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.

In the presence of palladium(II) acetate [PdA C H T U N G T R E N N U N G (OAc) 2 ] and an N-heterocyclic carbene (NHC) ligand, fluorene derivatives can be generated in good to excellent yields from 2-halo-2'-methylbiaryls through the benzylic C À H bond activation (14 examples; 81-97% yields). The scope and limitations of this protocol have been examined. A wide range of functional groups, such as alkyl, alkoxy, ester, nitrile, and others, is able to tolerate the reaction conditions herein. The cyclization of an isotope-labelled biphenyl gave the corresponding product with a primary kinetic isotope effect (k H /k D = 4.8:1), which indicates that the rate-determining step of this reaction is the activation of the benzylic C À H bond. Moreover, indenofluorenes were also accessed in excellent results from terphenyls (3 examples; 91-92% yields). The cascade reaction of 2,6-dichloro-2'-methylbiphenyl with diphenylacetylene produced 8,9-diphenyl-4H-cyclopentaA C H T U N G T R E N N U N G [def]phenanthrene in 60% yield through the activation of an aryl and a benzylic C À H bond.

The absorption spectra for the antimonide-based type-II superlattices (SLs) for detection in the long-wave infrared (LWIR) are calculated and compared to the measured data for SLs and bulk materials with the same energy gap (HgCdTe and InAsSb). We include the results for the metamorphic InAsSbx/InAsSby SLs with small periods as well as the more conventional strain-balanced InAs/Ga(In)Sb and InAs/InAsSb SLs on GaSb substrates. The absorption strength in small-period metamorphic SLs is similar to the bulk materials, while the SLs with an average lattice constant matched to GaSb have significantly lower absorption. This is because the electron-hole overlap in the strain-balanced type-II LWIR SLs occurs primarily in the hole well, which constitutes a relatively small fraction of the total thickness.

InAs0.6Sb0.4/Al0.75In0.25Sb-based barrier photodetectors were grown metamorphically on compositionally graded Ga1−xInxSb buffer layers and GaSb substrates by molecular beam epitaxy. At the wavelength of 8 μm and T = 150 K, devices with 1-μm thick absorbers demonstrated an external quantum efficiency of 18% under a bias voltage of 0.45 V.

Bulk unrelaxed InAsSb alloys with Sb compositions up to 65% were grown on compositionally graded GaInSb and AlInSb buffers on GaSb substrates by molecular beam epitaxy. The minimum energy gap for these materials at T = 77 K was estimated to be 90 meV. Benchmark material parameters were measured for barrier photodetector heterostructures with 1-lm-thick InAs 0.6 Sb 0.4 absorbers. A minority hole lifetime of 185 ns and a diffusion length of 9 lm at T = 77 K were determined from the transient response of barrier heterostructures. The data imply a hole mobility of 10 3 cm 2 /Vs, which was confirmed with frequency response measurements. A 100-lm square mesa contact nBn heterostructure demonstrated a À3 dB frequency response bandwidth of 50 MHz.