Hideki Gotoh

VLS Growth of Alternating InAsP/InP Heterostructure Nanowires for Multiple-Quantum-Dot Structures

We investigated the Au-assisted growth of alternating InAsP/InP heterostructures in wurtzite InP nanowires on InP(111)B substrates for constructing multiple-quantum-dot structures. Vertical InP nanowires without stacking faults were obtained at a high PH(3)/TMIn mole flow ratio of 300-1000. We found that the growth rate changed largely when approximately 40 min passed. Ten InAsP layers were inserted in the InP nanowire, and it was found that both the InP growth rate and the background As level increased after the As supply. We also grew the same structure using TBAs/TBP and could reduce the As level in the InP segments. A simulation using a finite-difference time-domain method suggests that the nanowire growth was dominated by the diffusion of the reaction species with long residence time on the surface. For TBAs/TBP, when the source gases were changed, the formed surface species showed a short diffusion length so as to reduce the As background after the InAsP growth.

Novel Selective Area Growth of AIGaAs and AIAs with HCI Gas by MOVPE

Abstract Selective area growth of AlGaAs and AlAs was successfully demonstrated in the conventional MOVPE (TMG/TMA/ AsH 3 /H 2 ) system by introducing a small quantity of HCl gas during the epitaxial growth. Highly selective epitaxy (HSE) for Al x Ga 1−x As with high Al composition, even for AlAs, was achieved using wide passivation masks (∼ 200 μm). The effective role of HCl in the HSE of AlAs can be explained by an suppression effect of reaction between the Al containing species and mask material. The growth of AlGaAs with or without HCl gas was studied over the temperature range of 500–800°C on unmasked substrates. The new method called HSE has provided good surface morphology and excellent uniformity of thickness and Al composition. The electrical and optical characteristics of epitaxially grown layers by the HSE method were essentially the same as those of the conventionally grown layers.

Transverse junction buried heterostructure (TJ-BH) laser diode grown by MOVPE

Abstract The sucessful application of a MOVPE growth method instead of the LPE method to fabricate a transverse junction buried heterostructure (TJ-BH) laser diode (LD) has been achieved in an attempt to improve the characteristics of this type of LD over LDs produced by the LPE method. Laser diodes fabricated by MOVPE/LPE hybrid processes have shown sufficiently good characteristics ( I th =3.5 mA, C =0.5 pF. to make up for the disadvantages of LPE, e.g. difficulties in control and uniformity over large areas, an MOVPE selective regrowth method was examined. Laser diodes grown by an entire MOVPE with in-situ HCI vapor phase etching have been successful in pulse oscillation at room temperature ( I th =37mA).

Abruptness of GaAs/AlInP hetero-interfaces grown by GS-MBE

Abstract The effect of the exposure of GaAs and AlInP surfaces to phosphorus and arsenis beams were studied using HR-TEM, RHEED, XPS, AES, and Raman scattering. The GaAs surface was found to be fairly reactive with respect to the phosphorus beam. The exposure of GaAs to a phosphorus beam for 60 s caused a surface roughness of at least 20 A, caused by the formation of a GaP-rich island. However, a flat surface of AlInP was found to be structurally stable with respect to the arsenic beam. The arsenic beam was found to induce a replacement of a few percent of P atoms by As atoms in an AlInP surface layer. An atomically flat AlInP-on-GaAs interface was obtained by a sequence in which the GaAs surface was not exposed to a P beam.

Au-free InAs nanowires grown in In-particle-assisted vapor-liquid-solid mode: growth, structure, and electrical property

We investigated the growth, structure, and electrical properties of InAs nanowires grown in the Au-free vapor-liquid-solid mode. We demonstrated the self-assisted vapor-liquid-solid growth of InAs nanowire with self-assembled In particles on InP substrates. We found that the III/V source mole ratio has a significant effect on the growth behavior and tapering shape. With a high III/V mole ratio (>0.11), a pure In particle at the tip of a nanowire makes it possible to grow the InAs nanowire in the self-assisted vapor-liquid-solid mode. We also found that the growth temperature range of the self-assisted vapor-liquid-solid growth was quite narrow compared with the conventional Au-assisted vapor-liquid-solid mode. A single InAs nanowire grown with a high III/V mole ratio exhibits distinct TO phonon peak in a Raman spectroscopy observation. We further verified that an undoped InAs nanowire grown in the self-assisted vapor-liquid-solid mode could function as a channel in a field-effect transistor device and the...

Vertically Aligned InP Nanowires Grown via the Self-Assisted Vapor–Liquid–Solid Mode

We have demonstrated the growth of vertical InP nanowires via the self-assisted vapor–liquid–solid mode on an InP(111) substrate. Single nanowires exhibit a highly uniform diameter along the axial direction despite their 15 µm length. We show direct evidence of the self-assisted growth mode by performing a compositional analysis of the NW tip. We demonstrated that the In particle at the NW tip could be removed by modifying the V/III source material ratio during growth. Single InP nanowires exhibit a distinct TO phonon peak and show the luminescence of the excitonic emission at 4 K.

Facet growth of AlxGa1-xAs with HCl gas by metalorganic vapor phase epitaxy

Abstract Facet growth of Al x Ga 1-x As over the entire range of Al composition with SiN x masks was successfully performed using low-pressure metalorganic vapor phase epitaxy (MOVPE). In this study, a small quantity of HCl gas was introduced into the MOVPE reactor during the selective growth in order to attain perfect selectivity. The facet shapes at the edges of the selectivity grown Al x Ga 1-x As stripes were little affected by the mask-to-window area ratio. The shape of the [0 1 1] oriented stripes was strongly affected by the Al composition. For the side facet of [0 1 1] oriented stripes with Ga-rich compositions, clear {111}A was obtained and side facet growth on {111}A plane was observed for Al-rich compositions. The side facet shape of [0 1 1] oriented AlAs stripes was strikingly influenced by changing V/III or HCl/III. On the other hand, the side facet of [011] oriented stripes was essentially {111}B for the whole Al composition. These results are discussed by considering a simple nucleation model, surface diffusion lengths of Group III atoms and production ofmetal chlorides.

Model for in-situ etching and selective epitaxy of AlxGa1-xAs with HCI gas by metalorganic vapor phase epitaxy

Abstract In-situ etching and selective epitaxy of Al x Ga 1-x As by introducing a small amount of HCl gas were carried out by low-pressure metalorganic vapor phase epitaxy (MOVPE). A thermodynamic model based on the equilibrium state is presented to explain the etch and growth rates. These results show that the reaction between gas phase and surface is in quasi-equilibrium. An increase in material migration length on the surface caused by introducing HCl gas is thought to be the main reason for improvement in selective epitaxy.

Fabrication of AlxGa1−xAs buried heterostructure laser diodes by in-situ gas etching and selective-area metalorganic vapor phase epitaxy

Abstract This paper presents the first successful fabrication of an AlxGa1-xAs buried heterostructure laser diode (BH-LD) entirely by metalorganic vapor phase epitaxy (MOVPE) without using the wet etching process. The BH-LDs were fabricated by the selective area etching and regrowth (SER) method, combining an in-situ HCl gas etching with a highly selective epitaxy (HSE). These devices operated in a single mode up to 35 mW CW output power. The threshold current was 10.7 mA at 25°C and the difference of the threshold current between 25°C and 60°C was as low as 3.5 mA.

Spatially modulated photoluminescence properties in dynamically strained GaAs/AlAs quantum wells by surface acoustic wave

Spatially resolved photoluminescence (PL) spectra and polarization anisotropy were investigated in GaAs/AlAs dynamic wires, which were formed by applying a surface acoustic wave (SAW) on GaAs/AlAs quantum wells along the [110] or [1-10] direction. A synchronized excitation method clearly demonstrates that the band gap energies are spatially modulated by the travelling-SAW-induced strain. It is found that both the spatial PL modulation and anisotropic polarization properties depend on the SAW direction. The spatial modulation of the polarization anisotropies and their dependence on the strain-induced valence band mixing are also discussed theoretically.