Formation of thermally stable low-resistance Ti/W/Au ohmic contacts on n-type GaN (original) (raw)
Related papers
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.
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.
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.
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.
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.
Thermally stable Ge/Cu/Ti ohmic contacts to n-type GaN
Journal of Electronic Materials
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 3 10 À5 V cm 2 after the 10 min. anneal for a net donor doping concentration of 9.2 3 10 17 cm À3 . Mean roughness (R a ) 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.
Temperature dependence of the specific resistance in Ti∕Al∕Ni∕Au contacts on n-type GaN
Journal of Applied Physics, 2006
The temperature dependence of the specific resistance c in annealed Ti/ Al/ Ni/ Au contacts on n-type GaN was monitored, obtaining information on the current transport mechanisms. After annealing at 600°C, the contacts exhibited a rectifying behavior and became Ohmic only after high temperature processes ͑Ͼ700°C͒, with c in the low 10 −5 ⍀ cm 2 range. The results demonstrated that the current transport is ruled by two different mechanisms: thermoionic field emission occurs in the contacts annealed at 600°C, whereas field emission dominates after higher temperature annealing. The significant physical parameters related to the current transport, i.e., the Schottky barrier height and the carrier concentration under the contact, could be determined. In particular, a reduction of the Schottky barrier from 1.21 eV after annealing at 600°C to 0.81 eV at 800°C was determined, accompanied by a strong increase of the carrier concentration, i.e., from 2 ϫ 10 18 cm −3 in the as-prepared sample to 4.6ϫ 10 19 cm −3 in the annealed contacts. The electrical properties were correlated to the microstructure of the interfacial region, providing a scenario to explain the transition from Schottky to Ohmic behavior in annealed Ti/ Al/ Ni/ Au contacts.
We present the results of structural and morphological investigations of interactions between phases in the layers of Au-Pd-Ti-Pd-n + -GaN contact metallization that appear at rapid thermal annealing (RTA). It is shown that formation of ohmic contact occurs in the course of RTA at Т = 900 C due to formation of titanium nitride. We studied experimentally and explained theoretically the temperature dependence of contact resistivity ρ с (Т) of ohmic contacts in the 4.2-380 K temperature range. The ρ с (Т) curve was shown to flatten out in the 4.2-50 K range. As temperature grew, ρ с decreased exponentially. The results obtained enabled us to conclude that current flow has field nature at saturation of ρ с (Т) and the thermofield nature in the exponential part of ρ с (Т) curve.
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.