Specific Contact Resistance Ρc Research Articles

A Modified Scheme to Reduce the Specific Contact Resistivity of NiSi/Si Contacts by Means of Dopant Segregation Technique

In this work, a proposed modified scheme to reduce the specific contact resistivity (ρc) of NiSi/Si contacts by means of dopant segregation (DS) technique is presented. In contrast to conventional scheme in which NiSi is formed at 500°C/30s followed by B or As implantation and subsequently drive-in anneals to induce DS at the NiSi/Si interface, this modified scheme consists of the following steps: (1) Deposited Ni films undergo a rapid thermal anneal (RTA1) at a low temperature 300°C/60 s to form Ni-rich silicide i.e. Ni2Si instead of NiSi followed by the removal of un-reacted Ni; (2) implant boron (B) or arsenic (As) into pre-formed Ni-rich silicide and perform RTA2 at 500–700°C/30 s to transform Ni-rich silicide to NiSi as well as to induce DS at the NiSi/Si interface. For NiSi/n- and p-Si contacts, the ρc values at 600°C drive-in anneal temperature is reduced from 6.5 × 10−9 Ω-cm2 and 1.3 × 10−7 Ω-cm2 using conventional scheme to 5.1 × 10−9 Ω-cm2 and 1.0 × 10−7 Ω-cm2 using modified scheme respectively, with the presence of As or B DS. Enhanced DS at the NiSi/Si interface accounts for improved ρc in the modified scheme. This proposed modified scheme can be also applied to reduce the ρc values in the state-of-the-art NiGe/Ge contacts.

Low Resistance Ohmic Contact for ZnSb Thin Film

To further improve the performance and power density of thermoelectric devices, the size of the device needs to be scaled down from macroscale to microscale. Different from the macroscale device, the specific contact resistivity ρc of the metal contact to the microscale device becomes a key point to the device's efficiency. In this study, a P type ZnSb thin film was deposited on glass substrate using a radio frequency magnetron sputtering system, followed by annealing at 325°C in an Ar atmosphere. X-ray diffraction, scanning electron microscopy, and the Hall measurement system were utilized for characterization of the ZnSb. The ohmic contact properties of metallic Co and Mo on the annealed ZnSb thin films were investigated, indicating that metallic Co has a lower specific contact resistivity ρc to ZnSb. The effect of a diluted HCl-etch prior to Co electrode deposition was also studied. The results show that a HCl-etch is effective for the reduction of the ρc. The dependence of ρc on the annealing temperature was also studied. Through HCl-etch and annealing at 200°C, specific contact resistivity ρc as low as 10−7 Ω cm2 is successfully obtained on the Co electrode, providing a good method to fabricate a highly efficient ZnSb-based micro device.

Low p-type contact resistance by field-emission tunneling in highly Mg-doped GaN

Mg-doped GaN with a net acceptor concentration (NA-ND) in the high 1019 cm−3 range was grown using ammonia molecular-beam epitaxy. Electrical properties of NiO contact on this heavily doped p-type GaN were investigated. A potential-barrier height of 0.24 eV was extracted from the relationship between NA-ND and the specific contact resistivity (ρc). We found that there is an optimum NA-ND value of 5 × 1019 cm−3 for which ρc is as low as 2 × 10−5 Ω cm2. This low ρc is ascribed to hole tunneling through the potential barrier at the NiO/p+-GaN interface, which is well accounted for by the field-emission model.

The Effect of Interfacial Dipoles on the Metal-Double Interlayers-Semiconductor Structure and Their Application in Contact Resistivity Reduction.

We demonstrate the contact resistance reduction for III-V semiconductor-based electrical and optical devices using the interfacial dipole effect of ultrathin double interlayers in a metal-interlayers-semiconductor (M-I-S) structure. An M-I-S structure blocks metal-induced gap states (MIGS) to a sufficient degree to alleviate Fermi level pinning caused by MIGS, resulting in contact resistance reduction. In addition, the ZnO/TiO2 interlayers of an M-I-S structure induce an interfacial dipole effect that produces Schottky barrier height (ΦB) reduction, which reduces the specific contact resistivity (ρc) of the metal/n-type III-V semiconductor contact. As a result, the Ti/ZnO(0.5 nm)/TiO2(0.5 nm)/n-GaAs metal-double interlayers-semiconductor (M-DI-S) structure achieved a ρc of 2.51 × 10-5 Ω·cm2, which exhibited an ∼42 000× reduction and an ∼40× reduction compared to the Ti/n-GaAs metal-semiconductor (M-S) contact and the Ti/TiO2(0.5 nm)/n-GaAs M-I-S structure, respectively. The interfacial dipole at the ZnO/TiO2 interface was determined to be approximately -0.104 eV, which induced a decrease in the effective work function of Ti and, therefore, reduced ΦB. X-ray photoelectron spectroscopy analysis of the M-DI-S structure also confirmed the existence of the interfacial dipole. On the basis of these results, the M-DI-S structure offers a promising nonalloyed Ohmic contact scheme for the development of III-V semiconductor-based applications.

Simultaneous ohmic contacts to p- and n-type 4H-SiC by phase segregation annealing of co-sputtered Pt-Ti

A new concept, Phase Segregation Annealing (PSA), was investigated for implementing simultaneous ohmic contacts (SOCs) to p- and n-type 4H-SiC. Test structures with selected ratio compositions of co-sputtered Pt:Ti contacts were fabricated in p-type 4H-SiC epitaxial layers having aluminum acceptor concentrations, Na = 2 × 1019, 7 × 1019, and 2.5 × 1020 cm−3, and a nitrogen doped n-type epitaxial layer having donor concentration, Nd = 7 × 1018 cm−3. The ratios of the co-sputtered Pt-Ti metallization were 80:20, 50:50, and 30:70 at. %. After rapid thermal annealing (RTA) ranging between 800 and 1200 °C in vacuum and confirming SOCs by linear current-voltage (I-V) measurement, the specific contact resistance (ρc) values were extracted using the Transfer Length Measurement method. SOCs were realized with the Pt80:Ti20 composition starting from 1000 °C, and the Pt30:Ti70 composition from 1100 °C, with both exhibiting eutectic and segregated phases. The Pt50:Ti50 composition produced no SOC and eutectic and segregated phases were absent. The Pt80:Ti20 composition had the lowest pair of average ρc values of 7 × 10−5 Ω cm2 and 7.3 × 10−4 Ω cm2 on the highest doped p-type and the n-type samples after RTA at 1000 °C, respectively. Auger electron spectroscopy and focused ion beam field emission scanning electron microscopy with energy dispersive x-ray spectroscopy indicated distinct phase segregation via the eutectic-liquidus-eutectic transitions, the coalescence of likely Pt3Si and Pt2Si binary phases, and solid phases of Ti3Si, Ti5Si3, and TiC, with all the active phases maintaining intimate contact to both the p- and n-type 4H-SiC surfaces. The SOC formation was attributed to the disparate work functions of these phases, which was in good agreement with the proposed PSA model.

Thermal stability of low-resistance Au Ohmic contacts to GeTe

Low-resistance Ohmic contacts for phase change materials (PCMs) such as GeTe are required for devices such as radio frequency switches. The contacts must also exhibit good thermal stability since the PCM is switched by heating. In this work, Au Ohmic contacts to GeTe have been examined, including the effect of pre-metallization surface preparation and annealing on the resistance of the contacts. Although some form of pre-metallization surface treatment must be performed after photolithography to produce contacts with low resistance, the contact resistance (Rc) and specific contact resistance (ρc) were insensitive to the pre-metallization surface treatment chosen, whether in-situ Ar+ plasma treatment was used, or UV-O3 treatments followed by immersion in deionized H2O, (NH4)2S, or HCl. In all cases, Rc was 0.007±0.001Ω·mm and ρc was 1.2–1.3×10−8Ω·cm2. Thermal stability was also investigated at 250, 300, and 350°C for 30min. The contact resistance increased as annealing temperature increased, and changes in the contacts were observed using field emission scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. No solid-state reaction occurred between Au and GeTe, even at 350°C. Rather, the increase in resistance could be attributed to slit-like defects that appeared and grew in the Au layer, through which sublimation of Te occurred.

Direct determination of the barrier height of Au ohmic-contact on a hydrogen-terminated diamond (001) surface

The barrier height ϕB of Au ohmic-contact on hydrogen-terminated p-type surface conductive layer (SCL) made on a boron-doped diamond (001) substrate has been directly determined by X-ray photoelectron spectroscopy (XPS). For this purpose, thin layer (thickness~3.6nm) of Au was deposited on the p-type SCL. The formation of nm-size Au-islands was identified by scanning electron microscopy. It became therefore evident that C 1s XPS spectra originate from diamond in the gap areas among Au-islands but not from diamond underneath the Au-islands. Two-dimensional energy band simulation was performed to show that the diamond band diagram in the gap areas among Au-islands become effectively identical to that of diamond underneath the Au-islands when SCL is eliminated only in the gap areas. In order to eliminate SCL in the gap area only, a VUV/ozone irradiation process was applied on the Au-island-covered sample. C 1s and Au 4f7/2 XPS spectra were measured for the sample before and after the VUV/ozone irradiation process. The peak binding energies and widths of C 1s and Au 4f7/2 XPS spectra are carefully considered to reach to the conclusion that ϕB=0.29±0.13eV. For the boron-doped present substrate, the current flow mechanism at the Au ohmic-contacts is expected to be thermionic emission and specific contact resistance RC is thus evaluated to be the order of 10−4Ωcm2.

(Invited) On the Manipulation of Phosphorus Diffusion as Well as the Reduction of Specific Contact Resistivity in Ge by Carbon Co-Doping

Thanks to its intrinsic high mobilities for carriers i.e. 3900 and 1900 cm2V-1s-1 for holes and electrons respectively, Ge has resurged as an alternative channel material for metal-oxide-semiconductor field-effect transistors (MOSFETs) [1]. To realize the-state-of-the-art high-performance Ge devices, the formation of highly activated shallow junctions especially n-type junction as well as the large contact specific contact resistivity (ρc), however, are still great challenges remained to be resolved, in spite of numerous efforts spent in the past decade [2, 3]. Impurity species such as carbon (C), nitrogen (N) and fluorine (F) are utilized to suppress the rapid diffusion of phosphorus in Ge by trapping vacancies [4, 5], while at the expense of a reduced activation level usually. Specifically, in this paper, the impact of C implantation parameters (energy and dose) on the diffusion and activation of P in Ge pre-amorphized (PAI) germanium epitaxial layers on Si (100), is systematically explored. All samples received a Ge PAI at 20 keV, 6×1014 at/cm2, followed by C implantation at different energies ranging from 3 keV to 20 keV and doses varying from 5×1014 to 2×101 5 at/cm2. P was implanted with a fixed condition using an energy of 5 keV and dose of 2×101 5 at/cm2 and was completely contained in the amorphous Ge layer. During annealing, to prevent out-diffusion of the implanted dopants, all samples were capped with a 20 nm thick SiO2 deposited by plasma enhanced chemical vapor deposition (PECVD) at 280 oC. The annealing process was carried out in N2 ambient at 600 oC for 60 s. It is illustrated in Fig. 1a that the shallowest N-type junction occurs for C implantation at 8 keV with a dose of 1×1015 cm-2. This optimum condition can be ascribed to the carbon distribution shown in Fig. 1b that carbon atoms straddles the amorphous/crystal (a/c) interface. As a result, both the diffusion of P in the amorphous layer and in the Ge virtual substrate beyond the a/c interface can be effectively suppressed. Except the control of P diffusion, the specific contact resistivity (ρc) between NiGe and n-Ge by the presence of C is also investigated. As illustrated in Fig. 2, the thermal stability of NiGe films is obviously enhanced by the presence of C and this can be inferred by the decreasing sheet resistance till 600 oC and the pretty smooth NiGe/Ge interface for samples with C. At 500 oC germanidation temperature, the rc values are reduced from 1.1×10-4 Ω-cm2 and 2.9×10-5 Ω-cm2 for NiGe/n- and p-Ge contacts without carbon to 7.3×10-5 Ω-cm2 and 1.4×10-5 Ω-cm2 for their counterparts with carbon, respectively, as illustrated in Fig. 3 and 4.

(Invited) In-Situ Doped Epitaxial Growth of Highly Dopant-Activated n +-Ge Layers for Reduction of Parasitic Resistance of Ge-nMISFETs

Ge has been expected as a high-performance scaled-CMOS platform due to its high carrier mobility. As for nMISFET application, fabrication of shallow n +/p junction having high electron concentration by ion-implantation method is problematic due to high diffusivity and low solubility limit of n-type dopants in Ge [1]. For a metal / n +-Ge interface, moreover, Fermi-level is pinned to near the valence band edge, resulting in high specific contact resistance (ρc) [2]. In order to reduce parasitic resistances of the Ge-nMISFETs caused by the drawbacks described above, a carrier concentration of around 1x1020 cm-3 is needed in the n +-S/D region. In this report, a shallow n +-Ge layer was grown with in-situ P doped epitaxy using conventional low-pressure (LP) CVD for reduction of ρc. Moreover, drive-current of GeOI-nMISFETs was enlarged by utilizing the n +-Ge:P layer to the S/D region. P-doped n +-Ge (Ge:P) layers were grown on p-Ge substrates with LP-CVD using SiH4, GeH4 (10% in H2), PH3 (10% in He) and H2 as a carrier gas to investigate the dopant activation rates. Growth temperature and mass-flow (F(gas)) ratio of GeH4 to H2 were fixed at 400 oC and F(GeH4)/F(H2) = 1.67 x 10-3, respectively. Growth pressure was varied from 5 to 80 Torr. Ti layers were deposited on the Ge:P layers to measure the ρc of Ti / Ge:P contact by a transmission line measurement (TLM). As a reference, Ti / Ge:P TLM patterns were also fabricated on a P ion-implanted (10 keV, 1x15cm-3) Ge layer on a p-Ge substrate after an activation anneal (600 oC, 1 min. in N2). GeOI-nMISFETs having the Ge:P S/D were fabricated to evaluate transistor characteristics. Dopant and activated carrier concentration profiles of Ge:P samples as a parameter of total growth pressure are shown in Fig.1 (a) and (b), respectively. Here, F(PH3)/F(GeH4) is fixed to 3.0 x 10-3. Both dopant and carrier concentrations exhibit almost uniform profiles throughout the Ge:P layers. From Fig.1 (a) and (b), dopant and carrier concentration were plotted as a function of growth pressure as shown in Fig.2. This result exhibits a peak dopant activation rate of 0.7 at a growth pressure of 15 Torr. Here, an electron concentration of 7x1019 cm-3 was observed. This value far exceeds the solid solubility of P in Ge of around 1x1019 cm-3 at the growth temperature. Next, I/V curves observed in the TLM for the Ti / Ge:P and the Ti / P-implanted Ge layers having the same dopant concentrations of 1 x 1020 cm-3 are shown in Fig. 3. This result indicates that ohmic contacts are formed on the P-doped epitaxial Ge layer with a carrier concentration of 7x1019 cm-3. In contrast, Schottky-like contacts are observed for the P-implanted Ge having a carrier concentration of 2x1019 cm-3 and the P-doped epitaxial Ge layer having a carrier concentration of 2x1019 cm-3. The ρc extrapolated from TLM are 1.2x10-6 Ωcm2 for the epitaxial layer having carrier concentration of 7 x 1019 cm-3 and 1.6 x 10-5 Ωcm2 for P-implanted one. Sheet resistances (Rsh) of the n +-Ge layers are plotted as a function of layer thickness as shown in Fig. 4. A low Rsh of 33 (Ω/sqr.) was shown for the 65-nm-thick P-doped Ge layer due to the high carrier concentration and the high dopant activation rate. The value of Rsh for the epi-layer agrees with the theoretically predicted value and is the lowest among the values ever reported for the Ti / Ge:P layer [3]. Finally, GeOI-nMISFETs with the Ti / Ge:P contacts were fabricated through gate-last process flow shown in Fig. 5. Here, electron concentration of the GeOI layer was 4x1017cm-3 and TaN/Al2O3 gate-stack was deposited after O3 passivation [4]. An XTEM image of the GeOI-nMISFET is shown in Fig.6. Gate-length, Lg, and GeOI thickness are 60 nm and 37 nm, respectively. Id-Vd curves are shown in Fig. 7. Id of 300 μA/mm was obtained at Vd=1V, Vg-Vth=1.5V. This is almost 2.7 times larger than the largest Id of Ge-nMISFETs ever reported [4, 5]. These results suggest that current drive of Ge-nMISFETs can be enhanced by reduction of parasitic resistances such as ρc and Rsh by utilizing the in-situ doped Ge:P layers to the S/D. This work was granted by JSPS through FIRST Program initiated by the CSTP. [1] M. Koike et al., JAP104, p.023523 (2008) [2] T. Nishimura., APEX1, p.051406 (2008) [3] B. Yang et al., Proc. of ISTDM, p.88 (2012) [4] Y. Kamimuta et al., Proc. of ISDRS, FP8-04 (2013) [5] C.T. Chung et al., Tech. Dig. IEDM, p.383 (2012) Figure 1

(Invited) On the Manipulation of Phosphorus Diffusion as Well as the Reduction of Specific Contact Resistivity in Ge by Carbon Co-Doping

In this work, the manipulation of phosphorus diffusion as well as the reduction of the specific contact resistivity in Ge by carbon co-doping is explored. It is found that there is an optimum condition for carbon implantation to suppress the rapid P diffusion effectively. For such a condition, the implanted carbon sits at the half range of the pre-amorphized Ge layer. In this case, both the diffusion of P in the amorphous layer and in the Ge virtual substrate beyond the amorphous/crystal (a/c) interface can be effectively manipulated. Except the control of P diffusion, the specific contact resistivity (ρc) between as-formed NiGe and the Ge substrate in the presence of C can be also reduced, compared with the reference without C. At 500°C germanidation temperature,the ρc values are reduced from 1.1x10-4 Ω-cm2 and 2.9x10-5 Ω-cm2 for NiGe/n- and p-Ge contacts without carbon to 7.3x10-5 Ω-cm2 and 1.4x10-5 Ω-cm2 for their counterparts with carbon, respectively.

Characterization of ohmic contacts in polymer organic field-effect transistors

It is well known that contact resistance Rc limits the performance of organic field-effect transistors (OFETs) that have high field-effect mobilities (μFET ≳ 0.3 cm2 V−1 s−1) and short channel lengths (Lch ≲ 30 μm). The usual transfer-line method (TLM) to analyze Rc calls for extrapolation of total resistance to zero Lch at constant drain and gate voltages. This requires an unrealistic assumption that Rc does not vary with source−drain current Isd (nor with channel carrier density σ). Here we describe a self-consistent TLM analysis that instead imposes the condition of constant Isd and σ. The results explicitly reveal the dependence of Rc on Isd and σ. We further describe how this Rc(Isd, σ) surface can be modelled to yield the specific contact resistivity ρc of the metal/organic semiconductor (OSC) interface, a key parameter that has so far been neglected in OFETs. We illustrate the application of these analyses to high-performance staggered top-gate bottom-contact poly(2,5-bis(alkyl)-1,4-dioxopyrrolo [3,4-c]pyrrole-3,6-diyl-terthiophene-2,5″-diyl) (DPPT2-T) OFETs fabricated on bottom Au source–drain electrode arrays, with high contact-corrected μFET of 0.5 cm2 V−1 s−1. We show that when these electrodes are modified to impose weak, and then strong hole-doping of the DPPT2-T interface, Rc diminishes and its dispersion, i.e. dependence on Isd and σ, weakens. The ultimate ρc attained for the strongly hole-doped contact is ca. 1 Ω cm2, broadly independent of Isd and σ, which we propose is a hallmark of a true metal/OSC ohmic contact. For comparison, the bare Au/DPPT2-T contact gives ρc of the order of 10 Ω cm2 with a marked σ dependence. The lowest ρc reached here shortens the current transfer length down to ca. 5 μm, enabling short electrode lengths to be advantageously employed in technology.

Contact resistivities of antimony-doped n-type Ge1−xSnx

As Ge1−xSnx is being investigated for CMOS applications, obtaining contacts to n-type Ge1−xSnx with low specific contact resistivity (ρc) is a major concern. Here, we present results on specific contact resistivities of Sb doped n-type Ge1−xSnx with 0 ≤ x ≤ 0.08 also with varying doping concentrations using Ni, Ag and Mn as contact metals. Our results show that Ni offers the lowest ρc for all x values of Ge1−xSnx. The lowest ρc measured for Ni contacts on highly n-doped Ge0.92Sn0.08 is 2.29 × 10−6 Ω cm2. We find a strong dependence of the specific contact resistivity on doping, which we attribute to the fact that strong Fermi level pinning is present in metal/n-Ge1−xSnx contacts.

Fabrication of Ohmic contact on semi-insulating 4H-SiC substrate by laser thermal annealing

The Ni contact layer was deposited on semi-insulating 4H-SiC substrate by magnetron sputtering. The as-deposited samples were treated by rapid thermal annealing (RTA) and KrF excimer laser thermal annealing (LTA), respectively. The RTA annealed sample is rectifying while the LTA sample is Ohmic. The specific contact resistance (ρc) is 1.97 × 10−3 Ω·cm2, which was determined by the circular transmission line model. High resolution transmission electron microscopy morphologies and selected area electron diffraction patterns demonstrate that the 3C-SiC transition zone is formed in the near-interface region of the SiC after the as-deposited sample is treated by LTA, which is responsible for the Ohmic contact formation in the semi-insulating 4H-SiC.

Characterization of interface reaction of Ti/Al-based ohmic contacts on AlGaN/GaN epitaxial layers on GaN substrate

The ohmic properties of Ti/Al/Mo/Au contacts on a high-quality AlGaN/GaN heterostructure epitaxially grown on a GaN substrate were investigated. Systematic structural and electrical analyses of the metal/AlGaN interface after annealing in N2 at 700 and 900 °C were conducted. After annealing at 900 °C, a new Al-rich interlayer with nitrogen vacancies was formed at the metal/AlGaN interface. Ohmic contacts with a low specific contact resistance (ρc) of 5.1 × 10−6 Ω cm2 and a dominant field emission carrier transport mechanism were achieved. The fabrication of recessed-AlGaN-structured ohmic contact with ρc as low as 2.4 × 10−5 Ω cm2 at a low annealing temperature of 650 °C, was also successfully demonstrated. This result indicates that a process methodology can be provided for fabricating low-resistivity ohmic contacts with a low thermal budget on a high-quality AlGaN/GaN structure, which is based on an appropriate control of the metal/AlGaN interface and AlGaN thickness rather than relying on the existence of threading dislocations.

Air-stable polythiophene-based thin film transistors processed using oxidative chemical vapor deposition: Carrier transport and channel/metallization contact interface

Oxidative chemical-vapor-deposition (oCVD) provides a facile route to polymerize and deposit insoluble monomers in thin film form. Here, we report on oCVD polythiophene (PT)-based organic thin film transistors (OTFTs) that present both high mobility and excellent stability over time in air. The measured field effect mobility (μFE) is ∼0.02 cm2/V sec with the low threshold voltage between −1 V and 0.3 V. Additionally the PT OTFTs show no evidence of performance degradation after 3 months exposure in air. The transmission line model (TLM) enables the determination of the specific contact resistance (ρC) of oCVD PT channel/metallization interface and reveals that ρC is improved with increasing gate bias. The oCVD PT channel conductivity (σch) and carrier density (p) were evaluated from more than 100 devices using TLM measurements and the relation of σch = qpμFE. Carrier transport analysis suggests that the charge screening effect governs hole carrier mobility in the carrier density regime below approximately 1018/cm3 where an increase in carrier density leads to higher mobility. We also demonstrate photo-conductivity of oCVD PT through an increase in device on-state current and the field effect mobility when the PT OTFT is illuminated. Strategies to further enhance the performance of the materials and devices are also suggested.

Ti/Pd/Ag Contacts to n-Type GaAs for High Current Density Devices

The metallization stack Ti/Pd/Ag on n-type Si has been readily used in solar cells due to its low metal/semiconductor specific contact resistance, very high sheet conductance, bondability, long-term durability, and cost-effectiveness. In this study, the use of Ti/Pd/Ag metallization on n-type GaAs is examined, targeting electronic devices that need to handle high current densities and with grid-like contacts with limited surface coverage (i.e., solar cells, lasers, or light emitting diodes). Ti/Pd/Ag (50 nm/50 nm/1000 nm) metal layers were deposited on n-type GaAs by electron beam evaporation and the contact quality was assessed for different doping levels (from 1.3 × 1018 cm−3 to 1.6 × 1019 cm−3) and annealing temperatures (from 300°C to 750°C). The metal/semiconductor specific contact resistance, metal resistivity, and the morphology of the contacts were studied. The results show that samples doped in the range of 1018 cm−3 had Schottky-like I–V characteristics and only samples doped 1.6 × 1019 cm−3 exhibited ohmic behavior even before annealing. For the ohmic contacts, increasing annealing temperature causes a decrease in the specific contact resistance (ρ c,Ti/Pd/Ag ~ 5 × 10−4 Ω cm2). In regard to the metal resistivity, Ti/Pd/Ag metallization presents a very good metal conductivity for samples treated below 500°C (ρ M,Ti/Pd/Ag ~ 2.3 × 10−6 Ω cm); however, for samples treated at 750°C, metal resistivity is strongly degraded due to morphological degradation and contamination in the silver overlayer. As compared to the classic AuGe/Ni/Au metal system, the Ti/Pd/Ag system shows higher metal/semiconductor specific contact resistance and one order of magnitude lower metal resistivity.

Ohmic Contact of Au/Mo on Hg1−x Cd x Te

The contact resistance between Au/Mo and HgCdTe was investigated. The influence of thermal annealing on metal–semiconductor contact on short and middle-wavelength HgCdTe is also discussed in this paper. The specific contact resistance ρc (300 K, 80 K) of Au/Mo/HgCdTe was measured by the transmission line method. Good ohmic contacts can be formed with Au/Mo on long-wavelength infrared p-HgCdTe (x = 0.23) with a low specific contact resistivity of 3.78E−04 Ωcm2 measured at 80 K. For the mid-wavelength infrared p-HgCdTe (x = 0.30), the metal–semiconductor contact is ohmic, and the minimum specific contact resistivity of 7.40E−04 Ωcm2 is obtained after annealing at 120°C/10 min. The as-deposited contact between Au/Mo and the short-wavelength infrared HgCdTe (x = 0.47) shows non-ohmic behavior. After annealing at 120°C/5 min, although the contact behavior is still a Schottky contact, the contact resistance decreases. For the n-HgCdTe (x = 0.27), the metal–semiconductor contact is ohmic with a specific contact resistivity of 5.70E−04 Ωcm2 at 80 K.

Reprint of "Palladium Ohmic contact on hydrogen-terminated single crystal diamond film"

Contact properties of Palladium (Pd) on the surface of hydrogen-terminated single crystal diamond were investigated with several treatment conditions. 150nm Pd pad was deposited on diamond surface by thermal evaporation technique, which shows good Ohmic properties with the specific contact resistivity (ρc) of 1.8×10−6Ωcm2 evaluated by Transmission Line Model. To identify the thermal stability, the sample was annealed in Ar ambient from 300 to 700°C for 3min at each temperature. As the temperature increased, ρc firstly decreased to 4.93×10−7Ωcm2 at 400°C and then increased. The barrier height was evaluated to be −0.15eV and −0.03eV for as-deposited and 700°C annealed sample by X-ray photoelectron spectroscopy analysis. Several surface treatments were also carried out to determine their effect on ρc, among which HNO3 vapor treated sample indicates a lower value of 5.32×10−6Ωcm2.

Temperature Dependence and High-Temperature Stability of the Annealed Ni/Au Ohmic Contact to p-Type GaN in Air

We report on the temperature-dependent contact resistivity and high-temperature stability of the annealed Ni/Au ohmic contacts to p-type GaN in air. As the measure temperature increases from 25°C to 390°C, both the specific contact resistivity (ρc) and sheet resistance (Rsh) decrease by factors ∼10, contributing to the 10-fold increase in current at 390°C compared with that at 25°C. It was also observed that the ρc was further reduced by 36%, i.e., from 2.2 × 10−3 Ω cm2 to 1.4 × 10−3 Ω cm2, during the 48-h high-temperature stability test at 450°C in air, showing excellent stability of the contacts. An increase in ρc was observed after the contacts were subjected to 500°C in air. Higher temperature stress led to a significant increase in ρc. The contacts show rectifying I–V characteristics after being subjected to 700°C for 1 h. The degradation mechanics were analyzed with the assistance of transmission electron microscopy and energy dispersive x-ray spectroscopy.

Contact resistance to SrRuO3 and La0.67Sr0.33MnO3 epitaxial films

Contact resistance to the metallic oxide electrodes, SrRuO3 (SRO) and La0.67Sr0.33MnO3 (LSMO), is an important parameter that affects the ferroelectric tunnel junction (FTJ) device performance. We have systematically studied the contact resistance between metallic oxide electrodes (SRO, LSMO) and contact metal overlayers (Ti, Pt) after exposure to various processing environments. Specific contact resistivity (ρc) for Ti and Pt contact metals and the sheet resistance (Rsh) of the metallic oxides are measured after exposure to different reactive ion plasma process steps. Sheet resistance degradation was observed for both SRO and LSMO films after exposure to plasma treatment. Severe contact resistance degradation was observed for Ti contacts as compared to Pt after reactive ion etching on LSMO films. The effect of oxygen (O2) plasma on LSMO was observed to be most severe with non-ohmic behavior with Ti contacts, which can affect the functionality of FTJ devices. Finally, the thermal stability of contacts was investigated, Pt contacts to SRO show low resistance ohmic behavior even after annealing at 900 °C, making it a suitable contact for FTJ devices.