Tomonari Shioda

InP–InGaAsP Integrated 1

An integrated semiconductor 1times5 InP-InGaAsP optical phased-array switch is fabricated and characterized. Using the carrier-induced refractive index change of InGaAsP waveguide, we achieve successful switching to five output ports with less than 60-mA current injection. Wide operating bandwidth covering the entire C-band (1520-1580 nm) and nanoseconds dynamic response are demonstrated, making it potentially applicable to large-capacity wavelength-multiplexed optical-packet-switching routers.

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Selective area metal-organic vapor phase epitaxy (SA-MOVPE) allows in-plane control of emission wavelength by tailored width of masks. For InGaN/GaN multiple quantum wells (MQWs), modulation of luminescence wavelength was achieved based on a balance between vapor-phase diffusion of group-III precursors and their surface incorporation. For the basic understanding of the SA-MOVPE of nitride semiconductors, thickness profiles of GaN, InN, AlN, and InGaN layers around relatively wide (>10 mum) masks were investigated. The effective lateral diffusion length D/ks, which is the ratio of the vapor-phase mass diffusivity of a precursor to its surface incorporation rate constant, was extracted for GaN and InN. The value was much larger for InN due to smaller surface incorporation rate. In the SA-MOVPE of InGaN bulk layer at around 800degC, indium incorporation rate seems to be limited by the surface flux of a gallium precursor, resulting in no variation in the indium content. Varied width of the InGaN wells by the existence of masks seems to govern the shift in the luminescence wavelength from InGaN/GaN MQWs. Therefore, design of the thickness distribution of GaN based on the quantitative model is essential to the controlled in-plane color modulation of solid-state lighting devices using SA-MOVPE.

5 Optical Switch Using Arrayed Phase Shifters

Fabrication of abrupt InGaP∕GaAs heterointerfaces has been difficult using metal organic vapor phase epitaxy (MOVPE) due to the exchange of P and As during the fabrication steps. An optimized gas-switching sequence to fabricate heterointerface of InGaP on GaAs layer by MOVPE was previously developed in which the unstable top surface layer of GaAs is stabilized and the exchange of P and As between InGaP and GaAs layers is suppressed. In this study, the effect of this optimized gas-switching sequence was quantitatively evaluated by using scanning transmission electron microscopy (STEM). Changes in atomic composition from GaAs to InGaP at the interface at the atomic layer level were revealed by using Z-contrast method in STEM. Quantitative evaluation using the Z-contrast method confirmed that the abruptness of the GaAs∕InGaP interface was improved by this optimized gas-switching sequence.

Selective Area Metal–Organic Vapor Phase Epitaxy of Nitride Semiconductors for Multicolor Emission

The selective area metal–organic vapor phase epitaxy (SA-MOVPE) of InN was realized and its kinetics was investigated. InN deposition selectivity between the mask and the crystal surface was found to strongly depend on the growth temperature, and good selectivity was obtained above 600 °C. Under this growth condition, the thickness profile of InN between the masks exhibited a catenary shape, which resulted from the vapor phase diffusion. This fact shows that vapor phase diffusion is the dominant supply mechanism in InN SA-MOVPE as well as for the growth of GaN and InGaAsP. These kinetic analysis will contribute to the development of monolithically integrated AlInGaN-based devices.

Abrupt InGaP∕GaAs heterointerface grown by optimized gas-switching sequence in metal organic vapor phase epitaxy

Thickness profiles of GaN grown by selective area metal–organic vapor phase epitaxy (SA-MOVPE) were successfully reproduced by a vapor phase diffusion model that employs only one parameter–effective diffusion length D/ks. The value of D/ks of Ga-containing precursors changes from 10 to 50 µm under growth temperature of 1000–1250 °C and reactor total pressure of 100 mbar. It was confirmed that, in the wide-stripe SA-MOVPE of GaN, the vapor phase diffusion of Ga-containing precursors govern the profile of growth rate. Numerical simulation using the vapor phase diffusion model is of great help for the design and control of thickness profiles in the SA-MOVPE of GaN.

Kinetic Analysis of InN Selective Area Metal–Organic Vapor Phase Epitaxy

An integrated semiconductor 1times5 optical phased-array switch is designed and demonstrated for the first time. Using the carrier-induced refractive index change in the InGaAsP bulk layer, we achieve successful switching to five output ports with less than 60-mA current injection.

GaN Selective Area Metal–Organic Vapor Phase Epitaxy: Prediction of Growth Rate Enhancement by Vapor Phase Diffusion Model

We have demonstrated monolithic integration of multicolor light-emitting diodes (LEDs) by selective-area metalorganic vapor phase epitaxy (SA-MOVPE). The use of relatively wide (>30 µm) masks resulted in a large in-plane modulation of both InGaN layer thickness and composition, allowing us a wide range of wavelength modulation. A wider mask shifted the electroluminescence spectrum to longer wavelengths due to vapor-phase diffusion of precursors. LED elements were formed at the center of the 60-µm-wide growth area, the peak wavelength of which covered 454–545 nm around turn-on voltages and 454–485 nm under a high-injection condition.

Design and Fabrication of Integrated 1×5 Optical Phased Array Switch on InP

We designed the strain and bandgap distribution of tensile InGaAs/InGaAsP grown by selective-area MOVPE using vapor-phase diffusion model. A design principle of selective-area growth for integrating polarization independent components is discussed.

Monolithically Integrated InGaN-Based Multicolor Light-Emitting Diodes Fabricated by Wide-Stripe Selective Area Metal–Organic Vapor Phase Epitaxy

The growth mechanism and rate constants of GaN metal-organic vapor-phase epitaxy (MOVPE) have been unclear in spite of the necessity for large-scale production of this material to meet the applications such as solid-state lighting. In this work, the major precursor of GaN has been identified and its surface reaction rate constant has been obtained through the analysis of multi-scale profiles. Usually, it is difficult to explore the surface reaction kinetics of MOVPE because the rate-limiting process of the growth is often vapor-phase mass transport. As shown in Fig. 1, the growth rate of GaN increased along the flow direction at the upstream part, reflecting the rate of mass transport from the inlet to the wafer. These profiles are sensitive only to the mass diffusivity D of a precursor of GaN layer, the value of which can be thus obtained by fitting the simulated profiles to the experimental ones with the value of D as a fitting parameter. In such a mass-transport-limited kinetics of growth, we can only access the surface reaction rate through the analysis of micrometer-scale profiles in selective-area growth. Figure 2 shows an example of the growth rate enhancement, the growth rate normalized by the value at the position far enough from masks, as a function of the mask width. This relationship is determined by the only parameter D/ks (vapor-phase mass diffusivity / the firstorder surface reaction rate constant of a GaN precursor). Through the comparison between the measured and simulated relationships, we can obtain the value of D/ks. This value can be converted to ks once we know the value of D from the reactor-scale profile of growth rate. The values of D/ks were obtained over a 2-inch wafer by putting the selective masks on the whole wafer. The value of D/ks seemed independent from the position on the wafer, as shown in Fig. 3, indicating that there exists only a single precursor of GaN because D/ks is dependent primarily on the kind precursor. Among the reaction models on the MOVPE of GaN proposed previously, we adopted the one in Fig. 4 that is consistent with the finding of the invariant value of D/ks. In this model, the intermediate precursor of GaN is the product between the source molecules (CH3)3Ga and NH3. According to the simulations incorporating these reactions and relevant rate constants in the literature, the precursor of GaN was (CH3)2Ga:NH2 over an entire wafer. The obtained values of D and ks then correspond to (CH3)2Ga:NH2. In this way, we proposed a reaction model of GaN with a measured value of ks corresponding to the intermediate precursor of GaN for the first time to our knowledge. This model is useful to simulate a complicated GaN MOVPE reactor in which the rate limiting step is not simply mass transport, such as a shower-head type reactor. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Design of Strain and Bandgap Profiles of InGaAsP Fabricated by Selective Area Metal-Organic Vapor Phase Epitaxy for Polarization Independent Operation

Selective-area growth (SAG) of InGaN/GaN multiple quantum wells (MQWs) for multiple-wavelength LED is fabricated and characterized. As a result, the emission peak shifts to longer wavelengths and the wider mask leads to longer wavelength.