Thermally stable Ge/Cu/Ti ohmic contacts to n-type GaN (original) (raw)
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Formation of thermally stable low-resistance Ti/W/Au ohmic contacts on n-type GaN
2005
A Ti(12 nm)/W(20 nm)/Au(50 nm) metallization scheme has been investigated for obtaining thermally stable low-resistance ohmic contacts to n-type GaN (4.0 × 10 18 cm −3). It is shown that the current-voltage (I-V) characteristics of the samples are abnormally dependent on the annealing temperature. For example, the samples that were annealed at temperatures below 750 • C for 1 min in a N 2 ambient show rectifying behavior. However, annealing the samples at temperatures in excess of 850 • C results in linear I-V characteristics. The contact produces a specific contact resistance as low as 8.4 × 10 −6 Ω cm 2 when annealed at 900 • C. It is further shown that the contacts are fairly thermally stable even after annealing at 900 • C; annealing the samples at 900 • C for 30 min causes insignificant degradation of the electrical and structural properties. Based on glancing angle X-ray diffraction and Auger electron microscopy results, the abnormal temperature dependence of the ohmic behavior is described and discussed.
physica status solidi (c), 2005
Tungsten metal layer was used for the first time as an effective diffusion barrier for the standard Ti/Al/Ti/Au ohmic metallization scheme to obtain thermally stable ohmic contact suitable for high temperature applications. Comparative studies were performed on three distinct metallization schemes: 1) standard . For the GaN with doping level of 5 × 10 17 cm -3 , the lowest specific contact resistance for the Ti/Al/Ti/W/Au metallization scheme annealed in argon at 750 °C for 30 sec was 5 × 10 -6 Ω.cm 2 , which is comparable to the standard Ti/Al/Ti/Au scheme. X-ray diffractions (XRD), auger electron spectroscopy (AES) depth profiling, fieldemission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (TEM) revealed that the Ti/Al/Ti/W/Au metallization has superior morphology and microstructural properties compared to standard Ti/Al/Ti/Au metallizations. Remarkably, this metallization was able to withstand thermal aging at 500 °C for 50 hrs with only marginal morphological and electrical deterioration. These studies revealed that the utilization of a compound diffusion barrier stack, as in the Ti/Al/Ti/W/Au metallization, yields electrically, structurally, and morphologically superior metallizations with exceptional thermal stability.
Thermally-stable low-resistance Ti/Al/Mo/Au multilayer ohmic contacts on n–GaN
Journal of Applied Physics, 2002
A metallization scheme consisting of Ti/Al/Mo/Au with excellent edge acuity has been developed for obtaining low-resistance ohmic contacts to n-GaN. Excellent ohmic characteristics with a specific contact resistivity as low as 4.7ϫ10 Ϫ7 ⍀-cm 2 were obtained by rapid thermal annealing of evaporated Ti/Al/Mo/Au at 850°C for 30 sec in a N 2 ambient. Additionally, no degradation in specific contact resistivity was observed for these contacts subjected to long-term annealing at 500°C for 360 h.
Electrical, microstructural, and thermal stability characteristics of Ta/Ti/Ni/Au contacts to n-GaN
Journal of Applied Physics, 2004
A metallization technique has been developed for obtaining low resistance Ohmic contact to n-GaN. The metallization technique involves the deposition of a metal layer combination Ta/Ti/ Ni/Au on an n-GaN epilayer. It is observed that annealing at 750°C for 45 s leads to low contact resistivity. Corresponding to a doping level of 5ϫ10 17 cm Ϫ3 , the contact resistivity of the contact S ϭ5.0ϫ10 Ϫ6 ⍀ cm 2 . The physical mechanisms underlying the realization of low contact resistivity is investigated using current-voltage characteristics, x-ray diffraction, Auger electron spectroscopy, transmission electron microscopy, and energy dispersive x-ray spectrometry.
Microstructural properties of thermally stable Ti/W/Au ohmic contacts on n-type GaN
Microelectronic Engineering, 2006
We have investigated the microstructural and electrical characteristics of Ti/W/Au ohmic contacts on n-type GaN (4.0 • 10 18 cm À3) using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) after annealing at 900°C. It is shown that the electrical properties are improved upon annealing at 900°C for 1 min in nitrogen ambient. The 900°C annealed contact produced a specific contact resistance of 8.4 • 10 À6 X cm 2. It is further shown that the contact exhibits thermal stability during annealing at 900°C. Based on the Auger electron microscopy and transmission electron microscopy studies, the formation of TiN layer results in an excess of N vacancies near the surface of the GaN layer, which could be the reason for the low-resistance of the Ti/W/Au contact.
Nonalloyed Cr∕Au-based Ohmic contacts to n-GaN
Applied Physics Letters, 2007
Nonalloyed Cr/ Au-based metal contacts to n-GaN have been demonstrated. The deposited Au/ Cr/ n-GaN contacts exhibited a specific contact resistance ͑ c ͒ of approximately 5.6 ϫ 10 −5 ⍀ cm 2. Although the nonalloyed Ti/ Al-based contacts to n-GaN can also exhibit a comparable c value, their thermal stability is inferior to the Cr/ Au-based contacts. This could be attributed to the fact that Al tends to ball up during thermal annealing. Thus, the surface morphology of most of the annealed Ti/ Al-based contacts was quite rough, and the contacts became rectified when they were annealed at a temperature below 700°C. However, the annealed Cr/ Au-based contacts exhibited an Ohmic characteristic and had a smooth surface when annealing temperatures did not exceed 700°C. In addition, the thermal stability could be further improved by inserting a Pt layer between the Cr and Au layers. This scheme could prevent the diffusion of Au into the Cr layer, thus preventing Au from reaching the Cr/ GaN interface where it could form a possible Ga-Au phase, which would degrade the Ohmic contacts.
Interface analysis of TiN/n-GaN Ohmic contacts with high thermal stability
Applied Surface Science, 2019
TiN-based contacts were fabricated to clarify the role of TiN layer in the Ohmic contact structures on n-type GaN. As-deposited TiN/Ti/Pt/Au multilayer contact exhibits Ohmic behavior, while the contact of Ti/TiN/Pt/Au is non-Ohmic. The Schottky barrier heights were estimated from X-ray photoelectron spectroscopy measurements to be 0.3 0.2 eV for TiN/n-GaN contact and 1.0 0.2 eV for Ti/n-GaN contact, respectively, as also confirmed by current-voltage measurements. The depth profiles of Time-Of-Flight Second Ion Mass Spectrometry (TOF-SIMS) revealed that TiN layer is a good diffusion barrier, keeping the TiN/GaN interface sharp even after being annealed at 700℃. Detailed interface analysis suggests the thermal stability behavior of metal/GaN contact is much related to atoms inter-diffusion and interface reaction. Our study demonstrates that low specific contact resistivity with high thermal stability can be achieved by adding a uniform TiN layer in the metal/n-GaN contact multi-structures.
Electrical and structural properties of low-resistance Ti/Al/Re/Au ohmic contacts to n-type GaN
Journal of Electronic Materials, 2004
Titanium (15 nm)/aluminum (60 nm)/rhenium (20 nm)/gold (50 nm) ohmic contacts to moderately doped n-type GaN (4.07 ϫ 10 18 cm Ϫ3) have been investigated as a function of annealing temperature. It is shown that the currentvoltage (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 ϫ 10 Ϫ6 Ωcm 2 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.
Effects of oxygen thermal annealing treatment on formation of ohmic contacts to n-GaN
Applied Physics Letters, 2012
A contact scheme to undoped and n-type GaN was identified that does not require a post deposition anneal. As-deposited Ti/Al/Ti/Au usually forms a Schottky contact. However, we find that by means of an oxygen rapid thermal annealing prior to metal deposition, the contact will develop an ohmic behavior with a specific contact resistance of 3.8 × 10−5 Ω cm2. In X-ray photoelectron spectroscopy, we find that the Ga 3 d electron binding energy increases with this pre-treatment, indicating a shift of the Fermi level closer to the conduction band. This sequence reversion of high temperature processing steps allows important gain in device fabrication flexibility.
Ohmic Contacts on N-Face n-Type GaN After Low Temperature Annealing
IEEE Photonics Technology Letters
The electrical properties of different metal systems for ohmic contacts on the nitrogen-face of c-plane n-type GaN substrates are investigated. The metal contacts are compatible with the fabrication process and the packaging technology for group III-nitride laser diodes. The metal system Ti/Al/Mo/Ti/Ni/Au/Ti/Pt is determined as the best suitable, since it is ohmic already after annealing at a temperature of 450°C for 60 s. This annealing temperature is high enough to make the contact insensitive against later soldering on a heat-sink at 330°C. At the same time, the temperature is low enough that the Pd-based p-contact, previously annealed at 530°C, does not degrade. In addition, the Ti/W/Al and Pd/Ti/Al metal systems form low-resistance ohmic contacts, too, although they require a longer annealing time of several minutes or a higher temperature of 500°C.