Au/P polysilicon Schottky diodes

Schottky barrier diodes were fabricated by evaporation of gold layers onto chemically etched polycrystalline silicon wafers. The wafers are p type (resistivityρ _⊥=160 Ωcm, the grains are columnar shape with some orientation). An average potential barrier of 0.087 eV appears to exist across the grain boundary between columns. Ohmic back contacts were made from a Ga-Al alloy. Diodes were investigated with the aid of (a)I-V characteristics at different temperatures, (b)C-V characteristics, (c) spectral response and (d) Fowler's plot of photoelectric measurements. The best diodes had characteristics similar to data typical of monocrystalline silicon. The low series columnar resistance (0.67Ω) of the cells is neglected in the analysis. The barrier height, fromI-V data (including temperature variation) was 0.67 to 0.73 eV. This is much lower than that obtained from Fowler's plot (0.9 eV). However, the barrier height obtained from theC-V graph is in agreement with the value of 0.9 eV. The diffusion potential is 0.4 eV. The value of the diode ideality factor (1.5 to 2.8) indicates that recombination generation processes play a dominant role. The normalized photovoltaic spectral response in the wavelength range 600 to 1300 nm was presented with a comparison from the theory taking into account bulk and surface recombination.     

Schottky diodes based on nanocrystalline p-GaN and n-GaN in thin film form

Nanocrystalline n-GaN and p-GaN in thin film form were deposited onto fused silica substrates by high-pressure d.c. magnetron sputtering of Si (1 at%) and Be (1 at%) doped GaN targets, respectively. Schottky diode structures for both the p- and n-type nanocrystalline GaN (Au/p-GaN/Al and Al/n-GaN/Au) were fabricated out of the above films. Corresponding current-voltage and capacitance-voltage characteristics of the Schottky diodes were recorded and analyzed in the light of the existing theories.     

Electrical characteristics of Au/n-GaAs Schottky barrier diodes with and without SiO2 insulator layer at room temperature

In this study, our main goal is fabricated with and without insulator layer Au/n-GaAs Schottky barrier diodes (SBDs) to explain whether or not the insulator layer is effective on some electric parameters such as Φ_B, n, N_ss, and R_s. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of metal-semiconductor (Au/n-GaAs) are investigated and compared with metal-insulator-semiconductor (Au/SiO₂/n-GaAs) Schottky diodes. From the room temperature I-V characteristics of these devices, the main electrical parameters such as, ideality factor (n) and zero bias barrier height (Φ_bo) values of 1.25 and 0.73 eV for Au/n-GaAs, and 1.51 and 0.75 eV for Au/SiO₂/n-GaAs, were obtained. The interface distribution profile (N_ss) as a function of (E_c − E_ss) was extracted from the forward-bias I-V measurements by taking into account the bias dependence of the effective barrier height (Φ_e) and series resistance (R_s) for the Schottky diodes. The N_ss values obtained taking into account the series resistance values are lower than those obtained without considering the series resistance. The diodes show non-ideal I-V behavior with ideality factor greater than unity. This behavior is attributed to the interfacial insulator layer and the interface states. The I-V characteristics confirmed that the distribution of N_ss, R_s, and interfacial insulator layer are important parameters that influence the electrical characteristics of metal-semiconductor and metal-insulator-semiconductor Schottky diodes.     

Electrical and photocurrent characteristics of Au/PVA (Co-doped)/n-Si photoconductive diodes

In this work, we investigate the some main electrical and photocurrent properties of the Au/PVA(Co-doped)/n-Si diodes by using current–voltage (I–V) measurements at dark and various illumination intensity. Two types of diodes with and without polyvinyl alcohol (PVA) (Co-doped) polymeric interfacial layer were fabricated and measured at room temperature. Results show that the polymeric interfacial layers and series resistance (R_s) strongly affect the main electrical parameters of these structures. Also, metal/polymer/semiconductor (MPS) diode with PVA (Co-doped) interfacial organic layer is very sensitive to the light such that the current in reverse bias region increase by 10³–10⁴ times with the increasing illumination intensity. The open circuit voltage V_oc and short-circuit current I_sc values of this MPS diode under 100 mW/cm² illumination intensity were found as 0.28 V and 19.3 μA, respectively.     

Electrical properties of Schottky diodes based on Carbazole

Sandwich structures of Carbazole thin films have been prepared by using vacuum deposition technique. The plot of current density versus voltage (J–V characteristics) shows two distinct regions. In the lower voltage region ohmic conduction and in the higher voltage region space charge limited conduction (SCLC) is observed. Number of states in the valence band (Nv) is calculated from the temperature dependence of J in the ohmic region. From the temperature dependence of J in the SCLC region trap density (Nt) and activation energy are determined. The values of Nv and Nt are in the order 10²³ m⁻³ and 10²⁷ m⁻³ respectively. The value of activation energy is nearly equal to 0.1 eV and that of the effective mobility is 4.5 × 10⁻⁷ cm² V⁻¹ S⁻¹. Schottky diodes are fabricated using Aluminium (Al) as Schottky contact. It is observed that gold (Au) is more suitable for ohmic contact compared to silver (Ag). From a semi logarithmic plot of J versus V, the barrier height (ϕb), diode ideality factor (n) and saturation current density (J₀) are determined. The value of n increases and ϕb decreases on annealing.     

Bilayer Cr/Au contacts on n-GaN

Cr/Au (40/65 nm) metal layers have been deposited by thermal evaporation onto n-GaN epitaxial layers grown by metal-organic chemical-vapour deposition (MOCVD) on a sapphire substrate. The samples have been annealed at 400, 700 and 900 °C for 10 min in vacuum. Techniques of TEM, EDS, HRTEM, FESEM, XRD and I-V characteristics have been used to characterize the micro-, and nanostructure, morphology, composition and electrical properties of the contacts before and after annealing. A binary phase of Cr₃Ga₄ and Au₇Ga₂ were identified at the interface of the n-GaN/Cr/Au contacts after annealing in vacuum at 700 and 900 °C. Current-voltage characterizations showed that the as-deposited and annealed Cr/Au contacts are rectifying up to 600 °C. After heat treatment in vacuum at 700 °C and 900 °C the Cr/Au contacts were linear.     

Electronic transport of lateral PtSi/n/n+-Si Schottky diodes

We investigated the transport properties of a lateral PtSi/n/n(+)-Si Schottky diode prepared on an n-type silicon-on-insulator (SOI) wafer with a special attention on the bipolar transport and the surface effect. With applying a back-gate bias changing from +18 V to -18 V, the unipolar transport behavior switched over to the bipolar one, where an enhanced surface recombination rate due to a high surface-to-volume ratio produced a current density approximately 3 x 10(3) A/cm2 for 2 V bias through a 40 nm-thick and 18 microm-long nanoribbon. The recombination time was estimated to be approximately 1 micros from independent CV measurements, which is much smaller value than that of a bulk. The local Fermi energy level for electrons at the channel center was monitored by an additional voltage probe during each I(D)-V(D) measurement and it revealed the intricate nature of the bipolar transport manifested by the huge asymmetrical hysteretic behavior on a drain bias cycle which is attributed to the charge storage effect and asymmetrical junction profiles.     

Electrical properties of Schottky diodes using high-resistivity CdTe crystals

The Schottky barrier height is measured for single crystals doped with the halogens Cl, Br, and I during growth by chemical transport reactions. The measurements are made using a modification of the F(V) function [N. V. Agrinskaya, Mater. Sci. Eng. B 16, 172 (1993)] proposed by the authors. Pis’ma Zh. Tekh. Fiz. 25, 23–28 (August 26, 1999)     

Analysis of surface states and series resistance in Au/n-Si Schottky diodes with insulator layer using current-voltage and admittance-voltage characteristics

In order to good interpret the experimentally observed Au/n-Si (metal-semiconductor) Schottky diodes with thin insulator layer (18 Å) parameters such as the zero-bias barrier height (Φ_bo), ideality factor (n), series resistance (R_s) and surface states have been investigated using current-voltage (I-V), capacitance-frequency (C-f) and conductance-frequency (G-f) techniques. The forward and reverse bias I-V characteristics of Au/n-Si (MS) Schottky diode were measured at room temperature. In addition, C-f and G-f characteristics were measured in the frequency range of 1 kHz-1 MHz. The higher values of C and G at low frequencies were attributed to the insulator layer and surface states. Under intermediate forward bias, the semi-logarithmic Ln (I)-V plot shows a good linear region. From this region, the slope and the intercept of this plot on the current axis allow to determine the ideality factor (n), the zero-barrier height (Φ_bo) and the saturation current (I_S) evaluated to 2.878, 0.652 and 3.61 × 10⁻⁷ A, respectively. The diode shows non-ideal I-V behavior with ideality factor greater than unity. This behavior can be attributed to the interfacial insulator layer, the surface states, series resistance and the formation barrier inhomogeneity at metal-semiconductor interface. From the C-f and G-f characteristics, the energy distribution of surface states (N_ss) and their relaxation time (τ) have been determined in the energy range of (E_c − 0.493E_v)-(E_c − 0.610) eV taking into account the forward bias I-V data. The values of N_ss and τ change from 9.35 × 10¹³ eV⁻¹ cm⁻² to 2.73 × 10¹³ eV⁻¹ cm⁻² and 1.75 × 10⁻⁵ s to 4.50 × 10⁻⁴ s, respectively.     

Cu3Ge Schottky contacts on n-GaN

The electrical properties and thermal stability of (hereafter referred to as ) Schottky contacts to n-GaN as a function of the Ge concentration and annealing temperature are studied. Upon rapid thermal annealing the /n-GaN Schottky diode is formed at 300 °C and is stable up to 650 °C. At 700 °C the agglomeration occurs in the films. For the Cu-25 at % Ge films the ideality factor, n, barrier height, , and flat band barrier height, , of the /n-GaN diodes are in the ranges of 1.22–1.36, 0.53–0.72 eV, and 0.65–0.97 eV, respectively, being decreased with the annealing temperature. Higher Ge concentration in the Cu-35 at % Ge films results in larger n, , and of /n-GaN Schottky diodes. The film is expected to be a suitable candidate for stable Schottky contacts to n-GaN at elevated temperatures.     

Graphene-silicon Schottky diodes

We have fabricated graphene-silicon Schottky diodes by depositing mechanically exfoliated graphene on top of silicon substrates. The resulting current-voltage characteristics exhibit rectifying diode behavior with a barrier energy of 0.41 eV on n-type silicon and 0.45 eV on p-type silicon at the room temperature. The I-V characteristics measured at 100, 300, and 400 K indicate that temperature strongly influences the ideality factor of graphene-silicon Schottky diodes. The ideality factor, however, does not depend strongly on the number of graphene layers. The optical transparency of the thin graphene layer allows the underlying silicon substrate to absorb incident laser light and generate a photocurrent. Spatially resolved photocurrent measurements reveal the importance of inhomogeneity and series resistance in the devices.     

Electrical and optical properties of p-SiC/n-GaN heterostructures

We report on the optical, electrical and structural properties of GaN films heteroepitaxially grown by low pressure chemical vapor deposition on 6H-SiC substrates. We employed photoluminescence (PL), Hall effect measurements, scanning tunneling microscopy (STM) and X-ray analysis to determine the quality of our films. Heterojunction diodes were fabricated on p-type SiC and characterized by temperature dependent current–voltage and capacitance–voltage techniques. The results are interpreted within the thermionic emission model and the barrier found is attributed to the conduction band offset between 6H-SiC and wurtzite GaN. The diodes show electroluminescence of the donor-acceptor pair recombination type of 6H-SiC at room temperature. By analysis of the injection behavior we can interpret our data, determining the high valence band offset between 6H-SiC and -GaN to 0.67 eV. This high valence band offset favors applications for hetero-bipolar transistors (HBT).     

Electrical characteristics of an organic thin copolymer/p-Si Schottky barrier diode

We have fabricated a poly(aniline-3-methyl thiophene) organic thin material on p-Si substrate by placing a solution of copolymer in acetonitrile on top of a p-Si substrate and then evaporating the solvent. The electrical and interface state density properties of the poly(aniline-3-methyl thiophene) copolymer/p-Si/Al diode have been investigated through methods using current-voltage (I-V), Cheung's, and a modified Norde's function. Good agreement was observed with the values of barrier height as obtained from all of these methods. The diode shows a non-ideal I-V behavior with an ideality factor greater than unity, which could be ascribed to the interfacial layer, interface states and series resistance. The interface state density of diode was determined using the forward-bias I-V characteristic technique at room temperature, and it decreases exponentially with bias from 1.39 × 10¹⁶ cm⁻² eV⁻¹ in (0.06 − E_v) eV to 4.86 × 10¹⁵ cm⁻² eV⁻¹ in (0.51 − E_v) eV.     

Carbon-silicon Schottky barrier diodes

The simple fabrication of high-performance Schottky barrier diodes between silicon and conductive carbon films (C-Films) is reported. By optimizing the interface, ideality factors as low as n = 1.22 for pyrolytic photoresist films (PPF) have been obtained. These remarkable values, which are not far away from those of commercial products are obtained repeatedly on non-optimized substrates with fully scalable processes.     

Properties of Au/W/GaAs Schottky barriers

The electrical and chemical properties of r.f. sputtered Au/W Schottky barriers on GaAs studied by Auger electron spectroscopy are reported. There is considerable interest in such work at present owing to the refractory nature and the thermal stability of tungsten on GaAs. The built-in potential of tungsten on GaAs was measured to be about 0.65 eV by both I–V and C–V techniques. Although tungsten alone has been reported to be stable on GaAs even at elevated temperatures of up to 500°C, the presence of a gold overlay and/or pinholes in the r.f. sputtered tungsten reduces its refractory nature. W/Au Schottky barriers annealed at 475 and 575°C for 10 min showed no appreciable degradation in their electrical properties. Samples annealed at 475°C for 2 h and 800°C for 15 min showed some degradation and migration of gold through the tungsten film. GaAs field effect transistors (FETs) with tungsten gates 0.7 μm long showed a maximum measured gain of 14 dB at 8 GHz.     

Electrical characterization of deep levels in N and P 6H-SiC Schottky diodes

Excess current at low forward bias is observed for large-area Ni Schottky diodes on n- and p-type 6H-SiC. Random telegraph signal (RTS) measurements, carried out on these defective devices, show discrete time switching of the current. The trap signatures (E_a=0.35eV>, =1.17×10^-18cm² for n-type, E_a=0.43eV, =1.8×10^-20cm² for p-type) extracted from deep level transient spectroscopy (DLTS) measurement are very close to those obtained from RTS. This strong correlation between the two different techniques is attributed to the presence of an extended defect which presents different charge states (i.e. an extended defect decorated by punctual traps). This assumption is reinforced by the DLTS measurements as a function of the filling time and as a function of the field.     

Characteristics of gold/cadmium sulfide nanowire Schottky diodes

Schottky diode junctions were formed between nanowires of cadmium sulfide and nanowires of gold, through sequential cathodic electrodeposition into the pores of anodized aluminum oxide (AAO) templates. Lengths of CdS and Au nanowires were 100-500 nm and 300-400 nm respectively, while the diameter was 30 nm, each. Analysis of Schottky diodes yielded an effective reverse saturation current (J_o), of 0.32 mA/cm² and an effective diode ideality factor (A) of 8.1 in the dark. Corresponding values under one sun illumination were, J_o = 0.92 mA/cm² and A = 10.0. Dominant junction current mechanisms are thought to be tunneling and/or interface state recombination.     

高温Ti/4H-SiC肖特基势垒二极管的特性

在研究高温下串联电阻Ron对肖特基势垒二极管正向特性的影响，以及各种反向电流密度分量对其反向特性的影响基础上，测量并理论计算了300－528K范围内Ti/4H-SiC肖特基势垒二极管的伏安特性。分别得到了理想因子、肖特基势垒高度和串联电阻在395K和528K温度下的数值。理论和实验的比较说明，高温下，热电子发射是正向电流的主要输运机理，反向电流除了以隧道效应为主外，热电子发射电流和耗尽层中复合中心产生电流都随温度的升高而大大增加，必须加以考虑。