A new W-structured type-II superlattice photodiode design, with graded band gap in the depletion region, is shown to strongly suppress dark currents due to tunneling and generation-recombination processes. The long-wave infrared (LWIR) devices display 19%–29% quantum efficiency and substantially reduced dark currents. The median dynamic impedance-area product of 216Ωcm2 for 33 devices with 10.5μm cutoff at 78K is comparable to that for state-of-the-art HgCdTe-based photodiodes. The sidewall resistivity of ≈70kΩcm for untreated mesas is also considerably higher than previous reports for passivated or unpassivated type-II LWIR photodiodes, apparently indicating self-passivation by the graded band gap.

We report on the integration of epitaxial colossal magnetoresistive La0.67Ba0.33MnO films on Si(100) semiconductor using SrTiO3 template layer by pulsed-laser deposition. X-ray diffraction reveals the superior quality of the manganite film that grows epitaxially on heteroepitaxially grown SrTiO3 template layer on Si substrate. The epitaxial films demonstrate remarkable surface morphology, magnetic transition and hysteresis, magnetoresistance, and ferromagnetic resonance, illustrating the ferromagnetic nature of the film and possible device applications at room temperature.

The precipitation of sigma phase within the ferrite component of a duplex stainless steel has been simulated using a two-dimensional computer model which takes into account the partitioning of alloy elements between ferrite and austenite. The model is based on a cellular automaton and, despite having a rather simple set of transition rules, is able to simulate changes in the volume fractions of the austenite, ferrite, and sigma phases. The microstructures produced are similar in appearance to those in the real system. Comparison of the model and the real system may assist in the assessment of the various phenomena occurring. Use is made of the model to examine many of the factors that might conceivably be harnessed to retard precipitation of the sigma phase in duplex stainless steels.

Time-resolved photoluminescence (TRPL) spectroscopy is used to study the minority-carrier lifetime in mid-wavelength infrared, n-type, InAs/Ga 1Àx In x Sb type II superlattices (T2SLs) and investigate the recombination mechanisms and trap states that currently limit their performance. Observation of multiple exponential decays in the intensity-dependent TRPL data indicates trap saturation due to the filling then emptying of trap states and different Shockley-Read-Hall (SRH) lifetimes for minority and majority carriers, with s maj (s n0 ) ) s min (s p0 ). Simulation of the photoluminescence transient captures the qualitative behavior of the TRPL data as a function of temperature and excess carrier density. A trap state native to Ga 1Àx In x Sb is identified from the low-injection temperature-dependent TRPL data and found to be located below the intrinsic Fermi level of the superlattice, approximately 60 ± 15 meV above the valence-band maximum. Low-temperature TRPL data show a variation of the minority-carrier SRH lifetime, s p0 , over a set of InAs/Ga 1Àx In x Sb T2SLs, where s p0 increases as x is varied from 0.04 to 0.065 and the relative layer thickness of Ga 1Àx In x Sb is increased by 31%.

No abstract