Structural and electrical properties of Au and Ti/Au contacts to n-type GaN

Au and Ti/Au layers were deposited on n-GaN. The samples were annealed at 400, 700 and 900 °C for 10 min in vacuum. The contacts were rectifying up to 700 °C and the highest Schottky barrier height of 1.07 eV was obtained for an Au single layer by current-voltage measurements. A binary phase of Au₂Ga was identified at the interface of the n-GaN/Ti/Au contact after annealing at 900 °C. The formation of Ti₂N and TiN (twin) phases epitaxially grown on GaN was also observed in the same contact as well as some gold diffusion into the topmost region of the GaN epilayer.     

SiC上Ti/Ni/Au多层金属的欧姆接触特性

采用Ti/Ni/Au多层金属在高掺杂n型4H-SiC外延层上制作了欧姆接触测试图形,通过传输线法(Transmission Line Method,TLM)测量得到的最小比接触电阻为1.4×10-5Ω·cm2,经500℃N2老化后接触电阻大约有一个数量级的增加并保持稳定.     

Au和Ni掺杂n型硅材料的制备及其热敏特性

为了制备高B低阻的硅单晶热敏材料,采用开管涂源的方法,对n型单晶硅进行Au、Ni两种过渡族金属的双重高温掺杂,得到对温度敏感的补偿硅材料,并对其进行测试和分析.掺杂后得到的硅单晶热敏材料,其导电类型仍为n型,且电阻率较低,为欠补偿,测试结果表明其常温电阻率ρ25=64～416Ω·cm,温度敏感系数(B值)在5300K左右;根据半导体中深能级杂质理论推导计算得到的材料的B值,与实验值基本一致.     

The formation of disilicides from bilayers of Ni/Co and Co/Ni on silicon: Phase separation and solid solution

Bilayers of Ni/Co and Co/Ni were deposited onto silicon by means of electron beam evaporation. The annealing behavior was investigated as a function of time in the temperature range 475–550 °C by Rutherford backscattering spectrometry, Auger electron spectroscopy, scanning electron microscopy and X-ray analysis. In this temperature range it is observed that the disilicide (solid solution) nucleates and grows from a film containing both the monosilicide of cobalt and that of nickel. These nearly insoluble monosilicides are separated into layers; the disilicide grows from the interface between the NiSi and the CoSi phase. If there are equal amounts of the two metals this interface is located approximately midway between the upper surface and the silicon substrate. The disilicide grows simultaneously both toward the free surface and toward the silicon substrate. The growth kinetics of the disilicide have been analyzed and are found to be complex. The general behavior of the disilicide formation is found to be similar to that found for Co-Ni alloy films and as for the latter case indicates the primacy of nucleation over diffusion as the controlling mechanism in the disilicide formation. The site of nucleation of the disilicide at the NiSi-CoSi interface is explained by a model based on (a) the phase separation of the two monosilicides and (b) the high entropy of mixing of the mixed disilicide. In agreement with this model the nucleation of the mixed disilicides is shown to occur at temperatures much lower than those for either CoSi₂ or NiSi₂. Given the common crystal structure and the almost identical lattice parameters, the mutual solubilities of CoSi₂ and NiSi₂ follow from elementary concepts of alloy phase theory. However, the behavior of the monosilicides is more unexpected. The limited solubilities of the monosilicides, CoSi and NiSi, in each other are shown to result from specific features of the electronic band structure of these two compounds, features which are not found for example in the isomorphous disilicides CoSi₂ and NiSi₂.     

Interdiffusion phenomena in Au/Cu and Cu/Au bilayers

The microstructures of epitaxial deposits of (111) Cu/(111) Au and (111) Au/(111) Cu at various stages of interdiffusion are described. The most prominent microstructural features of Au/Cu films (where gold deposition occurred at temperatures less than 400 °C) were (Matthews) coincidence lattice misfit dislocations lying along < 1$\text{1}$0 > directions in the film plane with $\text{|b| =}\text{a}\text{2}\text{< 110 >}$ directed out of the film plane. Their spacings, transmission electron microscopy (TEM) hot stage behavior and generation mechanisms are discussed. For more severe diffusion anneals, the coincidence dislocation density decreased and hexagonal networks identified as ( van der Merwe) natural lattice misfit dislocations became resolvable. They are edge type (lying along <11$\text{2}$> directions in the film plane) with $\text{|b| =}\text{a}\text{2}\text{< 1}\text{1}\text{0 >}$. For the case of Cu/(111) Au bilayers, copper deposited at and below 315 °C with a 20 min anneal again showed coincidence misfit networks. Higher temperature deposition of copper (or hot stage annealing) resulted in natural lattice misfit dislocations in the microstructure. The densities of both types of dislocations were determined and their TEM hot stage behavior was investigated. The method by which the two networks contribute to the relief of misfit strain in both bilayers is discussed.     

Sulfonated polyaniline/n-type silicon junctions

Sulfonated polyaniline thin films are deposited on n-type silicon substrates at a rate of 1.2 nm/h. The sulfonated polyaniline/n-Si junctions were characterized by current–voltage and capacitance–voltage measurements and present Schottky barrier behavior with an energy barrier ranging from 0.9 to 1.3 eV, depending on sulfonated polyaniline film thickness and method.     

Ni/Au、Pd/Au与p-AlGaN材料的接触特性

在AlGaNpin型日盲紫外探测器结构中的p-AlGaN层上生长了Ni/Au和Pd/Au,并在600～850℃温度下进行快速热退火,测量其退火前后传输线模型中各金属接触间的电学性质。实验发现,Ni/Au与Pd/Au在p-AlGaN上表现出了不同的接触性能。为了更好的说明金属与p-AlGaN材料接触之间在退火后电流的变化,还测量了p-AlGaN材料裸片两点之间I-V曲线在退火前后的变化。实验表明,比起Ni/Au来,Pd/Au在p-AlGaN材料上制备欧姆接触具有一定的优势,并在文中进行了分析。     

The influence of rapid thermal annealing on electrical and structural properties of Pt/Au Schottky contacts to n-type InP

The electrical and structural properties of Pt/Au Schottky contacts to n-InP have been investigated in the annealing temperature range of 200–500 °C by current–voltage (I–V), capacitance–voltage (C–V), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) measurements. The barrier height of as-deposited Pt/Au Schottky contact is found to be 0.46 eV (I–V) and 0.68 eV (C–V). For the contacts annealed at 300 °C, the barrier height is increased to 0.51 eV (I–V) 0.89 eV (C–V). Further increase in annealing temperature up to 500 °C, the barrier height has been found to decrease to 0.49 eV (I–V) 0.82 eV (C–V) from those values obtained at 300 °C. It has been found that the electrical characteristics are significantly improved for Pt/Au Schottky contacts upon annealing at 300 °C. Based on the Auger electron spectroscopy and X-ray diffraction results, the formation of Pt–In and Au–In intermetallic compounds at the interface may be the reason for the increase of barrier height after annealing at 300 °C for Pt/Au Schottky contacts. From the atomic force microscopy (AFM) results, it is evident that the surface becomes smooth with RMS roughness of 16.91 nm for the Pt/Au Schottky contacts after annealing at 500 °C compared to the 300 °C annealed sample (RMS roughness of 17.33 nm).     

Thermal annealing behaviour on Schottky barrier parameters and structural properties of Au contacts to n-type GaN

We have investigated the thermal annealing effects on electrical and structural properties of Au Schottky contacts on n-type GaN using current–voltage (I–V), capacitance–voltage (C–V), X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) measurements. The calculated Schottky barrier height of the as-deposited Au/n-GaN diode was 0.85 eV (I–V) and 1.4 eV (C–V), respectively. However, after annealing at 300 °C it was found that the Schottky barrier height (SBH) slightly decreased to 0.77 eV (I–V) and 1.24 eV (C–V), and then slightly increased to 0.83 eV (I–V) and 1.30 eV (C–V) when the contact was annealed at 400 °C. With further increase in annealing temperature to 500 °C the barrier height was decreased and the respective values are 0.73 eV (I–V) and 1.02 eV (C–V). Based on the X-ray diffraction and RBS results, the formation of gallide phases at the Au/n-GaN interface could be the reason for variation in the Schottky barrier heights upon annealing temperatures.     

Influence of tetramethylammonium hydroxide treatment on the electrical characteristics of Ni/Au/GaN Schottky barrier diode

The effect of tetramethylammonium hydroxide (TMAH) treatment on the electrical properties of Ni/Au/GaN Schottky diodes have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) techniques. The barrier heights and ideality factors measured from I–V characteristics are found to be 0.70 eV and 1.32 for without TMAH treatment, and 0.78 eV and 1.14 for with TMAH treatment, respectively. Cheung method is used to measure the series resistance and barrier height of the Schottky diodes, and the barrier height consistency is checked using the Norde method. The magnitude of interface state density for the diodes without and with TMAH treatment are varied from 7.45 × 10¹³ eV⁻¹ cm⁻² to 6.09 × 10¹² eV⁻¹ cm⁻² and 4.03 × 10¹³ eV⁻¹ cm⁻² to 1.79 × 10¹² eV⁻¹ cm⁻² in the below the conduction band from E_C-0.19 eV to E_C-0.63 eV and E_C-0.22 eV to E_C-0.73 eV. Based on the results, the TMAH treatment effectively removes of surface oxide (Ga_xO_y) layer, formed due to the incorporation of the residual oxygen with Ga atom at the GaN surface during the plasma etching. The decrease in interface state density at the Ni/Au/GaN interface could be the reason for the improvement in the electrical properties.     

Influence of thermal treatment on the formation of ohmic contacts based on Ti/Al/Ni/Au metallization to n-type AlGaN/GaN heterostructures

Interfacial reactions between Ti/Al/Ni/Au metallization and GaN(cap)/AlGaN/GaN heterostructures at various annealing temperatures ranging from 715 to 865 °C were studied. Electrical current-voltage (I?CV) characteristics, van der Pauw Hall mobility measurements and surface topography measurement with atomic force microscopy (AFM) were performed. The ohmic metallizations were annealed at various temperatures in a rapid thermal annealing system and the annealing time of 60 seconds was kept for all samples. To study the influence of the parameters of annealing process on the properties of the 2 dimensional electron gas (2DEG) the van der Pauw Hall mobility measurement was used. Interfacial reactions between the contact metals and heterostructures were analyzed through depth profiles of secondary ion mass spectroscopy. It was observed that transition from nonlinear to linear I-V behavior occurred after the annealing at 805 °C. For the studied samples, the most promising results were obtained for the annealing temperature of 805 °C. This temperatue ensured not only low contact resistance but also made possible to preserve the 2DEG.     

Microstructural and electrical characteristics of rapidly annealed Ni/Mo Schottky rectifiers on cleaned n-type GaN (0001) surface

We have investigated the electrical and microstructural properties of Ni/Mo Schottky rectifiers to n-type GaN by current–voltage (I–V) and transmission electron microscopy (TEM) before and after annealing at 600 °C. The obtained barrier height for as-deposited Ni/Mo contact is 0.66 eV. It is observed that the barrier height increases with annealing temperature up to 500 °C, reaching a maximum value of 0.75 eV at this temperature. However, the Schottky barrier height of the Ni/Mo Schottky contact slightly decreased to 0.67 eV (I–V) when the contact was annealed at 600 °C. According to the HRTEM, STEM and EDX analysis, the formation of Ga-Ni interfacial layer at the interface results in the accumulation of gallium vacancies near the surface of the GaN layer. This could be the reason for increase in barrier heights upon annealing at elevated temperatures. The variation in the measured barrier height after annealing at 600 °C may be due to the formation of native oxide layer at the interface compared to the 500 °C annealed contact.     

Thermally stable and low-resistance W/Ti/Au contacts to n-type GaN

We report on the formation of thermally stable and low-resistance Ti/Au-based ohmic contacts to n-type GaN (4.0 × 10¹⁸ cm⁻³) by using a W barrier layer. It is shown that the electrical characteristic of the sample is considerably improved upon annealing at 900 °C for 1 min in a N₂ ambient. The contacts produce the specific contact resistance as low as 6.7 × 10⁻⁶ Ω cm² after annealing. The Norde and current–voltage methods are used to determine the effective Schottky barrier heights (SBHs). It is shown that annealing results in a reduction in the SBHs as compared to that of the as-deposited sample. Auger electron spectroscopy (AES), scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD) examinations show that nitride and gallide phases are formed at the contact/GaN interface. Based on the AES, STEM and XRD results, a possible ohmic formation mechanism is described and discussed.     

Raman scattering and photoluminescence study of porous silicon formed on n-type silicon

We report Raman scattering and photoluminescence studies on porous silicon film formed on n-type silicon. The Raman spectra over the sample surface exhibit considerable variation whereas the photoluminescence spectra are practically identical. Our results indicate that, well inside the film surface, it consists of spherical nanocrystals of typical diameter ≈ 100Å, while on the edge these nanocrystals are ? 300Å. We further observe that there is no correlation between the photoluminescence peak position and the nanocrystal diameter. This suggests that the origin of the photoluminescence is due to radiative recombination between defect states in the bulk as well as on the surface of the nanocrystal.     

Photoconductivity studies of n-type hydrogenated amorphous silicon and microcrystalline silicon

Photoconductivity techniques serve as useful tools for the characterization of amorphous and microcrystalline silicon. From the link between the majority carrier mobility–lifetime product from steady-state photoconductivity and the position of the Fermi level, useful insight can be gained when comparing sample properties. The temperature dependence of the minority carrier mobility–lifetime product implies that the band-tail region of the density-of-states (DOS) is steeper in microcrystalline silicon than in amorphous silicon. Transient and modulated photoconductivity determine the DOS in the upper half of the band gap, for which we find an exponential variation. We indicate that the Fermi level or quasi-Fermi level impose limitations on the DOS extraction from the measured data. In samples in which the Fermi level is shifted towards the conduction band, the DOS calculation then yields values that are too low.     

A.c. electrical properties of Au/CIAIPc/Au device

The a.c. electrical properties of chloro aluminum phthalocyanine (CIAIPc) thin film sandwiched between two gold (Au) electrodes have been studied in the frequency range 10 Hz to 100 kHz and the temperature range 293 K to 400 K. The a.c. conductivity Σ(Ω) was found to vary as Ω ^s , with the index s < 1, indicating that a hopping process of conduction is dominant at low temperatures and higher frequencies. At higher temperatures and lower frequencies a free carrier conduction mechanism is likely to dominate. At low temperatures the capacitance of the Au-CIAIPc-Au device is temperature-insensitive and increases rapidly above 300 K. The capacitance and loss tangent decreased with frequency and increased with temperature. Such characteristics were found to be in good agreement with the devices Au/CuPc/Au and Au/PbPc/Au.     

Single p-type/intrinsic/n-type silicon nanowires as nanoscale avalanche photodetectors

We report the controlled synthesis of axial modulation-doped p-type/intrinsic/n-type (p-i-n) silicon nanowires with uniform diameters and single-crystal structures. The p-i-n nanowires were grown in three sequential steps: in the presence of diborane for the p-type region, in the absence of chemical dopant sources for the middle segment, and in the presence of phosphine for the n-type region. The p-i-n nanowires were structurally characterized by transmission electron microscopy, and the spatially resolved electrical properties of individual nanowires were determined by electrostatic force and scanning gate microscopies. Temperature-dependent current-voltage measurements recorded from individual p-i-n devices show an increase in the breakdown voltage with temperature, characteristic of band-to-band impact ionization, or avalanche breakdown. Spatially resolved photocurrent measurements show that the largest photocurrent is generated at the intrinsic region located between the electrode contacts, with multiplication factors in excess of ca. 30, and demonstrate that single p-i-n nanowires function as avalanche photodiodes. Electron- and hole-initiated avalanche gain measurements performed by localized photoexcitation of the p-type and n-type regions yield multiplication factors of ca. 100 and 20, respectively. These results demonstrate the significant potential of single p-i-n nanowires as nanoscale avalanche photodetectors and open possible opportunities for studying impact ionization of electrons and holes within quasi-one-dimensional semiconductor systems.     

Recrystallization behaviour and electrical properties of germanium ion implanted polycrystalline silicon films

The recrystallization behaviour of undoped and phosphorus-doped polycrystalline silicon films amorphized by germanium ion implantation at doses ranging from 1 × 10¹⁵ to 1 × 10¹⁶cm^-2 are investigated, and the electrical properties of phosphorus-doped films after recrystallization are studied. The phosphorus doping concentration ranges from 3 × 10¹⁸ to 1 × 10²⁰cm^-3. It is found that the nucleation rate decreases for undoped films and increases for phosphorus-doped films with increasing germanium dose; the growth rates decrease for both doped and undoped films. The decrease in nucleation rate is caused by the increase in implantation damage. The decrease in growth rate is considered to be due to the increase in lattice strain. The grain size increases with germanium dose for undoped films, but decreases for phosphorus-doped films. The dependence of the electrical properties of the recrystallized films as a function of phosphorus doping concentration with different germanium doses can be explained in terms of the grain size, crystallinity and grain boundary barrier height.     

n-type Polycrystalhne Si Thick Films Deposited on SiN_x-coated Metallurgical Grade Si Substrates

For photovoltaic applications,low-cost SiN_x-coated metallurgical grade silicon(MG-Si) wafers were used as substrates for polycrystalline silicon(poly-Si) thick films deposition at temperatures ranging from 640 to880 ℃ by thermal chemical vapor deposition.X-ray diffraction and Raman results indicated that high-quality poly-Si thick films were deposited at 880 ℃.To obtain n-type poly-Si,the as-deposited poly-Si films were annealed at 880 ℃ capped with a phosphosilicate glass.Electrical properties of the n-type poly-Si thick films were investigated by four-probe and Hall measurements.The carrier concentration and electron mobility of the n-type poly-Si film was estimated to be 1.7 x 10~(19) cm~(-3) and 68.1 cm~2 V~(-1) s~(-1),respectively.Highquality poly-Si thick films deposited on MG-Si wafers are very promising for photovoltaic applications.