Effect of microwave treatment on current flow mechanism in ohmic contacts to GaN

The temperature dependence of contact resistivity ρс of Ti-Al-TiB₂-Au ohmic contacts to n-GaN and effect of microwave treatment on ρс are investigated. The obtained dependences are described using a model of current flow via metal shunts associated with dislocations, the current being limited by diffusion supply of electrons. It is shown that microwave treatment increases the dislocation density in the near-contact region of contact structure and reduces the relative spread of resistivity values of contacts formed on the wafer

Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method

In this paper, we have considered the four-contact method for measurements of the specific contact resistivity of the ohmic contacts (ρc). The presented method for measuring ρc has been compared with several other methods. Limits of applying this method have been shown

Effect of microwave radiation on I-V curves and contact resistivity of ohmic contacts to n-GaN and n-AlN

We studied ohmic contacts Au-Pd-Ti-Pd-n-AlN and Au-TiB₂-Al-Ti-n-GaN with contact resistivity ρс = 0.18cm² and 1.6 *10⁻⁴ Ω∙cm² , respectively, and the effect of microwave treatment on their electrophysical properties. After microwave treatment for time t up to 1000 s, the contact resistivity dropped by 16% (60%) in the contact to AlN (GaN). This seems to result from increase of the number of structural defects in the semiconductor near-contact region caused by relaxation of intrinsic stresses induced by microwave radiation

Heat-resistant barrier and ohmic contacts based on TiBx and ZrBx interstitial phases to microwave diode structures

We investigated thermal stability of Au–TiBx (ZrBx) barrier contacts, as well as ohmic contacts with a TiBx diffusion barrier to n-Si (GaAs, InP, GaP, GaN, SiC). The electrophysical measurements of Schottky barrier diodes and ohmic contacts were performed both before and after rapid thermal annealing (RTA) up to 600 °С for the structures on Si, GaAs, InP and GaP, as well as up to higher temperatures for GaN (~900 °C) and SiC (~1000 °C). The concentration depth profiles of contact components were taken using Auger electron spectrometry, while phase composition and surface morphology of the metallization layers on test structures were determined using x-ray diffraction and atomic force microscopy. It was shown that the silicon, indium phosphide, gallium phosphide and gallium arsenide contact structures retained their properties and layer structure after RTA up to 600 °С. Contact degradation occurred at a temperature of 800 °С. The structures based on SiC (GaN) remained stable at temperatures up to 1000 °С (900 °С)

Temperature dependence of contact resistance of Au−Ti−Pd2Si−n⁺ -Si ohmic contacts

We investigated temperature dependence of contact resistance of an Au−Ti−Pd₂Si ohmic contact to heavily doped n⁺ -Si. The contact resistance increases with temperature owing to conduction through the metal shunts. In this case, the limiting process is diffusion input of electrons to the metal shunts. The proposed mechanism of contact resistance formation seems to realize also in the case of wide-gap semiconductors with high concentration of surface states and dislocation density in the contact

Some aspects of thermal resistance measurement technique for IMPATT and light-emitting diodes

Some aspects of measuring the thermal resistance to a constant heat flow at a p-n junction–package region in IMPATT and light-emitting diodes are considered. We propose a method of studying the thermal resistance of high-power light-emitting diodes. This method makes it possible to increase accuracy of measuring the thermal resistance by determining the temperature at a linear section of the voltage−temperature curve. A possibility to measure the thermal resistance of IMPATT diodes by using the pulse I-V curves is shown. This enables one to simplify calculations and increase accuracy of measuring the thermal resistance

Development of high-stable contact systems to gallium nitride microwave diodes

High-stable heat-resistant low-resistance contact systems with diffusion barriers involving quasi-amorphous TiBx layers are suggested and studied. We have performed the structural and morphological investigations along with studies of Auger concentration depth profiles in the contacts both before and after rapid thermal annealing. It is found that the Au−TiBx−Al−Ti−GaN contact layers with diffusion barriers retain both a layered structure of the contact metallization and the value of contact resistivity practically unchanged up to the temperature Т ≈ 700 ºС. At the same time, the layered structure of the metallization in standard Au−Ti−Al−Ti−GaN contact systems breaks down at such rapid thermal annealing. It is shown that the contact metallization of both types demonstrates the tunnel current flow mechanism in the temperature range 225−335 K, whereas the current flow mechanism is thermionic in the range 335−380 K, the Schottky barrier height being ~0.16 eV. For the best samples under consideration, the contact resistivity was no more than 10⁻⁶ Ohm∙cm²

Investigation of resistance formation mechanisms for contacts to n-AlN and n-GaN with a high dislocation density

We studied temperature dependences of the resistivity, Pc(T) , of Pd-Ti-Pd-Au ohmic contacts to wide-gap semiconductors n - GaN and n - AlN with a high dislocation density. BothPc(T) curves have portions of exponential decrease, as well as those with very slight Pc(T) dependence at higher temperatures. Besides, the Au-Pd-TiPd-n-GaN contacts have a portion of Pc(T) flattening out in the low-temperature region. This portion appears only after rapid thermal annealing (RTA). In principle, its appearance may be caused by preliminary heavy doping of the near-contact region with a shallow donor impurity as well as doping in the course of contact formation owing to RTA, if the contact-forming layer involves a material atoms of which serve as shallow donors in III N compounds. The obtained Pc(T) dependences cannot be explained by the existing mechanisms of current transfer. We propose other mechanisms explaining the experimental Pc(T) curves for ohmic contacts to n - GaN and n -AlN

Role of dislocations in formation of ohmic contacts to heavily doped n-Si

We present experimental results concerning a high density of structural defects (in particular, dislocations) in the near-contact region of heavily doped n-silicon. They appear in the course of firing Au Pd Ti Pd -Si n ohmic contact at 450С for 10 min in a vacuum of ~10 Pa⁻⁴ . These defects lead to appearance of metal shunts that determine the current flow mechanism in these ohmic contacts. The calculated and experimental temperature dependences of contact resistivity, ρс(Т), are in good agreement. It is shown that ρс increases with temperature. This is characteristic of a model of ohmic contacts with a high dislocation density in the near-contact region of semiconducto

Mechanism of current flow and temperature dependence of contact resistivity in Au-Pd-Ti-Pd-n⁺ -GaN ohmic 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 ρс(Т) of ohmic contacts in the 4.2-380 K temperature range. The ρс(Т) curve was shown to flatten out in the 4.2-50 K range. As temperature grew, ρс decreased exponentially. The results obtained enabled us to conclude that current flow has field nature at saturation of ρс(Т) and the thermofield nature in the exponential part of ρс(Т) curve