共查询到20条相似文献,搜索用时 31 毫秒
1.
Ariel Virshup Lisa M Porter Dorothy Lukco Kristina Buchholt Lars Hultman Anita Lloyd Spetz 《Journal of Electronic Materials》2009,38(4):569-573
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
2.
B. Krishnan S.P. Kotamraju G. Melnychuk H. Das J. N. Merrett Y. Koshka 《Journal of Electronic Materials》2010,39(1):34-38
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
3.
M. Gao S. Tsukimoto S.H. Goss S.P. Tumakha T. Onishi M. Murakami L.J. Brillson 《Journal of Electronic Materials》2007,36(4):277-284
We have investigated the roles of interfacial reaction, work function variation, and localized states of annealed Ti/Al ohmic
contacts to p-type 4H-SiC. The Al was found to be absent in the near interface region. The possibility of additional p-doping by Al indiffusion in the top SiC layer was ruled out. The work function of Ti3SiC2, the direct contact layer to SiC, was determined to be intermediate between Ti and p-SiC, leading to a considerably lowered Schottky barrier height. Reaction-induced interfacial states were observed in the near-interface
SiC, which may further reduce the barrier height and cause the formation of ohmic contact. 相似文献
4.
Indium tin oxide (ITO) thin films doped with Au, Ni, or Pt (3.5 at.% to 10.5 at.%) were deposited on p-GaN epilayers (Mg ~4 × 1019 cm−3) using direct-current (DC) sputter codeposition. It was found that undoped ITO con- tacts to p-GaN exhibited leaky Schottky behavior, whereas the incorporation of a small amount of Au (3.5 at.% to 10.5 at.%) significantly
improved their ohmic characteristics. Compared with standard Ni/ITO contacts, the Au-doped ITO contacts had a similar specific
contact resistance in the low 10−2 Ω cm−2 range, but were more stable above 600°C and more transparent at blue wavelengths. These results provide support for the use
of Au-doped ITO ohmic contact to p-type GaN in high-brightness blue light-emitting diodes. 相似文献
5.
Sung-Jae Joo Sangwon Baek Sang-Cheol Kim Jeong-Soo Lee 《Journal of Electronic Materials》2013,42(10):2897-2904
In this work, Ti/Ni bilayer contacts were fabricated on both p +- and n +-4H-SiC formed by ion implantation, and the effects of the Ti interlayer on the contact resistance and interfacial microstructure were studied. Adoption of a thin (10 nm) Ti interlayer resulted in specific contact resistance of 4.8 μΩ cm2 and 1.3 mΩ cm2 on n +- and p +-4H-SiC, respectively, comparable to the values for contacts using only Ni. Moreover, contacts using Ti/Ni provide a flat and uniform interface between Ni2Si and SiC, whereas discontinuous, agglomerated Ni2Si islands are formed without the use of a Ti interlayer. In addition, the Ti interlayer was demonstrated to effectively dissociate the thin oxide film on SiC, which is advantageous for low-resistance, reliable ohmic contact formation. In summary, use of a Ti/Ni bilayer is a promising solution for one-step formation of ohmic contacts on both p +- and n +-4H-SiC, being especially suitable for SiC n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) fabrication. 相似文献
6.
R. J. Graham R. W. Nelson P. Williams T. B. Haddock E. P. Baaklini R. J. Roede 《Journal of Electronic Materials》1990,19(11):1257-1263
The microstructure of Al-Ge-Ni ohmic contacts to bothn- andp-type GaAs has been investigated by high resolution transmission electron microscopy (TEM) and secondary ion mass spectrometry
(SIMS). Electrical assessment of these contacts shows that ohmic contacts with low specific contact resistances are formed
on bothn- andp-type material and that the thickness of Ge deposited and the alloying time have a large influence over the degree of ohmicity
observed, particularly in the case ofn-type material. TEM had previously shown the contact interface to be extremely flat and uniform in all cases with a continuous
single phase polycrystalline layer of Al3Ni adjacent to the semicon-ductor. SIMS shows that the contact components, especially the Al, diffuse into the un-derlying
semiconductor during alloying. The possible reasons for the observed varia-tions in ohmic behaviour as a result of processing
are discussed in terms of the microstructure. 相似文献
7.
S. Tsukimoto K. Nitta T. Sakai M. Moriyama Masanori Murakami 《Journal of Electronic Materials》2004,33(5):460-466
In order to understand a mechanism of TiAl-based ohmic contact formation for p-type 4H-SiC, the electrical properties and
microstructures of Ti/Al and Ni/Ti/Al contacts, which provided the specific contact resistances of approximately 2×10−5 Ω-cm2 and 7×10−5 Ω-cm2 after annealing at 1000°C and 800°C, respectively, were investigated using x-ray diffraction (XRD) and high-resolution transmission
electron microscopy (HRTEM). Ternary Ti3SiC2 carbide layers were observed to grow on the SiC surfaces in both the Ti/Al and the Ni/Ti/Al contacts when the contacts yielded
low resistance. The Ti3SiC2 carbide layers with hexagonal structures had an epitaxial orientation relationship with the 4H-SiC substrates. The (0001)-oriented
terraces were observed periodically at the interfaces between the carbide layers and the SiC, and the terraces were atomically
flat. We believed the Ti3SiC2 carbide layers primarily reduced the high Schottky barrier height at the contact metal/p-SiC interface down to about 0.3
eV, and, thus, low contact resistances were obtained for p-type TiAl-based ohmic contacts. 相似文献
8.
Surendra Srivastava Seong Mo Hwang Md. Islam K. Balakrishnan Vinod Adivarahan Asif Khan 《Journal of Electronic Materials》2009,38(11):2348-2352
We report on the effect of dry etching and the combination of metal stacks used to form ohmic contacts on silicon-doped high-Al-content
(>60%) n-AlGaN layers for deep-ultraviolet light-emitting diodes. The contact characteristics are compared for as-grown and plasma-etched
n-AlGaN samples. The Ti/Al/Ti/Au contacts to as-grown n-AlGaN were linear, with a specific contact resistivity of 5 × 10−5 Ω-cm2. The same metallic layer combinations yielded nonlinear contacts on the plasma-etched surface of the n-AlGaN layers. However, when Ni was used as the barrier layer instead of titanium, the contacts to plasma-etched AlGaN surfaces
became linear, with a specific contact resistivity of 5 × 10−4 Ω-cm2. 相似文献
9.
A. Moki P. Shenoy D. Alok B. J. Baliga K. Wongchotigul M. G. Spencer 《Journal of Electronic Materials》1995,24(4):315-318
The contact resistivities of Al and Ti ohmic contacts to n-type 3C-SiC were measured using the circular TLM method. The surface
doping concentration under the contact was increased by ion-implantation of nitrogen into SiC. The contact resistivity was
observed to decrease with increasing surface doping concentration for both Al and Ti contacts. The minimum value for the contact
resistivities for Aland Ti contacts was 1.4x 10-5and 1.5 x 10-5 ω cm2, respectively, at the surface doping concentration of 3 x 1020 cm-3 without any annealing of the contacts. These values are an order of magnitude lower than previously reported minimum values
for as-deposited ohmic contacts on n-type 3C-SiC. 相似文献
10.
Ariel Virshup Fang Liu Dorothy Lukco Kristina Buchholt Anita Lloyd Spetz Lisa M. Porter 《Journal of Electronic Materials》2011,40(4):400-405
The high-temperature stability of a Pt/TaSi2/Ni/SiC ohmic contact metallization scheme was characterized using a combination of current–voltage measurements, Auger electron
spectroscopy, and transmission electron microscopy imaging and associated analytical techniques. Increasing the thicknesses
of the Pt and TaSi2 layers promoted electrical stability of the contacts, which remained ohmic at 600°C in air for the extent of heat treatment;
the specific contact resistance showed only a gradual increase from an initial value of 5.2 × 10−5 Ω cm2. We observed a continuous silicon oxide layer in the thinner contact structures, which failed after 36 h of heating. Meanwhile,
thicker contacts with enhanced stability contained a much lower oxygen concentration that was distributed across the contact
layers, precluding the formation of an electrically insulating contact structure. 相似文献
11.
S. -K. Lee S. -M. Koo C. -M. Zetterling M. Östling 《Journal of Electronic Materials》2002,31(5):340-345
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
12.
P.Y. Emelie E. Cagin J. Siddiqui J.D. Phillips C. Fulk J. Garland S. Sivananthan 《Journal of Electronic Materials》2007,36(8):841-845
The electrical characteristics of organic (3,4-polyethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) contacts to
HgCdTe are studied as a potential alternative to metal/HgCdTe contacts. The use of organic PEDOT:PSS contacts offers the potential
for an improved contact technology for HgCdTe IR detector arrays. In this work, PEDOT:PSS contacts are deposited on n-type and p-type HgCdTe epilayers by spin coating and patterned using a metal mask. Current-voltage (I-V) characteristics are measured
on these contacts, showing nearly ohmic behavior. The temperature dependence of I-V characteristics (T = 40–300 K) shows increased resistance for decreasing temperature, consistent with the temperature dependence of HgCdTe resistivity,
suggesting that the I-V characteristics are primarily dominated by the HgCdTe material. 相似文献
13.
Walter Daves Andreas Krauss Volker Häublein Anton J. Bauer Lothar Frey 《Journal of Electronic Materials》2011,40(9):1990-1997
We report on wafer-level measurements of the long-term stability of Ti and Ni ohmic contacts to n-4H-SiC during thermal treatments in air or air/moisture environments up to 500°C. Contact metallizations with and without
a sputtered Ti (20 nm)/TaSi
x
(200 nm)/Pt (150 nm) diffusion barrier stack and Ti (20 nm)/TiN (10 nm)/Pt (150 nm)/Ti (20 nm) interconnects were compared.
A protective coating consisting of a SiO
x
(250 nm)/SiN
y
(250 nm) stack deposited by plasma-enhanced chemical vapor deposition (PECVD) was used. The stability of the contact metallizations
during long-term thermal treatments in air and air/moisture was studied. The best performance was achieved with Ti ohmic contacts
without the Ti/TaSi
x
/Pt stack. This system successfully withstood 1000 h thermal treatment at 500°C in air followed by 1000 h at 500°C in air/10%
moisture. After the aging, the contact failure ratio was below 1% and the specific contact resistivity amounted to (2.5 ± 1.1) × 10−4 Ω cm2. Scanning electron microscopy (SEM) cross-sectional analysis indicated no degradation in the contact metallization, demonstrating
the effectiveness of the SiO
x
/SiN
y
protective coating in preventing oxidation of the contacts. These results are very promising for applications in harsh environments,
where the stability of ohmic contacts is crucial. 相似文献
14.
P. Tomeš R. Robert M. Trottmann L. Bocher M. H. Aguirre A. Bitschi J. Hejtmánek A. Weidenkaff 《Journal of Electronic Materials》2010,39(9):1696-1703
Novel thermoelectric oxides were developed, produced, and characterized to demonstrate their promising thermoelectric conversion
potential in a thermoelectric converter. Four-leg thermoelectric oxide modules were fabricated by combining p- and n-type oxide thermoelements made of pressed polycrystalline GdCo0.95Ni0.05O3 and CaMn0.98Nb0.02O3, respectively. In these modules, the p- and n-type thermoelements were connected electrically in series and thermally in parallel. The materials were joined by electrical
contacts consisting of a Ag/CuO composite material. Fairly good thermal contacts were ensured by pressing the thermoelements
between alumina substrates. Cross-sections of the alumina/Ag–CuO mixture/thermoelement interface were investigated by scanning
electron microscopy. The temperature distribution across the module was monitored using K-type thermocouples and a micro-infrared
(IR) camera. The open-circuit voltage and the load voltages of the module were measured up to a temperature difference of
ΔT = 500 K while keeping the temperature of the cold side at 300 K. The output power and internal resistance were calculated.
The characteristics of the module evaluated from electrical measurements were compared with respective values of the p- and n-type leg materials. An output power of 0.04 W at ΔT = 500 K led to a power density of ~0.125 W/cm3, where the volume of thermoelectric material was determined by a cross-section of 4 mm × 4 mm and a leg length of 5 mm. 相似文献
15.
H. Sheng N. W. Emanetoglu S. Muthukumar S. Feng Y. Lu 《Journal of Electronic Materials》2002,31(7):811-814
Al nonalloyed ohmic contacts were fabricated and characterized on MgxZn1−xO (0≤×≤0.34) epilayers, which were grown on R-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD).
Specific contact resistances were evaluated by the transmission line method (TLM). A specific contact resistance of 2.5×10−5 Ωcm2 was obtained for Al contact to ZnO with an electron concentration of 1.6×1017 cm−3. The current flow mechanism was studied by investigating the dependence of specific contact resistances on electron concentration
and on temperature. For Al contact to Mg0.34Zn0.66O, specific contact resistance values are two orders of magnitude larger than that of Al ohmic contacts to ZnO. 相似文献
16.
K. V. Vasilevskii S. V. Rendakova I. P. Nikitina A. I. Babanin A. N. Andreev K. Zekentes 《Semiconductors》1999,33(11):1206-1211
Epitaxial films grown by low-temperature liquid phase epitaxy on p-type 4H-SiC were used as strongly doped subcontact layers for making low-resistance contacts to the p-type material. The layers had a bulk resistivity of ∼0.02 Ω · cm and an aluminum atom concentration of ∼1.5×1020 cm−3. The absence of polytype inclusions and the distinct crystalline quality of the strongly doped subcontact layers was confirmed
by x-ray diffraction methods. Ohmic contacts with resistivities less than 10−4 Ω · cm2 were prepared by depositing and then annealing multilayer metal mixtures containing Al and Ti. The structural properties
and energy characteristics of the resulting ohmic contacts are discussed.
Fiz. Tekh. Poluprovodn. 33, 1334–1339 (November 1999) 相似文献
17.
S. Tsukimoto T. Sakai T. Onishi Kazuhiro Ito Masanori Murakami 《Journal of Electronic Materials》2005,34(10):1310-1312
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
18.
Polycrystalline p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.7Se0.3 thermoelectric (TE) alloys containing a small amount (vol.% ≤5) of SiC nanoparticles were fabricated by mechanical alloying
and spark plasma sintering. It was revealed that the effects of SiC addition on TE properties can be different between p-type and n-type Bi2Te3-based alloys. SiC addition slightly increased the power factor of the p-type materials by decreasing both the electrical resistivity (ρ) and Seebeck coefficient (α), but decreased the power factor of n-type materials by increasing both ρ and α. Regardless of the conductivity type, the thermal conductivity was reduced by dispersing SiC nanoparticles in the Bi2Te3-based alloy matrix. As a result, a small amount (0.1 vol.%) of SiC addition increased the maximum dimensionless figure of
merit (ZT
max) of the p-type Bi0.5Sb1.5Te3 alloys from 0.88 for the SiC-free sample to 0.97 at 323 K, though no improvement in TE performance was obtained in the case
of n-type Bi2Te2.7Se0.3 alloys. Importantly, the SiC-dispersed alloys showed better mechanical properties, which can improve material machinability
and device reliability. 相似文献
19.
B. P. Luther S. E. Mohney J. M. Delucca R. F. Karlicek Jr. 《Journal of Electronic Materials》1998,27(4):196-199
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
20.
J. H. Wang S. E. Mohney S. H. Wang U. Chowdhury R. D. Dupuis 《Journal of Electronic Materials》2004,33(5):418-421
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