Specific Contact Resistance Values Research Articles

Ohmic contacts to n-type SiC: Influence of Au and Ta intermediate layers

In this study, the optimization of metal-semiconductor contacts to reduce the contact resistance of ohmic contacts on n-type 4H-SiC. The commonly used Ni/Au metal scheme served as a reference. We introduced two novel metal schemes: (i) incorporating a thin interfacial Au layer (2 nm) into Ni/Au, resulting in Au/Ni/Au, and (ii) introducing a thin intermediate barrier layer of Ta (20 nm) into Ni/Au, resulting in Ni/Ta/Au. Rapid thermal annealing (RTA) is performed at different temperatures and durations and the electrical characteristics of the contacts are measured. X-ray diffraction analysis was employed to investigate the intermediate phases formed during annealing. In the Au/Ni/Au metal scheme, the presence of Au at the interface promoted the formation of additional phases of nickel-silicide (Ni3Si and Ni3Si2). Compared to the traditional Ni/Au scheme, the modified metal schemes led to lower surface roughness and reduced contact resistance. Specific contact resistivity values are calculated, 2.2 × 10−5 Ω-cm2 for Ni/Au, 1.37 × 10−5 Ω-cm2 for Au/Ni/Au, and 4.84 × 10−5 Ω-cm2 for Ni/Ta/Au. This research offers valuable insights for the selection of metal schemes in designing ohmic contacts on n-type SiC, with potential applications in various semiconductor device technologies.

Hyaluronic acid mediated ZnO-NPs: In relation to electrical and photocatalytic activity for dye degradation

Various processes have been implemented to purify water; however, photocatalysis is comprehensively utilized in wastewater treatment and plays a significant role in water remediation. A photocatalyst is a nanostructured metal oxide ZnO nanoparticles, which boosts the reaction rate by its existence. ZnO nanoparticles show great performance in the absorption of various organic pollutants from wastewater. The objective of this research was to enhance the photocatalytic degradation performance of HA-added ZnO NPs using methylene blue as a model wastewater. Adjusting the main physical properties and photocatalytic efficiency of ZnO-NPs was performed using hyaluronic acid (HA), a natural bioactive stabilizer. The characterization of the fabricated ZnO-NPs samples with and without HA involved the utilization of FE-SEM, AFM, XRD, FTIR, PL, and I-V. As demonstrated by the FE-SEM analysis, ZnO formed rod-like structures, 3.0 % HA:ZnO exhibited cauliflower-like structures, and 5.0 % HA:ZnO displayed honeycomb-like structures. The X-ray diffraction (XRD) analysis demonstrated that the HA:ZnO nanoparticles exhibited hexagonal wurtzite structures. The average crystallite sizes of the ZnO, 3.0 % HA:ZnO, and 5.0 % HA:ZnO NPs were determined to be 25.20, 27.30, and 20.20 nm, respectively, using the XRD patterns. The surface area was 4.439, 2.987, and 5.204 m²/g of bare ZnO, 3.0 % HA:ZnO, and 5.0 % HA:ZnO-NPs were 4.439, 2.987, and 5.204 m2/g, respectively. It is very likely that there are two different decay and/or capture mechanisms in the emission spectra because the TRPL decay profile behaves in a double-exponential way. The fast decay time constant (τ1) was 212 ps for bare ZnO and 3.0 % HA:ZnO NPs and 231 ps for 5.0 % HA:ZnO NPs. The slow decay time constant (τ2) has a similar pattern, with values of 3.716, 2.836, and 2.984 ns. The specific contact resistance values of the ZnO NPs increased from 0.113 to 45.624 ( × 105 Ω cm2) as a function of the HA concentration, as evidenced by the results of the electrical studies. The outcomes of this research present comprehensive information on noble-modified ZnO-NP materials containing HA for direct applications in electronic materials and photocatalytic degradation of organic waste in water.

Construction of unary and ternary ZnO–CuO–CdO composite thin films and comprehensive analysis of their optical, electrical, and photocatalytic performance

In this study, unary ZnO, CuO, CdO, and ternary ZnO–CuO–CdO metal oxide thin film materials were fabricated using the SILAR procedure. The XRD spectra of the synthesized films show sharp and dominant diffraction lines, indicating the high crystallinity of both the unary and ternary composite films. The crystallite size values of unary ZnO, CuO, CdO, and ZnO–CuO–CdO ternary films were found to be 18.71 nm, 12.86 nm, 15.88 nm, and 21.96 nm, respectively. FESEM pictures exhibited that nanocomposites have spherical and nanorod-like hybrid morphology, and EDX showed that Cd has a higher content than Zn and Cu. The prepared samples’ FT-IR spectra in the wavenumber range of 500–4000 cm−1 revealed the existence of numerous vibrational modes. The optical bandgap values were found to be 1.47, 3.20, 2.21, and 2.51 eV for the CuO, ZnO, CdO, and ternary ZnO-CuO-CdO films, respectively. The photocatalytic efficiency of the ternary composites is higher than that of the unary metal oxides. The specific contact resistivity values were 780.83 kΩcm2, 213.33 kΩcm2 347.33 Ωcm2, and 1.97 kΩcm2 for ZnO, CuO, CdO, and ternary ZnO–CuO–CdO thin films, respectively. Our inventions provide advanced prompting for constructing new types of catalysts. The characterization results imply that the ternary nanocomposite can be used as a cost-effective alternative material for optoelectronic and photocatalytic implementations.

How to Accurately Determine the Ohmic Contact Properties on n-Type 4H-SiC

The electrical properties of ohmic contacts are classically investigated by using the transfer length method (TLM). In the literature, the TLM patterns are fabricated onto different substrate configurations, especially directly onto the 4H-SiC wafers. But, due to the high doping level of commercial substrates, the current is not confined close to the contact and, in this case, the specific contact resistance (SCR) value is overestimated. In this article, we propose, by the means of simulations, to investigate the influence of the layer under the contact towards the estimation of the SCR. The simulation results highlight that, for an accurate determination of the SCR values, an isolation layer between the contact and the silicon carbide substrate is mandatory. Thus, we have determined the characteristics (doping level and thickness) of a suitable isolation layer compatible with SCR values ranging from 10−3 to 10−6 Ω·cm2.

Structural, compositional, morphological and electrical characteristics of thermally evaporated Au Ohmic Contact on p-type HgCdTe substrate for possible infrared detectors

Gold (Au) thin films were deposited over the HgCdTe (mercury cadmium telluride) surface by a thermal-evaporation deposition technique. The thermally grown Au films were investigated using different characterization techniques, X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM), scanning electron microscopy (SEM), and current-voltage (I–V)/resistance measurement. The maximum film growth occurs along with the preferred orientation (111). The grown Au film possesses a cubic fcc structure, desired elemental compositions, and purity. The AFM confirms that the films were uniform, dense, and had very low roughness. The films attained the desired grain size of film-forming particles. The optimized Au films were established and further employed to fabricate the transfer length method (TLM) structure with configuration (Au/p-HgCdTe). The I–V and resistance measurements of the as-deposited TLM structure produced the Ohmic Au-contact with low specific contact resistance (ρc) of 2.73 × 10−3 Ω cm2. Annealing treatment (contacts annealed for 2 h at 80 °C in the air) was applied to the as-deposited TLM structure and the measured value of specific contact resistance (ρc) for the annealed Au contact (Ohmic behaviour) is 7.11 × 10−4 Ω cm2 that is relatively low than the as-deposited contacts. Thermal annealing has reduced the magnitude of ρc by about one order. TLM structures (as-deposited and annealed) exposed the efficiency of Au thin films as an effective Ohmic contact. Thus, Au thin films could be used to create a compelling and appropriate Ohmic p-contact to fabricate HgCdTe infrared detectors.

Ohmic contact structures on β-Ga2O3 with n+ β-Ga2O3 pulsed laser deposition layers

Thin (40–150 nm), highly doped n+ (1019–1020 cm−3) Ga2O3 layers deposited using pulsed laser deposition (PLD) were incorporated into Ti/Au ohmic contacts on (001) and (010) β-Ga2O3 substrates with carrier concentrations between 2.5 and 5.1 × 1018 cm−3. Specific contact resistivity values were calculated for contact structures both without and with a PLD layer having different thicknesses up to 150 nm. With the exception of a 40 nm PLD layer on the (001) substrate, the specific contact resistivity values decreased with increasing PLD layer thickness: up to 8× on (001) Ga2O3 and up to 16× on (010) Ga2O3 compared with samples without a PLD layer. The lowest average specific contact resistivities were achieved with 150 nm PLD layers: 3.48 × 10−5 Ω cm2 on (001) Ga2O3 and 4.79 × 10−5 Ω cm2 on (010) Ga2O3. Cross-sectional transmission electron microscopy images revealed differences in the microstructure and morphology of the PLD layers on the different substrate orientations. This study describes a low-temperature process that could be used to reduce the contact resistance in Ga2O3 devices.

Влияние режимов формирования контактной системы Pd/Ge/Au к n-GaAs на ее электрические характеристики

The investigations of Pd/Ge/Au contact system forming regimes influence on the specific contact resistivity to n-type conductivity GaAs layer were carried out. The method of samples surface treatment before the layers evaporation and thermal annealing regimes in H2, N2 and Ar atmosphere influence on contact system parameters was investigated. The specific contact resistivity value 2-3•10-6 Ohm•cm2 at the reduced annealing temperature 190 C was archived.

Forming regimes of Pd/Ge/Au contact system to n-GaAs influence on its electric parameters

The investigations of Pd/Ge/Au contact system forming regimes influence on the specific contact resistivity to n-type conductivity GaAs layer were carried out. The method of samples surface treatment before the layers evaporation and thermal annealing regimes in H2, N2 and Ar atmosphere influence on contact system parameters was investigated. The specific contact resistivity value (2-3)· 10-6 Ohm· cm2 at the reduced annealing temperature 190oC was archived.. Keywords: Pd/Ge/Au, n-GaAs, surface treatment, thermal annealing

Low ohmic contact resistivity realized by in situ SiNx insertion for high Al-composition-AlGaN/GaN heterostructure

A low ohmic contact resistance (Rc) is a challenge for an AlGaN/GaN heterostructure with a high Al-composition barrier, which is highly desired to further push the performance of GaN transistors. In this Letter, an effective ohmic contact technique with an in situ SiNx layer inserted between the conventional Ti/Al/Ni/Au metal stack and the III-nitride was proposed and the inside physical mechanisms were investigated for an Al0.65Ga0.35N/GaN heterostructure. The fabricated ohmic contact has a low Rc of 0.17 Ω·mm and a specific contact resistivity value (ρc) of 8.45 × 10−7 Ω·cm2, which is obviously improved compared with the Rc of 0.32 Ω·mm and ρc of 2.84 × 10−6 Ω·cm2 without in situ SiNx inserted. The strong temperature dependency of ρc with in situ SiNx insertion shows that the dominant current transport mechanism is the thermionic field emission. Transmission electron microscopy and energy dispersive x-ray spectroscopy analyses suggest that the enhanced ohmic contact is due to the possible formation of low-work function silicides and more TiN alloys during annealing.

Understanding the factors affecting contact resistance in nanowire field effect transistors (NWFETs) to improve nanoscale contacts for future scaling

In this paper, dry etched vertical nanowires (VNWs) are used in transmission line/transfer length analysis to study the contacts of gate-all-around devices for future technology nodes. VNW resistors with Mo and Pd based metal stack contacts to p-InGaAs show Schottky behavior, unlike the planar counterpart. The resistance for Mo contact is higher than Pd, however, Pd was found to form an alloy with InGaAs at temperatures as low as 190 °C, and the length of Pd diffusion into the InGaAs increased at smaller NW dimensions, hindering future scalability. The minimum extracted specific contact resistivity (ρC) values are 1.6 × 10−5 Ω cm2 (Mo) and 4.2 × 10−6 Ω cm2 (Pd) for a doping level of 1 × 1019 cm−3. An apparent dependence of ρC on the NW diameter was also observed. This has been attributed to the surface states under the un-gated region of NW devices and found to dominate at smaller diameters. An analytical model to account for such geometrical effects has also been developed and validated with technology computer-aided design simulations. The analysis presented in this paper effectively captures the 3D aspects of an NW contact at nanoscale dimensions and can be applied irrespective of the semiconductor and contact metal used.

Impact of oxygen partial pressure during Indium Tin Oxide sputtering on the performance of silicon heterojunction solar cells

TCO has multiple functions in SHJ solar cell design, including the lateral transport of the photogenerated current and also providing high transparency and anti-reflective behavior. While superior performance lies behind concurrently addressing its multi-functions. Hence the balance between the optical and electronic properties of TCOs need careful engineering. In this study, RF sputtered Indium Tin Oxide films are analyzed in terms of their optical and electrical properties. The variations in the resistivity, mobility, carrier concentration, and specific contact resistivity of the film concerning oxygen partial pressure are discussed. Specific contact resistivity value for screen-printed low-temperature Ag contacts is decreased down to 0.4mΩ.cm2. The total increment on short-circuit current density is 0.6 mA/cm2 by reactive ITO sputtering. The photoconversion efficiency values of SHJ cells fabricated on 170 cm2 area with reactive sputtering is 20.56%, and optical loss analysis is carried out for the SHJ solar cells to quantify the performance of solar cells.

Optimization of annealing conditions for Ag/p-GaN ohmic contacts.

The electrical and optical properties of Ag/p–GaN contacts have been investigated as a function of the annealing temperature, oxygen concentration, and annealing time. Specific contact resistance (ρc) values as low as 1.2 × 10–4 Ω·cm2 were obtained from the Ag/p–GaN contact annealed at 400 °C for 60 s in ambient O2/N2 (1:10). We found that the participation of oxygen improves the formation of ohmic contacts. Oxygen might remove the H in Mg–H complexes to activate the Mg acceptors and enhance Ga out-diffusion to form an Ag–Ga solid solution. We also found that the reflectivity of the Ag layer decreases with increasing annealing temperature in the O2-containing ambient environment. Thus, an optimal annealing condition of Ag/p–GaN for blue and green LEDs is suggested based on these results. We also used the suggested annealing conditions to form ohmic contacts on DUV LEDs and achieved good electrical performance. The forward voltages of UVC LEDs fabricated with annealed Ag contacts were 6.60 V (7.66 V) at a 40 mA (100 mA) injection current.

Electrical and mechanical properties of Au–Si bonds for 3D interconnect applications

Driven by high-density and high-reliability demands on three-dimensional (3D) interconnections, electrical and mechanical properties of interconnection structures have been paid more attention. Aiming at the novel enable-3D interconnections realized by Au–Si wafer bonding, this study demonstrates the design, fabrication and test results of testing structures for dimension-define parameters of Au–Si bonds. In order to measure closely-realistic ohmic contact resistances of Au–Si bonds after wafer bonding processes implemented under certain bonding pressures and temperatures, the convex Si structures formed by the local oxidation of silicon process have been designed. Therefrom the specific contact resistance values of Au–Si bonds have been measured as 3.9–8.1 × 10−10Ω m2 for different contact radii (3–20 μm), which indicates the low-resistance potentiality for Au–Si bonds applied on 3D interconnections. On the other hand, two findings on bonding strengths are summarized from finite element simulations and tensile experiments: (a) Au–Si bonding strengths of circular bonding patterns (35–75 MPa) are superior to the ones of square bonding patterns (18–30 MPa) due to the stress concentration phenomenon on four corners of square bonding patterns; (b) there is an inverse relationship between bonding strengths and bonding areas owing to uneven stress distributions in bonding structures. Overall, this study provides a basic optimization design strategy at electrical and mechanical levels for 3D interconnections actualized by Au–Si bonding. Incidentally, these introduced analysis methods are also feasible for homologous Si-based eutectic bonding techniques to extend the forms of 3D interconnections.

Microstructural and phase evolutions of Pt contact to N-type In0.53Ga0.47As driven by rapid thermal annealing and its correlation with specific contact resistivity

In this study, the microstructural and electrical characteristics of Pt contacts to n-type InGaAs were investigated as a function of rapid thermal annealing (RTA) temperatures in the range of 400–600 °C. RTA at 400 °C was inadequate for ensuring a good reaction between the deposited Pt films with InGaAs, forming only a thin amorphous PtAs2 layer, as evidenced from the high-resolution transmission electron microscope and energy dispersive X-ray spectrometer results. A significant reaction occurred upon RTA at 500 °C, leading to the formation of a PtAs2 phase with most of the Pt being unreactive, but with a reduction in the Pt lattice dimensions. With a smaller atomic radius than Pt, the accommodation of Ga and In atoms in a substitutional solid solution could be responsible for the reduction in the Pt lattice. The reaction between the Pt films and InGaAs after annealing at 600 °C resulted in complete consumption of the Pt films, forming PtIn2, Pt13In9, Pt2Ga3, and Pt5Ga3 phases along with the additional PtAs2 phase as clearly distinguishable layers. The minimum value of specific contact resistivity obtained with RTA at 600 °C could be associated with the metallic PtIn2 in combination with the Pt13In9 alloy embedded in the PtAs2 layer, which serves as a good carrier path.

Contact and Bulk Resistivity Screening for Advanced Crystalline Silicon Solar Cell Concepts by an Economical and Reliable Transfer Length Measurement Method Based on Laser Micro‐Patterning

Herein, test structures for transfer length measurements (TLMs) are prepared by means of a femtosecond laser micro‐machining process for quick and easy measurements of contact resistance and bulk resistivity in thin‐film multilayer stacks for advanced high‐efficiency silicon solar cells. In particular, silicon heterostructure layer systems composed of tin‐doped indium oxide (ITO)/n‐doped amorphous silicon (a‐Si) on crystalline silicon (c‐Si) substrates are used. To study the reliability of this novel laser‐based TLM test structure preparation method, measured data from laser structured TLM patterns are compared with conventional structures based on micro‐lithography. For small TLM test structures with contact distances between 100 and 1000 μm, the results suggest a significant dependence of the measured contact resistance values on the size of the laser prepared structures. This may be attributed to redeposited material during the laser ablation procedure at the flanks of the contact pads and insufficient mesa structuring. However, the laser and lithography‐based preparation methods yield comparable results when larger structures (contact distances between 200 and 2200 μm) are implemented. Herein, size effects can be neglected. For both methods, the specific contact resistance values of ITO/n‐doped a‐Si/c‐Si heterostructures are calculated from 8 to 45 mΩ cm2 for various samples from the same batch.

Thermal stability investigation for Ohmic contact properties of Pt, Au, and Pd electrodes on the same hydrogen-terminated diamond

Here, thermal stabilities for Ohmic contact properties of Pt, Au, and Pd on the same hydrogen-terminated diamond (H-diamond) epitaxial layer are investigated. A long-term annealing process is performed with an annealing temperature and time of 400 °C and 8 h, respectively. Before annealing, good Ohmic contact properties are observed for only two contacts of the Pt/H-diamond and Pd/H-diamond with specific contact resistivity (ρC) values of 2.7 × 10−3 Ω cm2 and 2.6 × 10−4 Ω cm2, respectively. After long-term annealing, all three contacts on the H-diamond show good Ohmic contact properties. The ρC values for the Pt/H-diamond and Au/H-diamond are 3.1 × 10−2 Ω cm2 and 4.2 × 10−4 Ω cm2, respectively. They are higher than that of the Pd/H-diamond (1.1 × 10−4 Ω cm2). Therefore, low ρC and good thermal stability for the Pd/H-diamond are achieved. This is meaningful for pushing forward the development of H-diamond-based electronic devices for high-temperature applications.

Characterization of screen printed and fire-through contacts on LPCVD based passivating contacts in monoPoly™ solar cells

In this work we have characterized screen-printed passivating contacts formed by different commercially available fire-through pastes on phosphorus doped (n+) polysilicon (poly-Si) layers at the rear side of monoPoly™ solar cells. Extremely low recombination current density under metal contacts (J01,metal) of 35–45 fA/cm2 and excellent specific contact resistivity (ρc) values of ~ 1.3 mΩ-cm2 are obtained for two different thicknesses of poly-Si (150 nm and 250 nm) used in this work. We demonstrate that, although the metal induced recombination increases with reducing thickness of the poly-Si layer, thinner poly-Si layers can lead to higher efficiencies on account of reduced parasitic absorption leading to higher cell current. A champion efficiency of 22.6% is reported for busbarless monoPoly™ cells with the best performing fire-through (FT) paste on large area (244.3 cm2) commercially available Czochralski grown Si wafers.

Characterization of electron-beam deposited SnS films: Processing, properties, and ohmic contacts

Nanocrystalline tin sulfide (SnS) thin films were deposited by electron-beam evaporation at growth temperatures ranging from room temperature to 300 °C and characterized prior to and after annealing at 300 °C in high vacuum. X-ray diffraction and Raman spectroscopy results indicated that SnS films deposited at 100 and 200 °C contained predominately a mixture of orthorhombic α-SnS and cubic π-SnS phases, whereas only α-SnS was detected in SnS films deposited at 300 °C. Contacts with a range of work functions were deposited onto p-type α-SnS films. All of the contacts investigated (Ti/Au, Ru/Au, Ni/Au, and Au) were ohmic as-deposited and yielded average specific contact resistance values that decreased with increasing metal work function, suggesting that the barrier height has at least a partial dependence on the work functions of the metals. Annealing at 350 °C for 5 min in Ar reduced the specific contact resistance value for Ru/Au contacts, resulting in the lowest value (1.9 × 10−3 Ω cm2) of contacts investigated to SnS thin films.

Ohmic contact to AlGaN/GaN HEMT with electrodes in contact with heterostructure interface

In order to alleviate the negative impacts of high temperature (850 °C) annealing on high electron mobility transistor (HEMT) technology, a process required only low temperature annealing (less than 600 °C) was introduced to form ohmic contact to HEMT. By the process, the electrode was in contact with the AlGaN/GaN interface. The value of specific contact resistivity (ρc) of the ohmic contact was 6.29 × 10−5 Ω cm2. An improved HEMT power device was presented. For comparison, a conventional device with Ti/Al/Ni/Au ohmic contact annealed at 850 °C was prepared. It was found that after annealing at 600 °C, the sheet resistance (Rsh) of the improved device decreased to 313 Ω/□ (74.5% of that of the conventional device), and the advantage of our process on device performance was greater as the distance between ohmic contacts increased. The saturation current of the improved device was increased by approximately 23% when the distance between source and drain was 40 μm.

Large Area Growth of MoS2 By Chemical Vapour Deposition

Transition Metal Dichalcogenindes (TMD) have considerable potential for applications spanning electronics, sensors and optoelectronics due to the wide ranging electronic and optical properties which are displayed by this class of 2D layered materials [1]. Research is focused on issues such as: large area growth [2, 3], stable approaches to doping [4] and achieving required values of specific contact resistivity [5]. We are contributing to the research effort by investigating the structural, optical and electronic properties of crystalline molybdenum disulfide (MoS2) grown by chemical vapour deposition (CVD) in a commercial 300mm atomic layer deposition reactor. In this work we report on the properties of monolayer and multilayer MoS2 growth at 550oC using Mo(CO)6 and H2S precursors on a number of different substrates, including SiO2, sapphire and amorphous alumina. This work focuses on the topology, Raman response and electronic properties of the CVD grown MoS2 thin films. Figure 1 (a) shows the Raman spectrum for an as-grown 10nm MoS2 on a SiO2/Si substrate. MoS2 can be determined by the peaks at approximately 385cm-1 (E1 2g) and 410cm-1 (A1g). There are two other peak characteristics of MoS2 which cannot be seen due to back-scattering at 286cm-1 (E1g), and lack of sensitivity below 200cm-1 at 32cm-1 (E2 2g )[6]. Additional peaks are detected at wavenumbers between 2000-3000cm-1, seen in Fig. 1 (b). Further investigation is needed to establish if these peaks are from photoluminescence, contaminants within the structure or purely a surface effect. Fig. 1 (c) shows an AFM image of an annealed 1.2nm MoS2 sample on a SiO2/Si substrate. The blue marks indicate areas on the material that are above a height of 0.6nm. Further results will be presented as a function of the number of MoS2 monolayers using Conductive AFM (C-AFM) and Kelvin Probe analysis. XTEM images seen in Fig. 1 (d), (e) show MoS2 grown on SiO2/Si and sapphire substrates respectively. They show that polycrystalline and layered MoS2 is formed at the growth temperature of 550oC, with no subsequent post growth annealing. There is no interfacial layer formed at the MoS2/SiO2 interface, but an amorphous interfacial layer of ~0.5nm is observed between MoS2 and sapphire, which is still being investigated. Plan view TEM analysis (not shown) confirms aligned MoS2 with grain sizes (over a local area of around 100 nm x 100nm) in the range 5nm to 20nm. The carrier concentration, carrier type and carrier mobility were studied with Hall measurements carried out at room temperature using a Van der Pauw structure (1cm x 1 cm). Excellent ohmic behavior is achieved on MoS2 (nominally 10nm) deposited on both sapphire and a-Al2O3/sapphire substrates. Table 1 provides a summary of the Hall analysis, showing that the non-intentionally doped MoS2 grown by CVD is n-type with very low carrier concentrations on the order of ~1014cm-3, electron mobility in the range 3.3-16.7cm2/V.s. Mobility values up to ~ 15 cm2/Vs for a grain size in the 10nm to 60nm range, is an interesting result, as in the work of K. Kang et al., [3], the monolayer grain size is around 1 mm with an associated electron mobility of 30 cm2/V. These results suggests that grain boundary defects in 2D MoS2 may not be the main factor limiting carrier mobility, as is typically the case in polycrystalline 3D semiconductors (see for example [7]). In addition, the unintentional n type doping in the CVD grown MoS2 is low, with values around 1-3x1014 cm-3. This low value of unintentional doping provides a useful baseline in-situ for doping studies with elements such as Nb [8] and Re [9].