The structural evolution of InN nanorods to microstructures on Si (111) by molecular beam epitaxy

We report the catalyst free growth of wurtzite InN nanorods (NRs) and microislands on bare Si(111) by plasma-assisted molecular beam epitaxy at various temperatures. The morphological evolution from NRs to three dimensional (3D) islands as a function of growth temperature is investigated. A combination of tapered, non-tapered, and pyramidal InN NRs are observed at 490 °C, whereas the InN evolves to faceted microislands with an increase in growth temperature to 540 °C and further developed to indented and smooth hemispherical structures at extremely high temperatures (630 °C). The evolution from NRs to microislands with increase in growth temperature is attributed to the lowering of the surface free energy of the growing crystals with disproportionate growth velocities along different growth fronts. The preferential adsorption of In atoms on the (0001) c-plane and (10-10) m-plane promotes the growth of NRs at relatively low growth temperature and 3D microislands at higher temperatures. The growth rate imbalance along different planes facilitates the development of facets on 3D microislands. A strong correlation between the morphological and structural properties of the 3D films is established. XRD studies reveal that the NRs and the faceted microislands are crystalline, whereas the hemispherical microislands grown at extremely high growth temperature contain In adlayers. Finally, photoluminescent emissions were observed at ∼0.75 eV from the InN NRs

Recent advances in the Van der Waals epitaxy growth of III‐V semiconductor nanowires on graphene

The recent discovery of the one‐atom‐thick, two‐dimensional graphene layers with exciting properties including superb optical transparency and high mechanical robustness has stimulated extensive research interest for use as an alternative nanowires (NWs) growth platform for applications in next generation, flexible, stretchable, and printable electronic and optoelectronic devices. When combined with the exceptional capabilities of semiconductor NWs including improved light absorption, reduced optical reflectance, enhanced carrier collection, and fast response, the performance of optoelectronic devices could be significantly improved in novel high‐performance, flexible nanodevices. However, the growth of semiconductor NWs on 2D graphene layers is highly challenging owing to the absence of surface dangling bonds on graphene. Intriguingly, the last decade has witnessed a flurry of research activity on the growth of III‐V semiconductor NWs on graphene. In this review, we highlight the significant advancements that have been made in circumventing this challenge to realize the growth of III‐V semiconductor NWs on graphene. We then summarize the recent progress made in the development of graphene‐based NWs devices including photodetectors and solar cells. Finally, a brief conclusion and outlook of the way forward in the growth of semiconductor NWs on graphene is presented

Photoluminescence characteristics of zinc blende InAs nanowires

A detailed understanding of the optical properties of self-catalysed (SC), zinc blende (ZB) dominant, nanowires (NWs) is crucial for the development of functional and impurity-free nanodevices. Despite the fact that SC InAs NWs mostly crystallize in the WZ/ZB phase, there are very limited reports on the photoluminescence (PL) properties of ZB InAs NWs. Here, we report on the PL properties of Molecular Beam Epitaxy grown, SC InAs NWs. The as-grown NWs exhibit a dominant band to band (BtB) peak associated with ZB, InAs with an emission energy of ~0.41 eV in good agreement with the band gap energy of ZB InAs and significantly lower than that of the wurtzite phase (~0.48 eV). The strong BtB peak persists to near room temperature with a distinct temperature-dependent red-shift and very narrow spectral linewidth of ~20 meV (10 K) which is much smaller than previously reported values. A narrowing in PL linewidth with increasing NWs diameter is correlated with a decline in the influence of surface defects resulting from an enlargement in NWs diameter. This study demonstrates the high optical property of SC InAs NWs which is compatible with the Si-complementary metal-oxide-semiconductor technology and paves the way for the monolithic integration of InAs NWs with Si in novel nanodevices

Effect of N2* and N on GaN nanocolumns grown on Si (111) by molecular beam epitaxy

The self-induced growth of GaN nanocolumns (NCs) on SixN1−x/Si (111) is investigated as a function of the ratio of molecular to atomic nitrogen species generated via plasma assisted molecular beam epitaxy. Relative concentrations of the molecular and atomic species are calculated using optical emission spectroscopy. The growth rate (GR), diameter, and density of NCs are found to vary with the molecular to atomic nitrogen species relative abundance ratio within the plasma cavity. With increasing ratio, the GR and diameter of NCs increase while the density of NCs seems to be decreasing. The morphologies and the coalescence of GaN NCs exhibit a trend for molecular/atomic ratios up to 11, beyond which they still change but at a lower rate. The detrimental effect of taperedness of the NCs decreases with increasing molecular/atomic ratios. This is possibly because of reduction in radial growth in NCs due to increase in diffusivity of nitrogen species with increasing ratios

Extended wavelength mid-infrared photoluminescence from type-I InAsN and InGaAsN dilute nitride quantum wells grown on InP

Extended wavelength photoluminescence emission within the technologically important 2–5 micrometer spectral range has been demonstrated from InAs1xNx and In1yGayAs1xNx type I quantum wells grown onto InP. Samples containing N 1% and 2% exhibited 4K photoluminescence emission at 2.0 and 2.7 lm, respectively. The emission wavelength was extended out to 2.9 lm (3.3 lm at 300 K) using a metamorphic buffer layer to accommodate the lattice mismatch. The quantum wells were grown by molecular beam epitaxy and found to be of a high structural perfection as evidenced in the high resolution x-ray diffraction measurements. The photoluminescence was more intense from the quantum wells grown on the metamorphic buffer layer and persisted up to room temperature. The mid-infrared emission spectra were analysed, and the observed transitions were found to be in good agreement with the calculated emission energies

Low bandgap mid-infrared thermophotovoltaic arrays based on InAs

We demonstrate the first low bandgap thermophotovoltaic (TPV) arrays capable of operating with heat sources at temperatures as low as 345 °C, which is the lowest ever reported. The individual array elements are based on narrow band gap InAs/InAs0.61Sb0.13P0.26 photodiode structures. External power conversion efficiency was measured to be ∼3% from a single element at room temperature, using a black body at 950 °C. Both 25-element and 65-element arrays were fabricated and exhibited a TPV response at different source temperatures in the range 345–950 °C suitable for electricity generation from waste heat and other applications

Room temperature mid-infrared InAsSbN multi-quantum well photodiodes grown by MBE

Room temperature photoresponse in the mid-infrared spectral region is demonstrated from InAsSbN/InAs multi-quantum well photodiodes grown by nitrogen plasma assisted molecular beam epitaxy. The structural quality of the InAsSbN MQWs was ascertained in-situ by reflection high energy electron diffraction and ex-situ by high resolution X-ray diffraction and photoluminescence measurements. The extended long wavelength photoresponse is identified to originate from the electron-heavy hole (e1-hh1) and electron-light hole (e1-lh1) transitions in the InAsSbN MQW, with a cut off wavelength ~ 4.20 µm and peak detectivity D* =1.25×109 cm Hz1/2 W-1

Recent trends in 8-14 µm type-II superlattice infrared detectors

Type-II superlattices (T2SLs) hold enormous potential for next-generation, 8 – 14μm long-wavelength infrared (LWIR) detectors for use at high operating temperature (HOT). The inherit flexibility of the material system has enabled the incorporation of unipolar barriers to eliminate generation-recombination currents and enhance device performance. In addition to suppressed Auger recombination and tunneling currents, this has led to sustained research interest in this material system over the past several decades. For these reasons they are theoretically predicted to outperform the current state-of-the-art Mercury Cadmium Telluride (MCT) detectors. This review provides an overview of LWIR T2SL detectors and highlights some recent developments towards HOT applications. Recent studies on the minority carrier lifetime and diffusion length of T2SLs are examined to appraise the extent to which they limit the performance of HOT LWIR T2SL detectors. Strategies for mitigating these limitations are also explicated

Peculiarities of the hydrogenated In(AsN) alloy

The electronic properties of In(AsN) before and after post-growth sample irradiation with increasing doses of atomic hydrogen have been investigated by photoluminescence. The electron density increases in In(AsN) but not in N-free InAs, until a Fermi stabilization energy is established. A hydrogen ε+/− transition level just below the conduction band minimum accounts for the dependence of donor formation on N, in agreement with a recent theoretical report highlighting the peculiarity of InAs among III–V compounds. Raman scattering measurements indicate the formation of N–H complexes that are stable under thermal annealing up to ∼500 K. Finally, hydrogen does not passivate the electronic activity of N, thus leaving the band gap energy of In(AsN) unchanged, once more in stark contrast to what has been reported in other dilute nitride alloys

Room temperature mid-infrared InAsSbN multi-quantum well photodiodes grown by MBE

Room temperature photoresponse in the mid-infrared spectral region is demonstrated from InAsSbN/InAs multi-quantum well photodiodes grown by nitrogen plasma assisted molecular beam epitaxy. The structural quality of the InAsSbN MQWs was ascertained in situ by reflection high energy electron diffraction and ex situ by high resolution x-ray diffraction and photoluminescence measurements. The extended long wavelength photoresponse is identified to originate from the electron–heavy hole (e1–hh1) and electron–light hole (e1–lh1) transitions in the InAsSbN MQW, with a cut off wavelength ~4.20 µm and peak detectivity D *  =  1.25  ×  109 cm Hz1/2 W−1