Yoichi Sasai

Monolithic integration of an InGaAsP/InP laser diode with heterojunction bipolar transistors

A monolithic integration of an InGaAsP laser diode together with current supplying circuit on a single InP substrate has been achieved. Heterojunction bipolar transistors (HBT’s) have been constructed utilizing the burying epitaxial layers of the buried heterostructure laser diode. The laser has been successfully modulated up to 1.6 GHz through the HBT’s driving circuit with sinusoidal electrical signal.

Characteristics of periodically domain‐inverted LiNbO3 and LiTaO3 waveguides for second harmonic generation

Characteristics of waveguides with periodically domain‐inverted regions in LiNbO3 and LiTaO3 for quasi‐phase‐matched (QPM) second harmonic generation are investigated. The domain‐inverted regions in LiNbO3 are formed by heat treatment using selective SiO2 mask and those in LiTaO3 are formed by heat treatment using selective proton exchange. The domain‐inverted region in LiTaO3 is fabricated up to 2.7 μm depth, which is twice as deep as that in LiNbO3. The channel waveguides incorporating the regions are fabricated using proton exchange by pyrophosphoric acid. The propagation loss (0.9 dB/cm) of LiTaO3 waveguide is much lower than that of LiNbO3 waveguide (2.9 dB/cm). The second harmonic power generated in LiTaO3 waveguide by third‐order QPM consequently has three time higher conversion efficiency, compared to that in LiNbO3 waveguide. In domain‐inverted LiNbO3 waveguide, we have observed optical damage. On the other hand, in domain‐inverted LiTaO3 waveguide, stable blue light (421 nm) has been obtained wi...

Deep Impurity Levels in InP LEC Crystals

Deep impurity levels in InP LEC single crystals have been investigated by deep-level transient spectroscopy (DLTS) and photoluminescence (PL) measurements. The effects of heat treatment on DLTS and PL signals have been investigated, the results indicating that a deep impurity level whose emission activation energy is 0.42 eV is closely related to the well-known PL emission band at 1.1 eV. It seems that these DLTS and PL signals originate from a certain complex including P vacancies and defects, since some behaviours of these signals can be well explained by a configuration-coordinate model. Two other deep levels with emission activation energies of 0.31 and 0.60 eV have also been observed. The origin of these deep impurity levels might be due to native defects in the InP LEC crystals.

Operation principle of the InGaAsP/InP laser transistor

A laser transistor functions both as a semiconductor laser and a heterojunction bipolar transistor. It generates stimulated emission light from the base region. We have obtained, typically, a maximum laser power of 3 mW, a current gain of 2000, and a transition frequency of 2.5 GHz for the fabricated devices. We show that the novel light output control can be obtained by changing its collector voltage. Both laser output and collector current can also be simultaneously controlled by changing the base current.

Electrically Pumped CdZnSe/ZnSe Blue-Green Vertical-Cavity Surface-Emitting Lasers

We demonstrate an electrically pumped CdZnSe/ZnSe blue-green vertical-cavity surface-emitting laser (VCSEL) with a SiO2/TiO2 dielectric multilayer mirror. Electrically pumped lasing was achieved at 77 K with a threshold current of 3 mA (pulsed). A low far-field radiation angle of 7° was observed above the threshold in a 10-µ m-diameter device, which indicates the spatial coherence expected for lasing.

Compound source molecular beam epitaxy for II–VI laser structures

Abstract Compound source molecular beam epitaxy (CSMBE) for II–VI laser structures is developed. This method employs compounds as source materials instead of elements. The surface of ZnSe during CSMBE at 100–350°C is Se-stabilized, in spite of the VI II ratio of unity. Study of defects observed on ZnCdSe/ZnSSe/ZnMgSSe laser structures indicates that defects are pairs of the stacking faults which form an unique hillock. The composition modulation was not observed for ZnMgSSe layers grown by CSMBE. These results are owing to hot and group-VI diatomic molecular beam generated from compound sources.

LPE growth and characterization of InGaAsP/InP multiquantum well epitaxial layers

Abstract This paper presents very thin InGaAsP/InP layers grown by the LPE-sliding growth technique and the characterization of the fabricated multiquantum well (MQW) layers. In the LPE growth mechanism of the very thin layer, the transient region having a thickness of 60 to 75 A is formed at the onset of the growth under nonequilibrium conditions of the solid-liquid interface, while a very thin layer is grown under diffusion-limited conditions. For MQW layers, the degeneration split between the heavy- and light-hole levels has been recognized from the photoluminescence measurements, and ±1st and ±2nd order satellite peaks of the superlattice have been observed in the rocking curves of the double X-ray diffraction. Furthermore, it has been recognized that the lattice constant of the very thin layers in the LPE-grown InGaAsP/InP MQW layers was shifted to that of the InP layers by the relaxation of the strain at the heterointerfaces.

Fabrication and lasing characteristics of 1.3‐μm InGaAsP multiquantum‐well lasers

This paper reports the fabrication and lasing characteristics of 1.3‐μm InGaAsP multiquantum‐well (MQW) buried heterostructure (BH) lasers grown by liquid‐phase epitaxy (LPE) technique. The MQW active region consists of five InGaAsP well layers (λg=1.3‐μm, Lz∼200 A and InGaAsP barrier layers (λg=1.1 μm, d∼400–600 A). These lasers have threshold currents of 15–20 mA at 25 °C, external quantum efficiencies of 50% at 25 °C, and T0 values of 130–145 °K in the temperature range of less than 300 °K. The beam divergences perpendicular and parallel to the junction plane were in the narrow range of 10–13°. Furthermore, the polarization‐dependent gain‐current relationship between the TE and TM mode of InGaAsP MQW lasers has been investigated in detail for the first time.

A 1.3 µm InGaAsP/InP Multiquantum Well Laser Grown by LPE

We have successfully achieved a 1.3 µm InGaAsP/InP BH laser with multiquantum well active layers grown by low-temperature LPE technique (Tg=589°C). The thickness of thin epitaxial layers was less than de Broglie wavelength. The laser has a threshold current of 19 mA, an external differential quantum efficiency of ~40%, and T0 value of ~145 K in the range from -5°C to 20°C and ~60 K from 20°C to 70°C.

Electric-field-induced absorption effect in LPE-grown InGaAsP/InP multi-quantum-well waveguides

Multi‐quantum‐well (MQW) strip‐loaded waveguides, which are composed of liquid‐phase‐epitaxy‐grown InGaAsP/InP systems, have been characterized in detail. Several MQW waveguides with well depths (Lz) ranging from 100 to 240 A have been compared with bulk ones about the electric‐field‐induced absorption effect, considering the zero‐bias propagation loss and the optical confinement factor in the region in which absorption occurs. It has been confirmed that the MQW (Lz∼100 A) waveguides have an absorption change under the electric field more than five times larger than the bulk ones with the same zero‐bias propagation loss.