Modification of metal/semiconductor junctions by self-assembled monolayer organic films

Two new metal/molecule/semiconductor contacts, Au/n-Si/TDA/Au and Au/p-Si/ODM/Au, were fabricated to understand effect of organic compounds, tridecylamine and octadecylmercaptan self-assembled monolayer (SAM) films, on electrical charge transport properties of the metal/semiconductor junctions. The morphology of the organic monolayers deposited on Si substrates was investigated by atomic force microscopy. The molecular coverage of ODM deposited on p-Si is poorer than that of TDA on n-Si substrate. The ideality factors of the p-Si/ODM and n-Si/TDA diodes were found to be 1.66 and 1.48, respectively. The electrical results show that the tridecylamine monolayer passivated junction has a lower ideality factor. The ideality factor indicates clear dependence on two different type functional groups R-SH (Thiol) and R-NH₂ (Amin) groups and it increases with different functional groups of organic molecule. The barrier height φ_b value of the n-Si/TDA diode is smaller than that of p-Si/ODM diode, as a result of chain length of the SAM organic molecules. The interface state density D_it values of the diodes were determined using conductance technique. The n-Si/TDA diode has the smaller interface state density according to p-Si/ODM diode.We have evaluated that the organic molecules control the electronic parameters of metal/semiconductor diodes and thus, organic modification helps to get one step closer towards to new organic assisted silicon based microelectronic devices.     

The current-voltage-temperature characteristics of Al/NPB/p-Si contact

The current-voltage (I-V) characteristics of the Al/NPB/p-Si contact shows rectifying behavior with a potential barrier formed at the contact interface. The barrier height and ideality factor values of 0.65 eV and 1.33 are measured at the forward bias of the diode. The barrier height of the Al/NPB/p-Si diode at room temperature is larger that (∼0.58 eV) of conventional Al/p-Si diode. It reveals the NPB organic film control the carrier transport of the diode at the contact interface. The temperature effect on the I-V measurement is also performed to reveal the junction characteristics. The ideality factor of the Al/NPB/p-Si contact increases with decreasing temperature. And the barrier height decreases with decreasing temperature. The effects are due to the existence of the interface states and the inhomogeneous of the barrier at the junction.     

Controlling of electrical and interface state density properties of ZnO:Co/p-silicon diode structures by compositional fraction of cobalt dopant

The heterojunction diodes based on cobalt doped zinc oxide (ZnO) were prepared by sol-gel deposition method. The compositional fraction of cobalt dopant was varied to control the electrical parameters of the diode. Atomic force microscopy was used to determine the structural properties of ZnO:Co films. The ZnO:Co films have a microfiber structure and the structure of microfibers was changed with the cobalt dopant. The ideality factor values of 5% and 15% Co doped ZnO:Co/p-Si diodes were determined to be 3.49 and 7.51, respectively. The barrier height of the ZnO:Co/p-Si diodes were found to vary from 0.75 eV to 0.78 eV.It is concluded that the electrical and interface state density properties of ZnO:Co/p-Si diodes can be controlled by compositional fraction of cobalt dopant.     

Controlling of electronic parameters of GaAs Schottky diode by poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic interlayer

The electronic properties of metal-organic semiconductor-inorganic semiconductor structure between GaAs and poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic film have been investigated via current-voltage and capacitance-voltage methods. The Au/PEDOT/n-GaAs contact exhibits a rectification behavior with the barrier height of 0.69 eV and ideality factor value of 3.94. The barrier height of the studied diode (0.67 eV) is lower than that of Ni/n-GaAs/In (0.85 eV) and Au/n-GaAs/In Schottky diodes. The decrease in barrier height of Au/n-GaAs/In Schottky diode is likely to be due to the variation in the space charge region in the GaAs. The obtained results indicate that control of the interfacial potential barrier for metal/n-GaAs diode was achieved using thin interlayer of the poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol).     

Damage induced in p-GaAs due to RIE in CH/sub 4//H/sub 2/ mixture

Damaged induced in p-GaAs due to RIE in pure H/sub 2/ and a mixture of CH/sub 4//H/sub 2/ has been investigated by I-V and C-V measurements on Au/p-GaAs Schottky diodes fabricated following the RIE process. The ideality factor, barrier height, depletion width and carrier concentration of the etched samples were compared with those of a control sample. Considerable eradication of induced damage was observed for the sample which was etched in CH/sub 4//H/sub 2/ mixture and was annealed prior to diode fabrication.<>     

Fabrication of a novel MOS diode by indium incorporation control for microelectronic applications

Control of the electronic parameters on a novel metal-oxide-semiconductor (MOS) diode by indium doping incorporation is emphasized and investigated. The electronic parameters, such as ideality factor, barrier height (BH), series resistance, and charge carrier density are extracted from the current-voltage (I-V) and the capacitance-voltage (C-V) characteristics. The properties of the MOS diode based on 4%, 6% and 8% indium doped tin oxide are largely studied. The Ag/SnO₂/nSi/Au MOS diode is fabricated by spray pyrolysis route, at 300℃ from the In-doped SnO₂ layer. This was grown onto n-type silicon and metallic (Au) contacts which were made by thermal evaporation under a vacuum@10^-5 Torr and having a thickness of 120 nm and a diameter of 1 mm. Determined by the Cheung-Cheung approximation method, the series resistance increases (334-534 Ω)with the In doping level while the barrier height (BH) remains constant around 0.57 V. The Norde calculation technique gives a similar BH value of 0.69 V but the series resistance reaches higher values of 5500 Ω. The indium doping level influences on the characteristics of Ag/SnO₂:In/Si/Au MOS diode while the 4% indium level causes the capacitance inversion and the device turns into p-type material.     

Schottky barriers on n-GaN grown on SiC

Characteristics of Schottky barriers fabricated on n-type GaN were investigated. The barriers were formed by vacuum thermal evaporation of Cr, Au, and Ni. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the barriers were measured in a wide temperature and current density range. Fundamental parameters (barrier height and built-in potential) of the Schottky barriers were determined. The dependence of the barrier ideality factor on doping concentration in GaN was measured. Correlation between the barrier height and metal work function was observed. The electron affinity for GaN was determined using both C-V and I-V characteristics. The current flow mechanism through the barriers is discussed.     

Current-voltage characteristics of p-Si/carbon junctions fabricated by pulsed laser deposition

Amorphous carbon/p-Si junctions were fabricated at different temperatures using KrF excimer laser (λ = 248 nm, pulsed duration 20 ns). The current-voltage measurements of the devices showed diode characteristics. The value of various junction parameters such as ideality factor, barrier height, and series resistance were determined from forward bias I-V characteristics, Cheung method, and Norde’s function. There was a good agreement between the diodes parameters obtained from these methods. The ideality factor of ∼1.12 and barrier height of ∼0.37 eV were estimated using current-voltage characteristics for films grown at room temperature.     

Schottky diode performance of an Au/Pd/GaAs device fabricated by deposition of monodisperse palladium nanoparticles over a p-type GaAs substrate

Au/Pd/p-GaAs Schottky diodes were fabricated by simple assembly of monodisperse Pd nanoparticles on a p-type GaAs semiconductor. Monodisperse 5-nm Pd nanoparticles were synthesized via reduction of palladium(II) acetylacetonate in oleylamine using a borane tert-butylamine complex. The Au/Pd/p-GaAs Schottky diodes provided a barrier height of 0.68 eV, which is higher than room-temperature values reported in the literature. A double distribution was observed for the barrier height for the Schottky diodes from I–V–T measurements. A decrease in temperature lowered the zero-bias barrier height and increased the ideality factor. These observations were ascribed to barrier height inhomogeneities at the interface that altered the barrier height distribution. Values of the series resistance obtained by the Norde method decreased with increasing temperature. Understanding the temperature dependence of the current–voltage characteristics of Au/Pd/p-GaAs devices might be helpful in improving the quality of Pd deposited on GaAs for future device technologies.     

ZnO/p-Si heterojunction photodiode by sol–gel deposition of nanostructure n-ZnO film on p-Si substrate

The electrical and photovoltaic properties of the nanostructure ZnO/p-Si diode have been investigated. The nanostructure ZnO/p-Si diode was fabricated using sol–gel spin coating method. The ideality factor and barrier height of the diode were found to be 3.18 and 0.78 eV, respectively. The obtained n ideality factor is higher than 2, indicating that the diode exhibits a non-ideal behavior due to the oxide layer and the presence of surface states. The nanostructure of the ZnO improves the quality of ZnO/p-Si interface. The diode shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 0.26 V and short-circuits current I_sc of 1.87×10^?8 A under 100 mW/cm². It is evaluated that the nanostructure ZnO/p-Si diode is a photodiode with the obtained electronic parameters.     

High-barrier Schottky diodes on p-type silicon due to dry-etching damage

It is known that the barrier height of Schottky diodes made to dry-etched silicon surfaces deviate from the barrier height values obtained for diodes fabricated on wet chemically etched or cleaved silicon. This effect, in cases where neither a substantial residue layer nor a surface film is formed, can be exploited to yield diodes on p-type Si that display barrier enhancement together with excellent diode ideality factors. It is shown that the barrier heights produced on p-type Si, by exploiting this effect of dry etching, can achieve a value of ∼0.75 eV which is ∼0.15 eV better than the best value reported for wet chemically etched or cleaved p-Si. When this barrier height value is attained, it is found to be independent of metallization. The same barrier height is achieved by two very different dry etching techniques: Ar⁺ion-beam etching (IBE) and CCl4reactive ion etching (RIE).     

Enhancement in electrical properties of Au/n-GaAs Schottky diodes exposed to 60Co gamma rays

The effect of γ-ray exposure on the electrical characteristics of Au/n-GaAs Schottky barrier diodes has been investigated using current–voltage and capacitance–voltage techniques. The results indicate that irradiation with a cumulative dose of 10 Mrad (Si) improves the electrical characteristics of the diode. The parameters like ideality factor, series resistance and reverse leakage current determined from the current–voltage data decreases, whereas the barrier height and rectification ratio increases upon irradiation. The effective barrier height deduced from the capacitance–voltage technique has also increased with irradiation. The irradiated diode shows a higher carrier concentration compared to the virgin diode. The observed overall improvement in the diode quality is attributed to the annealing effect of γ-rays.     

2700V4H-SiC结势垒肖特基二极管

在76.2 mm 4H-SiC晶圆上采用厚外延技术和器件制作工艺研制的结势垒肖特基二极管(JBS).在室温下,器件反向耐压达到2700 V.正向开启电压为0.8V,在VF=2V时正向电流密度122 A/cm2,比导通电阻Ron=8.8 mΩ·cm2.得到肖特基接触势垒qφв=1.24 eV,理想因子n=1.     

Electrical characteristics of schottky barriers on 4H-SiC: The effects of barrier height nonuniformity

Electrical properties, including current-voltage (I-V) and capacitance-voltage (C-V) characteristics, have been measured on a large number of Ti, Ni, and Pt-based Schottky barrier diodes on 4H-SiC epilayers. Various nonideal behaviors are frequently observed, including ideality factors greater than one, anomalously low I-V barrier heights, and excess leakage currents at low forward bias and in reverse bias. The nonidealities are highly nonuniform across individual wafers and from wafer to wafer. We find a pronounced linear correlation between I-V barrier height and ideality factor for each metal, while C-V barrier heights remain constant. Electron beam induced current (EBIC) imaging strongly suggests that the nonidealities result from localized low barrier height patches. These patches are related to discrete crystal defects, which become visible as recombination centers in the EBIC images. Alternative explanations involving generation-recombination current, uniform interfacial layers, and effects related to the periphery are ruled out.     

Effect of annealing temperature on the electrical characteristics of Platinum/4H-SiC Schottky barrier diodes

Pt/4H-SiC Schottky barrier diodes have been fabricated to investigate the effect of annealing on the electrical characteristics of the fabricated devices. The parameters such as barrier height, ideality factor and donor concentration were deduced from the current–voltage (I–V) and the capacitance–voltage (C–V) measurements at room temperature. Diodes showed non-ideal behaviour like high value of ideality factor and lower value of barrier height. A barrier height of 1.82?eV was obtained from C–V measurements and it was 1.07?eV when obtained from the I–V measurements with ideality factor 1.71 for as-deposited diodes at room temperature. The diodes, therefore, were annealed in the temperature range from 25°C to 400°C to observe the effect of annealing temperature on these parameters. Schottky barrier height and ideality factors were found to be temperature-dependent. After rapid thermal annealing upto 400°C, a barrier height of 1.59?eV from C–V measurements and the value of 1.40?eV from I–V measurements with ideality factor 1.12 were obtained. Barrier heights deduced from C–V measurements were consistently larger than those obtained from I–V measurements. To come to terms with this discrepancy, we re-examined our results by including the effect of ideality factor in the expression of the barrier height. This inclusion of ideality factor results in reasonably good agreement between the values of barrier height deduced by the above two methods. We believe that these improvements in the electrical parameters result from the improvement in the quality of interfacial layer.     

Correlation between barrier heights and ideality factors of H-terminated Sn/p-Si(1 0 0) Schottky barrier diodes

Schottky barrier diodes (SBDs) were prepared by evaporation on H-terminated p-Si(1 0 0) surfaces. The Si(1 0 0)-H surfaces were obtained by wet chemical etching in diluted hydrofluoric acid. The current–voltage (I–V) characteristics of real SBDs are described by using two fitting parameters that are the effective barrier height (EBH) and ideality factor n. They were determined from I–V characteristics of SBDs (30 diodes) fabricated under experimentally identical conditions. The obtained values of EBHs varied from 0.729 to 0.749 eV, and the values of ideality factors varied from 1.083 to 1.119. The results showed that both parameters of SBDs differ from one diode to another even if they are identically prepared. The EBH distributions were fitted by two Gaussian distribution functions, and their mean values were found to be 0.739 ± 0.003 eV and 0.733 ± 0.001 eV, respectively. The homogeneous barrier height of SBDs was found to be 0.770 eV from the linear relationship between EBHs () and ideality factors (n).     

无凹槽AlGaN/GaN肖特基势垒二极管正向电流输运机制

研究了无凹槽AlGaN/GaN肖特基势垒二极管(SBD)的正向电流输运机制。分别采用Ni/Au和TiN作为阳极金属材料制备了无凹槽AlGaN/GaN SBD,对比了两种SBD的直流特性。并通过测量器件的变温I-V特性,研究了器件的正向电流输运机制。结果表明,TiN-SBD(0.95 V@1 mA·mm^-1)与Ni/Au-SBD(1.15 V@1 mA·mm^-1)相比实现了更低的开启电压,从而改善了正向导通特性。研究发现两种SBD的势垒高度和理想因子都强烈依赖于环境温度,通过引入势垒高度的高斯分布模型解释了这种温度依赖性,验证了正向电流输运机制为与势垒高度不均匀分布相关的热电子发射机制。     

Effect of KOH treatment on the Schottky barrier inhomogeneity in Ni/n-GaN

The effect of KOH treatment on the Schottky barrier inhomogeneity in Ni/n-GaN Schottky diodes was investigated. It was observed that both the barrier heights and ideality factors varied from diode to diode with a linear relationship between barrier height and ideality factor, indicating the presence of a lateral inhomogeneity in the Schottky barrier. Simple extrapolation of the straight line obtained from the linear fitting to the barrier height versus ideality factor plot to the image-force controlled ideality factor produced the lateral homogeneous barrier heights, which were higher than those from current–voltage measurements. Furthermore, Gaussian fitting to the distribution of barrier heights exhibited the increased barrier height with the smaller standard deviation after KOH treatment, implying the improved barrier homogeneity. A possible explanation for this behavior can be an improvement of the Ni/n-GaN interface intrinsic properties, e.g., through a reduction of the surface states acting as low barrier region.     

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.     

Investigations on Au,Ag, and Al schottky diodes on liquid encapsulated czochralski grown n-GaAs〈100〉

The Schottky barrier heights of metals Au, Ag, and Al fabricated by vacuum vapor deposition on liquid encapsulated Czochralski (LEC) grown undoped ntype GaAs (n = 2.35 × 10¹⁵ cm⁻³) were measured with current-voltage (I-V) and capacitance-voltage (C-V) techniques. Good ohmic contacts were obtained through an after deposition anneal at 430°C for two minutes in an argon gas atmosphere. In the as-deposited state, Au, Ag, and Al gave very similar I-V characteristics for n-type substrates with the barrier height qϕ_b = 0.81-1.16 eV and ideality factor n = 1.02-1.15. The C-V measurement also gives the same value of barrier height. The distribution of carrier concentration along the radial distance of the wafer is of‘M’ shape. The Al/GaAs interfaces give the nonideal rectification behavior. The Au/GaAs interfaces give the near ideal rectification behavior. The barrier height of this interface is 0.89-0.92 eV and the ideality factor is about 1.10–1.19. Electron traps in the wafer have been found by constant capacitance deep level transient spectroscopy (CC-DLTS). Mainly the EL2, EL6, and EL3 (EI1) trap levels are prominent.