Duu Sheng Ong

Generation of THz signals based on quasi-ballistic electron reflections in double-heterojunction structures

The generation of THz signals by the periodic quasi-ballistic resonant motion of electrons on the basis of the combined action of electron acceleration in a potential well and reflection at the heterointerface is demonstrated by a Monte Carlo simulation. The electron dynamics in In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As heterostructures is investigated for different well widths and doping densities under the influence of fundamental-wave signals which conveniently can also be of square shape of 100 GHz and 200 GHz. It is found that the resulting quasi-ballistic electron motion produces oscillations within these wells which generate particularly high odd harmonics in the terahertz frequency range. Simulation results of this new type of resonance phenomenon show that the amplitude of the THz radiation strongly depends on the well width and voltage level of the square wave signal. This study shows that double-heterojunction structures with well width of ballistic electron transport length are promising candidates for the design of efficient THz sources.

Analytical band Monte Carlo analysis of electron transport in silicene

An analytical band Monte Carlo (AMC) with linear energy band dispersion has been developed to study the electron transport in suspended silicene and silicene on aluminium oxide (Al2O3) substrate. We have calibrated our model against the full band Monte Carlo (FMC) results by matching the velocity-field curve. Using this model, we discover that the collective effects of charge impurity scattering and surface optical phonon scattering can degrade the electron mobility down to about 400 cm2 V−1 s−1 and thereafter it is less sensitive to the changes of charge impurity in the substrate and surface optical phonon. We also found that further reduction of mobility to ~100 cm2 V−1 s−1 as experimentally demonstrated by Tao et al (2015 Nat. Nanotechnol. 10 227) can only be explained by the renormalization of Fermi velocity due to interaction with Al2O3 substrate.

The applicability of analytical-band Monte Carlo for modelling high field electron transport in GaAs

An analytical-band Monte Carlo model incorporating four non-parabolic spherical valleys to represent the first two conduction bands has been developed to model hot electron transport and impact ionization in GaAs. We have tested the performance of this simple model against full-band Monte Carlo simulations for calculating the probability distribution function of impact ionization path length, time and energy; and transient velocity overshoot at high fields. This simpler model is found capable of reproducing the full-band model results satisfactorily but at much lower computational cost.

One‐step Double‐layer Thermal Evaporation Method for Organic Light Emitting Diodes

A new one‐step double‐layer thermal evaporation method was used to fabricate organic light emitting diodes (OLEDs) with device structure of: ITO (anode)/N,N_‐diphenyl‐N,N_‐bis(3‐methylphenyl)‐1,1_‐diphenyl‐4,4_‐diamine (TPD) /tris‐(8‐hydroxyquinoline)aluminum(3) (Alq3)/Al (cathode). These OLEDs were fabricated in cleanroom on the ITO‐coated glass with a sheet resistivity of 20Ω/sq and an optical transmittance of 90%. The I–V and brightness characteristic showed that the new method could produce better performance achieving lower turn‐on voltage (‐2V), higher peak current efficiency (+29%) and higher brightness (+36%).