Wide-band-gap GaN and Ga-rich InGaN alloys, with energy gaps covering the blue and near-ultraviolet parts of the electromagnetic spectrum, are one group of the dominant materials for solid state lighting and lasing technologies and consequently, have been studied very well. Much less effort has been devoted to InN and In-rich InGaN alloys. A major breakthrough in 2002, stemming from much improved quality of InN films grown using molecular beam epitaxy, resulted in the bandgap of InN being revised from 1.9 eV to a much narrower value of 0.64 eV. This finding triggered a worldwide research thrust into the area of narrow-band-gap group-III nitrides. The low value of the InN bandgap provides a basis for a consistent description of the electronic structure of InGaN and InAlN alloys with all compositions. It extends the fundamental bandgap of the group III-nitride alloy system over a wider spectral region, ranging from the near infrared at ∼1.9 μm (0.64 eV for InN) to the ultraviolet at ∼0.36 μm (3.4 eV for GaN...

When group-III nitrides go infrared: New properties and perspectives

In this article, we provide an overview on the recent advances made in InN, including both planar and nanowire structures. With the improved epitaxial growth process, the background electron concentration can be reduced to low 1017 and 1013 cm−3 ranges in planar and nanowire structures, respectively, with the latter approaching the intrinsic limit of InN at room temperature. Extensive studies have shown that the measurement of p-type conduction in InN epilayers has been fundamentally limited by the presence of electron accumulation on the c-plane surfaces. In contrast, the nonpolar grown surfaces of InN are found to be completely free of electron accumulation. Moreover, through direct Mg dopant incorporation, the surfaces (nonpolar m-plane) of InN nanowires can be transformed from intrinsic to nearly p-type degenerate, which has led to the first direct measurement of p-type conduction in InN.

Extending group-III nitrides to the infrared: Recent advances in InN

Auger recombination in InN films grown by metal-organic chemical vapor deposition was studied by steady-state photoluminescence at different laser excitation powers and sample temperatures. It was dominant over radiative recombination and Shockley-Read-Hall recombination at low temperatures, contributing to the sub-linear relationship between the integrated photoluminescence intensity and laser excitation power. Auger recombination rates increased gradually with temperature with an activation energy of 10–17 meV, in good agreement with values from transient photoluminescence reported in literature. As the Auger recombination rates were independent of material quality, they may form an upper limit to the luminous efficiency of InN.

Auger recombination as the dominant recombination process in indium nitride at low temperatures during steady-state photoluminescence

A highly active visible light-induced BiVO4 photocatalyst was prepared by a simple co-precipitation method using ammonia solution as a pH adjustor and Triton X-100 (TX100) as a structure directing agent. The physical properties of the prepared BiVO4 photocatalyst were investigated by several techniques such as X-ray diffractometer (XRD), Brunauer-Emmett-Teller (BET) surface area measurement, scanning electron microscopy (SEM), energy dispersive analysis (EDS), Fourier-transformed infrared spectroscopy (FT-IR), photoluminescence (PL), and UV-Vis diffused reflectance spectroscopy (DRS). XRD results revealed the existence of a monoclinic scheelite structure in both the unmodified and the modified samples. The TX100 played a crucial role to control the cuboid-like shape morphology of BiVO4. The DRS results showed that the as-prepared cuboid BiVO4 possessed enhanced visible light absorption range compared with that of the unmodified BiVO4. The photocatalytic activity was evaluated via indigo carmine (IC) degradation under visible light irradiation. The modified BiVO4 showed higher photocatalytic efficiency than the unmodified BiVO4 and the commercial P25-TiO2 which could be ascribed to the better charge separation efficiency.

Triton X-100 induced cuboid-like BiVO 4 microsphere with high photocatalytic performance

High quality InN nanoparticles are grown using an atmospheric chemical vapour deposition technique via a self-seeded catalytic approach in the temperature range of 580–650 °C. In this temperature region, the nucleation barrier of InN is overcome by seeding low density In nanoparticles prior to introduction of reactive NH3. Samples with increasing carrier densities are grown, with the help of increasing growth temperature, to understand the role of carrier density in the optical phonon structure. Near-resonance Raman spectra show completely different phonon pictures compared to those for the off-resonance spectra. A Raman forbidden mode of B1(high), because of the possible breakdown of selection rules in the near-resonance conditions, is invoked for the first time. The intensity and frequency of this mode strongly depend on the carrier concentration in the sample. In off-resonance conditions, the A1(LO) mode for the sample with higher carrier concentration is dominated by Fano interference rather than plasmon–phonon coupling. Variation of the intensity of the B1(high) mode is correlated with a band filling effect, which is substantiated by the luminescence studies of the InN samples with different carrier concentrations.

Excitation dependent Raman studies of self-seeded grown InN nanoparticles with different carrier concentration.

http://ntur.lib.ntu.edu.tw/bitstream/246246/163691/1/107.pdf

Keewee Tan

Papers

Recombination mechanism of photoluminescence in InN epilayers