Effect of diode size and series resistance on barrier height and ideality factor in nearly ideal Au/n type-GaAs micro Schottky contact diodes

Small high-quality Au/n type-GaAs Schottky barrier diodes (SBDs) with low reverse leakage current are produced using lithography. Their effective barrier heights (BHs) and ideality factors from current-voltage (I-V) characteristics are measured by a Pico ampere meter and home-built I-V instrument. In spite of the identical preparation of the diodes there is a diode-to-diode variation in ideality factor and barrier height parameters. Measurement of topology of a surface of a thin metal film with atomic force microscope (AFM) shows that Au-n type-GaAS SD consists of a set of parallel-connected micro and nanocontacts diodes with sizes approximately in a range of 100-200 nm. Between barrier height and ideality factor there is an inversely proportional dependency. With the diameter of contact increasing from 5 μm up to 200 μm, the barrier height increases from 0.833 up to 0.933 eV and its ideality factor decreases from 1.11 down to 1.006. These dependencies show the reduction of the contribution of the peripheral current with the diameter of contact increasing. We find the effect of series resistance on barrier height and ideality factor.     

Effect of nanopatches on electrical behavior of Ni/n-type Si Schottky diode

Topological surface measurement of thin metal film using a conducting probe atomic force microscope (C-AFM) shows that thin metal film deposited on Ni/n-Si Schottky diode (SD) consists of patches. These patches are sets of parallel connected and electrically cooperating nano-contacts of size between 50 and 100nm. Every individual patch acts as an individual diode with different I-V curve, barrier height (BH) and ideality factor (n). Between these diodes or patches, there are spot field distributions; the patches with different local work functions are in direct electric contact with surrounding patches. As a result, a potential difference between surfaces of patches, the so-called electrostatic spot field E_f, is formed. It is shown that in real metal-semiconductor (MS) contacts, patches with quite different configurations, various geometrical sizes and local work functions are randomly distributed on the surface of metal; hence direction and intensity of spot field are non-uniformly distributed along the surface of metal. There is a linear dependence between barrier height and ideality factor, which is the consequence of reduction of distance of the maximum of BH from the interface. This dependency is the sign of reduction of contribution of a peripheral current.     

Barrier height homogeneity for 4.5 kV 4H-SiC Schottky diodes

4.5 kV SiC Schottky diodes have been fabricated using Ni as the Schottky contact. A manufacturing yield of 40% is reached for the bigger area diodes (1.6×1.6 mm²) and of 70% for the smaller ones (0.4×0.4 mm²). The measured variations of barrier height and ideality factor with temperature do not agree with the thermionic model. This has been interpreted in terms of barrier height inhomogeneities using the Werner model. We extracted an average barrier height and its standard deviation . These two parameters are almost independent of the diode size. The variation of the barrier height distribution with field has also been investigated and shows a dependence similar to that of Schottky diodes realized from other semiconductor materials.     

High-temperature current conduction through three kinds of Schottky diodes

Fundamentals of the Schottky contacts and the high-temperature current conduction through three kinds of Schottky diodes are studied. N-Si Schottky diodes, GaN Schottky diodes and AlGaN/GaN Schottky diodes are investigated by I--V--T measurements ranging from 300 to 523~K. For these Schottky diodes, a rise in temperature is accompanied with an increase in barrier height and a reduction in ideality factor. Mechanisms are suggested, including thermionic emission, field emission, trap-assisted tunnelling and so on. The most remarkable finding in the present paper is that these three kinds of Schottky diodes are revealed to have different behaviours of high-temperature reverse currents. For the n-Si Schottky diode, a rise in temperature is accompanied by an increase in reverse current. The reverse current of the GaN Schottky diode decreases first and then increases with rising temperature. The AlGaN/GaN Schottky diode has a trend opposite to that of the GaN Schottky diode, and the dominant mechanisms are the effects of the piezoelectric polarization field and variation of two-dimensional electron gas charge density.     

Prediction of lateral barrier height in identically prepared Ni/n-type GaAs Schottky barrier diodes

We have identically prepared Ni/n-GaAs/In Schottky barrier diodes (SBDs) with doping density of 7.3 × 10¹⁵ cm⁻³. The barrier height for the Ni/n-GaAs/In SBDs from the current-voltage characteristics have varied from 0.835 to 0.856 eV, and ideality factor n from 1.02 to 1.08. We have determined a lateral homogeneous barrier height value of 0.862 eV for the Ni/n-GaAs/In SBD from the experimental linear relationship between barrier heights and ideality factors.     

The modulation of Schottky barrier height of NiSi/n-Si Schottky diodes by silicide as diffusion source technique

This paper reports that the Schottky barrier height modulation of NiSi/n-Si is experimentally investigated by adopting a novel silicide-as-diffusion-source technique, which avoids the damage to the NiSi/Si interface induced from the conventional dopant segregation method. In addition, the impact of post-BF₂ implantation after silicidation on the surface morphology of Ni silicides is also illustrated. The thermal stability of Ni silicides can be improved by silicide-as-diffusion-source technique. Besides, the electron Schottky barrier height is successfully modulated by 0.11~eV at a boron dose of 10¹⁵~cm^-2 in comparison with the non-implanted samples. The change of barrier height is not attributed to the phase change of silicide films but due to the boron pile-up at the interface of NiSi and Si substrate which causes the upward bending of conducting band. The results demonstrate the feasibility of novel silicide-as-diffusion-source technique for the fabrication of Schottky source/drain Si MOS devices.     

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.     

Prediction of barrier inhomogeneities and carrier transport in Ni-silicided Schottky diode

Based on Quantum Mechanical (QM) carrier transport and the effects of interface states, a theoretical model has been developed to predict the anomalous current-voltage (I-V) characteristics of a non-ideal Ni-silicided Schottky diode at low temperatures. Physical parameters such as barrier height, ideality factor, series resistance and effective Richardson constant of a silicided Schottky diode were extracted from forward I-V characteristics and are subsequently used for the simulation of both forward and reverse I-V characteristics using a QM transport model in which the effects of interface state and bias dependent barrier reduction are incorporated. The present analysis indicates that the effects of barrier inhomogeneity caused by incomplete silicide formation at the junction and the interface states may change the conventional current transport process, leading to anomalous forward and reverse I-V characteristics for the Ni-silicided Schottky diode.     

Difference in the electric behavior of micro- and nano Schottky diodes

The real Schottky diode (SD) consists of set in parallel connected both electrically cooperating micro- and nano contact ever micro- and nano contacts separately differ from each other only in potential barrier height. They are in an environment of the next micro sites of the general contact surfaces of SD and because of their interaction there is an additional electric field. Under action of an additional electric field character of interrelation of barrier height and the ideality factor of micro-and nano contacts gets specific features. Between the experimental results and energy diagram of the real metal–semiconductor contact has been good agreement.     

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.     

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.     

Simulation studies of current transport in metal–insulator–semiconductor Schottky barrier diodes

The current–voltage characteristics of Schottky diodes with an interfacial insulator layer are analysed by numerical simulation. The current–voltage data of the metal–insulator–semiconductor Schottky diode are simulated using thermionic emission diffusion (TED) equation taking into account an interfacial layer parameter. The calculated current–voltage data are fitted into ideal TED equation to see the apparent effect of interfacial layer parameters on current transport. Results obtained from the simulation studies shows that with mere presence of an interfacial layer at the metal–semiconductor interface the Schottky contact behave as an ideal diode of apparently high barrier height (BH), but with same ideality factor and series resistance as considered for a pure Schottky contact without an interfacial layer. This apparent BH decreases linearly with decreasing temperature. The effects giving rise to high ideality factor in metal–insulator–semiconductor diode are analysed. Reasons for observed temperature dependence of ideality factor in experimentally fabricated metal–insulator–semiconductor diodes are analysed and possible mechanisms are discussed.     

Leakage current and sub-bandgap photo-response of oxygen-plasma treated GaN Schottky barrier diodes

The effect of oxygen plasma treatment on the performance of GaN Schottky barrier diodes is studied. The GaN surface is intentionally exposed to oxygen plasma generated in an inductively coupled plasma etching system before Schottky metal deposition. The reverse leakage current of the treated diodes is suppressed in low bias range with enhanced diode ideality factor and series resistance. However, in high bias range the treated diodes exhibit higher reverse leakage current and corresponding lower breakdown voltage. The X-ray photoelectron spectroscopy analysis reveals the growth of a thin GaO_x layer on GaN surface during oxygen plasma treatment. Under sub-bandgap light illumination, the plasma-treated diodes show larger photovoltaic response compared with that of untreated diodes, suggesting that additional defect states at GaN surface are induced by the oxygen plasma treatment.     

Fabrication and characteristics of lateral Ti/4H-SiC Schottky barrier diodes

This paper describes the fabrication and characteristics of the lateral Ti/4H-SiC Schottky barrier diodes (SBDs). SBDs are fabricated by nitrogen ion implantation into p-type 4H-SiC epitaxial layer. The implant depth profile is simulated using the Monte Carlo simulator TRIM. Measurements of the reverse I－V characteristics demonstrate a low reverse current, that is good enough for many SiC-based devices such as SiC metal-semiconductor field-effect transistors, and SiC static induction transistors. The parameters of the diodes are extracted from the forward I－V characteristics. The barrier height φ_b of Ti/4H-SiC is 0.95 eV.     

Electrical characteristics of the hydrogen pre-annealed Au/n-GaAs Schottky barrier diodes as a function of temperature

We investigated the passivation effects of hydrogen gas on the Au/n-GaAs Schottky barrier diodes in a wide temperature range. Reference diodes were prepared by evaporating barrier metal on semiconductor wafers un-annealed in N₂ gas atmosphere. The other diodes were made by evaporating barrier metal on n-GaAs semiconductor substrates annealed in H₂ atmosphere. Then, electrical measurements of all diodes were carried out by using closed-cycle Helium cryostat by steps of 20 K in the temperature range of 80-300 K in dark. The basic diode parameters such as ideality factor and barrier height were consequently extracted from electrical measurements. It was seen that ideality factors increased and barrier heights decreased with the decreasing temperature. The case was attributed to barrier inhomogeneity at the metal/semiconductor interface. Barrier heights of the diodes made from samples annealed in H₂ gas atmosphere were smaller than those of reference diodes at low temperatures. Here, it was ascribed to the fact that hydrogen atoms passivated dangling bonds on semiconductor surface in accordance with former studies.     

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.     

Effects of chemical treatment on barrier height and ideality factors of Au/GaN Schottky diodes

We have studied Au/n-GaN Schottky barrier diodes. GaN surfaces have been prepared by cleaning in HCl and (NH₄)₂S prior to metal deposition. The zero-biased barrier heights and ideality factors obtained from the current-voltage characteristics differ from diode to diode, although all the samples were prepared identically. The statistical analysis for the reverse bias C-V data yielded mean value of (1.35±0.04) eV for Schottky barrier height of HCl treated sample and (1.20±0.03) eV for (NH₄)₂S sample, where 9 dots were considered from each cleaning method. It was found that the barrier height values obtained from the C⁻²-V (1.43 eV) and I-V characteristics (0.89 eV) are different from each other by 0.54 eV. The inhomogeneous barrier heights were found to be related to the effect of the high series resistance on diode parameters (Akkiliç et al., 2004) [1].     

Modification of Al/Si interface and Schottky barrier height with chemical treatment

The influence of different chemical treatments on the electrical behaviour of n- and p-type Al/Si Schottky junctions was studied. A Schottky barrier height of 0.91 eV was achieved on p-type Si probably due to the unpinning of the Fermi-level at the Al/Si interface. This is one of the highest barrier height values reported so far for a solid-state Schottky junction prepared to p-Si. A doping level reduction was observed in the vicinity of the Si surface for wafers with native oxide and for those boiled in acetone or annealed in forming gas. It was observed unexpectedly that the reactive plasma etch used for the formation of mesa structures decreases the apparent Schottky barrier height. The relation between the sum of n- and p-type Schottky barrier heights and forbidden gap is discussed.