Munetaka Arita

Room-temperature triggered single photon emission from a III-nitride site-controlled nanowire quantum dot.

We demonstrate triggered single photon emission at room temperature from a site-controlled III-nitride quantum dot embedded in a nanowire. Moreover, we reveal a remarkable temperature insensitivity of the single photon statistics, and a g((2))[0] value at 300 K of just 0.13. The combination of using high-quality, small, site-controlled quantum dots with a wide-bandgap material system is crucial for providing both sufficient exciton confinement and an emission spectrum with minimal contamination in order to enable room temperature operation. Arrays of such single photon emitters will be useful for room-temperature quantum information processing applications such as on-chip quantum communication.

AlN air-bridge photonic crystal nanocavities demonstrating high quality factor

The authors report an achievement of high quality AlN ultraviolet photonic crystal nanocavities. Convex AlN air-bridge structures with embedded GaN quantum dots have been formed by utilizing photoelectrochemical etching of 6H-SiC substrates. Room-temperature microscopic photoluminescence measurements reveal the high quality of the nanocavities. For the lowest-order cavity mode of a 150-nm-period nanocavity with seven missing holes, the highest Q factor (>2400) ever reported in nitride-based photonic crystals has been obtained.

Hybrid p-n junction light-emitting diodes based on sputtered ZnO and organic semiconductors

We fabricated light-emitting hybrid p-n junction devices using low temperature deposited ZnO and organic films, in which the ZnO and the organic films served as the n- and p-type component, respectively. The devices have a rectification factor as high as ∼103 and a current density greater than 2 A/cm2. Electroluminescence of the hybrid device shows the mixture of the emission bands arising from radiative charge recombination in organic and ZnO. The substantial device properties could provide various opportunities for low cost and large area multicolor light-emitting sources.

Self-Organized CdSe Quantum Dots on (100)ZnSe/GaAs Surfaces Grown by Metalorganic Molecular Beam Epitaxy

II–VI semiconductor low-dimensional structures, quantum dots, have been grown on GaAs substrates by metalorganic molecular beam epitaxy (MOMBE). Before the heteroepitaxial growth, atomically flat, As-stabilized GaAs surfaces were prepared by high-temperature As cleaning using tris-dimethylamino-arsenic (TDMAAs). CdSe thin films deposited on (100)ZnSe/GaAs surfaces have been investigated with atomic force microscopy (AFM) and were found to form three-dimensional islands with rather uniform size distribution. A large mismatch (~7%) of lattice constants between CdSe and ZnSe pseudomorphically grown on GaAs possibly results in the Stranski-Krastanov growth mode. CdSe quantum dots with a diameter of 97±11 nm were successfully formed at 350°C.

High-Q (>5000) AlN nanobeam photonic crystal cavity embedding GaN quantum dots

We report on the fabrication and optical characterization of high-quality-factor AlN one-dimensional nanobeam photonic crystal cavities embedding GaN quantum dots and operating in the ultra-violet range. By means of electron-beam lithography, dry etching and photoelectrochemical etching, we implement a high-frequency nanobeam cavity design in an AlN epilayer containing GaN quantum dots. Room-temperature microphotoluminescence characterization of the fabricated nanobeams exhibits resonances with wavelengths as short as 320 nm and quality factors as high as Qexp = 5.0 × 103 at 380 nm. This constitutes a significant improvement over previously reported group-III nitride photonic crystal cavities in terms of operating wavelength.

Fabrication of AlGaN Two-Dimensional Photonic Crystal Nanocavities by Selective Thermal Decomposition of GaN

We report on the successful fabrication of InGaN/AlGaN single-quantum-well two-dimensional photonic crystal nanocavities with excellent structural properties by means of a novel method. GaN can be selectively decomposed at around 1000 °C under NH3/H2 ambient conditions, leaving air-bridge AlGaN membranes. The proposed method is remarkably simple and offers various advantages such as good crystalline quality and smooth surfaces over those previously reported. The high quality of the nanocavities has been proven by microscopic photoluminescence: quality factors as high as 5100 have been achieved with a 180-nm-period L7 nanocavity at room temperature.

High-Q AlN photonic crystal nanobeam cavities fabricated by layer transfer

High-quality-factor one-dimensional photonic crystal nanobeam cavities embedding GaN/AlN quantum dots are fabricated by an epilayer transfer method. The GaN/AlN quantum dots are first grown on SiC before being transferred to a Si substrate using a hydrogen silsesquioxane bonding layer and highly selective back-etching of the SiC. Nanobeam cavities are then fabricated by electron-beam lithography, dry etching, and HF underetching of the bonding layer. The resulting nanocavity exhibits quality factors larger than 6.3 × 103, the highest quality factor reported to date for an optically active group-III nitride photonic crystal nanocavity.

Observation of mid-infrared intersubband absorption in non-polar m-plane AlGaN/GaN multiple quantum wells

Mid-infrared (4.20–4.84 μm) intersubband absorption in non-polar m-plane Al0.5Ga0.5N/GaN multiple-quantum wells is observed at room temperature. 10 period Al0.5Ga0.5N/GaN multiple-quantum wells were grown on free-standing m-plane GaN substrates by metalorganic chemical vapor deposition (MOCVD), and the high-quality structural and optical properties are revealed by x-ray diffraction and photoluminescence studies. Through this we have demonstrated that MOCVD grown non-polar m-plane AlGaN/GaN quantum wells are a promising material for mid-infrared intersubband devices.

Long-lived electron spins in InxGa1−xN multiquantum well

We first observed spin relaxation at room temperature in InxGa1−xN multiquantum wells using spin-dependent pump and probe measurements. The spin lifetime increases with In molar fraction x. The observed spin lifetime obeys ∼x3.3, which shows different behavior from typical results for D’yakonov-Perel’ and Elliott-Yafet processes involving the alloy scattering. The increase of In molar fraction induces indium-composition fluctuations, which cause the electron localization. The remarkable increase of the spin lifetime is due to the formation of quantum dots through the phase separation in InxGa1−xN multiquantum-well layers.

Fabrication and optical properties of non-polar III-nitride air-gap distributed Bragg reflector microcavities

Using the thermal decomposition technique, non-polar III-nitride air-gap distributed Bragg reflector (DBR) microcavities (MCs) with a single quantum well have been fabricated. Atomic force microscopy reveals a locally smooth DBR surface, and room-temperature micro-photoluminescence measurements show cavity modes. There are two modes per cavity due to optical birefringence in the non-polar MCs, and a systematic cavity mode shift with cavity thickness was also observed. Although the structures consist of only 3 periods (top) and 4 periods (bottom), a quality factor of 1600 (very close to the theoretical value of 2100) reveals the high quality of the air-gap DBR MCs.