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Highly mismatched B-III–V alloys present a promising avenue for near-infrared (NIR), direct bandgap optoelectronics that can be integrated on GaAs or Si, owing to their ability to vary bandgap and lattice constant independently. Here, we report the epitaxial growth, fabrication, and characterization of nearly strain-free, all-BGaInAs, p-i-n photodiodes on GaAs substrates grown by molecular beam epitaxy. Incorporating boron effectively reduced the strain in InGaAs, yielding nearly lattice-matched BGaInAs layers with high surface quality, as confirmed by high-resolution x-ray diffraction and atomic force microscopy measurements. Strong photoluminescence (PL) intensity was observed for BGaInAs with up to 3.2% B (7% In). The operating wavelength consistently extended with increasing boron and indium incorporation as evidenced by PL and external quantum efficiency measurements, which agree with density functional theory predictions. Altogether, these results highlight precise control of the operating wavelength and suggest highly substitutional boron incorporation. BGaInAs photodiodes with low boron and indium concentrations demonstrated high sensitivity with low dark current. We also report the effective thermal conductivity of the BGaInAs p-i-n structures and find that the thermal conductivity is largely insensitive to boron content with dominant effects from the indium content. Altogether, these findings underscore the potential for strain-free BGaInAs photodiodes as promising candidates for high-performance NIR optoelectronics. 

We experimentally demonstrate primordial metamaterials - composite media supporting essentially nonlocal wave propagation, grown with molecular beam epitaxy. Our transmission measurements confirm the theoretically predicted spectral signature of coupling to nonlocal modes. 

The proposed Monte Carlo model reveals the effect of alloy scattering on the excess noise factor (F(M)) in Al_0.7InAsSb avalanche photodiodes. A comparison between the F(M) of different combinations of scattering rates is investigated. 

We present the results of direct measurements of the effect of mechanically applied biaxial strain on Auger recombination rates in InGaAs quantum wells grown on InP. By mounting these structures on a flexible membrane, we applied strain mechanically rather than by changing the quantum well alloy fraction. Specifically, we employed time-resolved photoluminescence spectroscopy to probe the recombination dynamics in the degenerate carrier regime. From these measurements, we extract the non-degenerate cubic Auger coefficient C30. We found that applying 1.59% tensile biaxial strain increased the Auger C30 coefficient by 325% in one of our samples. These results support the hypothesis that the mechanical strain induced by heteroepitaxy plays a direct role in mitigating Auger recombination in InP-based telecommunication-range lasers. 

The electronic structures of three highly mismatched alloys (HMAs)—GeC(Sn), Ga(In)NAs, and BGa(In)As—were studied using density functional theory with HSE06 hybrid functionals, with an emphasis on the local environment near the mismatched, highly electronegative atom (B, C, and N). These alloys are known for their counterintuitive reduction in the bandgap when adding the smaller atom, due to a band anticrossing (BAC) or splitting of the conduction band. Surprisingly, the existence of band splitting was found to be completely unrelated to the local displacement of the lattice ions near the mismatched atom. Furthermore, in BGaAs, the reduction in the bandgap due to BAC was weaker than the increase due to the lattice constant, which has not been observed among other HMAs but may explain differences among experimental reports. While local distortion in GeC and GaNAs was not the cause for BAC, it was found to enhance the bandgap reduction due to BAC. This work also found that mere contrast in electronegativity between neighboring atoms does not induce BAC. In fact, surrounding the electronegative atom with elements of even smaller electronegativity than the host (e.g., Sn or In) consistently decreased or even eliminated BAC. For a fixed composition, moving Sn toward C and In toward either N or B was always energetically favorable and increased the bandgap, consistent with experimental annealing results. Such rearrangement also delocalized the conduction band wavefunctions near the mismatched atom to resemble the original host states in unperturbed Ge or GaAs, causing the BAC to progressively weaken. These collective results were consistent whether the mismatched atom was a cation (N), anion (B), or fully covalent (C), varying only with the magnitude of its electronegativity, with B having the least effect. The effects can be explained by charge screening of the mismatched atom's deep electrostatic potential. Together, these results help explain differences in the bandgap and other properties reported for HMAs from different groups and provide insight into the creation of materials with designer properties. 

Al_xIn_1−xAs_ySb_1−yis a promising multiplier for avalanche photodiodes (APD) on InP for near-infrared applications. In this work, we investigated the potential of two different ternary-containing layer stacks for the growth of AlInAsSb digital alloys on InP and InP-on-Si templates with applications in future photodetectors. STEM measurements confirmed high-quality material and interfaces on both substrates with no evidence of phase separation. Low dark currents and high gains were measured from PIN diodes grown on both substrates, with slightly higher dark currents observed in the Si-based device due to defects resulting from lattice mismatch in the template. 

Nickel and aluminum ohmic contacts were formed on p-doped GeC and GeCSn epitaxial films with ∼1%C. When a 40 nm p-GeC contact layer was added to p-Ge, annealed contact resistivity (Rc) dropped by 87% to 9.3 × 10−7 Ω cm2 for Al but increased by 32% to 2.9 × 10−5 Ω cm2 for Ni. On the other hand, thick films of GeCSn, which showed lower active doping, had contact resistivities of 4.4 × 10−6 Ω cm2 for Al and 1.4 × 10−5 Ω cm2 for Ni. In general, Al contacts were better than Ni, regardless of anneal, and were further improved by adding carbon. Annealing reduced Rc for both Ni and Al contacts to GeCSn by 4×, 2× for Al on GeC, and 5 orders of magnitude for Ni on GeC. It is speculated that C forms bonds with Ni that inhibit diffusion of Ni into the Ge, thus preventing the formation of low-resistance nickel germanide. Adding C, either as bulk GeCSn or as GeC contact layers, seems to significantly reduce the contact resistivity for Al contacts when compared to bulk Ge of comparable doping.