of the surface plasmon–polariton and guided wave plasmon polariton modes is presented for the Sapphire/Ag/Polycarbonate/Air structure. Theoretical results are obtained by solving complex multilayer eigenvalue equations as well as the reflectivity equation for this structure. It is proposed that the mode attenuation can be significantly reduced by inserting a low index dielectric buffer between the metal and the guiding dielectric layer. The dispersion and attenuation curves are generated. Both the surface plasmon and guided wave plasmon polariton modes are studied experimentally. The experimental values of the effective refractive indices agree well with the theoretical values. The electric field profiles are generated and used to examine the nature of modes. After optimization of various parameters the condition for low loss single mode guiding is obtained for the proposed structure. Effect of metal thickness on surface plasmon mode is also discussed. It is inferred that in a properly optimized plasmonic waveguide, the losses can be reduced by a factor of 4.     

Effect of NO annealing on charge traps in oxide insulator and transition layer for 4H-SiC metal–oxide–semiconductor devices

The effect of nitric oxide(NO) annealing on charge traps in the oxide insulator and transition layer in n-type4H–Si C metal–oxide–semiconductor(MOS) devices has been investigated using the time-dependent bias stress(TDBS),capacitance–voltage(C–V),and secondary ion mass spectroscopy(SIMS).It is revealed that two main categories of charge traps,near interface oxide traps(Nniot) and oxide traps(Not),have different responses to the TDBS and C–V characteristics in NO-annealed and Ar-annealed samples.The Nniotare mainly responsible for the hysteresis occurring in the bidirectional C–V characteristics,which are very close to the semiconductor interface and can readily exchange charges with the inner semiconductor.However,Not is mainly responsible for the TDBS induced C–V shifts.Electrons tunneling into the Not are hardly released quickly when suffering TDBS,resulting in the problem of the threshold voltage stability.Compared with the Ar-annealed sample,Nniotcan be significantly suppressed by the NO annealing,but there is little improvement of Not.SIMS results demonstrate that the Nniotare distributed within the transition layer,which correlated with the existence of the excess silicon.During the NO annealing process,the excess Si atoms incorporate into nitrogen in the transition layer,allowing better relaxation of the interface strain and effectively reducing the width of the transition layer and the density of Nniot.     

Charge storage characteristics in Al/AlN/Si metal–insulator–semiconductor structure based on deep traps in AlN layer

Charge storage characteristics in an Al/AlN/p-Si metal–insulator–semiconductor (MIS) structure have been investigated by capacitance–voltage and long-term capacitance measurements. Good program/erase behavior is observed in the AlN/Si structure, which is attributed to the trapping and detrapping of charges in deep traps of the AlN layer. In the long-term retention mode, a clear memory window is found 2000 s after removing a program/erase voltage of ±3 V, indicating good charge retention capability of the MIS structure. Further investigation shows that for a program pulse width of 500 ms, the charge storage does not occur when the pulse amplitude is smaller than a threshold value of ∼1 V. The trapped charge density increases linearly with increase of the pulse amplitude (>1 V) and tends to saturate at 2.5 V. With increasing program pulse width, the trapped charged density increases a little more than logarithmically. PACS 73.40.Kp; 72.20.Jv; 71.55.Eq     

Monolithic integration of AlGaN/GaN metal—insulator field-effect transistor with ultra-low voltage-drop diode for self-protection

In this paper, we present a monolithic integration of self-protected AlGaN/GaN metal-insulator field-effect transistor (MISFET). An integrated field-controlled diode on the drain side of the AlGaN/GaN MISFET features self-protected function at reverse bias. This diode takes advantage of the recessed-barrier enhancement-mode technique to realize an ultra-low voltage drop and a low turn-ON voltage. In the smart monolithic integration, this integrated diode can block reverse bias (>70 V/μm) and suppress the leakage current (<5×10^-11 A/mm). Compared with conventional monolithic integration, the numerical results show that the MISFET integrated with a field-controlled diode leads to a good performance for smart power integration. And the power loss is lower than 50% in conduction without forward current degeneration.     

On the interface states and series resistance profiles of (Ni/Au)–Al0.22Ga0.78N/AlN/GaN heterostructures before and after 60Co (γ-ray) irradiation

The values of interface states (N _SS) and series resistance (R _S) of (Ni/Au)–Al_0.22Ga_0.78N/AlN/GaN heterostructures were obtained from admittance and current–voltage measurements before and after 250 kGy ⁶⁰Co irradiation. The analyses of these data indicate that the values of capacitance and conductance decrease, as the R _S increases with increasing dose rate due to the generation of N _SS. The increase in R _S with increasing dose rate was attributed to two main models. According to the first model, it has been attributed to a direct decrease in the donor concentration in semiconductor material as a result of the elimination of shallow donor states. According to the second model, it is a result of irradiation because of the formation of deep acceptor centers in the semiconductor bulk, and electrons from the shallow donor centers are captured by these acceptors.     

Investigation of trap states in Al_2O_3 InAlN/GaN metal–oxide–semiconductor high-electron-mobility transistors

In this paper the trapping effects in Al2O3/In0.17Al0.83N/Ga N MOS-HEMT(here, HEMT stands for high electron mobility transistor) are investigated by frequency-dependent capacitance and conductance analysis. The trap states are found at both the Al2O3/In Al N and In Al N/Ga N interface. Trap states in In Al N/Ga N heterostructure are determined to have mixed de-trapping mechanisms, emission, and tunneling. Part of the electrons captured in the trap states are likely to tunnel into the two-dimensional electron gas(2DEG) channel under serious band bending and stronger electric field peak caused by high Al content in the In Al N barrier, which explains the opposite voltage dependence of time constant and relation between the time constant and energy of the trap states.     

Linearity improvement of Cy5 fluorescence concentration detection using series photodetector frequency circuit system with ITO–PolySi–metal–semiconductor–metal photodetector and its application for DNA detection and bacterial identification

In this study, the 48 MHz series photodetector frequency circuit system with ITO–PolySi–metal–semiconductor–metal photodetector was developed for Cy5 fluorescence detection of DNA probe ET996. The theory analysis of series photodetector frequency circuit system showed that the circuit parameters such as C_p and A (tan θ) can be applied to improve the frequency sensitivity. In this research, the lower capacitance of ITO–PolySi–metal–semiconductor–metal photodetector (C_p) was made and selected to improve the frequency sensitivity. According to derived theory of A adjustment, the capacitance match C_m and bias of ITO–PolySi–metal–semiconductor–metal photodetector were adjusted to improve the frequency sensitivity for detection of fluorescence dye concentration. On the basis of optimal conditions of capacitance match C_m and bias of photodetector, the detection limit of ET996-Cy5 fluorescence dye concentration 2 pmol/L can be measured by 48 MHz sensor system. Moreover, the detection linearity of 48 MHz sensor system was improved and the frequency shift ΔF was linearly related to the logarithm of fluorescence dye concentration in the range 2 pmol/L–20 μmol/L; meanwhile, through the feature of probe uniqueness, Edwardsiella BCRC 10670 DNA and fluorescence probe ET996-Cy5 can be successfully judged for hybridization reaction.     

Quantum chemical studies on a series of transition metal carbon dioxide complexes: Metal–carbon bonding and electronic structures

The bonding features and electronic structures of a series of transition metal carbon dioxide complexes have been studied by density functional theory (DFT) calculations combined with natural bond orbital (NBO) analysis and energy-decomposition analysis (EDA). NBO analysis shows that the interaction between the metal center and the carbon atom of the carbon dioxide ligand (M–C) is stronger than the other interaction between the metal center and the carbon dioxide ligand. Natural hybrid orbital (NHO) analysis gives the detailed bonding features of the M–C bond for each complex. The NBO charge distribution on the carbon dioxide unit in all studied complexes is negative, which indicates charge transfer from the metal center to the carbon dioxide ligand for all studied complexes. The hyperconjugation effect of the metal center and the two C–O bonds of the carbon dioxide ligand has been estimated using the NBO second-order perturbation stabilization energy. It was found that the NBO second-order stabilization energy of C–O?→?nM* is sensitive to the coordinated sphere and the metal center. Frontier molecular orbital (FMO) analysis shows that complexes 1 and 4 may be good nucleophilic reagents for activation of the carbon dioxide molecule. However, the EDAs show that the M–CO₂ bond interaction energy of complex 4 is about two times as large as that of complex 1. The high M–CO₂ bond interaction energy of complex 4 may limit its practical application.     

Effect of annealing temperature on the electrical properties of Au/Ta2O5/n-GaN metal–insulator–semiconductor (MIS) structure

We report on the effect of an annealing temperature on the electrical properties of Au/Ta₂O₅/n-GaN metal–insulator–semiconductor (MIS) structure by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The measured Schottky barrier height (Φ _bo) and ideality factor n values of the as-deposited Au/Ta₂O₅/n-GaN MIS structure are 0.93 eV (I–V) and 1.19. The barrier height (BH) increases to 1.03 eV and ideality factor decreases to 1.13 upon annealing at 500 ^°C for 1 min under nitrogen ambient. When the contact is annealed at 600 ^°C, the barrier height decreases and the ideality factor increases to 0.99 eV and 1.15. The barrier heights obtained from the C–V measurements are higher than those obtained from I–V measurements, and this indicates the existence of spatial inhomogeneity at the interface. Cheung’s functions are also used to calculate the barrier height (Φ _bo), ideality factor (n), and series resistance (R _s ) of the Au/Ta₂O₅/n-GaN MIS structure. Investigations reveal that the Schottky emission is the dominant mechanism and the Poole–Frenkel emission occurs only in the high voltage region. The energy distribution of interface states is determined from the forward bias I–V characteristics by taking into account the bias dependence of the effective barrier height. It is observed that the density value of interface states for the annealed samples with interfacial layer is lower than that of the density value of interface states of the as-deposited sample.     

Effects of interface bound states on the shot noise in normal metal–low-dimensional Rashba semiconductor tunnel junctions with induced s-wave pairing potential

We consider the effects of interface bound states on the electrical shot noise in tunnel junctions formed between normal metals and one-dimensional(1 D) or two-dimensional(2 D) Rashba semiconductors with proximity-induced s-wave pairing potential. We investigate how the shot noise properties vary as the interface bound state is evolved from a non-zero energy bound state to a zero-energy bound state. We show that in both 1 D and 2 D tunnel junctions, the ratio of the noise power to the charge current in the vicinity of zero bias voltage may be enhanced significantly due to the induction of the midgap interface bound state. But as the interface bound state evolves from a non-zero energy bound state to a zero-energy bound state, this ratio tends to vanish completely at zero bias voltage in 1 D tunnel junctions, while in 2 D tunnel junctions it decreases smoothly to the usual classical Schottky value for the normal state. Some other important aspects of the shot noise properties in such tunnel junctions are also clarified.     

Preparation and characterization of CuI/PVA–PEDOT:PSS core–shell for photovoltaic application

In the present paper nano polymer composite of CuI/PVA blended with PEDOT:PSS has been prepared by growing CuI nano particles inside aqueous solution of PVA. The XRD characterization illustrated the growth of CuI nano crystals of 22–33 nm. The optical absorption showed direct transition with an energy band gap equals to 1.18 eV and 1.3 eV for colloidal and thin solid films respectively. The PL investigation illustrates a quenching with increasing PEDDOT:PSS concentration. The results are interpreted according to energy confinement enhanced by plasmon–exciton interaction of CuI–PVA/PEDOT:PSS core–shell. The frequency dependence of conductivity suggested hopping conduction where the bulk conductivity is thermally activated with an activation energy in the range varies from 0.07 to 0.46 eV by increasing PEDOT:PSS concentration. The cyclic voltammetry measurements have been performed to ascertain the position of both HOMO and LUMO levels which illustrated a movement of HOMO level toward vacuum level, with a decrease in the chemical band gap from 1.72 to 1.3 eV with increasing PEDOT:PSS concentration.     

Closed-form breakdown voltage/specific on-resistance model using charge superposition technique for vertical power double-diffused metal–oxide–semiconductor device with high-κ insulator

An improved vertical power double-diffused metal–oxide–semiconductor(DMOS) device with a p-region(P1) and high-κ insulator vertical double-diffusion metal–oxide–semiconductor(HKP-VDMOS) is proposed to achieve a better performance on breakdown voltage(BV)/specific on-resistance(Ron,sp) than conventional VDMOS with a high-κ insulator(CHK-VDMOS).The main mechanism is that with the introduction of the P-region,an extra electric field peak is generated in the drift region of HKP-VDMOS to enhance the breakdown voltage.Due to the assisted depletion effect of this p-region,the specific on-resistance of the device could be reduced because of the high doping density of the N-type drift region.Meanwhile,based on the superposition of the depleted charges,a closed-form model for electric field/breakdown voltage is generally derived,which is in good agreement with the simulation result within 10% of error.An HKP-VDMOS device with a breakdown voltage of 600 V,a reduced specific on-resistance of 11.5 m?·cm~2 and a figure of merit(FOM)(BV~2/Ron,sp)of 31.2 MW·cm~(-2) shows a substantial improvement compared with the CHK-VDMOS device.     

Structural and thermal studies of [PVA–LiAc] : TiO2 polymer nanocomposite system

Nanocomposite polymer electrolyte consisting of polyvinyl alcohol (PVA) and lithium acetate with TiO₂ filler has been synthesised by combination of solution cast technique and sol–gel process. The composite electrolyte films were characterised by different experimental techniques. The average particle size of composite electrolytes lies between 25 and 30?nm. System is essentially ionic with maximum conductivity of polymer electrolyte 90[80PVA–20LiAc]:10TiO₂ (～4.5?×?10^?6?S?cm^?1) at room temperature.     

Influence of interface states on the temperature dependence and current–voltage characteristics of Ni/p-InP Schottky diodes

The ideality factor n$n$ and the barrier height _Φap${\Phi }_{ap}$ of the sputtered Ni/p-InP Schottky diodes have been calculated from their experimental Current–voltage (I–V)$\left(I\text{–}V\right)$ characteristics in the temperature range of 60–400 K with steps of 10 K. The n$n$ and _Φap${\Phi }_{ap}$ values for the device have been obtained as 1.27 and 0.87 eV at 300 K and 1.13 and 0.91 eV at 400 K, respectively. The n$n$ values larger than unity at high temperatures indicate the presence of a thin native oxide layer at the semiconductor/metal interface. The barrier height (BH) has been assumed to be bias dependent due to the presence of an interfacial layer and interface states located at the interfacial layer-semiconductor interface. Interfacial layer-thermionic emission current mechanism has been fitted to experimental I–V$I\text{–}V$ data by considering the bias-dependence of the BH at each temperature. The best fitting values of the series resistance _Rs$R_s$ and interface state density _Ns$N_s$ together with the bias-dependence of the BH have been used at each temperature, and the _Rs$R_s$ and _Ns$N_s$ versus temperature plots have been drawn. It has been seen that the experimental and theoretical forward bias I–V$I\text{–}V$ data are in excellent agreement with each other in the temperature range of 60–400 K. It has been seen that the _Rs$R_s$ and _Ns$N_s$ values increase with a decrease in temperature, confirming the results in the literature.     

Near-field-enhanced,off-resonant laser sintering of semiconductor particles for additive manufacturing of dispersed Au–ZnO-micro/nano hybrid structures

Off-resonant near-field enhancement by gold nanoparticles adsorbed on crystalline zinc oxide significantly increases the energy efficiency of infrared laser sintering. In detail, ten different gold mass loads on zinc oxide were exposed to 1,064 nm cw-laser radiation. Variation of scan speed, laser power, and spot size showed that the energy threshold required for sintering decreases and sintering process window widens compared to laser sintering of pure zinc oxide powder. Transmission electron microscope analysis after focused ion beam cross sectioning of the sintered particles reveals that supported gold nanoparticles homogenously resolidify in the sintered semiconductor matrix. The enhanced sintering process with ligand-free gold nanoparticles gives access to metal–semiconductor hybrid materials with potential application in light harvesting or energy conversion.