Browsing by Subject "Effective energy"

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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
A PN-type quantum barrier for InGaN/GaN light emitting diodes
(Optical Society of American (OSA), 2013) Zhang, Z.-H.; Tan, S.T.; Ji, Y.; Liu W.; Ju, Z.; Kyaw, Z.; Sun X.W.; Demir, Hilmi Volkan
In this work, InGaN/GaN light-emitting diodes (LEDs) with PN-type quantum barriers are comparatively studied both theoretically and experimentally. A strong enhancement in the optical output power is obtained from the proposed device. The improved performance is attributed to the screening of the quantum confined Stark effect (QCSE) in the quantum wells and improved hole transport across the active region. In addition, the enhanced overall radiative recombination rates in the multiple quantum wells and increased effective energy barrier height in the conduction band has substantially suppressed the electron leakage from the active region. Furthermore, the electrical conductivity in the proposed devices is improved. The numerical and experimental results are in excellent agreement and indicate that the PN-type quantum barriers hold great promise for high-performance InGaN/GaN LEDs. © 2013 Optical Society of America.