Browsing by Author "Shih, CF"

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Energy states and magnetization in nanoscale quantum rings
(2002-10-15)
Voskoboynikov, O
;
Li, YM
;
Lu, HM
;
Shih, CF
;
Lee, CP
In this paper we calculate electron energy states and magnetization for torus shaped nanoscale quantum rings with external magnetic fields. We use the three-dimensional effective one-band Hamiltonian, the energy and position-dependent quasiparticle effective mass approximation, and the Ben Daniel-Duke boundary conditions. The dependence of the energy spectrum on the sizes and shapes of the quantum rings was calculated and the result agrees with experimental observations. Penetration of the magnetic field into torus region results in an aperiodic oscillation of magnetization at zero temperature. It saturates with the increasing of the magnetic field strength.
Performance of AlGaN/GaN heterostrucrure FETs over temperatures
(2004)
Lee, CC
;
Shih, CF
;
Lee, CP
;
Tu, RC
;
Chuo, CC
In this article, a comparison on the device performance of the undoped and modulation-doped AlGaN/GaN HFETs over temperatures was presented. The results obtained indicated that the device structure has a significant influence on the device performance. The modulation-doped devices are superior to the undoped devices over the temperatures studied. The stability (the temperature dependence of device performance), however. is not as good as the undoped devices.
Temperature-dependent electron transport properties of AlGaN/GaN heterostructures
(2004-06-01)
Lee, CC
;
Shih, CF
;
Lee, CP
;
Tu, RC
;
Chuo, CC
In this article, a comparison on the temperature dependence of the electron transport properties of the undoped and modulation-doped AlGaN/GaN heterostructures is presented. The results obtained indicate that the device structure plays an important role in the temperature-dependent transport behavior of the devices. The undoped structure has a nearly constant 2DEG concentration over a wide temperature range. The modulation-doped structure has a temperature-dependent electron concentration. The increase in electron concentration in the modulation-doped structure at high temperatures is due to the thermal activation of Si donors in the AlGaN layer. In addition, the modulation-doped structure shows comparable electron mobility with the undoped structure at high temperatures, indicating that the modulation-doped structure would exhibit a better device performance at high temperatures.