Ti/Al/Mo/Au Ohmic contacts to all-binary AlN/GaN high electron mobility transistors (original) (raw)
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Ti/Al/Ni/Au Ohmic contacts for AlInN/AlN/GaN-based heterojunction field-effect transistors
Journal of Applied Physics, 2010
The microstructure of AuNiAlTi/ Al 0.84 In 0.16 N / AlN/ GaN Ohmic contacts annealed from 700 to 900°C has been determined using transmission electron microscopy and associated analytical techniques. Intermixing and phase separation of the metal contact layers was observed to degrade the surface roughness. An optimal contact performance was obtained for contacts annealed at 800°C and was attributed to the formation of TiN contact inclusions that had penetrated through the AlInN layers into the GaN layers underneath. These TiN contact inclusions had an inverted mushroom shape with a density of ϳ10 8 cm −2 , and they were invariably located at the positions of mixed-type threading dislocations. These inclusion defects would act as a conduction path between the metal contacts and the two-dimensional electron gas of heterojunction field-effect transistor devices. The AlInN layer remained intact in dislocation-free areas of all samples.
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2020
The authors study the effect of etch chemistry and metallization scheme on recessed Au-free Ohmic contacts to AlGaN/GaN heterostructures on silicon. The effect of variation in the recess etch chemistry on the uniformity of Ohmic contact resistance has been studied using two different etch chemistries (BCl3/O2 and BCl3/Cl2). Experiments to determine the optimum recess etch depth for obtaining a low value of contact resistance have been carried out, and it is shown that near-complete etching of the AlGaN barrier layer before metallization leads to the lowest value of contact resistance. Furthermore, two metal schemes, namely, Ti/Al and Ti/Al/Ti/W, are investigated, and it is found that the Ti/W cap layer on Ti/Al leads to low contact resistance with a smooth contact surface morphology. The effect of maintaining unequal mesa and contact pad widths on the extracted values of contact resistance and sheet resistance using the linear transfer length method (LTLM) has been studied. This is ...
Formation of ohmic contacts to ultra-thin channel AlN/GaN HEMTs
Physica Status Solidi (c), 2008
AlN/GaN-based high electron mobility transistors with ultra-thin AlN barriers of 2.3 - 5 nm are attractive candidates for very high speed applications owing to the aggressive scalability such structures afford. We report the first study on formation of ohmic contacts to these high quality ultra-thin channel heterostructures (ns > 1x1013 cm–2 and μ > 900 cm2/Vs) with systematically varying barrier thicknesses. While the conventional ohmic contacts to AlGaN/GaN structures generally require high temperature annealing, these ohmic contacts were found to behave ohmic or near ohmic as-deposited. Annealing (400-860 0C) improves the contact resistance to a range of 0.8 - 2 ohm-mm but the annealing conditions strongly depend on the AlN thickness as well as the heterostructure quality (μ). All alloyed contacts show smooth morphology, making them suitable for e-beam lithographically defined gate patterning. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical Characteristics of Ti/Al Contacts on AlInN:Mg/GaN Heterostructures
Japanese Journal of Applied Physics, 2013
The electrical characteristics of a Ti/Al metal contact on Mg-doped AlInN/GaN heterostructures were investigated using a transmission line model. The as-deposited Ti/Al contact exhibited near Ohmic contact with a specific contact resistance of 1:78 Â 10 À2 cm 2 , while the thermal annealing performed at 600 C led to better Ohmic contact with a contact resistance of 9:38 Â 10 À4 cm 2 . This could be attributed to the formation of a direct Ohmic path connecting the contact and the two-dimensional electron gas beneath an AlInN:Mg barrier upon thermal annealing, namely, a spike contact through the indiffusion of Al as verified from secondary ion mass spectroscopy. Current-voltage-temperature measurements showed an insignificant temperature dependence in both the sheet resistance and the contact resistance, which seemed to be associated with the distinctive feature of the spike contact. #
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.
physica status solidi (a), 2016
Ohmic contacts to AlGaN/GaN heterostructures, which have low contact resistance and a good surface morphology, are required for the development of high temperature, high power and high frequency electronic devices. The paper presents the investigation of a Ti/Al based Ti/Al/Ni/Au ohmic contact to AlGaN/GaN heterostructures. Multilayer metallization of Ti/Al/Ni/Au was evaporated by an electron gun (titanium and nickel layers) and a resistance heater (aluminum and gold layers). The contacts were annealed by rapid thermal annealing (RTA) system in a nitrogen ambient atmosphere over the temperature range from 715 to 865°C. The time of the annealing process was 60 seconds. The chemical analysis, formation and deterioration mechanisms of Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures were studied as a function of the annealing process conditions by a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS).
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.
Ti/Au/Al/Ni/Au low contact resistance and sharp edge acuity for highly scalable AlGaN/GaN HEMTs
IEEE Electron Device Letters, 2018
In this letter, we have reported a novel metal scheme Ti/Au/Al/Ni/Au for ohmic contact on AlGaN/GaN high electron mobility transistors (HEMTs). The reported metal scheme is observed to show minimum metal out-diffusion and sharp edge acuity at high temperature annealing, which facilitates aggressive scaling of source drain separation (LSD). We have demonstrated LSD as low as 300 nm with gate length (Lg) of 100 nm for this metal stack. We observed improvement in ON-Resistance (RON) from 3 Ω.mm to 1.25 Ω.mm, transconductance (gm) from 276 mS/mm to 365 mS/mm, saturation drain current (IDS,sat) from 906 mA/mm to 1230 mA/mm and unity current gain frequency (fT) from 70 GHz to 93 GHz by scaling LSD from 3 µm to 300 nm. The gate length for all devices were 100 nm.