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The drift velocity of photo-generated electrons in CdTe by lasers with wavelengths of 532, 355, and 266 nm is studied by the Monte Carlo method. The effects of laser wavelengths on the electron drift velocity are systematically investigated under various laser fluxes, doping densities, and temperatures. It is found that the drift velocity as a function of electric field v d (E) has a close relationship with the laser wavelengths: the electron drift velocity in CdTe becomes larger when a longer photoexcitation wavelength is used. On the other hand, the doping effect, as well as the effect of the laser energy flux, on the v d (E) dependence demonstrates different characteristics for different laser wavelengths. The difference in electron drift velocity caused by the various wavelengths reduces with increasing temperatures. In the case of a low laser energy flux, doping in CdTe plays a remarkable role in v d (E) relations. These new results are helpful in understanding the microscopic mechanism of relaxation processes of photo-excited carriers and applications of CdTe-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Two dimensional electron gas (2DEG) transports in In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As multilayer structure (MLS) illuminated by an ultrashort optical pulse with the central wavelength at 1.55 μm is investigated by ensemble Monte Carlo simulations. Terahertz (THz) pulses are calculated according to the transient photocurrent in the InGaAs layers. It is found that InGaAs/InAlAs MLS with narrower InGaAs layers has an advantage in generating large temporal change in the transient photocurrent, which thereby is able to increase the intensity of THz emission. Beryllium (Be)-doping in InGaAs layers provides a scattering channel to speed the decay of photocurrent, and is shown to be a factor in shaping the bipolar structure of THz temporal waveforms. Bandwidth of the generated THz emission is found to be mainly controlled by the laser pulse duration at low doping level, but at high doping level, the bandwidth is determined together by laser pulse duration and doping density. • The electron transports in InGaAs/InAlAs multilayer structure has been discussed. • We find that the narrower InGaAs layer has advantages in increasing the intensity of THz emission. • Beryllium(Be)-doping in InGaAs layers provides a scattering channel to speed the decay of photocurrent. [ABSTRACT FROM AUTHOR]

The wurtzite AlGaN/GaN double quantum wells (DQWs) are designed and studied by numerical simulation based on ensemble Monte Carlo method. Structural parameters are carefully chosen for three-level and four-level DQWs to optimize intersubband absorption shapes in the wavelength range 9.3–10.6 μm. It is shown that three-level AlGaN/GaN DQWs have some advantages over four-level DQWs in structural design for optically pumped terahertz lasers. The requirements for resonant optical pumping and resonant LO-phonon scattering in terahertz lasers restrict the wide quantum well of four-level DQWs in quite narrower width range than the three-level DQWs. The results of this work should provide useful guidance for the design of optically pumped quantum well lasers. [ABSTRACT FROM AUTHOR]

Abstract: Based on the ensemble Monte Carlo methods, this paper analyzes the tetrahertz (THz) radiation dynamics which is related with the parameter choice for pump pulses, and gives a thorough explanation about the use of a longer pump wavelength for more intensive THz output. Our simulations show that the temporal waveforms of THz pulses have close relations with pump wavelengths. On the other hand, our studies also display that different pump pulse widths only change the rising side of THz temporal waveforms, and have no effect on its dropping side. [Copyright &y& Elsevier]

Streaming transports of the two-dimensional electron gas (2DEG) in AlGaN/GaN/AlGaN double heterostructures (DHs) are investigated by using the ensemble Monte Carlo simulation method. The dependence of streaming transport on basic parameters of DHs, such as Al composition, GaN channel width, interface roughness, and temperature, is obtained. It is demonstrated that streaming transports of 2DEG in DHs only can be realized by careful choice of those basic parameters and the externally applied electric field parallel to the interface. Weak alloy disorder (ADO) and interface roughness (IFR) scatterings, which can be obtained by using low Al compositions and wide GaN channels, are of benefit to streaming transport in DHs. On the other hand, it is found that dislocation scattering does not play an obvious influence on the transient drift velocity, compared to ADO and IFR scatterings. [ABSTRACT FROM AUTHOR]