T. Kamijoh

Electrical characteristics of directly‐bonded GaAs and InP

The electrical characteristics of directly bonded GaAs/InP heterointerfaces have been investigated for the first time. The mirror‐polished surfaces of GaAs and InP wafers were put face to face and bonded by heat treatment at temperatures ranging from 450 to 700 °C. The wafers were successfully bonded without using any solders at all the temperatures tested. 1.3 μm InP/GaInAsP lasers were fabricated on GaAs substrates using direct bonding at 450 °C, and room‐temperature lasing operation has been achieved with the threshold current identical to that of conventional InP lasers.

Polarization insensitive semiconductor laser amplifiers with tensile strained InGaAsP/InGaAsP multiple quantum well structure

Data on semiconductor laser amplifiers with a small tensile strain in the wells of multiple quantum well structures are presented. Semiconductor amplifiers with a small strain of 0.2% exhibit polarization insensitive characteristics with a signal gain of 15 dB in the 1.5 μm wavelength range. The enhancement of TM mode gain due to tensile strain is studied by measuring the dependence of amplified spontaneous emission spectra on device length and tensile strain.

Room-temperature CW operation of InGaAsP lasers on Si fabricated by wafer bonding

1.3-/spl mu/m InGaAsP-InP lasers have been successfully fabricated on Si substrates by wafer bonding with heat treatment at 400/spl deg/C. A pressure of 4 kg/cm/sup 2/ has been applied on the wafers before the heat treatment and this pressure application has enabled us to achieve bonding strength required for the device fabrication even when the bonding temperature is as low as 400/spl deg/C. Room-temperature continuous-wave operation with threshold current of 49 mA has been achieved for 7-/spl mu/m-wide mesa lasers.

A comparison of optical second-harmonic generation efficiency using Bessel and Gaussian beams in bulk crystals

Abstract The conversion efficiencies of optical second-harmonic generation (SHG) of light by Bessel beams and Gaussian beams in nonlinear crystals are compared. A Bessel beam, which has a quasi-nondiffractive nature, is generated by illuminating an axicon lens with a Gaussian beam. The interaction path lengths are the same for both beams, and are set to be twice the confocal parameter of the Gaussian beams. The Bessel beam is found to have greater SHG efficiency than the Gaussian beam regardless of the interaction path length and the fundamental wavelength.

Effects of Heat Treatment on Bonding Properties in InP-to-Si Direct Wafer Bonding

Effects of heat treatment on bonding properties, which include bonding strength, photoluminescence intensity, and electrical conduction through the interface, have been investigated in InP-to-Si direct wafer bonding for the first time. Bonding strength and electrical conduction were found to be improved by heat treatment. On the other hand, a degradation of photoluminescence intensity was observed with high-temperature treatment.

Interface structure of selectively oxidized AlAs/GaAs

We present studies of the interface abruptness of selectively oxidized AlAs/GaAs multilayer structures using transmission electron microscopy (TEM). High‐resolution cross‐sectional TEM images reveal that the interfaces between oxidized AlAs and unoxidized regions (GaAs and AlAs) are extremely abrupt on atomic scale. The widths of the transitional region are found to be within 4 monolayers for the interface between oxidized AlAs and unoxidized GaAs and 6.5 nm for the one between oxidized and unoxidized AlAs. The oxide layer thickness is found to decrease gradually from the oxidation front over a length of 200 nm.

Thermal Conductivity of Amorphous Silicon

We measured the thermal conductivity of amorphous silicon using a new simple steady state method implementing deposited Pt stripes as both resistive heaters and temperature monitors. Amorphous Si films were sputtered on Si substrates and heat was injected through the Pt resistive heaters. The increase in heater temperature was determined by the temperature-dependent electrical resistance of the Pt stripes. We thus determined the thermal conductivity of a-Si at room temperature to be 1.8 W/mK, which is about one-hundredth of that of crystal Si. This information is very important to properly design the thermal resistance of long-wavelength surface emitting lasers which use the a-Si in high-reflective stack mirrors.

1.3-μm AlGaInAs-AlGaInAs strained multiple-quantum-well lasers with a p-AlInAs electron stopper layer

1.3-/spl mu/m AlGaInAs-AlGaInAs strained multiple-quantum-well (MQW) lasers with a p-AlInAs electron stopper layer have been fabricated. The electron stopper layer was inserted between the MQW and p-side separate confinement heterostructure (SCH) layers to suppress the electron overflow from the MQW to p-SCH. The characteristic temperatures of the threshold currents and slope efficiencies were improved in the lasers with the stopper layers, especially at higher temperatures. As a result, a maximum operating temperature of 155/spl deg/C was achieved, which was 20/spl deg/C higher than that without the stopper layer.

Wafer bonding technology for optoelectronic integrated devices

Abstract Wafer bonding has been investigated as a key technology to integrate InP lasers on Si for optoelectronic integrated circuits. The bonding process has been optimized to allow the integration of InGaAsP/InP double-heterostructures (DHs) on Si with keeping the crystal qualities good enough to realize the lasers. As a result, room temperature continuous-wave (CW) operation of InP edge-emitting lasers has been achieved. In addition, as one of the building blocks to implement the optimal interconnections between Si LSIs, InP optical devices on Si integrated with the back-surface diffractive lenses have been demonstrated. A novel bonding process which allows an integration on structured wafers, such as Si LSI wafers, has also been proposed. The wafer bonding is thought to be a promising technique to implement optical interconnections between Si LSI chips.

Wafer Bonding of InP to Si and its Application to Optical Devices

Wafer bonding technology has been investigated to integrate InP lasers on Si wafers for optoelectronic integrated circuits. Room temperature continuous-wave (CW) operation of edge-emitting lasers and photo-pumped operation of surface-emitting lasers have been achieved. A novel bonding process which allows an integration of the optical devices on structured wafers, such as Si LSI wafers, has also been proposed. The wafer bonding is thought to be a promising technique to implement optical interconnections between Si LSI chips.