Akiko Gomyo

Evidence for the existence of an ordered state in Ga0.5In0.5P grown by metalorganic vapor phase epitaxy and its relation to band‐gap energy

The band‐gap energy (Eg) of metalorganic vapor phase epitaxially (MOVPE) grown Ga0.5In0.5P lattice matched to (001) GaAs is presented as a function of a wide range of V/III ratios and growth temperatures. Photoluminescence, Raman scattering spectroscopy, transmission electron microscopy, and impurity diffusion were used to investigate this functional relationship. Two pieces of evidence are shown which demonstrate that MOVPE Ga0.5In0.5P epitaxial layers with ‘‘abnormal’’ Eg∼1.85 eV and ‘‘normal’’ Eg∼1.9 eV correspond to an ordered and a random (Ga,In) distribution on column III sublattices, respectively. In an ordered state, a sequence of (110) planes...GaGaInInGaGaInIn...in the [110] direction is the most probable distribution.

Studies of GaxIn1−xP layers grown by metalorganic vapor phase epitaxy; Effects of V/III ratio and growth temperature

Abstract Properties of GaxIn1−xP grown by metalorganic vapor phase epitaxy at various V/III ratios and growth temperatures were studied by photoluminescence (PL) (300 K, 2 K), X-ray diffraction and Raman scattering measurements. PL peak energy, measured at 300 K, changed from ∼1.90 to ∼1.85 eV, both when V/III was varied from 62 to 412 at 700°C growth temperature and when growth temperature was varied from 750 to 650°C at a fixed V/III ratio of 62, while each GaxIn1−xP layer is lattice-matched t GaAs and has the same composition. The low Pl peak energy (∼1.85eV) was ascribed to the band edge luminescence and not to deep-level related luminiscence. Raman scattering spectra for these samples showed a systematic difference, corresponding only to the PL peak energy difference, indicating that the PL peak energy difference results from an energy band structure difference due to atomic-scale arrangement difference on the group III element sub-lattice. It is suggested that there is a greater degree of atomic-scale clustering on the group III element sub-lattice for samples with low PL peak energy than for samples with “normal” PL peak energy (∼1.9 eV).

Band-Gap Energy Anomaly and Sublattice Ordering in GaInP and AlGaInP Grown by Metalorganic Vapor Phase Epitaxy

The previously reported photoluminescence(PL)-peak-energy anomaly problem for Ga0.5In0.5P grown on GaAs by metalorganic vapor phase epitaxy (MOVPE) was studied in detail. X-ray microprobe analysis, and optical transmission spectra measurements were carried out to examine alloy compositions and band-gap energies (Egs), respectively. The MOVPE growth condition dependence of {1/2, 1/2, 1/2} superlattices (SLs) on the cation sublattice in Ga0.5In0.5P was studied in detail, using transmission electron microscopy. The correlation between the Eg anomaly and the SLs was examined in detail and established. Raman spectra seemed to show zone-folding effects due to the monolayer SL. A similar Eg anomaly was reported for AlGaInP. AlGaInP and AlInP were also found to show the same SLs.

Strong ordering in GaInP alloy semiconductors; Formation mechanism for the ordered phase

Abstract A formation mechanism for the naturally formed { 2 1 2 1 2 1 } monolayer superlattice (SL) on the column III sublattice, which has been observed in Ga 0.5 In 0.5 P and (Al x Ga 1− x ) 0.5 In 0.5 P grown by metalorganic vapor phase epitaxy (MOVPE), is proposed. The proposition is based on the experimental results for the substrate orientation dependence of the appearance asymmetry of the four equivalent { 2 1 2 1 2 1 } SLs. The mechanism is related to (1) the intra-plane ordering on (001) planes and (2) the inter-plane ordering for the successive (001) ordered planes. The intra-plane ordering is thought to be caused by the anisotropic site occupation affinity for column III atoms due to both a large bond-length difference and a dangling-bond direction asymmetry on the (001) surface. The cause of the inter-plane ordering is attributed to the “phase-locking” role of the [110] atomic steps. The mechanism seems to be well applicable to the explanation for the appearance asymmetry of the { 2 1 2 1 2 1 } SLs for other kinds of alloy semiconductors, such as GaInAs, GaAsSb and GaInPAs grown by vapor phase epitaxy and molecular beam epitaxy, as well as for MOVPE grown AlGaInP alloys. The MOVPE growth condition dependence of the SL formation for Ga 0.5 In 0.5 P is also discussed.

On-Chip Optical Interconnect

We describe a cost-effective and low-power-consumption approach for on-chip optical interconnection. This approach includes an investigation into architectures, devices, and materials. We have proposed and fabricated a bonded structure of an Si-based optical layer on a large-scale integration (LSI) chip. The fabricated optical layer contains Si nanophotodiodes for optical detectors, which are coupled with SiON waveguides using surface-plasmon antennas. Optical signals were introduced to the optical layer and distributed to the Si nanophotodiodes. The output signals from the photodiodes were sent electrically to the transimpedance-amplifier circuitries in the LSI. The signals from the photodiodes triggered of the circuitries at 5 GHz. Since electrooptical modulators consume the most power in on-chip optical interconnect systems and require a large footprint, they are critical to establish on-chip optical interconnection. Two approaches are investigated: 1) an architecture using a fewer number of modulators and 2) high electrooptical coefficient materials.

AlGaInP double heterostructure visible-light laser diodes with a GaInP active layer grown by metalorganic vapor phase epitaxy

AlGaInP double heterostructure laser diodes with a GaInP active layer constitute a basic laser structure for visible-light lasers using an AlGaInP alloy system. This paper gives a detailed description of (Al x Ga 1-x ) 0.5 In 0.5 P metalorganic vapor phase epitaxial growth, laser-fabrication processes, and basic device-characteristics for these lasers. The obtained pulsed-threshold-current was about 3.8 kA/cm2(3.2 kA/cm2minimum) for laser diodes with an 8-10 \mu m wide and 150-300 \mu m long injection stripe. High characteristic-temperature T 0 for the temperature dependence of pulsed threshold current was obtained and was found to be dependent on band-gap-energy differences between active layers and cladding layers. The maximum value for T 0 was 222 K. The lasing wavelength of an AlGaInP double heterostructure laser diode with a GaInP active layer was found to depend on growth conditions and dopant behavior during the growth, and it varied in a range from 664 to 690 nm, while the GaInP active layers were lattice-matched to GaAs substrates. This lasing wavelength difference caused by a crystal growth-condition difference, including a dopant effect, can be explained by the Ga 0.5 In 0.5 P band-gap-energy difference due to the crystal structure difference of Ga 0.5 In 0.5 P. Lasing operations (3-5 mW) over 2000 h at room temperature without significant degradation were obtained, demonstrating the highly promising nature of visible-light laser diodes using an AlGaInP alloy system.

P-Type Doping Effects on Band-Gap Energy for Ga0.5In0.5P Grown by Metalorganic Vapor Phase Epitaxy

Photoluminescence properties of Mg- or Zn-doped Ga0.5In0.5P grown by metalorganic vapor phase epitaxy were studied as a function of hole concentration (p). The band-gap energy (Eg) value for Mg- or Zn-doped Ga0.5In0.5P, grown under a condition in which undoped Ga0.5In0.5P shows an anomalously low Eg, showed a steep increase for p~>1×1018 cm-3. This anomalous behavior was attributed to the Mg or Zn diffusion-enhanced randomization of the previously observed naturally formed monolayer {1/2, 1/2, 1/2} superlattices on the column III sublattice.

Re-examination of the formation mechanism of CuPt-type natural superlattices in alloy semiconductors

The previously proposed natural superlattice (NSL) formation mechanism is experimentally re-examined by using Ga0.5In0.5P grown on (001) vicinal (6° off towards the [110] direction) GaAs substrate by metalorganic vapor phase epitaxy (MOVPE). Based mainly on the experimental results: non-existence of the (111)B micro-facets at the growing interface and extremely large (several hundred A) single NSL domain sizes compared with the average terrace width ( ∼ 27 A), a new NSL formation (step-terrace-reconstruction (STR)) mechanism is presented. The mechanism assumes a reconstruction of the steps and terraces at the column V atom stabilized vicinal (001) surface, on which parity of the number of the column III atoms for each terrace is even.

Observation of enhanced photoluminescence from silicon photonic crystal nanocavity at room temperature

We fabricated air-bridge-type silicon photonic crystal (PC) nanocavities and observed significant enhancement of photoluminescence (PL) from crystalline silicon at room temperature. Cavity-resonant peaks shifted toward longer wavelengths when the period of PC was increased and their polarization dependences agree with the calculation. At a cavity mode wavelength, a 310-fold enhancement of PL intensity, compared with that of unpatterned silicon-on-insulator substrate, was demonstrated.

Novel Window-Structure AlGaInP Visible-Light Laser Diodes with Non-Absorbing Facets Fabricated by Utilizing GaInP Natural Superlattice Disordering

Window-structure AlGaInP visible-light ( λL=680 nm) laser diodes (LDs) have been fabricated, for the first time, by utilizing GaInP natural superlattice (NSL) disordering with selective Zn diffusion. The bandgap energy for the active layer near the mirror facets is increased by 70 meV by the NSL disordering. An 80 mW output power in a fundamental transverse-mode has been achieved for the uncoated window LDs under 1 µsec long pulsed operations. The maximum output power density for the window LDs is estimated to be 10 MW/cm2, which is five times higher than that for conventional LDs.