Noise reduction in sputtered W/GaAs Schottky junctions

The noise characteristics of sputtered W/GaAs Schottky diodes, annealed at temperatures up to 700°C, have been investigated. A useful figure of merit for such millimeter and submillimeter mixer diodes is the noise performance at an RF where accurate measurements are available. Noise temperatures measured at a typical mixer intermediate frequency of 4GHz under DC biased conditions have been reduced significantly by rapid thermal annealing. The best noise data have been obtained with an annealing time of 2 minutes at 600°C and are consistent with good mixer performance.     

Structural and electrical properties of reactive magnetron sputtered yttrium-doped HfO_2 films

Hafnium oxide thin films doped with different concentrations of yttrium are prepared on Si(100) substrates at room temperature using a reactive magnetron sputtering system.The effects of Y content on the bonding structure,crystallographic structure,and electrical properties of Y-doped HfO_2 films are investigated.The x-ray photoelectron spectrum(XPS) indicates that the core level peak positions of Hf 4 f and O 1 s shift toward lower energy due to the structure change after Y doping.The depth profiling of XPS shows that the surface of the film is completely oxidized while the oxygen deficiency emerges after the stripping depths have increased.The x-ray diffraction and high resolution transmission electron microscopy(HRTEM) analyses reveal the evolution from monoclinic HfO_2 phase towards stabilized cubic HfO_2 phase and the preferred orientation of(111) appears with increasing Y content,while pure HfO_2 shows the monoclinic phase only.The leakage current and permittivity are determined as a function of the Y content.The best combination of low leakage current of 10-7 A/cm~2 at 1 V and a highest permittivity value of 29 is achieved when the doping ratio of Y increases to 9 mol%.A correlation among Y content,phase evolution and electrical properties of Y-doped HfO_2 ultra-thin film is investigated.     

Effect of heating on electrical transport in AlGaN/GaN Schottky barrier diodes on Si substrate

Thermal properties of the AlGaN/GaN Schottky barrier diodes were investigated, using a pulsed-IV measurement technique. The thermally degraded mobility in the DC-bias configuration was restored, when the pulse-bias voltages were applied. It was observed that heat generation was minimized, using a pulse width of 500 ns and pulse period of 10 ms. For the SBDs consisting of 5 μm of anode–cathode distance, on-resistance measured by the pulse-IV and DC-IV were 1.6 and 6.2 Ω-mm, respectively. We also demonstrated the device-width dependence of the thermal properties of the SBDs. We found that the performance of the power devices can be greatly influenced by the heat generation.     

Temperature dependent electrical characteristics of Sn/p-Si Schottky diodes

Current-voltage and capacitance-voltage characteristics of Sn/p-Si Schottky diodes measured in the temperature range 80-320 K are presented and analysed. Anomalous strong temperature dependencies of the ideality factor and apparent barrier height were obtained. There was also a considerable difference between the apparent barrier heights obtained from current-voltage and capacitance-voltage characteristics. These anomalies are explained by the domination of the current by a high level of thermionic-field emission, and by the presence of deep levels near the Sn/Si interface, which yield a reduction of free hole concentration and a significant temperature dependence of the charge stored near the metal-semiconductor (MS) interface. The evaluation of temperature dependence of forward current for thermionic-field emission resulted in the following parameters: characteristic energy E₀₀ = 9.8 meV, Schottky barrier height at zero bias Φ_b0 = 0.802 eV, bias coefficient of barrier height β = 0, and effective Richardson constant A* = 37.32 A cm⁻² K⁻².     

Comparative study of electrical properties of Au/n-Si (MS) and Au/Si3N4/n-Si (MIS) Schottky diodes

In this paper, the electrical parameters of Au/n-Si (MS) and Au/Si₃N₄/n-Si (MIS) Schottky diodes are obtained from the forward bias current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. Experimental results show that the rectifying ratios of MS and MIS diode at ± 5 V are found to be 1.25×10³ and 1.27×10⁴, respectively. The main electrical parameters of MS and MIS diode, such as the zero-bias barrier height (Φ _Bo) and ideality factor (n) are calculated to be 0.51 eV (I-V), 0.53 eV (C-V), and 4.43, and 0.65 eV (I-V), 0.70 eV (C-V), and 3.44, respectively. Also, the energy density distribution profile of the interface states (N_ss) is obtained from the forward bias I-V. In addition, the values of series resistance (R_s) for the two diodes are calculated from Cheung's method and Ohm's law.     

Tunneling current-voltage characteristics of Ti-silicide/p− Si/p+ Si Schottky diodes

The tunneling current-voltage characteristics of Ti-silicide/p^– Si/p⁺ Si Schottky diodes are analyzed to study the Ti/Si interface properties. By using an MBE-grown 7 nm p^– Si spacer layer, well-defined tunneling structures are obtained. The sharply peaked density of states in a Ga-impurity band is used as a tunneling probe. A state density gap 100 meV around the Fermi energy is observed for a rapidly (20s) annealed (T=550°C) reacted sample. The gap is interpreted by a Ti-rich interfacial silicide film of about 1 nm.     

Barrier-height non-uniformities of PtSi/Si(111) Schottky diodes

The forward current-voltage characteristics of PtSi Schottky contacts on epitaxial n-type Si (111) is studied in the temperature range from 100 to 300 K. A current contribution in excess to that predicted by thermionic emission diffusion theory is caused by a few thousand patches of reduced Schottky barrier height in a device area of 3.14 mm². The typical lateral extent of these patches is 70–250 nm. It correlates with the size of surface bumps observed. The number of patches is reduced upon increasing the silicidation temperature up toT _siI=550°C. Possible non-uniformities of the typical crystallite grain size of 20 nm are not resolved due to effective pinch-off.     

Comparative study of the electrical properties of Au/n-Si （MS） and Au/Si3N4/n-Si （MIS） Schottky diodes

In this paper,the electrical parameters of Au/n-Si(MS) and Au/Si3N4/n-Si(MIS) Schottky diodes are obtained from the forward bias current-voltage(I-V) and capacitance-voltage(C-V) measurements at room temperature.Experimental results show that the rectifying ratios of the MS and MIS diodes at±5 V are found to be 1.25 × 103 and 1.27 × 104,respectively.The main electrical parameters of the MS and MIS diodes,such as the zero-bias barrier height(ΦBo) and ideality factor(n),are calculated to be 0.51eV(I-V),0.53eV(C-V),and 4.43,and 0.65eV(I-V),0.70eV(C-V),and 3.44,respectively.In addition,the energy density distribution profile of the interface states(Nss) is obtained from the forward bias I-V,and the series resistance(Rs) values for the two diodes are calculated from Cheung's method and Ohm's law.     

Characterization and optimization of magnetron sputtered Sc/Si multilayers for extreme ultraviolet optics

Scandium/silicon multilayers have been deposited by magnetron sputtering and characterized by several techniques. Experimental peak reflectances of 0.22 and 0.37 have been measured respectively at wavelengths of 40 nm and 46 nm, for 10° incidence angle. The corresponding theoretical values for a perfect Sc/Si structure are respectively 0.38 and 0.57. In order to explain these differences between calculated and measured reflectivity, thin film and multilayer characterizations have been done. Effects of multilayer imperfections on the reflectivity have been estimated independently by means of simulation. Based on these results, a new design of Sc/Si multilayer is proposed with top layer thickness optimization. With this design, the experimental peak reflectance reaches 0.46 at a wavelength of 46 nm. PACS 78.67.Pt; 78.66.-W; 81.15.Cd     

Micro-structural and temperature dependent electrical characterization of Ni/GaN Schottky barrier diodes

Micro-structural investigation of Ni/GaN Schottky barrier diodes has been carried out using high-resolution transmission electron microscopy and electron diffraction spectrum in order to emphasize the role of Ni/GaN interface in controlling the Schottky diode behavior. Variable temperature Hall effect measurement of GaN samples along with the current–voltage (I–V) characteristics of Ni/n-GaN Schottky barrier diodes have been measured in 100–380 K temperature range. Results are analyzed in terms of thermionic emission theory by incorporating the concept of barrier inhomogeneity at the metal/semiconductor interface. The observed anomaly of temperature dependence of Schottky barrier height and ideality factor are explained by invoking two sets of Gaussian distribution of SBH in the temperature ranges of 100–180 K and 220–380 K, respectively. The value of A** (effective Richardson constant) as determined from the modified Richardson plot is 29.2 A/(cm² K²), which shows an excellent agreement with the theoretical value (26.4 A/(cm² K²)) in the temperature range of 220–380 K.     

Substrate temperature influenced structural, electrical and optical properties of dc magnetron sputtered MoO3 films

Molybdenum oxide (MoO₃) films were deposited on glass and (1 1 1) silicon substrates by sputtering of metallic molybdenum target in an oxygen partial pressure of 2 × 10⁻⁴ mbar and different substrate temperatures in the range 303-623 K using dc magnetron sputtering technique. X-ray photoelectron spectrum of the films formed at 303 K showed asymmetric Mo 3d_5/2 and Mo 3d_3/2 peaks due to the presence of mixed oxidation states of Mo⁵⁺ and Mo⁶⁺ while those deposited at substrate temperatures ≥473 K were in Mo⁶⁺ oxidation state of MoO₃. The films formed at substrate temperatures ≥473 K were polycrystalline in nature with orthorhombic α-phase MoO₃. Fourier transform infrared spectra of the films showed an absorption band at 1000 cm⁻¹ correspond to the stretching vibration of MoO, the characteristic of the α-MoO₃ phase. The electrical resistivity increased from 3.3 × 10³ to 8.3 × 10⁴ Ω cm with the increase of substrate temperature from 303 to 473 K respectively due to improvement in the crystallinity of the films. Optical band gap of the films increased from 3.03 to 3.22 eV with the increase of substrate temperature from 303 to 523 K.     

Comparison of electrical parameters of Zn/p-Si and Sn/p-Si Schottky barrier diodes

In this study, current-voltage (I-V) and capacitance-voltage (C-V) characteristics of metal-semiconductor (MS) Zn/p-Si and Sn/p-Si Schottky diodes, with high resistivity silicon structures, are investigated. The parameters of series resistance (R_S), the ideality factor (n) and the barrier height (Φ_b) are determined by performing different plots from the forward bias current-voltage (I-V) and reverse bias capacitance-voltage (C-V) characteristics. Thus, the barrier heights (Φ_b) for the Si Schottky diodes obtained between 0.725 and 1.051 eV, the ideality factor (n) between 1.043 and 1.309, and the series resistance (R_S) between 12.594 and 12.950 kΩ. The energy distribution of interface states density was determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height. It was concluded that the density of interface states in the considered energy range are in close agreement with each other values obtained for Zn/p-Si and Sn/p-Si Schottky diodes.     

Magnetic and transport properties of sputtered Fe/Si multilayers

The structural, magnetic and transport properties of sputtered Fe/Si multilayers were studied. The analyses of the data of the X-ray diffraction, resistance and magnetic measurements show that heavy atomic interdiffusion between Fe and Si occurs, resulting in multilayers of different complicated structures according to different sublayer thicknesses. The nominal Fe layers in the multilayers generally consist of Fe layers doped with Si, ferromagnetic Fe-Si silicide layers and nonmagnetic Fe-Si silicide interface layers, while the nominal Si spacers turn out to be Fe-Si compound layers with additional amorphous Si sublayers only under the condition either for the series or for the series multilayers. A strong antiferromagnetic (AFM) coupling and negative magnetoresistance (MR) effect, about 1%, were observed only in multilayers with iron silicide spacers and disappeared when -Si layers appear in the spacers. The dependences of MR on and on bilayer numbers N resemble the dependence of AFM coupling. The increase of MR ratio with increasing N is mainly attributed to the improvement of AFM coupling for multilayers with N. The dependence of MR ratio is similar to that in metal/metal system with predominant bulk spin dependent scattering and is fitted by a phenomenological formula for GMR. At 77 K both the MR effect and saturation field increase. All these facts suggest that the mechanisms of the AFM coupling and MR effect in sputtered Fe/Si multilayers are similar to those in metal/metal system. Received: 11 February 1998 / Revised: 9 March 1998 / Accepted: 9 March 1998     

Structural and optical characterization of DC magnetron sputtered molybdenum oxide films

Thin films of molybdenum trioxide were deposited on glass substrates employing direct current (DC) magnetron sputtering by sputtering of molybdenum at different oxygen partial pressures in the range 8 × 10⁻⁵–1 × 10⁻³ mbar and at a substrate temperature of 473 K. The glow discharge characteristics of magnetron cathode target of molybdenum were studied. The influence of oxygen partial pressure on the structural and optical properties of molybdenum trioxide films was investigated. The films formed at an optimum oxygen partial pressure of 2 × 10⁻⁴ mbar were polycrystalline in nature with orthorhombic α- phase and an optical band gap of 3.16 eV. The refractive index of the films formed at an oxygen partial pressure of 2 × 10⁻⁴ mbar decreased from 2.08 to 1.89 with increase of wavelength from 450 to 1,000 nm, respectively. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Comparison of electrical characteristic between AIN/GaN and AIGaN/GaN heterostructure Schottky diodes

Ni/Au Schottky contacts on A1N/GaN and A1GaN/GaN heterostructures are fabricated. Based on the measured current-voltage and capacitance-voltage curves, the electrical characteristics of AlN/GaN Schottky diode, such as Schottky barrier height, turn-on voltage, reverse breakdown voltage, ideal factor, and the current-transport mechanism, are analyzed and then compared with those of an A1GaN/GaN diode by self-consistently solving Schrodinger＇s and Poisson＇s equations. It is found that the dislocation-governed tunneling is dominant for both AlN/GaN and AlGaN/GaN Schottky diodes. However, more dislocation defects and a thinner barrier layer for AlN/GaN heterostrncture results in a larger tunneling probability, and causes a larger leakage current and lower reverse breakdown voltage, even though the Schottky barrier height of AlN/GaN Schottky diode is calculated to be higher that of an A1GaN/GaN diode.     

Comparison of electrical characteristic between AlN/GaN and AlGaN/GaN heterostructure Schottky diodes

Ni/Au Schottky contacts on AlN/GaN and AlGaN/GaN heterostructures are fabricated.Based on the measured current–voltage and capacitance–voltage curves,the electrical characteristics of AlN/GaN Schottky diode,such as Schottky barrier height,turn-on voltage,reverse breakdown voltage,ideal factor,and the current-transport mechanism,are analyzed and then compared with those of an AlGaN/GaN diode by self-consistently solving Schrdinger’s and Poisson’s equations.It is found that the dislocation-governed tunneling is dominant for both AlN/GaN and AlGaN/GaN Schottky diodes.However,more dislocation defects and a thinner barrier layer for AlN/GaN heterostructure results in a larger tunneling probability,and causes a larger leakage current and lower reverse breakdown voltage,even though the Schottky barrier height of AlN/GaN Schottky diode is calculated to be higher that of an AlGaN/GaN diode.     

Luminescence and electrical properties of diode Si/SiGe:Er/Si heterostructures

The diode Si/Si_{1 ? x} Ge _x :Er/Si heterostructures grown by sublimation molecular-beam epitaxy in a german atmosphere have been investigated. The electrical properties of Si_{1 ? x} Ge _x :Er heterolayers, the currentvoltage characteristics of the structures, and their photo-and electroluminescent properties in the forward-and reverse-bias modes have been analyzed. A relationship is established between the heterolayer parameters and the luminescence response features and characteristics of diode structures.     

Characterization of DC reactive magnetron sputtered NiO films using spectroscopic ellipsometry

Thin NiO films were deposited at 500 °C on n-type Si(1 1 1) by a DC reactive magnetron sputtering in a gas mixture of oxygen and argon. The ratio between the flow rates of oxygen and argon was respectively set at 1:4, 1:2, and 1:1. The dependence of structures and optical properties of NiO films were investigated using grazing incidence X-ray diffraction and spectroscopic ellipsometry in the spectral region of 1.5-5.0 eV. Ni-rich NiO films were obtained when the ratio between the flow rates of oxygen and argon was 1:4 and 1:2 in sputtering process. And when the ratio was 1:1, a relatively pure NiO film was formed. The partial pressure of oxygen could significantly influence the thickness and roughness of films. Refractive index n, extinction coefficient k, and direct gap energy and indirect gap energy of the NiO films were also subject to the influence of the partial pressure of oxygen.     

The effect of temperature on the electrical characteristics of Ti/n-GaAs Schottky diodes

Schottky diodes still attract researchers as they are used in various device applications. This study provides I–V characteristics of Ti/n-GaAs (80–300 K). Higher barrier height (Φ_B0) values were obtained for higher temperatures, whereas the ideality factor exhibited the opposite behavior. This was associated with a barrier inhomogeneity at the Ti/GaAs interface, which has a Gaussian distribution (GD). The mean barrier height values calculated from the modified Richardson and Φ_B0 - q/2 kT plots were found to be 0.584 eV and 0.575 eV in the temperature range of 80–160 K. They were found as 1.041 eV and 1.033 eV between 180 K and 300 K, respectively. The modified Richardson constant value, on the other hand, was calculated as 22.06 A cm⁻² K⁻² (80–160 K) and 13.167 A cm⁻² K⁻² (180–300 K). These values are higher than the theoretical value for n-GaAs, which is 8.16 A cm⁻² K⁻². This difference may stem from intense inhomogeneity at the Ti/n-GaAs interface.