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HgCdTe electron avalanche photodiodes (e-APDs) have been widely used for low-flux and high-speed application. To better understand the dark current transport and electron-avalanche mechanism of the devices and optimize the structures, we performed accurate numerical simulations of the current–voltage characteristics and multiplication factor in planar homojunction (p-i-n) HgCdTe APDs. Based on the Okuto–Crowell avalanche model, an efficient physical model has been obtained by concerning the major generation-recombination processes, such as trap-assisted tunneling and band-to-band tunneling (BBT) recombination. Simulated current–voltage characteristics were in good agreement with available data in the literature, which demonstrates the validity of the proposed model. The origins of dark current in high reverse voltages are jointly dominated by BBT and the avalanche mechanism. It is proved to be effective for reducing BBT by improving the uniformity of the electric field distribution across the junction. The electric performance of p-i-n e-APD can be improved by optimizing the APD structure, such as eliminating the sharp corners of junctions, light doping, and the appropriate thickness in multiplication region. Our works provide a good deal of insight into the fundamental carrier transport processes involved in HgCdTe e-APDs. [ABSTRACT FROM AUTHOR]

We have investigated terahertz (THz) resonant absorption spectra in grating-gate GaN high electron mobility transistors. The results indicate that both the symmetrical plasmon mode and the asymmetrical plasmon mode play an important role in the strong absorption of THz waves. The excitation process and dynamic response of these plasmons are investigated in detail. Our results also indicate that the asymmetrical plasmon is induced by the surface polarization field of the electrodes and the resonant strength of this plasmon is reduced significantly by the decay of the polarization field. Variations in the resonant strength of the plasmonic peaks are consistent with the surface resonant layer model showing that the method we used can be utilized for the study of coupling between THz radiation and plasmons in the channel. In order to achieve wider tunability, more advanced device structures can be explored such as a device that contains double channel layers, in which complicated plasmons can be excited. [ABSTRACT FROM PUBLISHER]

The direct current characteristics of AlGaN/GaN double-channel HEMTs (DC-HEMTs) are investigated by using 2-D numerical simulations. The output characteristics have been predicted with the drift-diffusion, thermodynamic, hydrodynamic, and hot-electron models, respectively. The prediction by the hydrodynamic model is in good agreement with the experiment. It is demonstrated that the hot-electron effect makes a negligible contribution to the negative differential conductance (NDC) of an AlGaN/GaN DC-HEMT; instead, the NDC effect is caused by the self-heating effect. The transfer and transconductance characteristics of an AlGaN/GaN DC-HEMT are also discussed in detail. Finally, a new \In0.18\Al0.82\N /GaN/AlGaN/GaN DC-HEMT structure is proposed for optimizing AlGaN/GaN DC-HEMTs. [ABSTRACT FROM PUBLISHER]