J. Wen

Distinguishing medium-range order in metallic glasses using fluctuation electron microscopy: A theoretical study using atomic models

We have simulated the variance in the diffracted electron intensity as a function of scattering vector in fluctuation electron microscopy for a range of fully amorphous and nanocrystal-containing metallic glass models. Variance peaks are obvious for glasses that contain well-developed short-to-medium range order but absent for their parent liquids. The variance peaks are very sensitive to the presence and especially the size of the nanocrystal embryos or nuclei embedded in the glass matrix but much less so to the variations in the type or degree of the cluster ordering developed in fully amorphous materials.

High hole mobility GeSn on insulator formed by self-organized seeding lateral growth

Tensile strained single-crystal GeSn on insulator (GSOI) was obtained using self-organized seeding lateral growth. Segregation of Sn atoms and Sn distribution occurred during the lateral growth of the GeSn stripe. At both edges of the GSOI, Sn concentration distribution was found in good agreement with calculation based on the Scheil equation. P-channel metal–oxide–semiconductor field effect transistors were fabricated using the GSOI materials. Good transistor performance with the low field peak hole mobility of 383 cm2 V−1 s−1 was obtained, which indicated the high quality of this GSOI structure.

Room temperature photoluminescence of Ge-on-insulator structures formed by rapid melt growth

Room temperature photoluminescence (PL) was observed along 50 μm long Ge strips on insulator on bulk Si substrates fabricated by rapid melt growth. The PL peaks evidently exhibited a redshift from the origin to the end of the Ge strip because of the shrinkage of the direct bandgap of Ge. Moreover, PL intensities increased along the direction of lateral epitaxial growth primarily because of the decrease in the energy difference between the direct and indirect gaps of Ge. The change in the Ge band structure, which facilitated changes in PL peaks and intensities, was found to have resulted from the variation of tensile strain ratios and Si fractions along Ge strips. Furthermore, the PL intensity at the end of the strip was one magnitude higher than that of bulk Ge, which indicates the high quality of Ge-on-insulator structures.

Effect of surface charge on the dark current of InGaAs/InP avalanche photodiodes

The effects of surface charge on the dark current of the separate-absorption-grading-charge-multiplication InGaAs/InP avalanche photodiodes (APDs) are discussed using drift-diffusion simulation. The dark current increases exponentially with the increasing of surface charge density, and gets multiplied, thus influencing the performance of the APDs, especially in Geiger mode. The mechanism of the surface charge leakage current is discussed, and a floating guard ring structure is proposed to suppress the influence of surface charge effectively.

Origin and optimization of large dark current increase in InGaAs/InP APD

Dark current of our InGaAs/InP planar SAGCM APD is simulated. Activation energy Ea obtained from the I-V test under temperature range of 240K~300K is cooperated in the simulation. Two origins of the dark current increasi of over one order of magnitude from the punchthrouth voltage to the breakthrough voltage are analyzed. Our results provide two critical points to reduce the dark current of an InGaAs/InP APD operated under the linear operation mode.

Research progress of Ge on insulator grown by rapid melting growth

Ge is an attractive material for Si-based microelectronics and photonics due to its high carries mobility, pseudo direct bandgap structure, and the compatibility with complementary metal oxide semiconductor (CMOS) processes. Based on Ge, Ge on insulator (GOI) not only has these advantages, but also provides strong electronic and optical confinement. Recently, a novel technique to fabricate GOI by rapid melting growth (RMG) has been described. Here, we introduce the RMG technique and review recent efforts and progress in RMG. Firstly, we will introduce process steps of RMG. We will then review the researches which focus on characterizations of the GOI including growth dimension, growth mechanism, growth orientation, concentration distribution, and strain status. Finally, GOI based applications including high performance metal–oxide–semiconductor field effect transistors (MOSFETs) and photodetectors will be discussed. These results show that RMG is a promising technique for growth of high quality GOIs with different characterizations. The GOI grown by RMG is a potential material for the next-generation of integrated circuits and optoelectronic circuits.

Origin of large dark current increase in InGaAs/InP avalanche photodiode

The large dark current increase near the breakdown voltage of an InGaAs/InP avalanche photodiode is observed and analyzed from the aspect of bulk defects in the device materials. The trap level information is extracted from the temperature-dependent electrical characteristics of the device and the low temperature photoluminescence spectrum of the materials. Simulation results with the extracted trap level taken into consideration show that the trap is in the InP multiplication layer and the trap assisted tunneling current induced by the trap is the main cause of the large dark current increase with the bias from the punch-through voltage to 95% breakdown voltage.

High efficiency optical coupling in long wavelength quantum cascade infrared detector via quasi-one-dimensional grating plasmonic micro-cavity

A combination of quasi-one-dimensional grating and plasmonic micro-cavity is proposed as a normal-illuminated optical coupler for a long wavelength quantum cascade infrared detector. A finite difference time-domain method is used to numerically simulate the reflection spectra and the field distributions of the optical coupler. The average |Ez|2 in the active layer reaches 4.1 (V/m)2 under the 13.5 μm infrared normal illumination with a strength of 1 (V/m)2. A mixed state of localized surface plasmon and surface plasmonic polariton is observed. The results confirm that the quasi-one-dimensional grating plasmonic micro-cavity structure could generate more plasma excitation source, and as a consequence, a high optical coupling efficiency of 410% in the active region is obtained. Moreover, an excellent polarization-discriminating performance is observed.