Kenji Yonei

Trench-type narrow InGaAs quantum wires fabricated on a (311)A InP substrate

InGaAs quantum wires (QWRs) with cross sections as narrow as 10 nm×20 nm have been fabricated on a (311)A InP V-grooved substrate under an As2 source. Trench-type InGaAs QWRs consist of (111)A and (331)B facets with an angle of about 22°. Cathode-luminescence and photoluminescence measurements confirmed the luminescence peak arising from the QWRs.

AlGaAs/InGaAs DFB Laser by One-Time Selective MOCVD Growth on a Grating Substrate

A gain-coupled distributed feedback (DFB) laser is realized using a high-density InGaAs/AlGaAs quantum wire (QWR) array formed within a finite area of 6×500 µm by electron beam lithography and one-time selective metalorganic chemical vapor deposition (MOCVD). The stable gain-coupled DFB mode is confirmed at 812 and 830 nm from the 360 and 370 nm pitch gratings, respectively. The mode analysis of the actual cross-sectional structure using a finite element method verified that modal gain has a single peak at the Bragg wavelength of the grating.

InGaAs/AlGaAs Quantum Wire DFB Buried HeteroStructure Laser Diode by One-Time Selective MOCVD on Ridge Substrate

A quasi-buried heterostructure (BH) quantum wire (QWR)-distributed feedback (DFB) laser was realized by one-time selective metalorganic chemical vapor deposition (MOCVD) on a ridge substrate with a submicron grating. One-time selective MOCVD led to the formation of a ridge waveguide with a BH structure and a QWR array for gain-guided DFB laser diode (LD) without additional etching or regrowth process. The threshold current is 15 mA, and the threshold current density is 850 A/cm2. A stable single longitudinal mode was preserved until 3 Ith, after which another mode emerged at a high drive current at 813.6 nm. This suggests a complex-coupled DFB-mode operation. The elimination of the regrowth step enlarges the range of material for extended wavelengths and operational temperatures.

EFFECTS OF AS2 FLUX AND ATOMIC HYDROGEN IRRADIATION FOR GROWTH OF INGAAS QUANTUM WIRES BY MOLECULAR BEAM EPITAXY

InGaAs/InAlAs quantum wire structures on V-grooved InP substrates have been fabricated with As2 flux and atomic hydrogen irradiation using molecular beam epitaxy. Under As2 flux, the V-grooves are preserved during the InAlAs barrier layer growth due to a small migration of the In atoms, but the V-shape is not preserved and hence the quantum wires cannot be fabricated under an As4 flux. The InGaAs quantum wires grown with atomic hydrogen have a narrow photoluminescence peak and a uniform cathode-luminescence image. These phenomena maybe caused by the absence of (311)A sidewall quantum wells due to re-evaporation of the group-III atoms by the atomic hydrogen irradiation.

Enhanced peak-to-valley current ratio in InGaAs∕InAlAs trench-type quantum-wire negative differential resistance field-effect transistors

Trench-type narrow InGaAs quantum-wire field-effect transistors (QWR-FETs) have been fabricated on (311)A InP V-groove substrates by hydrogen-assisted molecular-beam epitaxy. Enhanced negative differential resistance (NDR) effects with a peak-to-valley ratio (PVR) as high as 13.3 have been observed at an onset voltage of 0.16V in the QWR-FETs at 24K. The PVR increased with reductions in the InGaAs epitaxial layer thickness, which caused an enhanced mobility difference between the QWR and side quantum wells (QWs). This forms a velocity modulation transistor based on the real-space transfer of electrons from the high mobility QWR to the low mobility side QWs. The NDR effects were observed up to 230K as the gate length was decreased to 50nm. A unique feature of the QWR-FET is that NDR effects are controllable with the gate bias in a three-terminal configuration.

Difference in Diffusion Length of Ga Atoms under As2 and As4 Flux in Molecular Beam Epitaxy

The surface diffusion length of Ga adatoms under As2 or As4 flux has been measured using V-grooved GaAs (001) substrates in molecular beam epitaxy. The diffusion length on the (001) surface toward the [110] direction, of Ga adatoms under As2 flux is about half of that under As4 flux. A smaller number of Ga atoms under As2 flux migrate to the (001) ridge surface from the sidewall surface than those under As4 flux. Furthermore, the Al0.6Ga0.4As layer on the V-grooved GaAs substrate grown under As2 flux preserve the V-shape, whereas the V-shape cannot be preserved during the growth under As4 flux. The GaAs quantum wire structures which have Al0.6Ga0.4As barrier layeres are fabricated under As2 flux.

Negative differential resistance effects of trench-type InGaAs quantum-wire field-effect transistors with 50-nm gate-length

The effects of negative differential resistance (NDR) have been clearly observed in 50-nm-gate InGaAs/InAlAs trench-type quantum-wire (QWR) field-effect transistors (FETs), which are fabricated by atomic hydrogen-assisted molecular-beam epitaxy. The NDR onset voltage is as low as 0.1 V, and the highest peak-to-valley current ratio is 6.2 at 40 K. The equilateral symmetry of the NDR effect in a QWR FET is also observed. The pronounced NDR effects in a trench-type QWR FET are advantageous for high-speed and low power-consumption devices.

Observation of negative differential resistance of a trench-type narrow InGaAs quantum-wire field-effect transistor on a (311)A InP substrate

A trench-type narrow InGaAs quantum-wire field-effect transistor (QWR–FET) with a cross section of 8×25 nm has been fabricated on a (311)A InP V-grooved substrate by molecular-beam epitaxy. The trench-type InGaAs QWR–FET has normal static characteristics at room temperature, and demonstrates clear negative differential resistance characteristics at 40 K with a high peak-to-valley current ratio (PVR=4.3) and a low onset voltage of 0.12 V.

Quasi-one-dimensional transport characteristics of ridge-type InGaAs quantum-wire field-effect transistors

Ridge-type InGaAs/InAlAs quantum-wire field-effect transistors are realized by selective molecular-beam epitaxy and their transport characteristics are studied. An analysis of the depopulation of one-dimensional subbands in these structures reveals little evidence for sidewall depletion, and yields an estimate for the carrier density in good agreement with that found in two-dimensional InGaAs/InAlAs heterojunctions. Subband splittings as large as 7.4 meV are obtained in the wires, indicating their excellent one-dimensional transport properties.

InGaAs dual channel transistors with negative differential resistance

We demonstrate InGaAs dual channel transistors (DCTs) with negative differential resistance (NDR) fabricated on an InP (001) substrate. The dual channel structure consists of high and low mobility InGaAs quantum wells combined with an InAlAs barrier layer. NDR characteristics of the DCTs depend on the thicknesses of the low mobility and barrier layers and the indium content of the high mobility channel. The NDR mechanism is thought to be the carrier transfer from the high mobility channel to the low mobility channel.