Low-resistance smooth-surface Ti/Al/Cr/Mo/Au n-type Ohmic contact to AlGaN/GaN heterostructures (original) (raw)
Related papers
Improved surface morphology and edge definition for ohmic contacts to AlGaN/GaN heterostructures
Gallium Nitride Materials and Devices IV, 2009
We demonstrate that Ti/Al/Cr/Mo/Au ohmic contact has an extremely smooth surface morphology of 29.0 nm and a low specific contact resistivity (ρ c) of 1.1×10-6 ohm-cm 2 on n-type AlGaN/GaN heterostructures. The use of Cr interlayer in Ti/Al/Cr/Mo/Au contacts leads to significantly improved contact morphology without any degradation on the contact resistance. This is attributed to the reduced inter-diffusion and reaction between the layers in the contact stack.
Structural properties of alloyed Ti/Al/Ti/Au and Ti/Al/Mo/Au ohmic contacts to AlGaN/GaN
Solid-State Electronics, 2006
Two alloyed ohmic contact structures for AlGaN/GaN-Ti/Al/Ti/Au and Ti/Al/Mo/Au were studied. Both structures were optimized for minimum ohmic contact resistance. Structures grown on sapphire and SiC substrates were used to investigate structural properties of ohmic contacts to AlGaN/GaN. Ohmic contacts to AlGaN/GaN on SiC showed higher contact resistance values compared to contacts to AlGaN/GaN on sapphire. Ohmic contact metals were etched on samples after annealing. The alloyed interface was studied with backside illumination under an optical microscope. Alloyed inclusions associated with threading dislocations were observed on the surface. For the AlGaN/GaN on SiC sample the inclusion density was an order of magnitude lower than for the sample on sapphire. Conductive atomic force microscopy with carbon nanotube tip was used to investigate topography and conductivity profile of the surface after ohmic contact metal removal by etching.
Low Resistance Ti/Al/Mo/Au Ohmic Contacts for AlGaN/GaN Heterostructure Field Effect Transistors
Physica Status Solidi (a), 2002
A metallization scheme consisting of Ti/Al/Mo/Au was utilized to develop low-resistance ohmic contacts to AlGaN/GaN heterostructure field effect transistors (HFET). A contact resistance as low as 0.20 Wmm and a specific contact resistivity as low as 4.5 Â 10 --7 Wcm 2 were obtained using a pre-metallization surface treatment with SiCl 4 plasma at a self-bias voltage of --300 V in a reactive ion etching (RIE) system. X-ray photoelectron spectroscopy (XPS) measurements of the SiCl 4 plasma-treated surface revealed an increase in the N vacancies thereby increasing the donor concentration at the surface. Also a blue shift of the peak energy of the Ga 3d photoelectrons was observed showing that the Fermi level moved closer to the conduction band at the surface of the AlGaN.
Nb-Ti/Al/Ni/Au based ohmic contacts to AlGaN/GaN
2007
In this paper, we report on a novel Nb-Ti/Al/Ni/Au metallic system proposed to form ohmic contact to AlGaN/GaN heterostructure. The metallic system uses deposition of thin niobium layer as the first layer in contact with the AlGaN barrier layer before deposition of the conventional Ti/Al/Ni/Au metallic system. The fabrication and electrical characterization of the Nb-Ti/Al/Ni/Au based ohmic contacts are presented. We have shown that Nb-based ohmic contacts at optimal alloying temperatures seem to be superior to that of conventional Ti/Al/Ni/Au in both surface morphology and contact resistivity evaluation. Auger Electron Spectroscopy (AES) and Secondary Ion Mass Spectroscopy (SIMS) are also used to evaluate the improved ohmic contact formation. r
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.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2004
A novel two-step surface treatment method has been developed to realize low resistance nonalloyed ohmic contact to n-type GaN doped with Si to 6×1017 cm−3. The removal of native oxide (oxides and hydroxides) formed on GaN surface is crucial for successful creation of nonalloyed low resistance ohmic contact. In the case of GaN, plasma etching of the material surface prior to metal deposition holds promise for developing such nonalloyed ohmic contacts. In this article, the effects of the postetch chemical treatment of the n-type GaN surface on the Ti based nonalloyed contact performance have been investigated. Contacts on samples without reactive ion etching (RIE) showed Schottky behavior. However, contacts on samples with 15 s of RIE using Cl2 showed ohmic behavior. The contact resistivity of this contact reached to ρs=1.2×10−3 Ω cm2. Treating the RIE etched sample in boiling aqua regia for 5 min yielded a contact resistivity on the order of 3.6×10−4 Ω cm2. Dramatic improvement in cu...
Electric and Morphology Studies of Ohmic Contacts on AlGaN/GaN
MRS Proceedings, 2000
ABSTRACTAlGaN/GaN is a promising system for high power electron devices. Quality of ohmic contacts is a critical parameter in determining the performance of the device. Although we have achieved a transfer resistance (Rc) of 0.35Δmm and ρc of 9.5×10−7 Δcm−2 the morphology and edge acuity of the contacts are poor. The standard ohmic contact recipes consist of a combination of Titanium and Aluminum with Nickel and/or Gold. This is annealed at 800°C-950°C [1-5]. In this work we study ohmic contacts on unintentionally doped Al0.3Ga0.7N/GaN system. We look at ratios of Ti/Al from 0 to 2 to determine which is the optimum ratio in terms of surface morphology and electrical characteristics. From our studies we conclude that morphology of a Ti/Al contact is good over a ratio of 0.3 and the contact resistance is minimized at a Ti/Al of 0.6. The ohmic contacts are improved electrically if a layer of gold is added on top. The best electrical contacts however were obtained with a four layer reci...
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.
Very-low-specific-resistance Pd/Ag/Au/Ti/Au alloyed ohmic contact to p GaN for high-current devices
Applied Physics Letters, 2001
We report on Pd/Ag/Au/Ti/Au alloyed metallic contact to p GaN. An 800°C anneal for 1 min in flowing nitrogen ambient produces an excellent ohmic contact with a specific contact resistivity close to 1ϫ10 Ϫ6 ⍀ cm 2 and with good stability under high current operation conditions. This high-temperature anneal forms an alloy between Ag, Au, and p GaN resulting in a highly p-doped region at the interface. Using x-ray photoelectron spectroscopy and x-ray diffraction analysis, we confirm that the contact formation mechanism is the metal intermixing and alloying with the semiconductor.