Browsing by Subject "Drift velocity"
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Item Open Access Energy transfer in a bilayer Fermi gas in the non-linear regime(Wiley-VCH Verlag, 2017) Renklioğlu, B.; Oktel, M. Ö.; Tanatar, BilalWe consider a bilayer system of two-dimensional spin-polarized dipolar Fermi gas without any tunneling between the layers. We calculate the energy transfer rate between the layers in the nonlinear regime where the layers have a relative velocity, as a function of temperature and drift velocities of the particles of the system in each layer. The effective interactions describing the correlation effects and screening between the dipoles are obtained by the Hubbard approximation in a single layer (intralayer), and the random-phase approximation (RPA) across the layers (inter-layer). The energy transfer arises from the longrange nature of dipolar interactions between the particles of the system. As a result of the increasing drift velocities, the nonlinear heat transfer between the layers remarkably increases and the system reaches its equilibrium at lower temperatures. Our calculations show that cooling with dipolar interactions without any material contact can be utilized to cool the ultracold dipolar systems.Item Open Access Negative differential resistance observation and a new fitting model for electron drift velocity in GaN-based heterostructures(Institute of Electrical and Electronics Engineers, 2018) Atmaca, G.; Narin, P.; Kutlu, E.; Malin, T. V.; Mansurov, V. G.; Zhuravlev, K. S.; Lişesivdin, S. B.; Özbay, EkmelThe aim of this paper is an investigation of electric field-dependent drift velocity characteristics for Al0.3Ga0.7N/AlN/GaN heterostructures without and with in situ Si3N4 passivation. The nanosecond-pulsed current-voltage ( {I}-{V} ) measurements were performed using a 20-ns applied pulse. Electron drift velocity depending on the electric field was obtained from the {I}-{V} measurements. These measurements show that a reduction in peak electron velocity from \text {2.01} \times \text {10}^{\text {7}} to \text {1.39} \times \text {10}^{\text {7}} cm/s after in situ Si3N4 passivation. Also, negative differential resistance regime was observed which begins at lower fields with the implementation of in situ Si3N4 passivation. In our samples, the electric field dependence of drift velocity was measured over 400 kV/cm due to smaller sample lengths. Then, a well-known fitting model was fitted to our experimental results. This fitting model was improved in order to provide an adequate description of the field dependence of drift velocity. It gives reasonable agreement with the experimental drift velocity data up to 475 kV/cm of the electric field and could be used in the device simulators.Item Open Access Theoretical assessment of electronic transport in InN(Elsevier, 2004) Bulutay, C.; Ridley, B. K.Among the group-III nitrides, InN displays markedly unusual electronic transport characteristics due to its smaller effective mass, high peak velocity and high background electron concentration. First, a non-local empirical pseudopotential band structure of InN is obtained in the light of recent experimental and first-principles results. This is utilized within an ensemble Monte Carlo framework to illuminate the interesting transport properties. It is observed that InN has a peak velocity which is about 75% higher than that of GaN while at higher fields its saturation velocity is lower than that of GaN. Because of the strongly degenerate regime brought about by the high background electron concentration, the electron-electron interaction is also investigated, but its effect on the steady-state and transient velocity-field characteristics is shown to be negligible. Finally, hot phonon generation due to excessive polar optical phonon production in the electron scattering and relaxation processes is accounted for. The main findings are the appreciable reduction in the saturation drift velocity and the slower recovery from the velocity overshoot regime. The time evolution of the hot phonon distribution is analysed in detail and it is observed to be extremely anisotropic, predominantly along the electric force direction.