Some Aspects of Quantitative Analysis of Ternary Alloys of Group III-Nitrides by Auger Electron Spectroscopy
In this work, the quantities have been determined experimentally that are needed for reliable and precise quantitative interpretation of Auger spectra of nitrides AlN, GaN and of their ternary alloys AlxGa1 - xN. Measurements of reference samples AlN and GaN under various parameters of the primary electron beam (energy 3 and 5 keV, beam incidence angle with respect to the surface normal 12.5° and 45°) and of the ion beam (energy 0.5 and 1.0 keV, beam incidence angle with respect to the surface normal 67.5° and 35°) allowed to find the elemental sensitivity factors for these nitrides, and measurements on reference samples of ternary alloys AlxGa1 - xN allowed to find the component sputtering yields YGa/YAl. To the best of our knowledge there is a lack of such data for those materials in the literature.
Jozef Liday, Peter Vogrinčič, Ivan Hotový, Helmut Sitter and Alberta Bonanni
Ohmic Contacts to p-GaN Using Au/Ni-Zn-O Metallization
We have studied the electrical properties and depth concentration profiles of Au/Ni-Zn-O/p-GaN and Au/Ni-Zn/p-GaN, thus of structures containing zinc as a p-type dopant utilized to increase the concentration of free charge carriers in the subsurface region of GaN and to gain a low-resistance ohmic contact. The layers were deposited on p-GaN by DC reactive magnetron sputtering. The prepared contact structures were annealed in N2, structure Au/Ni-Zn/p-GaN also in O2. The contact structures containing zinc exhibited lower values of contact resistivity in comparison with those without zinc. It was also found that the values of contact resistivity for both Au/Ni-Zn-O/p-GaN and Au/Ni-Zn/p-GaN were the same, thus it was not affected by the presence of a small content of oxygen (< 0.2 at%) in the working atmosphere during the deposition of layers. Similarly, various gaseous ambients (N2 or a mixture of N2 + O2) during subsequent annealing of the contacts had no observable influence upon the magnitude of the contact resistivity. In our opinion the ohmic nature of the Au/Ni-Zn-O/p-GaN and Au/Ni-Zn/p-GaN contacts is related to a reconstruction of the contacts to a sequence metal/p-NiO/p-GaN due to annealing in nitrogen or in a mixture of oxygen and nitrogen and the ohmic properties of the contacts are predetermined by creating a thin NiO oxide layer on the metal/p-GaN interface. We believe that the lower values of the contact resistance in Au/Ni-Zn-O/p-GaN and Au/Ni-Zn/p-GaN contacts than in structure Au/Ni-O/p-GaN are caused by an enhanced hole concentration in the surface region of p-GaN due to zinc diffusion from the zinc-doped contact layer.
Jozef Liday, Gernod Ecke, Tim Baumann, Peter Vogrinčič and Juraj Breza
Contribution to the Quantitative Analysis of Ternary Alloys of Group III-Nitrides by Auger Spectroscopy
For correct quantitative interpretation of Auger spectra of group III-nitrides and their alloys it is necessary to have the relative sensitivity factors of elements and the sputtering yields measured for the material under analysis. These data are not available in the literature for those materials. In this work, the quantities have been determined experimentally that are needed for reliable and precise quantitative interpretation of Auger spectra of such materials, thus of AlN, GaN and their ternary alloys AlxGa1-xN. Measurements of reference AlN and GaN samples allowed to find the elemental sensitivity factors for these nitrides, and measurements on reference samples of ternary alloys AlxGa1-xN allowed to find the ratio of the component sputtering yields, YGa/YAl. It has been confirmed that if the relative sensitivity factors are obtained from measurements of reference samples of group III-nitrides, thus of compounds, and if in the alloys of such compounds no further change of the shapes of Auger peaks occurs, the both the areas below the Auger peaks in direct spectra and the Auger peak-to-peak heights in differentiated spectra can be used for quantitative analysis.
Jozef Liday, Peter Vogrinčič, Viliam Vretenár, Mário Kotlár, Marián Marton and Vlastimil Reháček
We have designed and verified a new structure for ohmic contacts to p-GaN, mainly for applications in light emitting devices based on a layer of single-walled carbon nanotubes (SWCNT) and metallic layers of Cr and Au, namely in configuration Au/Cr/SWCNT/p-GaN. The layer of carbon nanotubes was deposited on p-GaN by spraying a solution of synthesized SWCNTs, while the layers of Cr and Au were vapour deposited. The effects of the annealing temperature and time upon the electrical properties of Au/Cr/SWCNT/p-GaN contacts have been studied. It has been found that the contact structure provides a low resistivity ohmic contact after subsequent annealing in N2 ambient at 700 °C for 1 minute.
Jozef Liday, Peter Vogrinčič, Viliam Vretenár, Mário Kotlár, Marián Marton and Vlastimil Řeháček
Due to their properties, carbon nanotubes and reduced graphene oxide are highly promising materials for obtaining low-resistance ohmic contacts to p-GaN with good optical transparency for visible light. In this contribution we designed a combination of these two materials, along with a cap layer, to be used as structures for ohmic contacts to p-GaN. Carbon nanotube (CNT) and graphene oxide (GO) layers were deposited by spray coating using an off-the-shelf airbrush on p-GaN layers. The metallic layers of Au/Pd were vapour deposited. The structures for ohmic contacts were prepared in two configurations, namely as Au/Pd/r-GO/CNT/p-GaN and Au/Pd/CNT/r-GO/CNT/p-GaN. The prepared structures provide a low resistivity ohmic contact after subsequent annealing in air ambient at 600 °C for 3 minutes. The contact containing the sandwich CNT/r-GO/CNT interstructure exhibits lower values of contact resistance in comparison with the r-GO/CNT interstructure.
Jozef Liday, Peter Vogrinčič, Andrej Vincze, Juraj Breza and Ivan Hotový
The work investigates an increase of the density of free charge carriers in the sub-surface region of p-GaN by adding p-type dopants into the Ni-O layer of an Au/Ni-O metallization structure. We have examined electrical properties and concentration depth profiles of contact structures Au/Ni-Mg-O/p-GaN and Au/Ni-Zn-O/p-GaN, thus with magnesium and zinc as p-type dopants. The metallization layers were deposited on p-GaN by DC reactive magnetron sputtering in an atmosphere with a low concentration of oxygen (0.2 at%). The contacts were annealed in N2 . We have found that the structures containing magnesium or zinc exhibit lower values of contact resistivity in comparison with otherwise identical contacts without Mg or Zn dopants. In our opinion, the lower values of contact resistivity of the structures containing of Mg or Zn are caused by an increased density of holes in the sub-surface region of p-GaN due to diffusion of Mg or Zn from the deposited doped contact layers.
Jozef Liday, Peter Vogrinčič, Viliam Vretenár, Ivan Hotový, Mário Kotlár, Marián Marton and Vlastimil Řeháček
We have examined electrical properties and concentration depth profiles of contact structures Au/Ni-Mg-(O)/SWCNT/p- GaN and Au/Ni-Mg-O/p-GaN, thus with and without an interlaying layer of single-walled carbon nanotubes (SWCNT). The metallization layers were deposited on p-GaN by DC reactive magnetron sputtering in an atmosphere with and without a low concentration of oxygen (cca 0.2 at%). The contacts were annealed in N2 . We have found that the structure containing the SWCNT interlayer exhibits lower values of contact resistivity in comparison with an otherwise identical contact without the SWCNT interlayer
Jozef Liday, Peter Vogrinčič, Ivan Hotový, Alberta Bonanni, Helmut Sitter, Tibor Lalinský, Gabriel Vanko, Vlastimil Řeháček, Juraj Breza and Gernot Ecke
Ohmic contacts to p-GaN Using Au/Ni-Mg-O Metallization
Electrical characteristics and elemental depth profiles of ohmic contacts to p-GaN using Au/Ni-Mg-Ox metallization have been investigated. The objective was to examine the possibilities of increasing the charge carrier concentration in the surface region of GaN by adding Mg, thus of a p-type dopant into the Au/NiOx metallization structure. For this purpose, a Ni-Mg-Ox layer with a low concentration of Mg was deposited on p-GaN by dc reactive magnetron sputtering. The top Au layer was deposited in a similar way. The fabricated contact structures were annealed in N2. When the Ni-Mg layer in the Au/Ni-Mg-Ox/p-GaN structure was deposited in an atmosphere with a low concentration of oxygen (0.2 at%), the structure exhibited a low resistance ohmic nature. The contact resistance was lower than in the case of a Au/Ni-Ox/p-GaN structure without the Mg dopant in the metallic layer. An increase in the concentration of oxygen in the working atmosphere resulted in higher values of the contact resistance of the Au/Ni-Mg-Ox/p-GaN structure. In our opinion the ohmic nature of the contact structure is related to the existence of a metal/p-NiO/p-GaN scheme. The measured values of the contact resistance in the Au/Ni-Mg-Ox/p-GaN structure in comparison with the Au/Ni-Ox/p-GaN structure are caused by an increased charge carrier concentration in the surface region of p-GaN, which is a consequence of Mg diffusion from the Ni-Mg-Ox layer.
Liday Jozef, Vogrinčič Peter, Vretenár Viliam, Kotlár Mário, Marton Marián, Mikolášek Miroslav and Řeháček Vlastimil
We have designed and verified a new structure for ohmic contacts to p-GaN based on a layer of carbon nanotubes (CNT), reduced graphene oxide (r-GO) and metallic layers of Cr, Pd and Au, namely in configurations Au/Cr/r-GO/CNT/p-GaN and Au/Pd/r-GO/CNT/p-GaN. The effects have been studied of the annealing temperature and the gas ambient upon the electrical properties of the contacts. Annealing of the Au/Pd/r-GO/CNT/p-GaN structure in air at 500°C for 1 minute resulted in linear I - V curves measured between planar electrodes on the p-GaN. Hence, addition of r-GO to the CNT interlayer between p-GaN and the metallization layer is a highly promising procedure for further improvements of the ohmic contacts to p-GaN.