Ultraviolet light-emitting diodes grown on Si(111) by gas-source molecular-beam epitaxy with ammonia are described. The layers are composed of superlattices of AlGaN/GaN and AlN/AlGaInN. The layers are doped n and p type with Si and Mg, respectively. Hole concentration of 4×1017 cm−3, with a mobility of 8 cm2/Vs, is measured in Al0.4Ga0.6N/GaN. We demonstrate effective n- and p-type doping of structures based on AlN/AlGaInN. Light-emitting diodes based on these structures show light emission between 290 and 334 nm.
Hafnium dioxide films have been deposited using reactive electron beam evaporation in oxygen on hydrogenated Si(100) surfaces. The capacitance–voltage curves of as-deposited metal(Ti)–insulator–semiconductor structures exhibited large hysteresis and frequency dispersion. With post-deposition annealing in hydrogen at 300 °C, the frequency dispersion decreased to less than 1%/decade, while the hysteresis was reduced to 20 mV at flatband. An equivalent oxide thickness of 0.5 nm was achieved for HfO2 thickness of 3.0 nm. We attribute this result to a combination of pristine hydrogen saturated silicon surfaces, room temperature dielectric deposition, and low temperature hydrogen annealing.
The possibility is analyzed of preparing specially pure hydrogen (SPH) in a high-temperature converter-membrane equipment system drawing on model representations developed previously using heat-resistant palladium alloys. Dependences are calculated for the parameters of membrane separation of methane steam catalytic conversion products on membrane area with different ratios of C H 2 O /C CH 4 in the starting material. The high efficiency of preparing SPH is demonstrated, i.e., of the order of 1.28 m 3 per cubic meter of starting gas.Previously in membrane equipment and units for preparing specially pure hydrogen (SPH) there has mainly been use of palladium alloyed with silver distinguished by high hydrogen permeability. In Russia, the most extensively used alloy has been type V-1 [1] with the optimum combination of physical, mechanical, engineering, and operating properties. The majority of large test-industrial membrane equipment and units for producing SPH of 100-2100 m 3 /h [2] are fitted with membranes of this alloy. With membrane separation of hydrogen containing gas atmospheres that do not interact chemically, such as the products of ammonia dissociation [3] and technical-grade hydrogen after furnaces for "light" annealing of electrical engineering steels [4], use of alloy V-1 has made it possible to resolve practical problems quite effectively.In order to prepare SPH with use of natural gas as a starting material, consisting almost solely of methane, it is normal to carry out prior high-temperature vapor catalytic conversion of methane at 800-900°C with preparation of a multicomponent gas mixture (H 2 , H 2 O, CO 2 , CO, CH 4 ). Nickel applied to a porous ceramic carrier (for example Al 2 O 3 ) with a high internal surface is used as the active component of the conversion catalyst.Under conditions providing absence of carbon deposition, the ratio between the components given above for the gas phase is determined by two reversible chemical reactions:With the use of alloy V-1, direct membrane separation of methane conversion products is not sufficiently effective both with absence [5] and with presence [6] of a methane conversion catalyst in the high-pressure chamber of the membrane equipment. The reason for the low efficiency of SPH preparation from natural gas is connected with the limitation for the membrane material working temperature (600°C).
We have prepared large-area, 0.50×0.55mm2, metal-semiconductor-metal photodetectors based on AlN layers with different density of inversion domains (IDs). AlN layers were grown on (0001) sapphire substrates using gas source molecular beam epitaxy. The introduction of AlN∕GaN short period superlattices after growth of AlN nucleation layer yields significant reduction in the ID density. Photodetectors with ID density of 106cm−2 exhibit a very low dark current of 0.5fA at zero bias, which remains below 50fA up to a bias of ±30V. The peak responsivity of 0.08A∕W was obtained at a wavelength of ∼202nm.
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