Indium Tin Oxide (ITO) based Ohmic Contacts on Bulk n-GaN Substrate (original) (raw)
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ACS Applied Materials & Interfaces, 2009
Indium-tin-oxynitride (ITON) films have been fabricated by rf sputtering from an indium-tin-oxide target in nitrogen plasma. The influence of postdeposition annealing up to 800°C is analyzed by electrical, optical, and surface characterization of the films in comparison to indium-tin-oxide (ITO) films fabricated in argon plasma. High-temperature annealing resulted in ITO(N) films with similar carrier concentrations. However, the resistivity and optical transmittance of the ITON films were higher than those of the ITO films. Photoelectron spectroscopy revealed that nitrogen is incorporated into the ITON structure in an unbound state as well as through the formation of metal-nitrogen and oxynitride bonds that decorate oxygen vacancies. When the core level electron spectra of ITO and ITON films are compared, a correlation between carrier concentration and the incorporated nitrogen is found. Changes in ITON electrical properties are mainly induced by the release of nitrogen at temperatures above 550°C. In this context, ohmic contact behavior was achieved for ITON on p-type GaN after annealing at 600°C, while no ohmic contact could be realized using ITO.
Advanced science (Weinheim, Baden-Wurttemberg, Germany), 2018
The origin of plasma-induced damage on a -type wide-bandgap layer during the sputtering of tin-doped indium oxide (ITO) contact layers by using radiofrequency-superimposed direct current (DC) sputtering and its effects on the forward voltage and light output power (LOP) of light-emitting diodes (LEDs) with sputtered ITO transparent conductive electrodes (TCE) is systematically studied. Changing the DC power voltage from negative to positive bias reduces the forward voltages and enhances the LOP of the LEDs. The positive DC power drastically decreases the electron flux in the plasma obtained by plasma diagnostics using a cutoff probe and a Langmuir probe, suggesting that the repulsion of plasma electrons from the -GaN surface can reduce plasma-induced damage to the -GaN. Furthermore, electron-beam irradiation on -GaN prior to ITO deposition significantly increases the forward voltages, showing that the plasma electrons play an important role in plasma-induced damage to the -GaN. The ...
Ohmic contact formation to bulk and heterostructure gallium nitride family semiconductors
Applied Physics A-materials Science & Processing, 2009
We describe experiments investigating the quality of ohmic contacts to both bulk GaN and to III-nitride heterostructures. Titanium-based contacts were investigated to assess the role of intermixing and surface impurities for contact formation to n-type GaN. Direct contact to the two-dimensional electron gas in GaN/AlGaN heterostructures was also studied. These contacts were made by photochemical etching of the samples to expose the heterointerface. It was observed that even in the latter case contact annealing leads to a lower contact resistance by consuming surface contaminants and promoting beneficial interfacial reactions. Various passivation techniques were tried to reduce surface leakage current between contact pads and PECVD-deposited silicon nitride was found to be the best material for this application.
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.
Investigations on the Origin of the Ohmic Behavior for Ti/Al Based Contacts on n-Type GaN
Materials Science Forum, 2012
This work reports of investigation on the origin of the ohmic behavior for Ti/Al based contacts on n-GaN. Indeed, last publications tend to prove that the "nitrogen vacancy" theory is not confirmed by the experimental ground available. To find new answers, we first made electrical characterizations on some Al/Ti/n + -GaN contacts with different annealing conditions. Then, we performed SIMS depth profiles of annealed TiN/Ti/n + -GaN samples. Results developed in this paper tend to demonstrate that the ohmic behavior of Ti/Al based contact is mainly due to an increase of the doping concentration. Moreover, the high doping level can be explained by an in-diffusion of Ti and an exo-diffusion of Si elements close to the metal / semiconductor interface.
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...
Evaluation of metal/indium-tin-oxide for transparent low-resistance contacts to p-type GaN
Applied Optics, 2012
In search of a better transparent contact to p-GaN, we analyze various metal/indium-tin-oxide (ITO) (Ag/ITO, AgCu/ITO, Ni/ITO, and NiZn/ITO) contact schemes and compare to Ni/Au, NiZn/Ag, and ITO. The metal layer boosts conductivity while the ITO thickness can be adjusted to constructive transmission interference on GaN that exceeds extraction from bare GaN. We find a best compromise for an Ag/ITO (3 nm ∕ 67 nm) ohmic contact with a relative transmittance of 97% of the bare GaN near 530 nm and a specific contact resistance of 0.03 Ω • cm 2. The contact proves suitable for green light-emitting diodes in epi-up geometry.
Investigation of the mechanism for Ti/Al ohmic contact on etched n-GaN surfaces
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2000
In this study, the mechanism for ohmic contact of Ti/Al bilayer formation on as-grown, etched and postetch annealed GaN surfaces were investigated. A nonalloyed Ti/Al ohmic contact to etched GaN surface, with postetch annealing prior to metal deposition, was obtained. The specific contact resistance of 2.3ϫ10 Ϫ4 ⍀ cm 2 was obtained. The nonalloyed ohmic contact may be attributed to the postetch annealing which generates nitrogen vacancies that result in a heavily n-type surface thereby forming a tunneling junction. On the other hand, the nonalloyed Ti/Al contact on as-grown and as-etched GaN surfaces exhibits non-ohmic behavior. After alloying at 500°C for 5 min, Ti/Al contacts on as-grown, as-etched and postetched annealing GaN surfaces have specific contact resistances around 9.8ϫ10 Ϫ5 , 1ϫ10 Ϫ4 , and 7.2ϫ10 Ϫ5 ⍀ cm 2 , respectively. Nonalloyed Ti/Al ohmic contacts would be especially useful for fabricating high breakdown, recessed-gate field effect transistors on GaN since the moderate postannealing condition converts only the near surface layer to heavily n type.
Effects of cap layer on ohmic Ti/Al contacts to Si + implanted GaN
Applied Surface Science, 2009
A low resistivity ohmic contact to Si-implanted GaN was achieved using a metal combination of Ti/Al. The effect of a protection cap during post-implantation annealing is investigated, and how it affects the specific contact resistivity (ρc). Relevant differences between the protected (PR) sample with SiO2 and unprotected (UP) sample during the post-implantation annealing were observed after metal alloying at 700 °C. The lower values of ρc have been obtained for UP sample, but with very low reproducibility. In contrast, SiO2 cap layer has demonstrated its relevance in yielding a much more uniformity of a relatively low ρc around 10−5 Ω cm2. Related mechanism for the uniformity in ρc was discussed based on the results obtained from electrical measurements, XRD (X-ray diffraction) analysis, AFM (atomic force microscopy) and SEM (scanning electron microscopy) observations.
MRS Proceedings, 1999
When the stoichiometric TiN was deposited directly on GaN, we obtained columnar TiN grains of 5-20 nm section which cross the whole film thickness and are rotated mostly around the [111] axis. The conventional epitaxial relationship is obtained and no amorphous patches are observed at the interface. The deposition of TiN on Si doped GaN layers lead to the formation of an ohmic contact, whereas we obtain a rectifying contact on p type layers.