Terahertz generation in submicron GaN diodes within the limited space-charge accumulation regime J. Appl. Phys. 98, 064507 (2005); 10.1063/1.2060956 Monte Carlo study of hot-carrier transport in bulk wurtzite GaN and modeling of a near-terahertz impact avalanche transit time diode J. Appl. Phys. 95, 7925 (2004); 10.1063/1.1702144 Monte Carlo analysis of GaN-based Gunn oscillators for microwave power generation J. Appl. Phys. 93, 4836 (2003); 10.1063/1.1562734
Monte Carlo calculation of electron initiated impact ionization in bulk zinc-blende and wurtzite GaNThe conditions for microwave power generation at low temperatures under optical phonon emission are analyzed by Monte Carlo simulations of both small-and large-signal responses in bulk zinc blende and wurtzite GaN. As a result of the high optical phonon energy and the strong interaction of electrons with optical phonons in GaN a general improvement on the transit-time resonance and a considerable increase in the maximum generation frequency and power can be achieved in comparison to the widely studied III-V materials such as GaAs and InP. A dynamic negative differential mobility caused by transit-time resonance occurs in a wide frequency range of about 0.05-3 THz and persists in the THz frequency range up to the liquid nitrogen temperature with doping levels up to about 5ϫ10 16 cm Ϫ3 . The efficiency of the amplification and generation is found to depend nonmonotonously on static and microwave electric field amplitudes, generation frequency, and doping level so that for each generation frequency there exists an optimal range of parameter values. Under optimal conditions a generation efficiency of about 1% to 2% can be achieved in the 0.5-1.5 THz frequency range.
Temperature- and electric field-dependent electron transport in 3C–, 4H–, and 6H–SiC has been calculated by the Monte Carlo technique. Due to the freezeout of deep donor levels the role of ionized impurity scattering in 6H–SiC is suppressed and the role of phonon scattering is enhanced, compared to 3C– and 4H–SiC. There are indications of impurity band formation for impurity concentrations exceeding 1019 cm−3. It is found that ionized impurity scattering along with the deep donor ionization is responsible for the temperature dependence of mobility anisotropy ratio. Electron effective masses and electron-phonon coupling constants have been deduced from the comparison of Monte Carlo simulation results with available experimental data on low-field electron mobility. The extracted model parameters are used for high-field electron transport simulations. The calculated velocity-field dependencies agree with experimental results. The saturation velocities in all three polytypes are close, but the transient velocity overshoot at high electric field steps is much more pronounced in 3C–SiC.
Ni/4H-SiC Schottky photodiodes of 5 mm x 5 mm area have been fabricated and characterized. The photodiodes show less than 0.1 pA dark current at -4 V and an ideality factor of 1.06. A quantum efficiency (QE) between 3 and 400 nm has been calibrated and compared with Si photodiodes optimized for extreme ultraviolet (EUV) detection. In the EUV region, the QE of SiC detectors increases from 0.14 electrons/photon at 120 nm to 30 electrons/photon at 3 nm. The mean energy of electron-hole pair generation of 4H-SiC estimated from the spectral QE is found to be 7.9 eV.
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