We developed an electrically driven near-infrared broadband light source based on self-assembled InAs quantum dots (QDs). By combining emissions from four InAs QD ensembles with controlled emission center wavelengths, electro-luminescence (EL) with a Gaussian-like spectral shape and approximately 85-nm bandwidth was obtained. The peak wavelength of the EL was blue-shifted from approximately 1230 to 1200 nm with increased injection current density (J). This was due to the state-filling effect: sequential filling of the discrete QD electron/hole states by supplied carriers from lower (ground state; GS) to higher (excited state; ES) energy states. The EL intensities of the ES and GS emissions exhibited different J dependence, also because of the state-filling effect. The point-spread function (PSF) deduced from the Fourier-transformed EL spectrum exhibited a peak without apparent side lobes. The half width at half maximum of the PSF was 6.5 µm, which corresponds to the estimated axial resolution of the optical coherence tomography (OCT) image obtained with this light source. These results demonstrate the effectiveness of the QD-based device for realizing noise-reduced high-resolution OCT.

We report on the fabrication and analysis of basic digital circuits containing InAs nanowire transistors on a host substrate. The nanowires were assembled at predefined positions by means of electric field-assisted self-assembly within each run generating numerous circuits simultaneously. Inverter circuits composed of two separated nanowire transistors forming a driver and an active load have been fabricated. The inverter circuits exhibit a gain (>1) in the MHz regime and a time constant of about 0.9 ns. A sample & hold core element is fabricated based on an InAs nanowire transistor connected to a hold capacitor, both on a Silicon and an InP isolating substrate, respectively. The low leakage read-out of the hold capacitor is done by InP-based metal-insulator heterojunction FET grown on the same substrate prior to nanowire FET fabrication. Experimental operation of the circuit is demonstrated at 100 MHz sampling frequency. The presented approach enables III/V high-speed, low-voltage logic circuits on a wide variety of host substrates which may be up scaled to high volume circuits.

We report a new approach to creating a 'solid ink' and direct patterning of InAs nanowires on a Si substrate using dip-pen nanolithography (DPN). The normal method to prepare an 'ink' is a solution-based process using sonication to liquidize nanoparticles, which we call 'liquid ink' in this paper. As ink-solution-based DPN patterning has been prevalent in most studies, herein we propose a new method, 'solid inking', by which the inking process is solution-free. In our work, InAs nanowires were transferred to an AFM tip by directly scanning the tip over an InAs nanowire wafer at humidity over 80%. By this method, the preparation of ink and the 'inking' process is combined into one step, and a large amount of nanowires can be collected onto the tip to ensure the formation of a continuous ink flow for the direct patterning.

We theoretically study the performance limits of current-gain cutoff frequency, fT, for the HEMTs with InAs or In0.70Ga0.30As middle layers in the multi-quantum-well (MQW) channels by means of the quantum-corrected Monte Carlo (MC) method. We calculate the distribution of the delay time along the channel, τ(x), and define the effective gate length, Lg,eff, as the corresponding length to τ(x). By extrapolating Lg,eff to Lg = 0 nm, we estimate the lower limit of Lg,eff, Lg(0),eff. Then we estimate the performance limit of fT, fT(0), by extrapolating fT to Lg,eff(0). The estimated fT(0) are about 3.6 and 3.7 THz for the HEMTs with InAs middle layers of 5 and 8 nm in thickness, and about 3.0 THz for the HEMT with In0.70Ga0.30As middle layer of 8 nm in thickness, respectively. The higher fT(0) in the HEMTs with InAs middle layers are attributed to the increased average electron velocity, υd, in the channel. These results indicate the superior potential of the HEMTs using InAs in the channels. The HEMT with InAs middle layer of 8 nm in thickness shows the highest fT on condition of the same Lg because of its highest υd. However, the increased total channel thickness results in the longer Lg,eff(0), which leads to the restriction of fT(0). Therefore, in order to increase fT(0), it is essential to make Lg,eff short in addition to making υd high. Our results strongly encourage in making an effort to develop the HEMTs that operate in the terahertz region.

Heterostructure field-effect transistors (HFETs) composed of antimonide-based compound semiconductor (ABCS) materials have intrinsic performance advantages due to the attractive electron and hole transport properties, narrow bandgaps, low ohmic contact resistances, and unique band-lineup design flexibility within this material system. These advantages can be particularly exploited in applications where high-speed operation and low-power consumption are essential. In this paper, we report on recent advances in the design, material growth, device characteristics, oxidation stability, and MMIC performance of Sb-based HEMTs with an InAlSb upper barrier layer. The high electron mobility transistors (HEMTs) exhibit a transconductance of 1.3 S/mm at VDS = 0.2 V and an fTLg product of 33 GHz-µm for a 0.2 µm gate length. The design, fabrication and improved performance of InAlSb/InGaSb p-channel HFETs are also presented. The HFETs exhibit a mobility of 1500 cm2/V-sec, an fmax of 34 GHz for a 0.2 µm gate length, a threshold voltage of 90 mV, and a subthreshold slope of 106 mV/dec at VDS = -1.0 V.

We have successfully demonstrated a GaInAs/InP multiple quantum well (MQW)-based wavelength switch composed of the straight arrayed waveguide with linearly varying refractive index distribution by changing the refractive index using thermo-optic effect. Since optical path length differences between waveguides in the array were achieved through refractive index differences that were controlled by SiO2 mask design in selective metal-organic vapor phase epitaxy (MOVPE), wavelength demultiplexing, and the output port switching in each wavelength of light by the refractive index change in the array waveguides through the thermo-optic effect were achieved. We have obtained the wavelength switching and the change of transmission spectra in each output ports.

A GaInAs/InP multiple quantum well (MQW)-based wavelength demultiplexer composed of a waveguide array in which the refractive index varies across the array yielded successful results of wavelength demultiplexing and optical deflection. Since optical path length differences between waveguides in the array are achieved through refractive-index differences controlled by the SiO2 mask design in selective metal-organic vapor phase epitaxy (MOVPE), a straight waveguide grating can be formed with reduced optical propagation losses. A straight waveguide array device with a 1.4% refractive-index difference was fabricated. The fabrication of a preliminary wavelength demultiplexer was also achieved, for which a wavelength separation with an approximately 25 nm spacing and free spectral range (FSR) of approximately 100 nm were obtained. Moreover, an optical deflector was investigated and primitive deflection was achieved at 1460 and 1490 nm incident wavelengths.

We fabricated 1.3µm AlGaInAs inner-stripe laser diodes (LDs), employing a GaInAsP waveguide layer and an n-InP current blocking layer. We compared the effects of the thickness of n-InP current blocking layer. A blocking layer with 500nm thick restricts the leakage current significantly. The inner-stripe LD was compared with the conventional ridge LD. I-L characteristics of both types of LDs were measured. Threshold currents of the inner-stripe LD and the ridge LD were 8.5 and 10.6mA, respectively. A threshold current of the inner-stripe LD is smaller than that of ridge LD. And the resistance of the inner-stripe LD was a few ohms lower than that of the ridge LD. Output power of 88mW was obtained at 200mA with 300µ m-long cavity. This was twice the power of a conventional ridge laser. The characteristic temperature of the inner-stripe LD was obtained 76 K from 20 to 85. We obtained a good linearity up to 100mA at 85. Therefore the inner-stripe LD has an advantage of high power devices.

In this paper, we investigate the electron-hole energy states and energy gap in three-dimensional (3D) InAs/GaAs quantum rings and dots with different shapes under external magnetic fields. Our realistic model formulation includes: (i) the effective mass Hamiltonian in non-parabolic approximation for electrons, (ii) the effective mass Hamiltonian in parabolic approximation for holes, (iii) the position- and energy-dependent quasi-particle effective mass approximation for electrons, (iv) the finite hard wall confinement potential, and (v) the Ben Daniel-Duke boundary conditions. To solve the 3D nonlinear problem without any fitting parameters, we have applied the nonlinear iterative method to obtain self-consistent solutions. Due to the penetration of applied magnetic fields into torus ring region, for ellipsoidal- and rectangular-shaped quantum rings we find nonperiodical oscillations of the energy gap between the lowest electron and hole states as a function of external magnetic fields. The nonperiodical oscillation is different from 1D periodical argument and strongly dependent on structure shape and size. The result is useful to study magneto-optical properties of the nanoscale quantum rings and dots.

A 0.15 µm T-shaped gate AlInAs/InGaAs high electron mobility transistor (HEMT) with an excellent RF performance has been developed using selective wet gate recess etching. The gate recess is formed by a pH-adjusted citric acid/NH4OH/H2O2 mixture with an etching selectivity of more than 30 for InGaAs over AlInAs. The standard deviation of saturation drain current (Idss) is as small as 3.2 mA for an average Idss of 47 mA on a 3 inch diameter InP wafer. The etching time for recess formation is optimized and an ft of 130 GHz and an MSG of 10 dB at 60 GHz are obtained. The extremely low minimum noise figure (Fmin) of 0.9 dB with an associated gain (Ga) of 7.0 dB has been achieved at 60 GHz for a SiON-passivated device. This noise performance is comparable to the lowest value of Fmin ever reported for an AlInAs/InGaAs HEMT with a passivation film.

Long-wavelength 1.3 µm GaInAsP/InP vertical cavity surface-emitting lasers (VCSELs) have been demonstrated in an array configuration. With the strong current confinement by a buried heterostructure and the efficient optical feedback by a dielectric cavity, five VCSEL elements in a 24 array operated at room temperature with 5 mW total power output and wavelength error within 5%. The stacked planar optics including the VCSEL array is a promising optical transmitter in ultra large scale parallel optical communication systems.

Ultrathin GaAs, AlGaAs and GaAs/InAs wire crystals (whiskers) as thin as 20-50 nm are grown by organometallic vapor phase epitaxy (OMVPE) using Au as a growth catalyst. It is found that the whisker shape and width can be controlled by adjusting the thickness of the Au deposited on the substrate surface and the substrate temperature duing OMVPE. A new technique employing a scanning tunneling microscope (STM) for controlling the whisker growth position on the substrate surface is described. Photoluminescence spectra from the GaAs whiskers show a blue shift of the luminescene peak energy as the whisker width decreases. The amount of blue shift energy is rather small compared to that calculated by a simple square potential well model. The discrepancy is explained by the cylindrical potential well model including the surface depletion effect. Atomic composition within the portion of 1-20 nm along the AlGaAs and GaAs/InAs whiskers has been analyzed by energy dispersive X-ray analysis in combination with transmission electron microscopy. This shows the exsitence of Au at the tip of the whisker and the composition change occurs over a length of less than 5 nm at the GaAs/InAs heterojunction.

We have achieved the room temperature cw lasing operation of GaInAsP/InP surface emitting lasers for the first time. By employing a buried heterostructure with 1.3 µm range active region and a MgO/Si heat sink mirror, cw operation was obtained up to 14 with the threshold current of 22 mA.

GaSb/InAs hot electron transistors (HETs) composed of a type-II misaligned quantum well operate at room temperature. The collector current is well described by the thermionic emission from the emitter. In order to get insight of the electron transport in the HET, the base width was varied or the collector barrier was modulated. The emitter's barrier height for the thermionic emission decreases with decreasing base width. This is caused by the increase of the quantum confinement energy in the InAs base with decreasing base width. Among HETs with a GaSb collector, a GaInSb abrupt layer, or a GaInSb graded layer at the collector edge, the latter type has the largest collector current. This indicates that collector grading reduces not only the collector barrier height, but also the quantum mechanical reflection of electrons. Collector-graded HETs with a 5 nm-thick base show a current gain of 8. The sheet resistance of InAs base is one order of magnitude less than bulk InAs without doping. This reduction is partly due to the accumulation of electrons transferred from the GaSb valence band to the InAs conduction band.

We discuss delay times derived from the current gain cutoff frequency of a heterostructure field effect transistor and describe three types of novel channel structures for millimeter-wave InP-based HFETs. The first structure discussed is a lattice-matched InGaAs HEMT with high state-of-the art performance. The second structure is an InAs-inserted InGaAs HEMT which harnesses the superior transport properties of InAs. Fabricated devices show high electron mobility of 12,800 cm2/Vs and high transconductance over 1.4 S/mm for a 0.6-µm-gate length. The effective saturation velocity in the device derived from the current gain cutoff frequency in 3.0107 cm/s. The third one is an InGaAs/InP double-channel HFET that utilizes the superior transport properties of InP at a high electric field. Fabricated double-channel devices show kink-free characteristics, high carrier density of 4.51012 cm-2 and high transconductance of 1.3 S/mm for a 0.6-µm-gate length. The estimated effective saturation velocity in these devices is 4.2107 cm/s. Also included is a discussion of the current gain cutoff frequency of ultra-short channel devices.

The static characteristics of GaInAs(P)/GaInAsP quantum well laser diodes (QW LDs), with graded-index separate-confinement-heterostructure (GRIN-SCH) grown by metalorganic chemical vapor deposition (MOCVD), have been investigated experimentally in terms of threshold current density, internal waveguide loss, differential quantum efficiency and light output power. Very low threshold current density of 410 A/cm2, high characteristic temperature of 113 K, low internal waveguide loss of 5 cm-1, high differential quantum efficiency of 82% and high light output power of 100 mW were obtained in 1.3 µm GRIN-SCH multiple quantum well (MQW) LDs by optimizing the quantum well structure including confinement layer and cavity design. Excellent uniformity for the threshold current, quantum efficiency and emission wavelength was obtained in all MOCVD grown buried heterostructure GRIN-SCH MQW LDs. Lasing characteristics of 1.5 µm GRIN-SCH MQW LDs are also described.