Shinji Saito

• Ph.D.
• Fellow at Toshiba Corporation

We present our recent development of the surface-emitting quantum cascade laser with a PC (photonic crystal) resonator and a strain-compensated MQW (multiple quantum well) active layer operating at around 4.3 μm. We describe the laser performance mainly from the viewpoint of the design and analysis of the PC resonators, which include both numerical...

We fabricated surface-emitting quantum cascade lasers with photonic crystal resonators whose active layers were strain-compensated InGaAs/AlInAs multiple quantum wells to operate at 4.3 μm. We tested two kinds of square-lattice photonic crystals consisting of circular and pentagonal InGaAs cylinders as a unit structure. We examined their output pow...

We have succeeded in improving the gain of the base quantum cascade laser (QCL) through experiments and device simulations using the nonequilibrium Green’s function (NEGF) method, and we investigate the factor that increases the gain by reducing the thickness of the barrier by 10%. Specifically, we analyzed the minibands (Wannier–Stark states), den...

We study the angle-dependent reflection spectra of two-dimensional photonic crystal (PC) slabs, which we use for developing mid-infrared surface-emitting lasers. The PC design produces a perfect resonance between material gain frequencies and the [Formula: see text]-point band edge in the first Brillouin zone. Hence, we expect laser emission to occ...

A surface photonic structure to shape a laser beam profile for a surface-emitting quantum cascade laser that consists of a photonic crystal and an edge-emitting laser source is proposed here.

The heat dissipation of a quantum cascade laser (QCL) for a mounted structure with and without a diamond submount was evaluated by temperature and structure function measurements and three-dimensional simulation. From the structure function, it was shown that the thermal resistance between the QCL on the InP substrate and the CuW mount was reduced...

Photonic crystal resonators with the C 4v symmetry were designed and fabricated on quantum cascade lasers with a strain-compensated multiple quantum well to achieve single-mode and vertical surface emission at 4.32 μ m. Their fabrication accuracy was confirmed by high-resolution reflection spectroscopy. The maximum output power was 10 mW at 77 K. A...

Photonic crystals (PCs) offer unique ways to control light-matter interactions. The measurement of dispersion relations is a fundamental prerequisite if we are to create various functionalities in PC devices. Angle-resolved spectroscopic techniques are commonly used for characterizing PCs that work in the visible and near-infrared regions. However,...

Photonic crystals (PCs) offer unique ways to control light-matter interactions. The measurement of dispersion relations is a fundamental prerequisite if we are to create novel functionalities in PC devices. Angle-resolved spectroscopic techniques are commonly used for characterizing PCs that work in the visible and near-infrared regions. However, t...

A hybrid method to calculate a multi-distance beam profile emitted perpendicular from a surface of a photonic crystal (PhC) is proposed here based on the finite-domain time-difference (FDTD) method and the diffraction theory. Although the FDTD method is available to calculate a near-field emitted from the PhC, it needs too many voxels to calculate...

A study to overcome the “green gap” problem is introduced. We show a breakthrough achieved by two-step growth with adopting AlGaN interlayer in this chapter. Bright yellow, amber with red LEDs and an application of phosphor-free white LED are demonstrated.

We investigated band-profile control by introducing interlayers between a semiconductor and metal contact layers to improve the electrical properties of GaN-based semiconductor devices. We evaluated the electronic structure of the semiconductor surface and the metal/semiconductor interface by hard X-ray photoelectron spectroscopy. We also performed...

We report on the optical properties of the InGaN-based red LED grown on a c-plane sapphire substrate. Blue emission due to phase separation was successfully reduced in the red LED with an active layer consisting of 4-period InGaN multiple quantum wells embedding an AlGaN interlayer with the Al content of 90% on each quantum well. The light output p...

High-efficiency yellow InGaN-based light-emitting diodes (LEDs) were grown by metal-organic chemical vapor deposition on conventional c-plane sapphire (0001) substrates. Optimization of the growth temperature of barrier layers eliminated surface inclusions and resulted in improved output properties of the fabricated yellow LEDs. They exhibited a hi...

High-efficiency InGaN light-emitting diodes (LEDs) in the "green gap'' range were fabricated on c-face sapphire (0001) substrates. Optical properties were enhanced by band engineering of active layers and optimization of growth conditions. Output power and external quantum efficiency of 11.0mW and 24.7% for a 559nm green-yellow LED and 4.7mW and 13...

We have performed photoluminescence (PL) measurements for green--yellow InGaN/GaN multiple quantum wells (MQWs) in which InGaN layer was embedded in the barrier layer to verify the effect on the crystal quality and the internal electric field (F0). From the analysis of both the time-resolved PL and the excitation-power dependence of PL, it has been...

A light emitter according to one embodiment has a fiber shape. And it includes a core portion containing a light emitting material, the material absorbing excitation light and emitting light having a wavelength longer than a wavelength of the excitation light. And also it includes a clad portion provided outside the core portion, the clad portion h...

We have performed photoluminescence measurements (PL) for green-yellow InGaN/GaN multiple quantum wells (MQWs) in which InGaN layer was embedded in the barrier as a strain-controlling interlayer to verify the effect on the crystal quality and the internal electric field (F0). From the analysis of both the time-resolved PL and the excitation-power d...

High-power 2.8 W blue-violet InGaN LD was fabricated, applying AlN facet coating technology. The AlN was found to be crystallized on the facets and very stable even after 2200 h cw operation. Luminous flux over 380 lm is obtained with a phosphor-converted LD excitation white light source using just a single laser chip at 1A operating current.

Characterization by reciprocal space mapping of x-ray diffraction (XRD) intensity was carried out for epitaxial layers of GaN-based laser structures on two GaN substrates: GaN substrate and GaN template on sapphire substrate. The difference between these two substrates was shown clearly. The distribution of XRD intensity of the epitaxial layers on...

GaN-based laser diodes (LDs) with a slope efficiency of 2.6 W/A are presented. The white light source was fabricated by using 405 nm LDs and phosphors. The luminous flux was estimated to be 200 lm.

We investigate the internal quantum efficiency of InGaN-based Light Emitting Diodes (LEDs) from the semiconductor rate equation of pulse current injection. A method is presented for estimating the internal quantum efficiency based on data of electroluminescence decay times measured as a function of current in the pulse injection. For the screening...

A general device simulator has been constructed for designing high-efficiency light-emitting diodes (LEDs). The optical characteristics, including the spatial profiles of the light extracted from LEDs, are important for practical LED applications such as display and illumination. The radiation patterns are affected by device structures such as elec...

We investigated the far-field patterns perpendicular to the junction plane under room-temperature current excitation and analyzed the transverse modes of nitride-based laser diodes with various types of AlGaN cladding layers. It was found that nitride-based laser structures with thin AlGaN cladding layers induce leakage of high-order transverse mod...

The individual elements attributing to the excess voltage drop in the nitride-based laser diodes were investigated. The specific contact resistivity ρc to p-type GaN was estimated by transmission line model (TLM) method and was estimated to slightly vary from 3.2×10−3 to 6×10−4 Ω cm2 in the current range of 1–10 kA cm−2. It is found that a low spec...

Carrier overflow and perpendicular transverse mode in InGaN multi-quantum-well lasers have been analyzed by numerical calculation. A high acceptor concentration for the p-type cladding layer and the reduction of the active layer volume have a large effect on the reduction of carrier overflow. Anti-guide-like behavior of the waveguide mode is formed...

The analysis of the perpendicular far field patterns of nitride-based laser diodes with various types of AlGaN cladding layers is demonstrated. Other results obtained with our nitride-based laser diodes are also demonstrated and discussed

The room temperature photoluminescence (PL) of InGaN-based multiple quantum well (MQW) structures was studied. The PL intensity was significantly dependent on the well width and depth. The maximum PL intensity from an MQW with In0.15Ga0.85N wells was produced for a 2nm well; the intensity decreased significantly for thinner and thicker ones. Also,...

We demonstrate room temperature pulsed operation of nitride based multi-quantum-well (MQW) laser diodes with cleaved mirror facets grown on a conventional C-face sapphire substrate. Cleavage was performed along the (1120) direction of the sapphire substrate, and the resultant facet was analyzed using an atomic force microscope (AFM) and theoretical...

On proposing the existence of a significant barrier between n-type GaAs and n-type ZnSe, in ZnSe-based devices, we examined various offset reduction buffers, in standard light-emitting diode structures, to assess their ability to reduce the excess voltages applied across this interface during operation. The main buffers investigated were CdZnSe and...

The influence of surface treatment prior to the deposition of Pd/Au metallic contacts to p-type ZnSe is discussed. The methods studied being a sulphur based treatment and a CuSex contact treatment. The results show that both of these form better quality contacts, with lower applied voltages for set current densities, in comparison to an untreated s...

We have demonstrated the relationship between the structural and electrical properties of the chemically treated p-type ZnSe surface. The unstable Se-rich ZnSe surface, formed by an acid etchant, is shown to be removed by sulfur treatment. The sulfur treatment has been found to have the effect of lowering the Schottky barrier height at the Au/p-typ...

The structural properties of undoped and nitrogen-doped ZnSe grown on (001) substrates and substrates cut at 15° from the (001) plane towards the [110] direction are compared. In the case of layers grown on the 15° off substrates, a marked improvement in the structural quality of the layers is observed for layers doped p-type using N.

The effect of thermal annealing on nitrogen-doped ZnSe grown by molecular beam epitaxy has been investigated as a function of nitrogen concentration. It was found that thermal stability of the nitrogen acceptors in highly nitrogen-doped ZnSe markedly degraded. Furthermore, in order to avoid significant decreases in net acceptor concentration by the...

Summary form only given. A low voltage current injection is demonstrated theoretically and experimentally for ZnSe/CdZnSe blue-green lasers. Insertion of InGaAlP layers reduce the excess voltage drop, due to the large valence band offset between the p-type GaAs substrate and p-type ZnSe layer. The InGaAlP layers are also useful as high concentratio...

The authors have developed a ZnSe based blue-green (500 m) light emitting diode, employing a mesa type structure, exhibiting low voltage and high brightness operation. This device displayed an output power of 200 μW (3 cd) for a current of 30 mA, under an operating voltage of 8.6 V, and had a record efficiency of 0.26%

Far infrared reflectivity spectra of hydrogen-bonded ferroelectric KH2PO4 are measured by using synchrotron radiation in the photon-energy region from 5 to 250 cm-1. The strong relaxational mode is found in the infrared spectra. This result is consistent with the results which have been obtained by the hyper-Raman and Raman scattering, but inconsis...

The effect of InGaP surface preparation has been investigated for the molecular beam epitaxial (MBE) growth of ZnSe. The net acceptor concentration profile near the interface of nitrogen-doped p-type ZnSe layers was strongly affected by the surface preparation of InGaP layers. The low net acceptor concentration region for the samples grown on a the...

Nitrogen incorporation and electrical activity have been investigated for ZnSe grown on GaAs substrates (100) oriented and misoriented 15° toward the [011] direction, by molecular beam epitaxy. It was found that nitrogen incorporation in the 15° misoriented case was enhanced by a factor of two compared with that on the (100) oriented substrate. Ele...

A novel contact technology using In(Ga,Al)P layers, lattice matched to p-type GaAs, is proposed for low voltage operation in ZnSe-based laser diodes (LDs). Laser operation is demonstrated at 77K in CdZnSe/ZnSe multiquantum well LDs grown on InGaP band offset reduction layers for the first time.

A GaAs laser diode employing InGaAlP as the cladding has been investigated. Continuous wave (CW) operation was obtained at temperatures as high as 212°C. A large characteristic temperature T ₀ of 190 K was maintained up to 150°C. These results were attributed to a reduction of electron overflow by a large band-gap difference between the...