M. Qi

Gamma Radiolysis of Ionic Liquid 1-Butyl-3-methylimidazolium Hexafluorophosphate

Abstract Qi, M. Y., Wu, G. Z., Chen, S. M. and Liu, Y. D. Gamma Radiolysis of Ionic Liquid 1-Butyl-3-methylimidazoliumHexafluorophosphate. Radiat. Res. 167, 508–514 (2007). The applications of room-temperature ionic liquids in the nuclear fuel cycle and radiation chemistry depend on a comprehensive knowledge of their stability and chemical properties under radiation conditions. In this work, the effect of γ radiation on pure ionic liquid [bmim][PF6] was investigated in detail. The radiolysis of [bmim][PF6] leads to an increase of UV-vis absorbance and a decrease of fluorescence intensity with increasing radiation dose. Raman spectra proved that γ radiation induced significant chemical scission of the n-butyl group (e.g. C-H and C-C scission) and damage to the [PF6]− anion. When the irradiated [bmim][PF6] samples were cooled, two crystal structures were found to coexist, and they suffered a continuous destruction under irradiation; their dose dependence, however, was different.

Molecular beam epitaxial growth, characterization and performance of high-detectivity GaInAsSb/GaSb PIN detectors operating at 2.0 to 2.6 μm

Abstract Molecular beam epitaxy has been employed to grow Ga x In 1− x As 1− y Sb y PIN detectors operating at 2.0 to 2.6 μm on (100)-oriented GaSb substrates. The epitaxial layers were characterized by X-ray double-crystal diffraction, Fourier transform infrared spectroscopy, electron microprobe analysis, and Hall effect measurements. The background hole concentration and mobility at room temperature are (4–5) × 10 16 cm −3 , 254 cm 2 /V·s and 9 × 10 15 cm −3 , 970 cm 2 /V·s for GaInAsSb and GaSb, respectively. For a PIN mesa front-illuminated photodetector, a maximum external quantum efficiency of 65% without anti-reflection coating and a peak detectivity D λ ∗ at 2.5 μm of 3.0 × 10 9 cm Hz 1/2 / W with a cut-off wavelength of 2.6 μm at room temperature have been achieved.

Difference of luminescent properties between strained InAsP/InP and strain-compensated InAsP/InGaAsP MQWs

Abstract Strained InAs 0.43 P 0.57 /InP and strain-compensated InAs 0.43 P 0.57 /In 0.7 Ga 0.3 As 0.43 P 0.57 multiple quantum well (MQW) structures were grown by gas source molecular beam epitaxy. The observations of up to 5 satellite-diffraction peaks from the high-resolution X-ray diffraction measurements demonstrate good crystalline quality for both structures. The temperature dependence of the 1e–1hh transition energies, the line width of photoluminescence (PL) spectra and emission efficiency η of the two quantum well structures are compared by low-temperature PL measurements. The temperature dependence of the 1e–1hh transitions of the two quantum well structures is similar to that of InAs 0.43 P 0.57 bulk material. The thermal activation energies obtained for strain-compensated MQW are larger than those obtained for the strained one. Consequently, the PL emission efficiency decays much slower for the strain-compensated MQW than that for the strained one when temperature increases, indicating the superior temperature stability of luminescent efficiency for the strain-compensated MQW. The obtained results can be used as references to the design and fabrication of optoelectronic devices.

Parametric study on lattice-matched and pseudomorphic InGaAs/InAlAs/InP modulation-doped heterostructures grown by GSMBE

Abstract Modulation-doped In x Ga 1 − x As/In y Al 1 − y As/InP heterostructures have been grown with a diffusion pumped V80H gas source molecular beam epitaxy system. Their electrical properties have been studied with Hall measurements. The effects of spacer layer thickness and buffer layer structure (InAlAs or InAlAs + InP) on lattice-matched and pseudomorphic In x Ga 1 − x As/In y Al 1 − y As/InP 2DEGs and HEMTs characteristics have been investigated in detail. Crystalline and interface qualities can be improved by adding an InP buffer layer before the InAlAs buffer, resulting in an improvement in material electrical properties. A thicker spacer layer will cause a decrease of electron gas density and an increase of electron mobility. Adopting strained channel and Schottky layers can dramatically improve material electrical performance. For InGaAs/InAlAs/InP pseudomorphic 2DEG (P-2DEG) structures, electron mobilities of 11 230 cm 2 /V · s at n s of 2.3 × 10 12 cm −2 at 300 K and 6.52 × 10 4 cm 2 /V · s at n s of 2.1 × 10 12 cm −2 at 77 K were obtained and μ of 9273 cm 2 /V · s at 3.6 × 10 12 cm −2 and 4.5 × 10 4 cm 2 /V · s at n s of 3.1 × 10 12 cm −2 for both strained InGaAs channel layers and InAlAs Schottky layers in P-HEMT structures were achieved.

The effect of III–V ratio at the substrate surface on the quality of InP grown by GSMBE

Abstract High quality InP layers with a good surface morphology, a high electron mobility (μ = 112041 cm2/V · s at 77 K), a low background carrier concentration (n = 1.17 × 1014cm−3at 77 K) and a narrow photoluminescence spectrum width (FWHM = 1.5 meV at 5 K) have been obtained by using gas-source molecular beam epitaxy (GSMBE) through the optimization of the growth conditions. The effects of the growth conditions on the quality of InP grown by GSMBE are demonstrated and discussed.

GSMBE grown In0.49Ga0.51P/(In)GaAs/GaAs high hole mobility transistor structures

In this paper, we report novel In 0.49 Ga 0.51 P/(In)GaAs/GaAs high-hole mobility transistor structures with different p-channel and doping methods. Electrical and optical properties of the grown structures were investigated by Van der Pauw Hall measurement and low-temperature photoluminescence. The current-voltage characteristics were performed on field effect transistors with T-shaped gates. By using delta-doping technique, 2DHG densities of 2.78 ×10 12 and 1.02 x 10 12 cm - 2 with mobility of 191 and 2831 cm 2 /V s at 300 and 77 K for In 0.49 Ga 0.51 P/GaAs structures have been achieved. For In 0.49 Ga 0.51 P/In 0.2 Ga 0.8 As/GaAs structures, 2DHG densities increased to 2.84×10 12 and 1.29 ×10 12 cm -2 with mobility increasing to 208 and 2972 cm 2 /V s at 300 and 77 K, respectively. Photoluminescence spectra of In 0.49 Ga 0.51 P/In 0.2 Ga 0.8 As/GaAs modulation doped heterostructure shows a peak located at 1.310 eV, which is attributed to a transition from V 3/2 band to conduction band. The processed high-hole mobility transistors have a maximum extrinsic transconductance of 35mS/mm and a maximum saturation current of 57mA/mm at 300 K.

Device quality InGaAs/InAlAs/InP heterostructures grown by gas source molecular beam epitaxy

In this paper, we report the growth of device quality InGaAs/InAlAs/InP materials by gas source molecular beam epitaxy (GSMBE) and their applications to HEMTs and MSM-PDs. Larger conduction band discontinuity and larger electron mobility which led to improved electrical performance of HEMT materials and devices can be obtained by adoption of dual strained InGaAs channel layer and InAlAs Schottky layer.