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1.
Hwe Jae Lee Soon Jae Yu Hajime Asahi Shun-Ichi Gonda Young Hwan Kim Jin Koo Rhee S. J. Noh 《Journal of Electronic Materials》1998,27(7):829-832
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
2.
Th. Gessmann Y. -L. Li E. L. Waldron J. W. Graff E. F. Schubert J. K. Sheu 《Journal of Electronic Materials》2002,31(5):416-420
Thin p-doped InGaN layers on p-doped GaN were successfully used to demonstrate a new type of low-resistance ohmic contact.
A significant reduction of specific contact resistance can be achieved by increasing the free-hole concentration and the probability
for hole tunneling through the Schottky barrier as a consequence of polarization-induced band bending. As obtained from the
transmission-line method, the specific contact resistances of Ni (10 nm)/Au (30 nm) contacts deposited on InGaN capping layers
were 1.2×10−2 Ωcm2 and 6×10−2 Ωcm2 for capping layer thicknesses of 20 nm and 2 nm, respectively. 相似文献
3.
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
4.
M. Kocan G.A. Umana-Membreno J.S. Chung F. Recht L. McCarthy S. Keller U.K. Mishra G. Parish B.D. Nener 《Journal of Electronic Materials》2007,36(9):1156-1159
This paper reports results of a study of non-alloyed ohmic contacts on Si-implanted AlGaN/GaN heterostructures, obtained from
current–voltage characteristics of transfer-length method (TLM) test structures. It is shown that the measured contact resistance
from the Ti/Au/Ni metal contacts, deposited on Si-implanted regions, to the two-dimensional electron gas channel at the AlGaN/GaN
heterointerface of the non-implanted region, is formed by three different components: (i) contact resistance between the metal␣and
the semiconductor (0.60 ± 0.16 Ω mm), (ii) resistance of the implanted region (0.62 ± 0.03 Ω mm) and (iii) an additional resistance
(0.72 ± 0.24 Ω mm) giving a total value of 1.9 ± 0.3 Ω mm. The specific ohmic contact resistance was determined to be (2.4 ± 0.5) × 10−5 Ω cm2. 相似文献
5.
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
6.
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
7.
Au/n-GaN Schottky diodes with the Au electrode deposited at low temperature (LT=77K) have been studied. In comparison, the
same chip of GaN epitaxial layer was also used for room temperature Schottky diodes. The low temperature Schottky diodes exhibit
excellent performance. Leakage current density as low as 2.55×10−11 A·cm−2 at −2.5 V was obtained in the LT Schottky diodes. The linear region in the current-voltage curve at forward bias extends
more than eight orders in current magnitude. Current-voltage-temperature measurements were carried out to study the characteristics
of the LT Schottky diodes. A typical barrier height of about 1.32 eV for the LT diode, which is the highest value ever reported,
was obtained. The obvious enhancement in electrical performance makes the LT processing a very promising technique for GaN
device application although the detailed mechanisms for the LT Au/n-GaN Schottky diodes are still under investigation. 相似文献
8.
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
9.
Jong Kyu Kim Jung Ho Je Jae Won Lee Yong Jo Park Taeil Kim In-Ok Jung Byung-Teak Lee Jong-Lam Lee 《Journal of Electronic Materials》2001,30(2):L8-L12
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
10.
Ja-Soon Jang Dong-Jun Kim Seong-Ju Park Tae-Yeon Seong 《Journal of Electronic Materials》2001,30(2):94-98
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
11.
Nadeemullah Mahadik Mulpuri V. Rao Albert V. Davydov 《Journal of Electronic Materials》2006,35(11):2035-2040
The performance of a novel Ge/Cu/Ti metallization scheme on n-type GaN has been investigated for obtaining thermally and electrically
stable low-resistance ohmic contacts. Isochronal (2 min.) anneals in the 600–740°C temperature range and isothermal (690°C)
anneals for 2–10 min. duration were performed in inert atmosphere. For the 690°C isothermal schedule, ohmic behavior was observed
after annealing for 3 min. or longer with a lowest contact resistivity of 9.1 × 10−5 Ωcm2 after the 10 min. anneal for a net donor doping concentration of 9.2 × 1017 cm−Ω3. Mean roughness (Ra) for anneals at 690°C was almost constant at around 5 nm, up to an annealing duration of 10 min., which indicates a good
thermal stability of the contact scheme. 相似文献
12.
Ping Jian Douglas G. Ivey Robert Bruce Gordon Knight 《Journal of Electronic Materials》1994,23(9):953-962
Two Pd-based metallizations have been systematically studied, i.e., Au/Ge/Pd and Pd/Ge contacts to n-type InP, in an attempt
to better understand the role of the metallization constituents in forming ohmic contacts. Ohmic contacts were obtained with
minimum specific resistances of 2.5 × 10−6 Ω-cm2 and 4.2 × 10−6 Ω-cm2 for the Au/Ge/Pd and the Pd/Ge contacts, respectively. The annealing regime for ohmic contact formation is 300-375°C for
the Au/Ge/Pd/InP system and 350-450°C for the Pd/GelnP system. Palladium, in both cases, reacts with InP to form an amorphous
layer and then an epitaxial layer at low temperatures, providing good metallization adhesion to InP substrates and improved
contact morphology. Ohmic contact formation in both contacts is attributed to Ge doping, based on the solid state reaction-driven
decomposition of an epitaxial layer at the metallization/InP interface, producing a very thin, heavily doped InP layer. Gold
appears to be responsible for the difference in contact resistance in the two systems. It is postulated that Au reacts strongly
with In to form Au-In compounds, creating additional In site vacancies in the InP surface region (relative to the Au-free
metallization), thereby enhancing Ge doping of the InP surface and lowering the contact resistance. Both contacts degrade
and ultimately become Schottky barriers again if over annealed, due to consumption of additional InP, which destroys the heavily
doped InP layer. 相似文献
13.
Yow-Jon Lin Hsin-Ying Lee Fu-Tsai Hwang Ching-Ting Lee 《Journal of Electronic Materials》2001,30(5):532-537
Ohmic contacts to n-type GaN with low contact resistance were developed by (NH4)2Sx and KOH+(NH4)2Sx surface treatments prior to Ti/Al metal deposition. The lowest specific contact resistance of 3.0×10−6 Ω-cm2 was obtained for Ti/Al contacts in an (NH4)2Sx-treated GaN layer alloyed at 300°C for 3 min. To obtain the lowest specific contact resistance for a low temperature alloy,
the (NH4)2Sx treatment conditions for both (NH4)2Sx and KOH+(NH4)2Sx-treated n-GaN layers have been investigated and the mechanism for ohmic formation in low temperature alloys analyzed. 相似文献
14.
InxGa1−xAs-based ohmic contacts which showed excellent contact properties for n-GaAs were demonstrated to be applicable to p-GaAs
ohmic contacts. These contacts, prepared by radio-frequency sputtering, provided low contact resistance (0.2 Ω-mm), excellent
thermal stability, smooth surface, and good reproducibility. The contact resistances had a weak dependence on the annealing
temperatures, which was desirable in a manufacturing view point. This weak temperature dependence was explained to be due
to a unique Schottky barrier height at the metal/p-InxGa1−xAs interface which does not depend on the In concentration in the InxGa1−xAs layer. The present experiment showed the possibility of simultaneous preparation of ohmic contacts for both n and p-GaAs
using the same contact materials. 相似文献
15.
T. E. Murphy J. O. Blaszczak K. Moazzami W. E. Bowen J. D. Phillips 《Journal of Electronic Materials》2005,34(4):389-394
The electrical properties of several metal contacts to n-type ZnO (0001) were studied. The ZnO samples consisted of bulk single-crystal
material, epitaxial layers on sapphire grown by molecular beam epitaxy (MBE), and polycrystalline thin films on sapphire obtained
by pulsed laser deposition (PLD). Ohmic and rectifying contacts were observed dependent upon both the metal material and the
ZnO surface. Ohmic contacts were characterized using the circular transmission line method (c-TLM), where contact resistivity
was found to be in the range of 10−4−10−5 Ω-cm2. Schottky behavior was observed using Ag contacts exhibiting varying leakage current and breakdown voltage dependent on the
polarity of the ZnO surface. 相似文献
16.
H. Sheng N. W. Emanetoglu S. Muthukumar B. V. Yakshinskiy S. Feng Y. Lu 《Journal of Electronic Materials》2003,32(9):935-938
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
17.
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
18.
We have investigated Nb single and Nb/Au metallization schemes for the formation of thermally stable ohmic contacts to p-GaN.
It is shown that the asdeposited Nb and Nb/Au contacts exhibit rectifying behavior. However, both the contacts produce ohmic
characteristics when annealed at 850°C. Measurements show that the 850°C Nb/Au and Nb contacts yield a specific contact resistance
of 1.9×10−8 and 2×10−2 ωcm2, respectively. Schottky barrier heights are found to decrease with increasing annealing temperature. A comparison of the
XRD and electrical results shows that the formation of gallide phases such as Ga-Nb and Ga-Au compounds, play a role in forming
ohmic contacts. Atomic force microscopy results show that the surface morphology of the Nb contacts is fairly stable up to
850°C, while the Nb/Au contacts are slightly degraded upon annealing at 850°C. 相似文献
19.
Hui-Chan?Seo Seung Jae?Hong Patrick?Chapman Kyekyoon?Kim 《Journal of Electronic Materials》2008,37(5):635-640
To achieve very low ohmic contact resistance, an n
+-GaN layer was selectively deposited using plasma-assisted molecular beam epitaxy (PAMBE). During this process polycrystalline
GaN grew on the patterned SiO2 region, which was subsequently removed by a heated KOH solution, resulting in damage to the n
+-GaN surface. To prevent this damage, an additional SiO2 layer was selectively deposited only on the n
+-GaN region. To optimize the fabrication process the KOH etching time and n
+-GaN layer thickness were adjusted. This damage-proof scheme resulted in a specific contact resistance of 4.6 × 10−7 Ω cm2. In comparison, the resistance with the KOH etching damage was 4.9 × 10−6 Ω cm2 to 24 × 10−6 Ω cm2. The KOH etching produced a large number of pits (4.1 × 108 cm−2) and degraded the current transport. X-ray photoelectron spectroscopy (XPS) and secondary-ion mass spectrometry (SIMS) analysis
indicated that KOH etching was very effective in removing the oxide from the GaN surface and that the O-H bonding at the GaN
surface was likely responsible for the degraded contact performance. The optimum n
+-GaN thickness was found to be 54 nm. 相似文献
20.
Pressure and pressureless electrical contacts were evaluated by measuring the contact electrical resistivity between copper
mating surfaces. Pressure electrical contacts with a contact resistivity of 2×10−5 Ω·cm2 have been attained using a carbon black paste of a thickness of less than 25 μm as the interface material. In contrast, a
pressureless contact with silver paint as the interface material exhibits a higher resistivity of 3×10−5 Ω·cm2 or above. A pressureless contact with colloidal graphite as the interface material exhibits the same high contact resistivity
(1×10−4 Ω·cm2) as a pressure contact without any interface material. On the other hand, pressureless contacts involving solder and silver
epoxy exhibit lower contact resistivity than carbon black pressure contacts. 相似文献