The reduction of efficiency droop by Al0.82In0.18N/GaN superlattice electron blocking layer in (0001) oriented GaN-based light emitting diodes Ultraviolet light-emitting diodes operating at 280 nm, grown by gas source molecular-beam epitaxy with ammonia, are described. The device is composed of n-and p-type superlattices of AlN͑1.2 nm thick͒/AlGaInN͑0.5 nm thick͒ doped with Si and Mg, respectively. With these superlattices, and despite the high average Al content, we obtain hole concentrations of (0.7-1.1)ϫ10 18 cm Ϫ3 , with the mobility of 3-4 cm 2 /V s and electron concentrations of 3ϫ10 19 cm Ϫ3 , with the mobility of 10-20 cm 2 /V s, at room temperature. These carrier concentrations are sufficient to form effective p -n junctions needed in UV light sources.

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.

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The bandgap energy of the alloy InAsSb has been studied as function of composition with special emphasis on minimization of strain-induced artifacts. The films were grown by molecular beam epitaxy on GaSb substrates with compositionally graded buffer layers that were designed to produce strain-free films. The compositions were precisely determined by high-resolution x-ray diffraction. Evidence for weak, long-range, group-V ordering was detected in materials exhibiting residual strain and relaxation. In contrast, unstrained films having the nondistorted cubic form showed no evidence of group-V ordering. The photoluminescence (PL) peak positions therefore corresponds to the inherent bandgap of unstrained, unrelaxed, InAsSb. PL peaks were recorded for compositions up to 46% Sb, reaching a peak wavelength of 10.3 μm, observed under low excitation at T=13K. The alloy bandgap energies determined from PL maxima are described with a bowing parameter of 0.87 eV, which is significantly larger than measured for InAsSb in earlier work. The sufficiently large bowing parameter and the ability to grow the alloys without ordering allows direct bandgap InAsSb to be a candidate material for low-temperature long-wavelength infrared detector applications.

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.

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GaSb-based type-I quantum-well diode lasers emitting at 3.36 m at 12°C with 15 mW of continuous wave output power are reported. Devices with two or four InGaAsSb compressively strained quantum wells and AlInGaAsSb quinternary barriers were fabricated and characterized. It was shown that increase in the quantum-well number led to improved laser differential gain and reduced threshold current.The growing demand for light emitters capable of high power room temperature operation in spectral region from 3 to 3.5 m encourages intensive search for appropriate design approach to fabricating such photonic devices. Both monopolar and bipolar lasers based on cascade and multiple quantum well ͑QW͒ active region designs are being extensively researched for this purpose ͑see, for instance, Refs. 1 and 2͒. GaSb-based type-I QW diode lasers operate in continuous wave ͑cw͒ at room temperature in spectral region above 3 m. 3,4 Diode lasers grown by molecular beam epitaxy on GaSb substrates and operating up to 3.1 m at room temperature in cw mode have been recently reported by our group. 5 Further increase in the operating wavelength of type-I QW GaSb-based lasers faces two major complications ͑a͒ gradual decrease in the valence band offset between InGaAsSb QW and Al containing barrier layers when In and As concentrations in QW are increased 6 and ͑b͒ possible increase in the nonradiative Auger recombination rate when QW bandgap decreases. The latter is thought to be fundamental in nature.The lack of valence band offset in GaSb-based heterostructures can be overcome by introduction of heavy compressive strain above 1% into InGaAsSb QWs 7 and utilization of the quinternary AlInGaAsSb barrier material. 4,8 The contribution of the Auger recombination processes to threshold current can be minimized by a reduction in the threshold carrier concentration through improvement of the hole confinement itself and by increase in the number of QWs in device active region.In this work we report on the development of the 3.36 m emitting lasers with strained active region and quinternary barrier material. We demonstrate that increase in the number of QWs from two to four decreases the device threshold current through improvement in the laser differential gain ͑with respect to current͒. Diode lasers with four QW active regions operate in cw mode at 12°C with 15 mW of output power at 3.36 m.Laser heterostructures were grown at State University of New York at Stony Brook by solid-source molecular beam epitaxy using Veeco GEN-930 reactor equipped with As and Sb valved cracker sources. Te and Be were used for nand p-doping, respectively. Laser active region contained either two or four 16 nm wide 1.5% compressively strained InGaAsSb QWs with nominal In composition of 54%. The interwell spacings were 40 and 20 nm in two-QW and four-QW devices, respectively. The waveguide ͑total width of 1 m͒ and barrier materials were Al 0.20 In 0.25 Ga 0.55 As 0.26 Sb 0.74 . The cladding material was Al 0.9 Ga 0.1 As 0.07 Sb 0.93 . Graded bandgap heavily doped transiti...

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