Hidefumi Mori

Dislocation generation of GaAs on Si in the cooling stage

In situ measurements are carried out for the etch pit density (EPD) of GaAs on Si at growth temperature using a newly developed HCl‐GaCL vapor phase etching method. The EPD obtained is 4×104 cm−2 at growth temperature. However, after the temperature cools down to room temperature, the EPD is 8×106 cm−2 using molten KOH etching. GaP on Si is also carried out, and almost the same result is obtained; that around 107 cm−2 dislocations are generated in the cooling stage. This is the first evidence that thermal stress in the cooling stage determines the quality of GaAs and GaP heteroepitaxial layers on Si.

Stable cw operation at room temperature of a 1.5‐μm wavelength multiple quantum well laser on a Si substrate

Room‐temperature cw operation of an InGaAs/InGaAsP multiple quantum well (MQW) laser diode on a Si substrate is reported. The MQW laser emits at a 1.54 μm wavelength and exhibits no degradation after over 2000 h of operation. Employing a hybrid organometallic vapor phase epitaxy/vapor mixing epitaxy method and a layer structure for improving crystalline quality, high‐quality MQW layers are obtained. A stable longitudinal mode spectrum demonstrates the effectiveness of the MQW active layer.

Room‐temperature operation of an InGaAsP double‐heterostructure laser emitting at 1.55 μm on a Si substrate

The room‐temperature operations of an InGaAsP double‐heterostructure (DH) laser emitting at 1.55 μm on a Si substrate is reported. A pulsed threshold current as low as 46 mA has been measured for a ridge waveguide laser with a 4 μm strip width and a 200 μm cavity length. This successful laser operation is due to the high crystalline quality of the DH structure with full width at half maximum of x‐ray rocking curves as low as 110 arcsec grown on a Si substrate by the organometallic vapor phase epitaxy/vapor mixing epitaxy hybrid method. A correlation between the optical property of an InGaAsP DH and its crystalline quality is also discussed.

Deposited silica waveguide for intergrated optical circuits

Embedded single and multimode waveguides on fused quartz substrates have been fabricated by high‐speed silica deposition and accurate reactive sputter etching by a C2F6 gas plasma. These waveguides have rectangular cross sections with an aspect ratio close to unity. Total waveguide loss was approximately 5 dB/cm, and absorption loss measured by laser calorimetry at 637‐nm wavelength was less than 0.1 dB/cm.

New hydride vapor phase epitaxy for GaP growth on Si

Gallium phosphide films are successfully grown on (100) Si substrates by a new hydride vapor phase epitaxy. Mixing of reactant vapors just above the substrate makes the growth rate as high as 50 nm/min even in the temperature range of 350–450 °C. This makes the two‐step growth procedure applicable for growing a single domain GaP film on Si from H2‐HCl‐PH3‐Ga reactants. An etch pit density of 7.5×106 cm−2 and a full width at half‐maximum of 93 arcsec in a double‐crystal x‐ray rocking curve are achieved. Green light‐emitting diodes with 565 nm peak wavelength are successfully fabricated using nitrogen‐doped GaP films grown on Si.

GaAs heteroepitaxy on an epitaxial Si surface with a low‐temperature process

This letter reports the growth of an anti‐phase‐free GaAs layer on a (100) epitaxial Si substrate offset by 0.5° without high‐temperature treatment prior to growth. Atomic force microscopy shows that the epitaxial Si surface has regular steps prior to growth. The average terrace width is 25.6 nm, and the step height is calculated to be 0.22 nm from the terrace width and offset angle, which approximately corresponds to a double atomic layer height of (100) Si of 0.27 nm. This single domain structure of the epitaxial Si surface gives the heteroepitaxial GaAs a high crystalline quality. Secondary ion mass spectrometry profiles show an abrupt GaAs‐Si interface. Laser diodes on epitaxial Si substrates show room‐temperature cw operation which confirms device applicability.

7000 h continuous wave operation of multiple quantum well laser on Si at 50 °C

A 1.55 μm multiple quantum well laser heteroepitaxially grown on Si substrate operates under the severe aging condition of the light output of 5 mW/facet at 50 °C. The laser has been operating for more than 7000 h. The threshold current and the slope efficiency of the laser on Si at 20 °C are 32 mA and 0.19 W/A, respectively. The maximum operation temperature is above 80 °C.

1.5 µm-Long-Wavelength Multiple Quantum Well Laser on a Si Substrate

Room-temperature cw operation of an InGaAs/InGaAsP multiple quantum well (MQW) laser diode on a Si substrate is reported. The MQW laser emits at 1.54-µm wavelength and exhibits no degradation after over 1,000 hours of operation. Employing a hybrid organometallic vapor-phase epitaxy/vapor mixing epitaxy method and a layer structure for improving crystalline quality, high-quality MQW were obtained. The stable longitudinal mode spectrum demonstrates the effectiveness of the MQW active layer and results in low-intensity noise. Annealing phenomena under cw operation are also discussed.

Multimode deposited silica waveguide and its application to an optical branching circuit

A fabrication procedure has been developed for multimode deposited silica waveguide (DS guide), consisting of uniform and thick glass layer formation for core and cladding, and amorphous Si mask film for reactive sputter etching. The embedded multimode DS guide with a square core cross section has a transmission loss of 1.3 dB/cm at 633 nm wavelength. Waveguide parameters, such as core dimension, refractive index, and index difference, are similar to those of a multi-mode silica fiber. A multimode optical branching circuit with eight output ports was demonstrated by the above fabrication procedure. Excess insertion loss was 2 dB.

Aging tests of InP-based laser diodes heteroepitaxially grown on Si substrates

Aging tests were performed for InP-based laser diodes heteroepitaxially grown on Si substrates. To define the degradation mode, we studied the change in the device characteristics and electroluminescence (EL) images during the aging tests. The degradation proceeds in a mode characterized by a gradual increase in the threshold current without a change in the current–voltage characteristics. During the aging, dark spot defects (DSDs) appear in the EL images, where no defects were observed initially. However, after a certain number of DSDs are generated, no more degradation occurs in the current–light-output characteristics and EL images. The correlation of the saturation behavior between the threshold current and DSD number is quite good, and strongly suggests that the device degradation is dominated by the development of nonradiative defects in the active layer. Judging from the saturation density of DSDs, we can assume that the origin of the nonradiative defects is closely related to the dislocation that ...