High-duty-cycle operation of GaAs/AlGaAs quantum cascade laser above liquid nitrogen temperature

We present a detailed study of lambda similar to 9.75 mu m GaAs/AIGaAs quantum cascade lasers. For a coated 2-mm-long and 40-mu m-wide laser, an optical power of 85 mu W is observed 95% duty cycle at 80 K. At a moderate driving pulse (1 kHz and 1% duty cycle), the device presents a peak power more than 20 mW even at 120 K. At 80 K, the fitted result of threshold current densities shows evidence of potential cw operation.

Liquid-phase-epitaxy-grown InAsxSb1-x/GaAs for room-temperature 8-12 mu m infrared detectors

High-quality InAsxSb1-x (0 < x <= 0.3) films are grown on GaAs substrates by liquid phase epitaxy and electrical and optical properties of the films are investigated, revealing that the films exhibit Hall mobilities higher than 2x10(4) cm(2) V-1 s(-1) and cutoff wavelengths longer than 10 mu m at room temperature (RT). Photoconductors are fabricated from the films, and notable photoresponses beyond 8 mu m are observed at RT. In particular, for an InAs0.3Sb0.7 film, a photoresponse of up to 13 mu m with a maximum responsivity of 0.26 V/W is obtained at RT. Hence, the InAsxSb1-x films demonstrate attractive properties suitable for room-temperature, long-wavelength infrared detectors. (c) 2006 American Institute of Physics.

Determination of the interdiffusion coefficients of liquid Zn and Sn using Ta/Zn-Sn/Si trilayers

In this paper we present a new method for measuring diffusion coefficients in liquid metals under convection-less conditions with solid/liquid-liquid/solid trilayer. The advantage of this kind of trilayer is that effects from gravity-induced convection and Marangoni-convection can be omitted, so that the diffusion coefficient is determined more accurately. The Ta/Zn-Sn/Si trilayer were prepared with a multi-target ion-beam sputtering deposition technique and annealed in an electric furnace under an argon atmosphere. The interdiffusion of liquid zinc and tin at 500 degrees degree C was investigated. The diffusion concentration profiles were determined by energy dispersive spectroscopy. The interdiffusion coefficients range from 1.0x10(-6)cm(2)/s to 2.8x10(-6)cm(2)/s, which is less than previous values measured by capillary reservoir technique under 1g-environment where various convection exist. The precise interdiffusion coefficients of liquid zinc and tin result from the removing of disturbances of various kinds of convection.

Compensation ratio-dependent concentration of a VInH4 complex in n-type liquid encapsulated Czochralski InP

The concentration of hydroen-indium vacancy complex VInH4 in liquid encapsulated Czochralski undoped and Fe-doped n-type InP has been studied by low-temperature infrared absorption spectroscopy. The VInH4 complex is found to be a dominant intrinsic shallow donor defect with concentrations up to similar to 10(16) cm(-3) in as-grown liquid encapsulated Czochralski InP. The concentration of the VInH4 complex is found to increase with the compensation ratio in good agreement with the proposed defect formation model of Walukiewicz [W. Walukiewicz, Phys. Rev. B 37, 4760 (1998); Appl. Phys. Lett. 54, 2094 (1989)], which predicts a Fermi-level-dependent concentration of amphoteric defects. (C) 1998 American Institute of Physics, [S0003-6951(98)04435-0].

Threshold reduction in strained-layer InGaAs/GaAs quantum well lasers by liquid phase epitaxy regrowth

When liquid phase epitaxy regrowth at 780 degrees C for 2 h is applied to the samples after molecular beam epitaxy, a decrease of the threshold current density in strained InGaAs/GaAs quantum well lasers by a factor of 3 to 4 is obtained. We suggest that this improvement is attributed to the reduction of nonradiative centers associated with deep levels at the three regions of the active region, the graded layer and the cladding layer. Indeed, a significant reduction of deep center densities has been observed by using minority and majority carrier injection deep level transient spectroscopy measurements. (C) 1998 Elsevier Science B.V. All rights reserved.

Growth of GaSb and GaInAsSb layers for thermophotovolatic cells by liquid phase epitaxy - art. no. 68411E

GaSb based cells as receivers in thermophotovoltaic system have attracted great interest and been extensively studied in the recent 15 years. Although nowadays the manufacturing technologies have made a great progress, there are still some details need to make a further study. In this paper, undoped and doped GaSb layers were grown on n-GaSb (100) substrates from both Ga-rich and Sb-rich solutions using liquid phase epitaxy (LPE) technique. The nominal segregation coefficients k of intentional doped Zn were 1.4 and 8.8 determined from the two kinds of GaSb epitaxial layers. Additionally, compared with growing from Ga-rich solutions, the growing processes from Sb-rich solutions were much easier to control and the surface morphologies of epitaxial layers were smoother. Further-more, in order to broaden the absorbing edge, Ga1-xInxAsySb1-y quaternary alloys were grown on both GaSb and InAs substrates from In-rich solutions, under different temperature respectively.

Liquid nitrogen flowrate alarm system for MBE

Liquid nitrogen is very important for MBE system. Most MBE systems use the liquid nitrogen to absorb the impurity molecules. If MBE cryoshroud is lack of liquid nitrogen, the pressure of the growth chamber will grow. This will affect the film quality. But too much liquid nitrogen is a waste. We have developed a liquid nitrogen flowrate alarm system to monitor the liquid nitrogen status in MBE cryoshroud. In this method, a temperature sensor is placed at the end of the cryoshroud. The temperature varies with changing of the liquid nitrogen status in cryoshroud. If the liquid nitrogen level in the cryoshroud is too low or too high, the LNFA will send out an alarm to warn the user to adjust the liquid nitrogen flowrate. In our experiments, we found this method works well, and the temperature responds sensitively. With the help of this system, people can view the liquid nitrogen status of the entire growth process. Compare with other method. it is very cheap.

Controlled growth of silicon nanowires by solid-liquid-solid method and their formation mechanism

High quality silicon nanowires (SiNWs) were grown directly from n-(111) silicon single crystal substrate by using Au film as a metallic catalyst. The diameter and length of the formed nanowires are 30-60 nm and from several micrometers to sereral tens of micrometers, respectively. The effects of Au film thickness, annealing temperature, growth time and N-2 gas flow rate on the formation of the nanowires were experimentally investigated. The results confirmed that the silicon nanowires with controlled diameter, length, shape and orientation can be obtained via reasonably choosing and optimizing various technical conditions. The formation process of the silicon nanowires is analyzed qualitatively based on solid-liquid-solid growth mechanism.

Blue Luminescent Properties of Silicon Nanowires Grown by a Solid-Liquid-Solid Method

Silicon nanowires (SiNWs) were grown directly from n-(111) single-crystal silicon (c-Si) substrate based on a solid-liquid-solid mechanism, and Au film was used as a metallic catalyst. The room temperature photoluminescence properties of SiNWs were observed by an Xe lamp with an exciting wavelength of 350 nm. The results show that the SiNWs exhibit a strongly blue luminescent band in the wavelength range 400-480 nm at an emission peak position of 420 nm. The luminescent mechanism of SiNWs indicates that the blue luminescence is attributed to the oxygen-related defects, which are in SiOx amorphous oxide shells around the crystalline core of SiNWs.

High resistance AlGaAs/GaAs quantum cascade detectors grown by solid source molecular beam epitaxy operating above liquid nitrogen temperature

This work was supported by the National Research Projects of China (grant numbers are 60525406, 60736031, 60806018, 60906026, 2006CB604903, 2007AA03Z446 and 2009AA03Z403, 10990100, respectively). The authors would like to thank P Liang, Y Hu, H Sun, X L Zhang, B J Sun, H L Zhen and N Li for their help in processing and characterization.

Upgrading of liquid fuel from the vacuum pyrolysis of biomass over the Mo-Ni/gamma-Al2O3 catalysts

High amounts of acid compounds in bio-oil not only lead to the deleterious properties such as corrosiveness and high acidity, but also set up many obstacles to its wide applications. By hydrotreating the bio-oil under mild conditions, some carboxylic acid compounds could be converted to alcohols which would esterify with the unconverted acids in the bio-oil to produce esters. The properties of the bio-oil could be improved by this method. In the paper, the raw bio-oil was produced by vacuum pyrolysis of pine sawdust. The optimal production conditions were investigated. A series of nickel-based catalysts were prepared. Their catalytic activities were evaluated by upgrading of model compound (glacial acetic acid). Results showed that the reduced Mo-10Ni/gamma-Al2O3 catalyst had the highest activity with the acetic acid conversion of 33.2%. Upgrading of the raw bio-oil was investigated over reduced Mo-10Ni/gamma-Al2O3 catalyst. After the upgrading process, the pH value of the bio-oil increased from 2.16 to 2.84. The water content increased from 46.2 wt.% to 58.99 wt.%. The H element content in the bio-oil increased from 6.61 wt.% to 6.93 wt.%. The dynamic viscosity decreased a little. The results of GC-MS spectrometry analysis showed that the ester compounds in the upgraded bio-oil increased by 3 times. it is possible to improve the properties of bio-oil by hydrotreating and esterifying carboxyl group compounds in the bio-oil.