The lateral diffusion length ( L h ) of minority carriers in LWIR InAs/GaSb superlattice detectors grown by metalorganic chemical vapour deposition was evaluated. The deeply‐etched PNn device exhibits a diffusion‐limited behaviour at 80 K, with a dark current density as low as 9.1 × 10 −6 A/cm 2 at −0.1 V and a 50% cut‐off of 10.1 μm. In shallow‐etched pixels with a common absorber, both the photo‐current and the dark current show a size‐dependent behaviour. L h deduced from the two methods are 211 and 251 μm, respectively, which are longer than those in superlattice materials grown by molecular beam epitaxy.
High-angle annular dark-field (HAADF) imaging and electron energy loss spectroscopy (EELS) in a Cs-corrected scanning transmission electron microscope were utilized to analyze the interfacial atomic structure of InAs/GaSb superlattices (SLs) grown by metalorganic chemical vapor deposition (MOCVD) on InAs substrates. Despite high growth temperature, narrow interface (IF) widths of less than 2.5 monolayers (MLs) and 3.8 MLs were extracted from HAADF and EELS, respectively, indicating that the IF quality of MOCVD-grown InAs/GaSb SLs is comparable to those grown by molecular beam epitaxy. GaAs-type IFs are considered to account for the narrow IF width. In addition, GaSb-on-InAs IFs were found to be sharper and more strained than InAs-on-GaSb IFs, which is correlated with the special gas supply and switching sequence during MOCVD growth. The strain profile deduced from the HAADF image suggests that little Sb is incorporated into InAs sublayers and 7% In is incorporated into GaSb sublayers.
We demonstrate two short-wavelength infrared avalanche photodiodes based on InAs/GaSb superlattice grown by metal-organic chemical vapor deposition. The difference between the two devices, namely, p + n − n + and p + nn − n + , is that the p + nn − n + device possesses an additional middle-doped layer to separate the multiplication region from the absorption region. By properly controlling the electric field distribution in the p + nn − n + device, an electric field of 906 kV/cm has been achieved, which is 2.6 times higher than that in the p + n − n + device. At a reverse bias of –0.1 V at 77 K, both devices show a 100% cut-off wavelength of 2.25 μm. The p + n − n + and p + nn − n + show a dark current density of 1.5 × 10 −7 A/cm 2 and 1.8 × 10 −8 A/cm 2 , and a peak responsivity about 0.35 A/W and 0.40 A/W at 1.5 μm, respectively. A maximum multiplication gain of 55 is achieved in the p + nn − n + device while the value is only less than 2 in the p + n − n + device. Exponential nature of the gain characteristic as a function of reverse bias confirms a single carrier hole dominated impact ionization.
After analyzing the meaning of the responsibility in a book with more responsible persons, this paper puts forward that we must recognize the principal responsibility and the secondary responsibility so as to describe the responsibility area correctly.
Abstract Tight formations with extremely low matrix permeabilities, such as gas shale, can produce at economical rates is due to inborn fissures and fractures introduced during hydraulic stimulation. Hydraulic fracturing in gas shale can connect/generate these microfractures, causing them to become much more complex fracture networks. During a fracturing treatment, a pair of main fractures firstly is generated perpendicular to the wellbore direction. As the fluids continue to pump, more micro-sized fractures are generated near the main fractures. These microfractures have much more contact area with the matrix and therefore hold the majority of the productivity potential of gas shale. Slickwater fracturing has been proved to be an effective method by which to increase the recovery of shale gas reservoirs. Friction reducer is the primary component of this fluid. It can decrease the flowing friction in macro tubing. Lab tests and field applications have addressed this issue thoroughly. However, the flow characteristics of this solution in microfractures are not clear. The present study attempts to represent how this solution flows in microfractures by considering how it flows in microchannels. A commercial friction reducer was prepared with deionized water. The size of the particles in the FR first was analyzed from the macro to the nano scale. Then, the FR solution fluxed the microchannels with various velocities. Different solution concentrations, microchannel size effects and Reynolds number (Re) were investigated in detail. The Microchannels wettabilities, fluid shear rates and residual resistance factors also were studied. Finally, the experimental results were compared with field data, and its impact on the gas shale matrix was analyzed.
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