Investigation of TiO2 on AlGaAs prepared by liquid phase deposition and its application

The study explored titanium dioxide (TiO₂) on aluminum gallium arsenide (AlGaAs) prepared by liquid phase deposition (LPD) at 40 °C. The leakage current density was about 8.4 × 10^?6 A/cm² at 1 MV/cm. The interface trap density (D_it) and the flat-band voltage shift (ΔV_FB) were 2.3 × 10¹² cm^?2 eV^?1 and 1.2 V, respectively. After rapid thermal annealing (RTA) in the ambient N₂ at 350 °C for 1 min, the leakage current density, D_it, and ΔV_FB were improved to 2.4 × 10^?6 A/cm² at 1 MV/cm, 7.3 × 10¹¹ cm^?2 eV^?1, and 1.0 V, respectively. Finally, the study demonstrates the application to the AlGaAs/InGaAs metal–oxide–semiconductor pseudomorphic high-electron-mobility transistor (MOS-PHEMT). The results indicate the potential of the proposed device with a LPD-TiO₂ gate oxide for power application.     

Effects of post-annealing on the passivation interface characteristics of AlGaN/GaN high electron mobility transistors

We examined the effects of post-annealing in forming-gas ambient on the spin-on-dielectric (SOD)-buffered passivation as well as the conventional plasma-enhanced chemical vapor deposition (PECVD) Si₃N₄ passivation structure in association with the quantitative analysis of defects at the passivation interfaces of AlGaN/GaN high electron mobility transistors (HEMTs). Before the annealing, the interface state densities (D_it) of the PECVD Si₃N₄ are one-order higher (10¹²–10¹³ cm⁻² eV⁻¹) than those of the SOD SiO_x (10¹¹–10¹² cm⁻² eV⁻¹) as derived from C–V characterization. Clear reduction in D_it from the PECVD Si₃N₄ is extracted to a level of 10¹¹–10¹² cm⁻² eV⁻¹ with a stronger absorption from Si–N peak in Fourier transform infrared spectroscopy spectra after the post-annealing. On the other hand, negligible difference in D_it value is obtained from the SOD SiO_x. In this paper we propose that much lower measurement levels (~156 mA/mm) before the annealing and substantial recovery (~13% increase) after the annealing in maximum drain current density of the AlGaN/GaN HEMTs with Si₃N₄ passivations are due to the original higher density before the annealing and greater reduction in D_it of the PECVD Si₃N₄ after the annealing. Significant reduction after the annealing in gate–drain leakage current (from ~10⁻³ to ~10⁻⁵ A, 100-μm gate width) of the HEMTs with the Si₃N₄ passivation is also supposed to be attributed to the reduction of D_it.     

Electrical and optical properties of Cu2ZnSnS4 grown by a thermal co-evaporation method and its diode application

Cu₂ZnSnS₄ (CZTS) is low cost and constitutes non-toxic materials abundant in the earth crust. Environment friendly solar cell absorber layers were fabricated by a thermal co-evaporation technique. Elemental composition of the film was stated by energy dispersive spectroscopy (EDS). Some optical and electrical properties such as absorption of light, absorption coefficient, optical band gap charge carrier density, sheet resistance and mobility were extracted. Optical band gap was found to be as 1.44 eV, besides, charge carrier density, resistivity and mobility were found as 2.14×10¹⁹ cm⁻³, 8.41×10⁻⁴ Ω cm and 3.45×10² cm² V⁻¹ s⁻¹, respectively. In this study Ag/CZTS/n-Si Schottky diode was fabricated and basic diode parameters including barrier height, ideality factor, and series resistance were concluded using current–voltage and capacitance–voltage measurements. Barrier height and ideality factor values were found from the measurements as 0.81 eV and 4.76, respectively, for Ag/CZTS/n-Si contact.     

A detailed comparative study on the main electrical parameters of Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes

We have fabricated Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes (SBDs) to investigate the effect of organic interfacial layer on the main electrical characteristics. Zn doped poly(vinyl alcohol) (PVA:Zn) was successfully deposited on n-Si substrate by using the electrospinning system and surface morphology of PVA:Zn was presented by SEM images. The current–voltage (I–V) characteristics of these SBDs have been investigated at room temperature. The experimental results show that interfacial layer enhances the device performance in terms of ideality factor (n), zero-bias barrier height (Φ_B0), series resistance (R_s), and shunt resistance (R_sh) with values of 1.38, 0.75 eV, 97.64 Ω, and 203 MΩ whereas those of Au/n-Si SBD are found as 1.65, 0.62 eV, 164.15 Ω and 0.597 MΩ, respectively. Also, this interfacial layer at metal/semiconductor (M/S) interface leads to a decrease in the magnitude of leakage current and density of interface states (N_ss). The values of N_ss range from 1.36×10¹² at E_c—0.569 eV to 1.35×10¹³ eV^?1 cm^?2 at E_c—0.387 eV for Au/PVA:Zn/n-Si SBD and 3.34×10¹² at E_c—0.560 eV to 1.35×10¹³ eV^?1 cm^?2 at E_c—0.424 eV for Au/n-Si SBD. The analysis of experimental results reveals that the existence of PVA:Zn interfacial layer improves the performance of such devices.     

Characterization of an Au/n-Si photovoltaic structure with an organic thin film

We demonstrate that a copper(II) organic complex can control the electrical characteristics of conventional Au/n-Si metal–semiconductor (MS) contacts. We investigated the electronic and photovoltaic properties of a Cu(II) complex/n-Si heterojunction diode. The ideality factor n and barrier height Φ_b of the diode were 2.22 and 0.736 eV, respectively. An ideality factor greater than unity indicates that the diode exhibits non-ideal current–voltage behavior. This behavior results from the effect of series resistance and the presence of an interfacial layer. The series resistance and barrier height determined using Norde’s method were 6.7 kΩ and 0.77 eV, respectively. The device showed photovoltaic behavior, with a maximum open-circuit voltage of 0.24 V and a short circuit current of 1.7 μA under light of 8 mW/cm².     

High dielectric constant TiO2 film grown on polysilicon by liquid phase deposition

In this study, titanium dioxide (TiO₂) films were grown on polycrystalline silicon by liquid phase deposition (LPD) with ammonium hexafluoro-titanate and boric acid as sources. The film structure is amorphous as examined by X-ray diffraction (XRD). A uniform composition of LPD-TiO₂ was observed by SIMS examination. The leakage current density of an Al/LPD-TiO₂/poly-Si/p-type Si metal–oxide–semiconductor (MOS) structure is 1.9 A/cm² at the negative electric field of 0.7 MV/cm. The dielectric constant is 29.5 after O₂ annealing at 450 °C. The leakage current densities can be improved effectively with a thermal oxidized SiO₂ added at the interface of LPD-TiO₂/poly-Si. The leakage current density can reach 3.1×10⁻⁴ A/cm² at the negative electric field of 0.7 MV/cm and the dielectric constant is 9.8.     

Current–voltage and capacitance–voltage characteristics of Al Schottky contacts to strained Si-on-insulator in the wide temperature range

The electrical characteristics of Al/strained Si-on-insulator (sSOI) Schottky diode have been investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements in the wide temperature range of 200–400 K in steps of 25 K. It was found that the barrier height (0.57–0.80 eV) calculated from the I–V characteristics increased and the ideality factor (1.97–1.28) decreased with increasing temperature. The barrier heights determined from the C–V measurements were higher than those extracted from the I–V measurements, associated with the formation of an inhomogeneous Schottky barrier at the interface. The series resistance estimated from the forward I–V characteristics using Cheung and Norde methods decreased with increasing temperature, implying its strong temperature dependence. The observed variation in barrier height and ideality factor could be attributed to the inhomogeneities in Schottky barrier, explained by assuming Gaussian distribution of barrier heights. The temperature-dependent I–V characteristics showed a double Gaussian distribution with mean barrier heights of 0.83 and 1.19 eV and standard deviations of 0.10 and 0.16 eV at 200–275 and 300–400 K, respectively. From the modified Richardson plot, the modified Richardson constant were calculated to be 21.8 and 29.4 A cm⁻² K⁻² at 200–275 and 300–400 K, respectively, which were comparable to the theoretical value for p-type sSOI (31.6 A cm⁻² K⁻²).     

Determination of the laterally homogeneous barrier height of palladium Schottky barrier diodes on n-Ge (1 1 1)

We have studied the experimental linear relationship between barrier heights and ideality factors for palladium (Pd) on bulk-grown (1 1 1) Sb-doped n-type germanium (Ge) metal-semiconductor structures with a doping density of about 2.5×10¹⁵ cm^?3. The Pd Schottky contacts were fabricated by vacuum resistive evaporation. The electrical analysis of the contacts was investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements at a temperature of 296 K. The effective barrier heights from I–V characteristics varied from 0.492 to 0.550 eV, the ideality factor n varied from 1.140 to 1.950, and from reverse bias capacitance–voltage (C^?2–V) characteristics the barrier height varied from 0.427 to 0.509 eV. The lateral homogenous barrier height value of 0.558 eV for the contacts was obtained from the linear relationship between experimental barrier heights and ideality factors. Furthermore the experimental barrier height distribution obtained from I–V and (C^?2?V) characteristics were fitted by Gaussian distribution function, and their mean values were found to be 0.529 and 0.463 eV, respectively.     

Region-dependent behavior of I–V characteristics in n-ZnO:Al/p-Si contacts

The discrepancy of rectifying characteristics in n-ZnO:Al/p-Si heterojunctions from diode to diode was demonstrated by region dependent dark I–V characteristics, where the junction is laterally cut to sequentially decrease the area. Further investigation shows that the junction (2.1×2.1 cm²) with the barrier height Φ=0.693 eV consists of one part (2.1×1.4 cm²) with Φ=0.695 eV and the other part (2.1×0.7 cm²) with Φ=0.686 eV. It is found that reverse currents saturate with different values of 3.6×10^?3, 2.5×10^?3 and 1.58×10^?3 A for the light I–V curves of the three junctions with the same areas. To explain this peculiarity, the probable reason is discussed in terms of carrier transportation through the spatially fluctuating barrier.     

Characteristics of RF reactive sputter-deposited Pt/SiO2/n-InGaN MOS Schottky diodes

All RF sputtering-deposited Pt/SiO₂/n-type indium gallium nitride (n-InGaN) metal–oxide–semiconductor (MOS) diodes were investigated before and after annealing at 400 °C. By scanning electron microscopy (SEM), the thickness of Pt, SiO_2, n-InGaN layer was measured to be ~250, 70, and 800 nm, respectively. AFM results also show that the grains become a little bigger after annealing, the surface topography of the as-deposited film was smoother with the rms roughness of 1.67 nm and had the slight increase of 1.92 nm for annealed sample. Electrical properties of MOS diodes have been determined by using the current–voltage (I–V) and capacitance–voltage (C–V) measurements. The results showed that Schottky barrier height (SBH) increased slightly to 0.69 eV (I–V) and 0.82 eV (C–V) after annealing at 400 °C for 15 min in N₂ ambient, compared to that of 0.67 eV (I–V) and 0.79 eV (C–V) for the as-deposited sample. There was the considerable improvement in the leakage current, dropped from 6.5×10⁻⁷ A for the as-deposited to 1.4×10⁻⁷ A for the 400 °C-annealed one. The annealed MOS Schottky diode had shown the higher SBH, lower leakage current, smaller ideality factor (n), and denser microstructure. In addition to the SBH, n, and series resistance (R_s) determined by Cheungs׳ and Norde methods, other parameters for MOS diodes tested at room temperature were also calculated by C–V measurement.     

Investigation of structural and optoelectronic properties of annealed nickel phthalocyanine thin films

Thin films of nickel phthalocyanine (NiPc) were prepared by thermal evaporation and the effects of annealing temperature on the structural and optical properties of the samples were studied using different analytical methods. Structural analysis showed that the grain size and crystallinity of NiPc films improved as annealing temperature increased from 25 to 150 °C. Also, maximum grain size (71.3 nm) was obtained at 150 °C annealing temperature. In addition, NiPc films annealed at 150 °C had a very smooth surface with an RMS roughness of 0.41 nm. Optical analysis indicated that band gap energy of films at different annealing temperatures varied in the range of 3.22–3.28 eV. Schottky diode solar cells with a structure of ITO/PEDOT:PSS/NiPc/Al were fabricated. Measurement of the dark current density–voltage (J–V) characteristics of diodes showed that the current density of films annealed at 150 °C for a given bias was greater than that of other films. Furthermore, the films revealed the highest rectification ratio (23.1) and lowest barrier height (0.84 eV) demonstrating, respectively, 23% and 11% increase compared with those of the deposited NiPc films. Meanwhile, photoconversion behavior of films annealed at 150 °C under illumination showed the highest short circuit current density (0.070 mA/cm²) and open circuit voltage of (0.55 V).     

Effect of thermal annealing on the electrical properties of P3HT:PC70BM nanocomposites

We studied the electrical properties of organic photovoltaic (OPV) devices based on poly (3-hexylthiophene) and fullerene derivative [6, 6]-Phenyl-C₇₀-butyric acid methyl ester nanocomposite (P3HT:PC₇₀BM) as a function of the annealing temperature. Thermal annealing enables crystallization of the polymer and diffusion of the PC₇₀BM molecules. Diode parameters, such as the barrier height ϕ_b and the ideality factor n were calculated. They were found to be depend strongly on the annealing temperature. This dependence is attributed to surface states, inhomogeneity in the material and series resistance. Best OPV devices had a short circuit current density of 3.35 mA/cm², an open circuit voltage of 0.68 V, a fill factor of 0.45, and a power conversion efficiency of 2.2%, by applying a thermal annealing temperature of 150 °C for 10 min.     

The effects of surface states and series resistance on the performance of Au/SnO2/n-Si and Al/SnO2/p-Si (MIS) Schottky barrier diodes

We have fabricated two types of Schottky barrier(SBDs),Au/SnO₂/n-Si (MIS1) and Al/SnO₂/p-Si (MIS2), to investigate the surface (N_ss) and series resistance (R_s) effect on main electrical parameters such as zero-bias barrier height (Φ_Bo) and ideality factor (n) for these SBDs. The forward and reverse bias current–voltage (I–V) characteristics of them were measured at 200 and 295 K, and experimental results were compared with each other. At temperatures of 200 and 295 K, Φ_Bo, n, N_ss and R_s for MIS1 Schottky diodes (SDs) ranged from 0.393 to 0.585 eV, 5.70 to 4.75, 5.42×10¹³ to 4.27×10¹³ eV^?1 cm^?2 and 514 to 388 Ω, respectively, whereas for MIS2 they ranged from 0.377 to 0.556 eV, 3.58 to 2.1, 1.25×10¹⁴ to 3.30×10¹⁴ eV^?1 cm^?2 and 312 to 290 Ω, respectively. The values of n for two types of SBDs are rather than unity and this behavior has been attributed to the particular distribution of N_ss and interfacial insulator layer at the metal/semiconductor interface. In addition, the temperature dependence energy density distribution profiles of N_ss for both MIS1 and MIS2 SBDs were obtained from the forward bias I–V characteristics by taking into account the bias dependence of effective barrier height (Φ_e) and R_s. Experimental results show that both N_ss and R_s values should be taken into account in the forward bias I–V characteristics. It has been concluded that the p-type SBD (MIS2) shows a lower barrier height (BH), lower R_s, n and N_ss compared to n-type SBD (MIS1), which results in higher current at both 200 and 295 K.     

Characteristics of ZnOV2O5MnO2Nb2O5Er2O3 semiconducting varistors with sintering processing

The effects of sintering temperature on the microstructure, electrical properties, and dielectric characteristics of ZnOV₂O₅MnO₂Nb₂O₅Er₂O₃ semiconducting varistors have been studied. With increase in sintering temperature the average grain size increased (4.5–9.5 μm) and the density decreased (5.56–5.45 g/cm³). The breakdown field decreased with an increase in the sintering temperature (6214–982 V/cm). The samples sintered at 900 °C exhibited remarkably high nonlinear coefficient (50). The donor concentration increased with an increase in the sintering temperature (0.60×10¹⁸–1.04×10¹⁸ cm^?3) and the barrier height exhibited the maximum value (1.15 eV) at 900 °C. As the sintering temperature increased, the apparent dielectric constant increased by more than four-fold.     

Electrical parameters of a DC sputtered Mo/n-type 6H-SiC Schottky barrier diode

A Mo/n-type 6H-SiC/Ni Schottky barrier diode (SBD) was fabricated by sputtering Mo metal on n-type 6H-SiC semiconductor. Before the formation of Mo/n-type 6H-SiC SBD, an ohmic contact was formed by thermal evaporation of Ni on n-type 6H-SiC and annealing at 950 °C for 10 min. It was seen that the structure had excellent rectification. The electrical parameters were extracted using its current–voltage (I–V) and capacitance–voltage (C–V) measurements carried out at room temperature. Very high (1.10 eV) barrier height and 1.635 ideality factor values were reported for Mo/n-type 6H-SiC using ln I–V plot. The barrier height and series resistance values of the diode were also calculated as 1.413 eV and 69 Ω from Norde׳s functions, respectively. Furthermore, 1.938 eV barrier height value of Mo/n-type 6H-SiC SBD calculated from C–V measurements was larger than the one obtained from I–V data.     

Electrical properties and barrier modification of GaAs MIS Schottky device based on MEH-PPV organic interfacial layer

We report fabrication and electrical characterization of GaAs based metal-interfacial layer-semiconductor (MIS) device with poly[2-methoxy-5-(2^/-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV), as an interfacial layer. MEH-PPV raises the barrier height in Al/MEH-PPV/p-GaAs MIS device as high as to 0.87 eV. A Capacitance-Voltage (C–V) characteristic exhibits a low hysteresis voltage with an interface states density of 1.69×10¹¹ cm⁻² eV⁻¹. Moreover, a high transition frequency (f_c) of about 50 kHz was observed in the accumulation mode. The photovoltaic response of Al/MEH-PPV/p-GaAs device was measured under the air masses (AM) 1.0 and 1.5. The open circuit voltage (V_OC), short circuit current (I_SC), fill factor and the efficiency of the Al/MEH-PPV/p-GaAs device were found to be 1.10 V, 0.52 mA, 0.65, and 5.92%, respectively, under AM 1.0 condition.     

Pulse electrodeposited copper indium sulpho selenide films and their properties

Copper indium sulpho selenide films of different composition were deposited by the pulse plating technique at 50% duty cycle (15 s ON and 15 s OFF). X-ray diffraction studies indicated the formation of single phase chalcopyrite copper indium sulpho selenide films. Transmission Electron Microscope studies indicated that the grain size increased from 10 nm–40 nm as the selenium content increased. The band gap of the films was in the range of 0.95 eV–1.44 eV. Room temperature resistivity of the films is in the range of 16.0 Ω cm–33.0 Ω cm. Films of different composition used in photoelectrochemical cells have exhibited photo output. Films of composition, CuInS_0.9Se_0.1 have exhibited maximum output, a V_OC of 0.74 V, J_SC of 18.50 mA cm^?2, ff of 0.75 and efficiency of 11.40% for 60 mW cm^?2 illumination.     

A study on phase transformation of SnOx thin films prepared by reactive magnetron sputtering

In the paper, SnO_x thin films were deposited by reactive magnetron sputtering from a tin target in O₂ containing working gas. The evolution from Sn-containing SnO to tetravalent SnO₂ films was investigated. The films could be classified into three groups according to their optical band gaps, which are E_g<2.5 eV, E_g=3.0–3.3 eV and E_g>3.7 eV. The electric measurements show that high conductivity can be obtained much easier in SnO₂ than in SnO films. A high electron mobility of 15.7 cm² V⁻¹ s⁻¹, a carrier concentration of 1.43×10²⁰ cm⁻³ and a resistivity of 2.8×10⁻³ Ω cm have been achieved in amorphous SnO₂ films. Films with the optical band gap of 3.0–3.3 eV remain amorphous though the substrate temperature is as high as 300 °C, which implies that °btaining high mobility in p-type SnO is more challenging in contrast to n-type SnO₂ films.     

Self-aligned inversion n-channel In0.2Ga0.8As/GaAs metal–oxide–semiconductor field-effect-transistors with TiN gate and Ga2O3(Gd2O3) dielectric

A self-aligned process for fabricating inversion n-channel metal–oxide–semiconductor field-effect-transistors (MOSFET’s) of strained In_0.2Ga_0.8As on GaAs using TiN as gate metal and Ga₂O₃(Gd₂O₃) as high κ gate dielectric has been developed. A MOSFET with a 4 μm gate length and a 100 μm gate width exhibits a drain current of 1.5 mA/mm at V_g = 4 V and V_d = 2 V, a low gate leakage of <10^?7 A/cm² at 1 MV/cm, an extrinsic transconductance of 1.7 mS/mm at V_g = 3 V, V_d = 2 V, and an on/off ratio of ～10⁵ in drain current. For comparison, a TiN/Ga₂O₃(Gd₂O₃)/In_0.2Ga_0.8As MOS diode after rapid thermal annealing (RTA) to high temperatures of 750 °C exhibits excellent electrical and structural performances: a low leakage current density of 10^?8–10^?9 A/cm², well-behaved capacitance–voltage (C–V) characteristics giving a high dielectric constant of ～16 and a low interfacial density of state of ～(2～6) × 10¹¹ cm^?2 eV^?1, and an atomically sharp smooth Ga₂O₃(Gd₂O₃)/In_0.2Ga_0.8As interface.