Browsing by Author "Ilgaz, A."

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Open Access
Comparison of the transport properties of high quality AlGaN/AlN/GaN and AllnN/AlN/GaN two-dimensional electron gas heterostructures
(AIP Publishing LLC, 2009-01-07) Tülek, R.; Ilgaz, A.; Gökden, S.; Teke, A.; Öztürk, M. K.; Kasap, M.; Özçelik, S.; Arslan, E.; Özbay, Ekmel
The transport properties of high mobility AlGaN/AlN/GaN and high sheet electron density AlInN/AlN/GaN two-dimensional electron gas (2DEG) heterostructures were studied. The samples were grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The room temperature electron mobility was measured as 1700 cm(2)/V s along with 8.44 X 10(12) cm(-2) electron density, which resulted in a two-dimensional sheet resistance of 435 Omega/square for the Al(0.2)Ga(0.8)N/AlN/GaN heterostructure. The sample designed with an Al(0.88)In(0.12)N barrier exhibited very high sheet electron density of 4.23 X 10(13) cm(-2) with a corresponding electron mobility of 812 cm(2)/V s at room temperature. A record two-dimensional sheet resistance of 182 Omega/square was obtained in the respective sample. In order to understand the observed transport properties, various scattering mechanisms such as acoustic and optical phonons, interface roughness, and alloy disordering were included in the theoretical model that was applied to the temperature dependent mobility data. It was found that the interface roughness scattering in turn reduces the room temperature mobility of the Al(0.88)In(0.12)N/AlN/GaN heterostructure. The observed high 2DEG density was attributed to the larger polarization fields that exist in the sample with an Al0.88In0.12N barrier layer. From these analyses, it can be argued that the AlInN/AlN/GaN high electron mobility transistors (HEMTs), after further optimization of the growth and design parameters, could show better transistor performance compared to AlGaN/AlN/GaN based HEMTs. c 2009 American Institute of Physics.
Open Access
Energy relaxations of hot electrons in AlGaN/AlN/GaN heterostructures grown by MOCVD on sapphire and 6H-SiC substrates
(E D P Sciences, 2011-08-18) Ilgaz, A.; Gökden, S.; Tülek, R.; Teke, A.; Özçelik, S.; Özbay, Ekmel
In this work, we investigated the hot-electron dynamics of AlGaN/GaN HEMT structures grown by MOCVD on sapphire and SiC substrates at 80 K. High-speed current-voltage measurements and Hall measurements over the temperature range 27-300 K were used to study hot-electron dynamics. At low fields, drift velocity increases linearly, but deviates from the linearity toward high electric fields. Drift velocities are deduced as approximately 6.55 × 10 6 and 6.60 × 106 cm/s at an electric field of around E ∼ 25 kV/cm for samples grown on sapphire and SiC, respectively. To obtain the electron temperature as a function of the applied electric field and power loss as a function of the electron temperature, we used the so-called mobility comparison method with power balance equations. Although their low field carrier transport properties are similar as observed from Hall measurements, hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. We found that LO-phonon lifetimes are 0.50 ps and 0.32 ps for sapphire and SiC substrates, respectively. A long hot-phonon lifetime results in large non- equilibrium hot phonons. Non-equilibrium hot phonons slow energy relaxation and increase the momentum relaxation. The effective energy relaxation times at high fields are 24 and 65 ps for samples grown on sapphire and SiC substrates, respectively. They increase as the electron temperature decreases.
Open Access
Temperature dependent hot electron transport in slightly lattice mismatched AlInN/AlN/GaN heterostructures
(National Institute of Research and Development for Optoelectronics, 2014-10) Ilgaz, A.; Gökden, S.; Tülek, R.; Teke, A.; Özçelik, S.; Özbay, Ekmel
In this work, the hot-electron transport properties of AlInN/AlN/GaN HEMT structures with a high sheet electron density of 4.84x10(13) cm(-2) grown by MOCVD (Metal Organic Chemical Vapor Deposition) on sapphire substrate were investigated at lattice temperature ranging from 10 K to 300 K. High speed current voltage measurements and Hall measurements were used to study hot-electron transport. Current-voltage characteristics show that current and drift velocity increase linearly but deviate from the linearity towards high voltages, as would be expected from the increased scattering of hot electrons with LO phonons. However, no saturation of current and drift velocity were observed at the highest voltage reached. Drift velocities were deduced as approximately 6.7x10(6) and 6.1x10(6) cm/s at an electric field of around E similar to 23 kV/cm at lattice temperatures T-L = 10 K and 300 K, respectively. To obtain the electron temperature as a function of the applied electric field and power loss as a function of the electron temperature, the so-called mobility comparison method with power balance equations were used. The effect of hot-phonon production on the phonon lifetime and effective energy relaxation of hot electrons was investigated as a function of lattice temperature.