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This paper reports the design and application of test structures for extracting the resistance of features formed when fabricating evaporated platinum (Pt) thin film structures on patterned, sputtered tantalum nitride (TaN). The combination of these two layers is used to produce an integrated resistive sensor structure. Two resistive features were considered during the test structure design: firstly the contact resistance between the two metal layers and secondly, the additional resistance introduced in the upper metal layer due to step coverage effects. more...

The temperature (both measurement temperature and annealing temperature) and doping dependence of specific contact resistivity of Ti/Au/Pd/Au multilayer ohmic contact have been studied. The metallization for the contact involves the deposition of the composite metal layer Ti/Au/Pd/Au (200 A/600 A/400 A/500 A) on n-GaN. When the contacts were annealed at 800 °C for 30 s in air it was observed that the contact resistivity decreases with increasing doping concentration of the n-GaN, but increases with increasing measurement temperature of the contact. Within the framework of the transmission line measurement method, the specific contact resistivity for doping ND=6×1017 cm−3 was ρS=1.0×10−4 Ω cm2, and for doping ND=1020 cm−3 was ρS=2.38×10−9 Ω cm2. The resistivity ρS=1.0×10−4 Ω cm2 for ND=6×1017 cm−3 decreased to ρS≈8×10−7 Ω cm2 after a second annealing. Thus annealing, some times more than once, appears to play an important role in shaping the best value of the resistivity. The physical cause underlying the ... more...

The detection of doping dependent values like contact- and path resistances along nanowires (NWs) still proves to be rather challenging compared to planar structures. Unfortunately, the usually used and well established TLM (transmission line measurement) setup exhibits some drawbacks. Complex preliminary preparation steps and the necessity of ohmic contacts limit the investigation to certain semiconductor materials. The simultaneous determination of contact- and path resistances with an unknown distribution makes an analysis on complex structures like tapered nanowires very challenging. Our approach is the utilization of a multi-tip scanning tunneling microscope (MT-STM) as a four point prober, which allows the investigation of freestanding nanowires with an increased spatial resolution. Here, the used measurement setup allows a local separation of current injection and potential measurement and thus a highly precise determination of path resistances. Tapered p-doped GaAs-NWs were used to compare both techniques. Whereas the evaluation of the axial doping profile by MT-STM was rather simple, correction factors had to be introduced for the TLM measurement to calculate the specific resistances and transfer length. By comparing the results of both methods for the very same NW-sample, the precision and accuracy of MT-STM measurements was demonstrated. We found an agreement, which allows the conclusion that both methods exhibit advantages; however the MT-STM was determined as the more precise setup, which enables additional characterization capabilities, such as surface, temperature or light dependent measurements. more...

Thin (200 A) layers of SiO2 were deposited by plasma enhanced chemical vapor deposition onto GaN and InGaP patterned with transmission line measurement contact pads. The sheet resistance of n-GaN and n- and p-InGaP was measured as a function of N2O/SiH4 ratio, rf chuck power, pressure and substrate temperature during the SiO2 deposition. The sheet resistance ratio before and after the deposition varied from 0.7 to 1.2, reflecting a competition between mechanisms that decrease doping (hydrogen passivation, ion-induced deep traps) and those that increase it (creation of shallow donor states in n-type material through preferential ion of the group V elements, gettering of hydrogen in p-type material). Under most conditions, SiO2 deposition creates minimal changes to the electrical properties of GaN and InGaP. more...

We report both the device fabrication and characterization of InGaN/GaN single quantum well LEDs grown on sapphire substrates using multi-wafer MOVPE reactor. To improve current spreading of the LEDs, a self-aligned process is developed to define LED mesa that is coated with a thin, semi-transparent Ni/Au (40 Å/40 Å) layer. A detailed study on the ohmic contact resistance of Ni/Cr/Au on p-GaN versus annealing temperatures is carried out on transmission line test structures. It was found that the annealing temperatures between 300 to 500 °C yield the lowest specific contact resistance rc ( 0.016 Ω-cm2 at a current density of 66.7 mA/cm). Based on the extracted rc from the transmission line measurement, we estimate that the contact resistance of the p-type GaN accounts for ∼ 88% of the total series resistance of the LED. more...

There are numerous dielectric property characterization techniques available in the microwave regime each with its own uniqueness, advantages and disadvantages. The two-port completely-filled waveguide (transmission line) technique is a robust measurement approach which is well suited for solid dielectric materials. In this case, the dielectric material can be relatively easily machined to fit inside the waveguide and the subsequent measurement of the scattering parameters of this two-port device renders the dielectric properties of the material filling the waveguide. However, this technique is not well suited for measuring the dielectric properties of granular and liquid materials. These materials are used in the production of various composites which are increasingly replacing the use of metals in many environments. If this technique is directly applied to these types of materials, several approximations either in the measurement apparatus or the formulation must be made. To overcome this problem, this paper describes a modification to this measurement technique utilizing two dielectric plugs which are used to house the granular or the liquid dielectric material. In this approach no approximation to the measurement apparatus is made while the presence of the plugs are fully accounted for in the derivations. Using this technique, the dielectric properties of cement powder, corn oil, antifreeze solution and tap water, constituting low- and high-loss dielectric materials (granular and liquid) were measured. In addition, the important issue of measurement uncertainty associated with this technique is also fully addressed. The issue of optimal choice of various measurement parameters is also discussed as it relates to the measurement uncertainty. more...

A bilayer Nd/Al metallization structure has been deposited onto low pressure organometallic vapor phase epitaxy grown n-type GaN ( 1 × 1018 cm−3) by electron-beam evaporation. Ohmic metal contacts were patterned photolithographically for standard transmission line measurement, and then thermally annealed at temperatures ranging from 200 to 350°C and from 500 to 650°C using conventional thermal annealing (CTA) and rapid thermal annealing (RTA), respectively. The lowest values for the specify contact resistivity of 9.8 × 10−6 Ω−cm2 and 8 × 10−6 Ω−cm2 were obtained using Nd/Al metallization with CTA of 250°C for 5 min and RTA of 600°C for 30 s. Examination of the surface morphology using atomic force microscopy as a function of annealing temperature revealed that the surface roughness was strongly influenced by conventional thermal annealing, it was smooth in the temperature range from 550 to 650°C for rapid thermal annealing. Auger electron spectroscopy depth profiling was employed to investigate the metallurgy and interdiffusion of contact formation. more...

Optical modulators operating at near-infrared wavelengths are of interest for a variety of applications including bidirectional communications and optical interconnects. The fabrication of 1.06 {micro}m and 1.32 {micro}m operating wavelength strained-layer-superlattice vertical-cavity optoelectronic modulators requires the formation of a p-type ohmic contact to the InAlAs/InGaAs quarter-wave bottom mirror stack. In this study, BeAu and TiPtAu p-type ohmic contact metallization schemes were evaluated for use on molecular beam epitaxy (MBE) grown In{sub .10}Al{sub .90}As/In{sub .12}Ga{sub .88}As and In{sub .32}Al{sub .68}As/In{sub .33}Ga{sub .67}As device heterostructures. Recessed and nonrecessed transmission line measurement (TLM) structures were fabricated and evaluated as a function of rapid thermal anneal (RTA) temperatures over the range of 360 C--420 C. Atomic force microscopy (AFM) was used to determine the surface morphology of each sample for evidence of metal or material degradation. For contacts directly on InGaAs layers, TiPtAu contacts had relatively high specific contact resistance values of {rho}{sub c} {approximately} 3 {times} 10{sup {minus}4} {Omega}cm{sup 2} and displayed no dependence on the anneal. The BeAu contacts had minimum specific contact resistance values of {rho}{sub c} {approximately} 5 {times} 10{sup {minus}7} {Omega}cm{sup 2} but showed evidence of degradation at higher temperatures. Contacts directly made to InAlAs layers had minimum specific contact resistances of {rho}{sub c} {approximately} 4 {times} 10{sup {minus}5} {Omega}cm{sup 2} and were improved slightly with the addition of a thin GaAs layer. more...

Electrical contacts of Ni, NiSi, Cu, Au, Al, and Ti electrodes to an n-type nanocrystalline diamond film are studied at temperatures between room temperature and 500 °C in a vacuum by the transmission line measurement. Direct current-voltage characteristics measured between pairs of electrodes on the film show almost straight lines, typical of ohmic contacts, for all kinds of electrode materials. The measured series resistance is divided into resistance of the film, resistance of the electrode, and the contact resistance between the electrode and film. The Ni electrode has the lowest contact resistance, which decreases from about 380 to 200 mΩ cm2 with temperature. The contact resistance accounts for a large portion of the total resistance at low temperatures. The results confirm that the contact resistance has a close relation with the work function of electrodes such that the larger the work function, the lower the contact resistance. more...

In this paper, a new de-embedding technique based on open-pad and Transmission Line (TL) measurement is discussed. This technique can be used as an alternative to the conventional de-embedding approaches in order to characterize on-chip passives in the millimeter wave range of frequencies. Using open-pad measurement, parallel parasitics are extracted and removed in the first step. Cross-talk parasitics between two pads that are kept at a constant distance can be assumed constant, and thus both cross-talk and parallel parasitics can be removed. Subsequently, the transfer function matrix of a single-ended TL is used to de-embed series parasitics from the measurement results. The measurement results are in a close agreement with the simulations up to 110 GHz. more...

The Pd‐In‐Ge nonspiking Ohmic contact to n‐GaAs has been investigated using the transmission line, the Kelvin, and the Cox and Strack structures. It has been found that a layered structure of Pd/In/Pd/n‐GaAs with 10–20 A of Ge imbedded in the Pd layer adjacent to the GaAs can lead to a hybrid contact. When the Ohmic formation temperature is above 550 °C, a layer of InxGa1−xAs doped with Ge is formed between the GaAs structure and the metallization. When the Ohmic formation temperature is below 550 °C, a regrown layer of GaAs also doped with Ge is formed at the metallization/GaAs interface. The contact resistivity of 2–3×10−7 Ω cm2 for this contact structure is nearly independent of the contact area from 900 to 0.2 μm2. Low‐temperature Ohmic characteristics and thermal stability are also examined. more...

Reproducibility of transmission line (TL) measurement of bipolar current-voltage (I-V) characteristics of grounded gate MOSFET's has been examined. It is observed that the reproducibility is related to the duration of the pulses generated by the transmission line, and a longer pulse duration gives a better reproducibility. For a short pulse duration, it is more difficult to reproduce the I-V characteristics in the triggering region than in other regions (i.e., the pretriggering and snapback regions). more...

The contact resistance of metal/graphene is becoming a major limiting factor for graphene devices. Among various kinds of contact resistance test methods, the transmission line model is the most common approach to extract contact resistance in graphene devices. However, experiments show that in some cases there exists large inaccuracy and instability using this method. In this study, we added a cross-bridge structure at the terminal of the transmission line as a supporting test. This modified transmission line measurement structure can easily compare not only the transmission line and Kelvin contact resistance, getting a more reliable value, but also the other contact-related parameters, such as specific contact resistivity, transfer length and the graphene sheet resistance under and outside contact metal at the same time. The new measurement test is very helpful in enabling us to study the contact property accurately. The specific contact resistivity in our experiment is in the range of 2.0 × 10(-6) Ω · cm(2) and 3.0 × 10(-6) Ω · cm(2) at room temperature. With the temperature decreasing from 290 K to 60 K, the transfer length fluctuates around 1.7 μm, and the specific contact resistivity reduces to less than 2.0 × 10(-6) Ω · cm(2). more...

International audience; The power dissipation in a semiconductor device usually generates a self-heating effect, which becomes very significant for gallium nitride power applications. The operating temperature of these devices increases significantly, and the transport properties are then degraded (IEEE Electron Device Lett., vol. 24, p. 375, 2003; IEEE Electron Device Lett., vol. 49, p. 1496, 2002; IEEE Trans. Electron Devices, vol. 52, p. 1683, 2005). Taking heating effects into account explains the physical phenomena observed in experiments, due in particular to the fact that temperature greatly affects the velocity. In this paper, numerical simulations are carried out to study the influence of thermal effects on the static characteristics of GaN transmission line measurement (TLM) model structures. A transport-thermal model is thus developed in order to take into account both the electrical and the thermal phenomena in a coupled way. This paper uses GaN TLMs on sapphire substrates. Simulations have shown that the saturation current is reached for electric fields much lower than the saturation electric field, thus confirming the experimental results more...

One of the major challenges affecting the performance of Npn AlGaN/GaN heterojunction bipolar transistors (HBTs) is the high base access resistance, which is comprised of the base contact resistance and the base bulk resistance. A novel concept is proposed to reduce the base access resistance in Npn AlGaN/GaN HBTs by employing polarization-enhanced contacts and selective epitaxial growth of the base and emitter. In addition, this technique reduces the exposed base surface area, which results in a lower surface recombination current. Such a structure would enable better performance of AlGaN/GaN HBTs in terms of higher current gain and a lower offset voltage. Theoretical calculations on polarization-enhanced contacts predict p-type specific contact resistance lower than 10-5 Ωcm2. Experimental results using transmission line measurement (TLM) technique yield specific contact resistances of 5.6×10-4 Ωcm2 for polarization-enhanced p-type contacts and 7.8×10-2 Ωcm2 for conventional p-type contacts. more...

We analyze three accurate broadband techniques for measuring the complex permittivity of dielectric substrates using coplanar waveguide transmission-line measurements and demonstrate good agreement with single-frequency cavity measurements. more...

We study the current-voltage characteristic of AuGeNi contacts made on arsenic-ion-implanted GaAs by using the transmission line measurement. The GaAs:As + samples were rapid-thermal annealed at 600 degrees C for ranged from 30 to 300 seconds. The mechanism responsible for the large dark current in the as-implanted GaAs:As + is attributed to the hopping conduction of trapped carriers among the dense deep-level defects. After annealing, the defect density gradually reduces and the perfection of crystal lattice recovers. This results in the evanescence of the hopping conduction and the increasing resistance for GaAs:As + . A turning point at contact spacing between 10 micrometers and 15 micrometers on the curve of resistance as a function of contact spacing is discussed. The change in the contact resistance measured at larger spacing is dominated by bulk GaAs substrate since that the electric field may distribute deeper into the substrate as the contact spacing become larger. The measured resistance at below the turning point is primarily dominated by the implanted GaAs:As + layer. The contact resistances are estimated to be ranged from 7.8 X 10 4 to 8 X 10 9 (Omega) as the annealing time increases from 0 to 300 seconds, respectively. The sheet resistances are increased from 2.4 X 10 4 to 2 X 10 10 (Omega) /$DAL, and the specific contact resistances are increased form 13.8 to 1.6 X 10 5 (Omega) -cm 2 as the annealing time increases. In comparison, the characteristic parameters of the GaAs:As + annealed for 5 minutes is already better than that of a semi-insulating GaAs substrate. These observations facilitate us to obtain the optimized process condition of an ultra-high resistive GaAs:As + material for fabrication of ultrafast optoelectronic switches. more...

The interfaces between metals and semiconductors are very crucial to the performance and reliability of solid-state devices. At the moment information on the interfaces between metals and group III-nitride semiconductors are very rare. In this study, linear I-V characteristics of titanium and aluminum to A1xIn1-xN of three different composition (x=0.18, 0.50,0.85) were obtained exhibiting ohmic characteristics. Specific contact resistance of these metals to A1.18In.82N and Al.5In.5N was measured by transmission line measurement. Interdiffusion between the metals and the semiconductors, induced by annealing in N2 ambient, was determined using RBS and thermal stability was evaluated. more...

A programme of measurement to establish traceable complex permittivity values for dielectric reference liquids at frequencies up to 5 GHz and at temperatures in the interval 10–50 °C has been completed and the results have been tabulated in a National Physical Laboratory Report (NPL Report MAT 23, 2009). The liquids measured were high-purity methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, ethanediol and dimethyl sulfoxide. This paper describes the high-frequency coaxial cell measurement techniques that were used to obtain these data and the approach taken to uncertainty evaluation in this programme of work. Measurement results are summarized and compared with data from the scientific literature. Dielectric relaxation equations (Debye, double-Debye and Davidson–Cole) have been fitted to the data, to allow users to obtain best-fit values of complex permittivity at any frequency up to 5 GHz. A Monte Carlo modelling method has been used to evaluate permittivity uncertainties—this incorporates models of the behaviour of systematic measurement error. This uncertainty evaluation enables the dielectric data to be presented in a way that should maximize their utility. more...

We present a novel passivating contact structure based on a nanostructured silicon-based layer. Traditional poly-Si junctions feature excellent junction characteristics but their optical absorption induces current losses when applied to the solar cell front side. Targeting enhanced transparency, the poly-Si layer is replaced with a mixed-phase silicon oxide/silicon layer. This mixed-phase layer consists of an amorphous SiO x matrix with incorporated Si filaments connecting one side of the layer to the other, and is referred to as nanocrystalline silicon oxide (nc-SiO x ) layer. We investigate passivation quality, measured as saturation current density, and nanostructural changes, characterized by Raman spectroscopy and transmission electron microscopy, carefully studying the influence of annealing dwell temperature. Excellent surface passivation on n-type and also p-type wafers is shown. An optimum annealing temperature of 950 °C is found, resulting in a saturation current density of 8.8 fA cm −2 and 11.0 fA cm −2 for n-type and p-type wafers, respectively. Even before forming gas annealing, emitter saturation current densities of 27.9 fA cm −2 (n+/n junction) and 32.0 fA cm −2 (n+/p junction) are reached. Efficient current extraction is presented with specific contact resistivities of 86 mΩ cm 2 on n-type wafer and 19 mΩ cm 2 on p-type wafers, respectively. High-resolution transmission electron microscopy reveals that the layer stack consists of intermixed SiO x and Si phases with the Si phases being partly crystalline already in the as-deposited state. Thermal annealing at temperatures ≥850 °C further promotes crystallization of the Si-rich regions. The addition of the SiO x phase enhances the thermal stability of the contact and should allow to tune the refractive index and improve transparency, while still providing efficient electrical transport through the crystalline Si phase, which extends throughout almost the entire contact. more...

The structural and electrical properties of silicon-implanted borosilicate glass (BSO:Si+) are studied. The nearly amorphous phase of as-implanted BSO:Si+ with a weak and broadened X-ray diffraction peak transforms into crystallite phases with associated peaks positioned at azimuth angles of 29° and 14° after thermal annealing. These peaks correspond to (111)-oriented Si nanocrystals of 0.6–0.8 nm size and the regrown (021)-oriented BSO host, respectively. The intensity of the photoluminescent (PL) peak of the BSO:Si+ centered at 520 nm is found to decrease due to both the elimination of the radiative defects and the precipitation of Si nanocrystals, however, nanocrystal-related PL is not initiated even after low-temperature and long-term (> 4 h) annealing. Relatively high leakage current Schottky diodes with contact patterns for transmission line measurement (TLM) made on as-implanted BSO:Si+ reveal the defect-enhanced current transport mechanism. After annealing at 500°C for 60 min or longer, the leakage current of the BSO:Si+ diode dramatically decreases by at least two orders of magnitude. The current–voltage analysis attributes the disappearance of the resonant tunneling behavior of the TLM diode made on as-implanted BSO:Si+ with negative differential resistance to the annealing-induced reduction of radiative defect concentration. more...

Ohmic contacts were studied on structures which utilize the fact that for InAs surfaces Fermi level pinning occurs at or in the conduction band. It was found that an epitaxial layer of n‐Ga1−xInxAs grown by molecular beam epitaxy on n‐GaAs which is graded in composition from x = 0 at the GaAs interface to 0.8?x?1.0 at the surface will produce a structure with a nearly zero Schottky barrier height for the metal–Ga1−xInxAs interface and hence a low resistance ohmic contact. A transmission line measurement of non‐alloyed contact resistance of 5×10−7 more...

Measurement of ferromagnetic resonance linewidths over a range of microwave frequencies is facilitated by the use of a nonresonant waveguide system. The loading effect encountered in such a transmission line system, however, becomes significant when the linewidth is less than a few tens of oersteds. The effect of transmission line loading was avoided by the use of an automatic compensation network. more...