Low Specific Contact Resistance Research Articles

Achieving ultralow contact resistivity in Si via Te hyperdoping and millisecond post-metallization annealing

Achieving extremely low specific contact resistance (ρc) has become a critical challenge for nanoelectronics to achieve high device performance with increased miniaturization. In this work, we explore the use of Tellurium hyperdoping and millisecond-range post-metallization flash lamp annealing as a potential solution to overcome this bottleneck. The epitaxially-resolidified hyperdoped Si layers with tunable carrier densities approaching 1021 cm−3 are achieved, which consequently alters the band diagrams as simulated by COMSOL Multiphysics®. This results in a sufficiently narrow Schottky barrier, which enables electron tunneling and can ultimately achieve extremely low ρc on the order of 10−9 Ω·cm2 in a Au/Ti/Te-hyperdoped Si junction. This study introduces an alternative fabrication process for Schottky barrier engineering, providing a viable method for the realization of future miniaturized nanoelectronics devices with high carrier density and extremely low ρc.

Large-area and few-layered 1T′-MoTe2 thin films grown by cold-wall chemical vapor deposition

This study employs cold-wall chemical vapor deposition to achieve the growth of MoTe2 thin films on 4-inch sapphire substrates. A two-step growth process is utilized, incorporating MoO3 and Te powder sources under low-pressure conditions to synthesize MoTe2. The resultant MoTe2 thin films exhibit a dominant 1T′ phase, as evidenced by a prominent Raman peak at 161 cm−1. This preferential 1T′ phase formation is attributed to controlled manipulation of the second-step growth temperature, essentially the reaction stage between Te vapor and the pre-deposited MoO x layer. Under these optimized growth conditions, the thickness of the continuous 1T′-MoTe2 films can be precisely tailored within the range of 3.5–5.7 nm (equivalent to 5–8 layers), as determined by atomic force microscopy depth profiling. Hall-effect measurements unveil a typical hole concentration and mobility of 0.2 cm2 Vs−1 and 7.9 × 1021 cm−3, respectively, for the synthesized few-layered 1T′-MoTe2 films. Furthermore, Ti/Al bilayer metal contacts deposited on the few-layered 1T′-MoTe2 films exhibit low specific contact resistances of approximately 1.0 × 10−4 Ω cm2 estimated by the transfer length model. This finding suggests a viable approach for achieving low ohmic contact resistance using the 1T′-MoTe2 intermediate layer between metallic electrodes and two-dimensional semiconductors.

Low contact resistance and high breakdown voltage of AlGaN/GaN HEMT grown on silicon using both AlN/GaN superlattice and Al0.07Ga0.93N back barrier layer

In this study, the growth of a high-quality AlGaN/GaN high electron mobility transistor (HEMT) heterostructure on silicon (Si) by metal–organic chemical vapor deposition was investigated by utilizing both the AlN/GaN superlattice (SL) and Al0.07Ga0.93N back barrier (BB) techniques. An atomic force microscope and high-resolution x-ray diffractometer confirm a low surface roughness of 0.26–0.34 nm and the formation of a high-quality AlN/GaN SL and GaN channel. The AlGaN/GaN heterostructures exhibit a high electron mobility of up to 1700 cm2 V−1∙s and a high carrier concentration density of (1.02–1.06 × 1013 cm−2) for both heterostructures. The AlGaN/GaN HEMT devices demonstrate a low specific contact resistivity (ρ c) of 2.7 × 10−6 Ω·cm2 and a low contact resistance (RC ) of 0.3 Ω·mm for the heterostructure with a BB layer. Furthermore, the DC characteristics demonstrate that incorporating Al0.07Ga0.93N BB in the heterostructure results in a 19.2% increase in lateral breakdown voltage (with a 10 µm spacing) and a 27.5% increase in vertical breakdown voltage (at 1 mA cm−2) compared to heterostructures without Al0.07Ga0.93N BB within the AlN/GaN SL structure. Moreover, an improvement of 10.6% in the maximum saturation current (I DS) and 15.2% in on-resistance (R ON) has been achieved for the device fabricated on an Al0.07Ga0.93N BB structure. The insertion loss of the buffer layer improves to −1.40 dB mm−1 at 40 GHz. Consequently, the proposed heterostructure investigated in this study demonstrates suitability for electronic device applications.

Localized Surface Doping Induced Ultralow Contact Resistance between Metal and (Bi,Sb)2Te3 Thermoelectric Films.

Micro thermoelectric devices are expected to further improve the cooling density for the temperature control of electronic devices; nevertheless, the high contact resistivity between metals and semiconductors critically limits their applications, especially in chip cooling with extremely high heat flux. Herein, based on the calculated results, a low specific contact resistivity of ∼10-7 Ω cm2 at the interface is required to guarantee a desirable cooling power density of micro devices. Thus, we developed a generally applicable interfacial modulation strategy via localized surface doping of thermoelectric films, and the feasibility of such a doping approach for both n/p-type (Bi,Sb)2Te3 films was demonstrated, which can effectively increase the surface-majority carrier concentration explained by the charge transfer mechanism. With a proper doping level, ultralow specific contact resistivities at the interfaces are obtained for n-type (6.71 × 10-8 Ω cm2) and p-type (3.70 × 10-7 Ω cm2) (Bi,Sb)2Te3 layers, respectively, which is mainly attributed to the carrier tunneling enhancement with a narrowed interfacial contact barrier width. This work provides an effective scheme to further reduce the internal resistance of micro thermoelectric coolers, which can also be extended as a kind of universal interfacial modification technique for micro semiconductor devices.

Monolithic 24 cm2 flexible triple-junction solar cell encapsulated module based on the ipsilateral electrode welding technology

The inverted metamorphic multi-junction solar cell is anticipated to be widely applied in stratospheric flight because of its exceptional properties of flexibility and light weight. We propose an ipsilateral welding technology based on Ti/Au electrodes to simplify the fabrication process of GaInP/GaAs/InGaAs solar cells and encapsulate large-sized flexible solar cells. After annealing at 200°C for 2 h, the Ti/Au electrode achieved a low specific contact resistivity of 2.9×10−7Ω⋅cm2. The performance of the ohmic contact remains stable after the thermal cycling tests. The Ti/Au electrode can require less heat input for welding to reduce the risk of microcrack formation of the solar cells. By employment of this electrode, a 24cm2 solar cell achieved a conversion efficiency of 34.74%. A flexible solar cell module with an efficiency of 32.82% under AM 1.5G illumination was obtained by the ipsilateral electrode welding technology.

Thermal annealing induced graphite/diamond structure processed by high-voltage hydroxide ion treatments

Ohmic contacts with low specific contact resistance are necessary for fabrication of diamond electronic devices. This work reports that graphite/diamond ohmic contacts can be obtained by thermal annealing of diamond, patterned by hydroxide ion treatment. Surface graphitization of diamond is achieved through rapid thermal annealing at 1050 °C in vacuum. The thickness of graphite layer is found to be dependent on the duration of annealing with an approximate rate of 3.3 ∼ 3.6 nm/minute. The alteration in surface structure is analyzed using Raman spectra, showing a continuously enhanced G peak with increasing annealing time. Early stages of graphitization are discovered by X-ray photoelectron spectroscopy, after annealing diamond samples for merely 0.5 ∼ 2 min. Additionally, a distinct atomic interface between graphite and diamond is observed via cross-sectional transmission electron microscopy. Further, the surface graphite is selectively etched by hydroxide ion treatments, protected by gold patterns. In the end, the specific contact resistance of the graphite/diamond contact is determined to be 2.53 × 10-4 Ω cm2 employing the transmission line model.

Metal Contact on P-Type 4H-SiC With Low Specific Contact Resistance and Micrometer-Scale Contact Area

Metal Contact on P-Type 4H-SiC With Low Specific Contact Resistance and Micrometer-Scale Contact Area

Carrier transport mechanism of Mg/Pt/Au Ohmic contact on p-GaN/AlGaN/GaN platform with ultra-low resistivity

In this work, the carrier transport mechanism of Mg/Pt/Au Ohmic contact on p-GaN/AlGaN/GaN with a very low specific contact resistivity of 1.98 × 10−5 Ω cm2 is investigated. Secondary ion mass spectroscopy measurement results show that the Mg concentration near the p-GaN surface increases form 8 × 1019 to 7 × 1020/cm3 for Mg/Pt/Au contact after annealing. It indicates that Mg atoms from the Mg/Pt/Au metal stack diffuse into the p-GaN during annealing, forming a heavily Mg doped p++-GaN layer with a depth of about 3 nm. The sheet resistance Rsh depends on temperature for Mg/Pt/Au contacts on p-GaN/GaN, indicating that the influence of 2DHG on carrier transport mechanisms at the metal/p-GaN interface was eliminated. For Mg/Pt/Au contacts at ≥360 K, specific contact resistivity reasonably follows T−1, which indicates that the band conduction of Schottky theory dominates the carrier transport. For Mg/Pt/Au contacts at 200–360 K, the electrical resistivity reasonably follows T−1/4, indicating variable-range hopping (VRH) conduction through Mg-related deep-level defects (DLD). Based on the VRH conduction model, the effective barrier height (qφ) of the Mg-related DLD band is extracted as 0.265 eV, which well matches the excellent Ohmic contact.

Improved efficiency of AlGaN-based flip-chip deep-ultraviolet LEDs using a Ni/Rh/Ni/Au p-type electrode.

Here, we propose a thermally stable and high-reflectivity Ni/Rh/Ni/Au p-type electrode for AlGaN-based deep-ultraviolet (DUV) flip-chip light-emitting diodes (FCLEDs). We discover that the reflectance of Ni/Au electrode deteriorated significantly after rapid thermal annealing. Experiments show that Ni and Au agglomerate at high temperatures, and more incident photons traverse the gaps between the agglomerates, leading to a decrease in reflectance of Ni/Au after annealing. In contrast, the proposed Ni/Rh/Ni/Au p-type electrode shows remarkable thermal stability as a result of the suppression of Ni agglomeration by the Rh layer at high temperatures. Besides, due to the higher reflectivity of the Ni/Rh/Ni/Au electrode and its lower specific contact resistivity formed with p-GaN, the external quantum efficiency and wall-plug efficiency of a DUV FCLED with Ni/Rh/Ni/Au electrode are increased by 13.94% and 17.30% in comparison with the one with Ni/Au electrode at an injection current of 100 mA. The Ni/Rh/Ni/Au electrode effectively solves the long-standing dilemma of efficiency degradation of DUV FCLEDs with a Ni/Au electrode after high-temperature annealing.

Interface Engineering Boosting High Power Density and Conversion Efficiency in Mg2Sn0.75Ge0.25‐Based Thermoelectric Devices

AbstractElectrode contact interfaces for practical thermoelectric (TE) devices require high bonding strength, low specific contact resistivity, and superb stability. Herein, the state‐of‐the‐art Cu2MgFe/Mg2Sn0.75Ge0.25 interface is designed for Mg2Sn0.75Ge0.25‐based TE devices, adhering to the general strategy of high bonding propensity, thermal expansion matching, diffusion passivation, and dopant inactivation. The interfacial stability is verified by the in situ transmission electron microscopy analysis, thereby confirming the contributions from decreasing the chemical potential gradient and increasing the diffusion activation energy barrier. The single‐leg device exhibits a high power density (ωmax) of 2.6 W cm−2 and conversion efficiency (ηmax) of 8% under a temperature difference (ΔT) of 370 °C, which is the record‐breaking value in comparison to other Mg2(Si, Ge, Sn)‐based TE devices. Additionally, a two‐couple device with p‐type Bi2Te3 shows an excellent ωmax of 1.3 W cm−2 and ηmax of 5.4% under a ΔT of 270 °C, comparable to commercial Bi2Te3 devices. The proposed interface design strategy provides a general technique for constructing high‐performance devices using cutting‐edge TE materials.

Potassium hydroxide surface modification for low temperature Cu/SiO2 hybrid bonding

This paper reports a novel plasma-free surface modification approach for low temperature Cu/SiO2 hybrid bonding. A 1-M KOH solution was employed, which acts as a hydroxyl group supply and further modifies the surface of SiO2 dielectric layer by the Si–OH transformation. Such a KOH solution makes the Cu surface more hydrophilic without increasing its surface roughness. We found that the contact angles significantly decreased after dipping into 0.5–3 M of KOH. A contact angle below 5° was achieved with > 1 M KOH. The X-ray photoelectron spectroscopy (XPS) results showed an increase in Si–OH (7.8% to 40.6%) and decreases in Si–O–Si (64% to 55%), Si–O and CO (28.2% to 4.4%) intensities after KOH wet treatment. Furthermore, the KOH treatment almost does not etch nor roughen the Cu surfaces. Therefore, the bonding temperature could be lowered to 200 °C while keeping high bonding strength and reliability performance. A low specific contact resistance of 5 × 10−8 Ω.cm2 was obtained. Results obtained by scanning electron microscope (SEM) and transmission electron microscope (TEM) show the excellent bonding quality of both SiO2–SiO2 and Cu–Cu interface. Additionally, energy-dispersive X-ray spectrometry (EDS) analyses show no signs of oxides and potassium contaminations at the bonding interfaces.

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.

Homoepitaxial growth of (100) Si-doped β-Ga2O3 films via MOCVD

Homoepitaxial growth of Si-doped β-Ga2O3 films on semi-insulating (100) β-Ga2O3 substrates by metalorganic chemical vapor deposition (MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in (100) β-Ga2O3 films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga2O3 film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the (400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 1015 – 1.74 × 1020 cm−3. Hall measurements demonstrate a high electron mobility value of 51 cm2/(V·s), corresponding to a carrier concentration of 7.19 × 1018 cm−3 and a high activation efficiency of up to 61.5%. Transmission line model (TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10-4 Ω·cm2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 1019 cm−3, confirming the effective Si doing in the MOCVD epitaxy.

Low specific contact resistance between InAs/Ni–InAs evaluated by multi-sidewall TLM

The specific contact resistance ρint of the InAs/Ni–InAs interface was evaluated by the multi-sidewall transmission line method (MSTLM), where Ni–InAs was formed by alloying Ni and InAs-on-insulator substrates. The revised test structure for MSTLM has been proposed, which can be easily fabricated. By evaluating each component of the parasitic resistance separately, the specific contact resistance of the InAs/Ni–InAs was accurately extracted. As a result, the record low ρint of (4.3 ± 2.5) × 10−9 Ω cm2 among metal/III-V contacts was obtained for the 30-nm-thick InAs/Ni–InAs interface with the average electron concentration of 9.1 × 1018 cm−3 for InAs, which is close to the Landauer limit. The comparison of the experimental and theoretical ρint indicates that there is no potential barrier at the InAs/Ni–InAs interface, which is attributable to the negative Schottky barrier height for electrons of InAs.

Ag nanodot/Mg/Al reflective Ohmic contacts simultaneously suitable for n-type and p-type GaN

This work reports on high-reflectivity Ag nanodot (AgND)/Mg/Al Ohmic contacts suitable for both p-GaN and n-GaN. The lowest specific contact resistances are found to be 2.25 × 10−2 Ω·cm2 on p-GaN and 2.56 × 10−5 Ω·cm2 on n-GaN. Ag was deposited and converted into AgNDs by annealing, and Mg/Al was then deposited. A second annealing process at different temperatures was performed to check the thermal stability of the contacts. Both the p-GaN and n-GaN contacts were Ohmic after annealing at 300 °C or below. The AgND/Mg/Al contacts annealed at 250 °C or less showed a reflectivity of over 91% for wavelengths from 400 to 550 nm. X-ray photoelectron spectroscopy and x-ray diffraction measurements were performed to investigate the contact mechanisms. We propose that in AgND/Mg/Al on p-GaN, the effective barrier is lowered due to the presence of an Ag2O intermedia layer and the tunneling effect enables Ohmic contact. When the annealing temperature is 350 °C or higher, the Ag2O changes to β-AgGaO2 or is decomposed and the height and width of the barrier for holes increase, which causes the Ohmic contact to deteriorate. The Ohmic behavior of AgND/Mg/Al contacts on n-GaN is assumed to be mainly due to the high direct coverage ratio of Mg and the good Ohmic contact behavior of Mg/n-GaN. These results show that AgND/Mg/Al Ohmic contacts can be fabricated simultaneously on both p-GaN and n-GaN, which is a possible solution for improving the density of both GaN-based ICs and micro-light emitting diodes (LEDs). This contact scheme can also improve the light output efficiency of GaN-based LEDs.

Role of Ti and W in the Ni-based ohmic contacts to n-type 4H-SiC

The paper investigated the influence mechanism of Ti and W on the electrical and structural properties of the Ni-based ohmic contacts to n-type 4H-SiC. The variation of specific contact resistances (SCRs) with different contact structures was found to be correlated to the relative proportion of the total contact area occupied by the (220) plane than that of the (301) plane at the contact interface for the polycrystalline and textured δ-Ni2Si films characterized by the X-ray diffraction (XRD). Due to the formation of metal carbides, the W layer was found to be beneficial for a higher relative proportion contributing to a reduction of SCR. In contrast, the Ti layer was detrimental owing to the incorporation of metal oxides and carbides. Therefore, W is considered a better candidate to improve the thermal stability of Ni-based ohmic contacts to n-type 4H-SiC while maintaining a low specific contact resistance. Moreover, it was found that the free carbon atoms were immobilized or blocked by the W or Ti layer, and a greater distance of free carbon away from the contact surface led to a smoother and more uniform surface morphology. We believe that this discovery provides a valuable insight into the tuning of surface morphology for the wire bonding challenge.

Corrosion‐Resistive and Low Specific Contact Resistance Ohmic Contacts to Semiconducting Diamonds Using Nanocarbon Electrodes

The realization of diamond‐based advanced devices is interrelated with the fabrication of practical ohmic contacts. Contrary to boron‐doped, the phosphorus‐doped diamonds with interface carbide forming Ti‐based conventional ohmic contacts find their limitation in device fabrication due to the high contact resistance. Herein, nanocarbon ohmic contacts are deposited by a coaxial arc plasma gun on semiconducting diamonds, and their composite structure which facilitates exceptional contact properties is explored. A comparative electrical characterization between nanocarbon ohmic contacts and conventional Ti‐based contacts is performed on a heavily phosphorus‐doped diamond, and they exhibited one‐order declination in specific contact resistance. In addition to the low contact resistance, an ideal ohmic electrode is preferable to have good mechanical adhesion and corrosion resistance for device applications. The contact behavior of n‐type diamond/nanocarbon against an extremely corrosive environment realized by boiling H2SO4 + HNO3 solution is analyzed. The nanocarbon ohmic contacts exhibit excellent corrosion resistance and mechanical adhesion over conventional Ti‐based contacts. A similar trend is also observed for nanocarbon contacts on boron‐doped diamonds. The modest effect on the transfer length of the nanocarbon contacts with respect to acid treatment sessions indicates a tightly bonded diamond/nanocarbon interface and actively suggests their application in highly‐corrosive and harsh environments.

A Refined Ladder Transmission Line Model for the Extraction of Significantly Low Specific Contact Resistivity

In this article, a refined ladder transmission line model (R-LTLM) test structure capable of extracting significantly low specific contact resistivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho _{c}$ </tex-math></inline-formula> ) eliminating parasitic metal resistance is proposed. Theoretical derivations, technology computer-aided design (TCAD) simulations, and experiments are performed to verify the validity and superiority of R-LTLM. Compared with refined transmission line model (RTLM) and ladder transmission line model (LTLM), R-LTLM not only achieves higher extraction accuracy than RTLM but also relieves the impact of process variation during the formation of contact area patterns and contact spacings. Moreover, the impacts of process variation on the extraction of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho _{c}$ </tex-math></inline-formula> using LTLM and R-LTLM are analyzed. As for experimental verification, RTLM, LTLM, and R-LTLM test structures are fabricated to extract <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho _{c}$ </tex-math></inline-formula> of TiSix/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{n}^{+}$ </tex-math></inline-formula> -Si Ohmic contacts. Results show that R-LTLM can eliminate parasitic metal resistance, leading to higher extraction accuracy than RTLM.

Low Temperature Epitaxy of In Situ GaDoped Si1-XGex: Dopant Incorporation, Structural and Electrical Properties

Over the last few decades, MOSFET architectures have evolved from planar to 3D structures (FinFET and, more recently, gate-all-around and Forksheet devices) to improve the channel control at very scaled dimensions. In this framework, highly doped conformal Si1-xGex epitaxial films are used for source/drain (S/D) regions in pMOS devices to form ohmic metal-semiconductor contacts with low specific contact resistivities (ρc). Boron is the main p-type dopant in Si1-xGex thanks to its high active concentration (~ 1×1021 at./cm3) for Ge concentrations of ~ 50 at.% [1]. For higher Ge/Si ratios, gallium is considered a promising doping element due to its higher solid solubility in Ge compared with boron. However, a strong Ga surface segregation is reported to occur during the epitaxy of in situ doped Si1-xGex, leading to a Ga-rich second phase at the epilayer surface [2]. In films grown at temperatures ≥ 450°C, the Ga surface segregation limits the bulk Ga concentration ([Ga]chem) to 1×1018 at./cm3 [3]. This low doping level results in inferior electrical properties for current MOSFET applications. Models in the literature [4] indicate that, at sufficiently low temperature, dopant segregation is limited by surface kinetic mechanisms. Thus, the segregation ratio could be controlled by changing the process temperature. Based on this approach, low temperature, Si2H6 + Ge2H6 based processes with improved Ga incorporation were developed [5].In this contribution, we report on novel in situ Ga doped Si1-xGex epitaxial layers grown at temperatures ≤ 400°C. Using a HCl surface clean, necessary to avoid the SIMS Ga decay from the surface which can mask the real concentration profile [3], Ga box-shaped profiles with concentrations above 1×1020 at./cm3 are found (Fig. 1). Two growth temperatures are compared: 400°C and 350°C. For each temperature, variable Ga precursor (tri-tert-butyl gallium) flows (fTTBGa) were used. A reduction in the growth temperature enhances the Ga incorporation, as evidenced from the two SEM morphology inspections displayed in Fig. 1. Here, two samples with a similar bulk [Ga]chem of ~ 6 ×1019 at./cm3, as measured by SIMS, exhibit either a clustered or smooth surface depending on the deposition temperature applied.This improved Ga incorporation allows for systematic studies of in situ Ga doping on the structural and electrical properties of Si1-xGex. In both series of samples, the layer resistivities (ρ) follow a similar trend, characterized by a steep decrease at smaller fTTBGa and a plateau for higher flows (Fig. 2). The lowest ρ values are found for the layers grown at 350°C. This denotes that different saturation levels in the active Ga concentration ([Ga]act) exist for the process conditions used here. In a similar way to what is typically observed for B doping, an increase in the Ga doping level causes a boost in epilayer growth rate. This growth rate trend saturates simultaneously with ρ, suggesting that the phenomenon is linked to the level of incorporated substitutional Ga atoms. In addition, the resulting Ge concentrations of the Si1-xGex layers are found to increase with Ga concentration. From HR-XRD analysis, strain-relaxation is also found to progressively increase with the TTBGa flow and so the incorporated Ga may not be fully active. For this reason, X-ray absorption fine structure spectra (XAFS) were acquired at the Ga K-edge on Si0.4Ge0.6:Ga and Ge:Ga epilayers with the results obtained reported in Fig.3. Based on comparative analysis of the first coordination Ga shell with DFT simulation results, Ga dopants appear to be placed in substitutional positions for both materials. Furthermore, a shorter nearest-neighbors distance is measured for Ga in Si0.4Ge0.6 compared to Ge, indicating a difference in the local strain associated to the dopant for the two considered matrixes.[1] R. Loo et al., “Processing Technologies for Advanced Ge Devices,” ECS J. Solid State Sci. Technol., vol. 6, no. 1, pp. P14–P20, 2017.[2] J. Margetis et al., “Epitaxial Growth of Ga-doped SiGe for Reduction of Contact Resistance in finFET Source/Drain Materials,” ECS Trans., vol. 93, no. 1, pp. 7–10, 2019.[3] G. Rengo et al., “B and Ga Co-Doped Si1−xGex for p-Type Source/Drain Contacts,” ECS J. Solid State Sci. Technol., vol. 11, no. 2, 024008, 2022.[4] C. B. Arnold and M. J. Aziz, “Unified kinetic model of dopant segregation during vapor-phase growth,” Phys. Rev. B - Condens. Matter Mater. Phys., vol. 72, no. 19, 195419, 2005.[5] A. Y. Hikavyy et al., “Cutting-Edge Epitaxial Processes for Sub 3 Nm Technology Nodes: Application to Nanosheet Stacks and Epitaxial Wrap-Around Contacts,” ECS Trans., vol. 104, no. 4, pp. 139–146, Oct. 2021. Figure 1

Low Resistance Ohmic Contact on Epitaxial MOVPE Grown β-Ga2O3 and β-(AlxGa1−x)2O3 Films

We report on the realization of record low resistance Ohmic contacts to MOVPE-grown heavily Si-doped $\beta$-Ga$_2$O$_3$ and $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$ epitaxial films. Transfer length measurement (TLM) patterns were fabricated on the heavily Si-doped homoepitaxial $\beta$-Ga$_2$O$_3$ films with electron concentration (n) ranging from 1.77 to 3.23e20 cm^-3. Record low specific contact resistance and total contact resistance (Rc) of 1.62e-7 Ohm.cm^2 and 0.023 Ohm.mm were realized for $\beta$-Ga$_2$O$_3$: Si films with n > 3e20 cm^-3. TLM structures were also fabricated on heavily Si doped coherently strained $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$ (x=12%, 17% and 22%) films. The film with 12% Al composition (n=1.23e20 cm^-3) showed \r{ho}c of 5.85e-6 Ohm.cm^2, but it increased to 2.19e-4 Ohm.cm^2 for a layer with a 22% Al composition. Annealing the samples post metal deposition has generally led to a decrease in contact resistance, but for high Al content $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$, the contact resistance did not change significantly after the annealing process. The low contact resistance values measured in this work are very promising for the fabrication of high frequency power devices.