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1.
Titanium (15 nm)/aluminum (60 nm)/rhenium (20 nm)/gold (50 nm) ohmic contacts to moderately doped n-type GaN (4.07×1018 cm−3) have been investigated as a function of annealing temperature. It is shown that the current-voltage (I–V) characteristics of the contacts are improved upon annealing at temperatures in the range of 550–750°C. Specific contact resistance as low as 1.3 × 10−6 Ωcm2 is obtained after annealing at 750°C for 1 min in a nitrogen ambient. X-ray photoemission spectroscopy (XPS) results show that the Ga 2p core level for the sample annealed at 750°C shifts toward the high binding side by 0.71 eV compared with that of the as-deposited one. It is also shown that the contact does not seriously suffer from thermal degradation even when annealed at 750°C for 30 min. Based on Auger electron spectroscopy (AES), glancing angle x-ray diffraction (GXRD), and XPS results, possible explanations for the annealing-induced improvement of the ohmic behavior are described and discussed.  相似文献   

2.
Ta/Au ohmic contacts are fabricated on n-type ZnO (∼1 × 1017 cm−3) epilayers, which were grown on R-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). After growth and metallization, the samples are annealed at 300°C and 500°C for 30 sec in nitrogen ambient. The specific contact resistance is measured to be 3.2×10−4 Ωcm2 for the as-deposited samples. It reduces to 5.4×10−6 Ωcm2 after annealing at 300°C for 30 sec without significant surface morphology degradation. When the sample is annealed at 500°C for 30 sec, the specific contact resistance increases to 3.3 × 10−5 Ωcm2. The layer structures no longer exist due to strong Au and Ta in-diffusion and O out-diffusion. The contact surface becomes rough and textured.  相似文献   

3.
Electrical properties of Ni/Au ohmic contacts on p-type GaN were interpreted with the change of microstructure observed under transmission electron microscopy. The contact resistivity was decreased from 1.3×10−2 to 6.1×10−4 Ωcm2 after annealing at 600°C. The reduction is due to the dissolution of Ga atoms into Au−Ni solid solution formed during annealing, via the generation of Ga vacancies. Thus, net concentration of holes increased below the contact, resulting in the reduction of contact resistivity. At 800°C, N atoms decomposed; reacted with Ni, and forming cubic Ni4N. Consequently, N vacancies, acting as donors in GaN, were generated below the contact, leading to the increase of contact resistivity to 3.8×10−2 Ωcm2.  相似文献   

4.
Fabrication procedures for silicon carbide power metal oxide semiconductor field effect transistors (MOSFETs) can be improved through simultaneous formation (i.e., same contact materials and one step annealing) of ohmic contacts on both the p-well and n-source regions. We have succeeded with the simultaneous formation of the ohmic contacts for p- and n-type SiC semiconductors by examining ternary Ni/Ti/Al materials with various compositions, where a slash symbol “/” indicates the deposition sequence starting with Ni. The Ni(20 nm)/Ti(50 nm)/Al(50 nm) combination provided specific contact resistances of 2 × 10−3 Ω-cm2 and 2 × 10−4 Ω-cm2 for p- and n-type SiC, respectively, after annealing at 800°C for 30 min, where the doping level of Al in the SiC substrate was 4.5 × 1018 cm−3 and the level of N was 1.0 × 1019 cm−3.  相似文献   

5.
We report on low-resistance and thermally stable Pd/Ru ohmic contacts to surface-treated p-GaN (3 × 1017 cm−3). It is shown that annealing at 500°C for 2 min in a N2 ambient improves ohmic contact properties. Specific contact resistance is measured to be 9.2(±0.2) × 10−4 and 2.4(±0.2) × 10−5 Ωcm2 for the as-deposited and annealed samples, respectively. Atomic force microscopy results show that the surfaces of both the contacts are remarkably smooth with a root-mean-square (rms) roughness of about 0.6 nm. The current-voltage-temperature (I-V-T) and calculation results indicate that, for the as-deposited contact, thermionic field emission is dominant, while for the annealed contact, field emission dominates the current flow.  相似文献   

6.
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.  相似文献   

7.
The electrical and thermal properties of Ru and Ru/Au ohmic contacts on two-step-surface-treated p-GaN have been investigated using current-voltage (I–V) measurements and Auger electron spectroscopy. It is shown that annealing at 700°C for 2 min in a flowing N2 atmosphere improves the I–V characteristics of the contacts. For example, the annealed Ru and Ru/Au schemes produce a specific contact resistance of 3.4 (±0.9)×10−3 and 1.2 (±1.1)×10−3 Ωcm2, respectively. It is also shown that annealing results in a large reduction (by ∼100 meV) in the Schottky barrier heights of the Ru and Ru/Au contacts, compared to the as-deposited ones. The electrical properties of the two-step-surface-treated Ru/Au contacts are compared with those of the conventionally treated contacts.  相似文献   

8.
Ohmic contacts with low resistance are fabricated on n-GaN films using Al/Ti bilayer metallization. GaN films used are 0.3 μm thick layers with carrier concentrations of 1 × 1019 cm−3 grown on the c-plane sapphire by ion-removed electron cyclotron resonance molecular beam epitaxy. The lowest value for the specific contact resistivity (ρc) of 1.2×10−8 Ω·cm2 was obtained with furnace annealing at 500°C for 60 min. This result shows the effectiveness of high carrier concentration GaN layers and the low temperature annealing for the realization of low resistance ohmic contacts. Sputtering Auger electron spectroscopy analysis reveals that Al diffuses into Ti layer and comes into contact with the GaN surface.  相似文献   

9.
The annealing conditions and contact resistivities of Ta/Al ohmic contacts to n-type GaN are reported for the first time. The high temperature stability and mechanical integrity of Ti/Al and Ta/Al contacts have been investigated. Ta/Al (35 nm/115 nm) contacts to n-type GaN became ohmic after annealing for 3 min at 500°C or for 15 s at 600°C. A minimum contact resistivity of 5×10−6Ω cm2 was measured after contacts were repatterned with an Al layer to reduce the effect of a high metal sheet resistance. Ti/Al and Ta/Al contacts encapsulated under vacuum in quartz tubes showed a significant increase in contact resistivity after aging for five days at 600°C. Cross section transmission electron microscopy micrographs and electrical measurements of aged samples indicate that the increased contact resistivity is primarily the result of degradation of the metal layers. Minimal reactions at the metal/GaN interface of aged samples were observed.  相似文献   

10.
Ohmic contacts have been fabricated on p-type 6H-SiC using CrB2. Two hundred nanometer thick films were sputter-deposited on substrates of doping concentration 1.3×1019 cm−3 in a system with a base pressure of 3×10−7 Torr. Specific contact resistances were measured using the linear transmission line method, and the physical properties of the contacts were examined using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and transmission electron microscopy. The as-deposited CrB2 contacts exhibited rectifying characteristics and contained oxygen as a major contaminant. Ohmic behavior with linear current-voltage characteristics was observed following short anneals at 1100°C for 2 min at a pressure of 5×10−7 Torr. The oxygen in the CrB2 films was removed by the annealing process, and the lowest value of the specific contact resistance (rc) measured at room temperature was 8.2×10−5 Ω-cm2. Longer anneals at 1100°C for 3.5 h and 1200°C for 2 h reduced the room temperature values of r to 1.4×10−5 Ω-cm2. A thin reaction region has been identified at the CrB2/SiC interface; however, the interface remains essentially stable. Thermal stressing at 300°C in vacuum for over 2200 h produced only a slight increase in the specific contact resistance. The low value of the specific contact resistance and the excellent high temperature stability of the CrB2/SiC interface make this contact a candidate for high power/high temperature SiC device applications.  相似文献   

11.
The use of TaN, TiN, and ZrN diffusion barriers for Ti/Al-based contacts on n-GaN (n ∼ 3 × 1017 cm−3) is reported. The annealing temperature (600–1,000°C) dependence of the Ohmic contact characteristics using a Ti/Al/X/Ti/Au metallization scheme, where X is TaN, TiN, or ZrN, deposited by sputtering was investigated by contact resistance measurements and Auger electron spectroscopy (AES). The as-deposited contacts were rectifying and transitioned to Ohmic behavior for annealing at ≥600°C. A minimum specific contact resistivity of ∼6 × 10−5 Ω-cm−2 was obtained after annealing over a broad range of temperatures (600–900°C for 60 s), comparable to that achieved using a conventional Ti/Al/Pt/Au scheme on the same samples. The contact morphology became considerably rougher at the high end of the annealing range. The long-term reliability of the contacts at 350°C was examined; each contact structure showed an increase in contact resistance by a factor of three to four over 24 days at 350°C in air. AES profiling showed that the aging had little effect on the contact structure of the nitride stacks.  相似文献   

12.
In this work, heavily aluminum (Al)-doped layers for ohmic contact formation to p-type SiC were produced by utilizing the high efficiency of Al incorporation during the epitaxial growth at low temperature, previously demonstrated by the authors’ group. The low-temperature halo-carbon epitaxial growth technique with in situ trimethylaluminum (TMA) doping was used. Nearly featureless epilayer morphology with an Al atomic concentration exceeding 3 × 1020 cm−3 was obtained after growth at 1300°C with a growth rate of 1.5 μm/h. Nickel transfer length method (TLM) contacts with a thin adhesion layer of titanium (Ti) were formed. Even prior to contact annealing, the as-deposited metal contacts were almost completely ohmic, with a specific contact resistance of 2 × 10−2 Ω cm2. The specific contact resistance was reduced to 6 × 10−5 Ω cm2 by employing a conventional rapid thermal anneal (RTA) at 750°C. Resistivity of the epitaxial layers better than 0.01 Ω cm was measured for an Al atomic concentration of 2.7 × 1020 cm−3.  相似文献   

13.
Excellent ohmic characteristics for undoped-AlGaN/GaN heterostructures have been achieved by using a Si nano-interlayer: a 1-nm Si layer has been evaporated followed by Ti/Al/Mo/Au evaporation. A contact transfer resistance of 0.18 Ω-mm and a specific contact resistivity of 1 × 10−6 Ω-cm2 have been achieved along with excellent surface morphology at an optimized annealing temperature (800°C). Both ohmic contact characteristics and surface morphology are significantly better than those obtained without the Si nano-interlayer. Auger depth profiles and temperature-dependent current-voltage characteristics were investigated to understand ohmic formation. It is suggested that titanium silicide formation at the interface during rapid thermal annealing lowers the barrier height and enhances thermionic emission current.  相似文献   

14.
Four vanadium-based contacts to n-type Al0.6Ga0.4N were compared in this work. Both V/Al/Pd/Au and V/Al/V/Au contacts with optimized layer thicknesses provided lower specific-contact resistances than did the previously reported V/Al/Pt/Au ohmic contact. Specific contact resistances of the V/Al/Pd/Au (15 nm/85 nm/20 nm/95 nm) and V/Al/V/Au (15 nm/85 nm/20 nm/95 nm) contacts were 3×10−6 Ω·cm2 and 4×10−6 Ω·cm2, respectively. On the other hand, an analogous V/Al/Mo/Au contact never became ohmic, even after it was annealed at 900°C for 30 sec. Compared to the V/Al/Pd/Au contact, the V/Al/V/Au contact required a less severe annealing condition (30 sec at 700°C instead of 850°C). The V/Al/V/Au contact also provided a smoother surface, with a root-mean-square (RMS) roughness of 39 nm.  相似文献   

15.
The effects of implanted Ge on the resistance of nickel-metal contacts to n-type and p-type 4H-SiC are reported. The Ge was implanted with an energy of 346 keV and a dose of 1.7×1016 cm−2, and the wafer was annealed up to 1700°C for 30 min. Contact resistance measurements using the transfer length method (TLM) were performed on etched mesas of n-type and p-type 4H-SiC, with and without the Ge. For the annealed-Ni metal contacts, the Ge lowered the specific contact resistivity from 5.3×10−4 Ωcm2 to 6.0×10−5 Ωcm2 for n-type SiC and from 1.2×10−3 Ωcm2 to 8.3×10−5 Ωcm2 for p-type SiC. For the as-deposited (unannealed) Ni, the Ge produced ohmic contacts, whereas the contacts without Ge were rectifying. These results suggest that the addition of Ge can be an important process step to reduce the contact resistance for SiC-device applications.  相似文献   

16.
We report on the investigation of ohmic contact formation using sputtered titanium-tungsten contacts on an inductively coupled plasma (ICP) etch-damaged 4H-SiC surface. Transfer length method (TLM) measurements were performed to characterize how ICP-etch damage affects the performance of ohmic contacts to silicon carbide. In order to recover etch damage, high-temperature oxidation (1250°C for 1 h) was evaluated for one of the samples. Some of the etch damage was recovered, but it did not fully recover the etch damage for the sample etched with medium platen power (60 W). From our TLM measurements, the specific contact resistance (ρ C of sputtered titanium tungsten on highly doped n+-type 4H-SiC epilayers with a doping of 1.1×1019 cm−3 for the unetched reference sample, 30-W etched, and 60-W etched with and without sacrificial oxidation was as low as 3.8×10−5 Ωcm2, 3.3×10−5 Ωcm2, 2.3×10−4 Ωcm2, and 1.3×10−3 Ωcm2, respectively. We found that the low-power (30 W) ICP-etching process did not affect the formation of ohmic contacts, and we did not observe any difference between the unetched and the 30-W etched sample from our TLM measurements, having the same value of the ρ C. However, medium-platen-power (60 W) ICP etching showed significant influence on the ohmic contact formation. We found that the specific contact resistance is highly related to the surface roughness and quality of the metals, and the lower, specific contact resistance is due to smoother and denser ohmic contacts.  相似文献   

17.
We investigated the thermal stability of Pt/TaSi x /Ni/SiC ohmic contacts, which have been implemented in SiC-based gas sensors developed for applications in diesel engines and power plants. The contacts remained ohmic on lightly doped n-type (~1 × 1016 cm−3) 4H-SiC for over 1000 h in air at 300°C. Although a gradual increase in specific contact resistance from 3.4 × 10−4 Ω cm2 to 2.80 × 10−3 Ω cm2 was observed, the values appeared to stabilize after ~800 h of heating in air at 300°C. The contacts heated at 500°C and 600°C, however, showed larger increases in specific contact resistance followed by nonohmic behavior after 240 h and 36 h, respectively. Concentration profiles from Auger electron spectroscopy and electron energy-loss spectroscopy show that loss of ohmic behavior occurs when the entire tantalum silicide layer has oxidized.  相似文献   

18.
A study of Pt ohmic contacts with Si interlayers on p-type SiC (7.0×1018 cm−3) was performed as a function of the Si interlayer thickness, deposition temperature, and dopant incorporation. All contacts were ohmic after annealing at 1100°C for 5 min in vacuum. The use of a Si layer was found to decrease the specific contact resistance (SCR) relative to Pt contacts that did not contain Si, regardless of the deposition conditions used in this study. The SCR values were reduced further by three independent effects: the deposition of the Si layer at 500°C, the incorporation of B in the layer, and the design of the Pt:Si layer thicknesses in a 1:1 atomic ratio. By combining all of these effects, the lowest average SCR values (2.89×10−4 Ω cm2) were obtained. After annealing for 5 min at 1100°C, x-ray diffraction of the contacts with the 1:1 Pt:Si ratio showed a single phase of PtSi. Analyses by cross-sectional transmission electron microscopy revealed no reaction of the films with the SiC substrate. The electrical characteristics of these contacts were stable after annealing at 400°C and 600°C for 96 h and 60 h, respectively. These results are in contrast to those observed for pure Pt contacts and for contacts containing a higher Pt:Si ratio.  相似文献   

19.
Type conversion of p-GaN by direct Si+ ion implantation and subsequent annealing was demonstrated by the fabrication of lateral Schottky diodes. The Si+ activation percentage was measured as a function of annealing time (30–300 sec) and temperature (1,000–1,200°C), reaching a maximum of ∼30% for 1,200°C, 2-min anneals. The resulting n-type carrier concentration was 1.1×1018 cm−3 for a moderate Si+ ion dose of ∼2×1014 cm−2. The lateral Schottky diodes displayed a negative temperature coefficient of −0.15 V·K for reverse breakdown voltage.  相似文献   

20.
Pd-Ge based ohmic contact to n-GaAs with a TiW diffusion barrier was investigated. Electrical analysis as well as Auger electron spectroscopy and the scanning electron microscopy were used to study the contact after it was subjected to different furnace and rapid thermal annealing and different aging steps. All analyses show that TiW can act as a good barrier metal for the Au/Ge/Pd/n-GaAs contact system. A value of 1.45 × 10−6 Ω-cm2 for the specific contact resistance was obtained for the Au/TiW/Ge/Pd/n-GaAs contact after it was rapid thermally annealed at 425°C for 90 s. It can withstand a thermal aging at 350°C for 40 h with its ρc increasing to 2.94 × 10−6Ω-cm2 and for an aging at 410°C for 40 h with its ρc increasing to 1.38 × 10−5 Ω-cm2.  相似文献   

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