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We measured the two-color laser oscillation from a GaAs/AlGaAs-coupled multilayer cavity at 18–42 °C using current injection. We confirmed simultaneous lasing by detecting the sum frequency generation signal generated by the two-color laser light, and performed time-resolved measurement using a streak camera with a spectrometer. From the observed time transient of the spectra at various temperatures, it it is clarified that the temperature change of the device, induced by current injection, modulates the effective cavity length. Therefore, the temperature control of the device is a key factor in stable two-color lasing and THz wave generation.

GaAs/Ge/GaAs and AlAs/Ge/AlAs heterostructures were grown both on (113)B and (113)A GaAs substrates by molecular beam epitaxy. Sublattice reversal in these heterostructures were identified by comparing the anisotropic etching profile of the epitaxy sample with that for reference (113)B and (113)A GaAs substrates. Sublattice reversal in GaAs/Ge/GaAs heterostructures was achieved on (113)B GaAs substrate. On the other hand, sublattice reversal on (113)A GaAs substrate was obtained by using AlAs/Ge/AlAs heterostructures.

We measured the two-color laser oscillation from a GaAs/AlGaAs-coupled multilayer cavity at 18–42 °C using current injection. We confirmed simultaneous lasing by detecting the sum frequency generation signal generated by the two-color laser light, and performed time-resolved measurement using a streak camera with a spectrometer. From the observed time transient of the spectra at various temperatures, it it is clarified that the temperature change of the device, induced by current injection, modulates the effective cavity length. Therefore, the temperature control of the device is a key factor in stable two-color lasing and THz wave generation.

Room-temperature two-color lasing was demonstrated by current injection into a GaAs/AlGaAs coupled multilayer cavity for terahertz emitting devices utilizing its difference-frequency generation (DFG) inside the structure. We prepared two epitaxial wafers with (001) and (113)B orientations and they were directly bonded to form the coupled multilayer cavity. The (001) side cavity contains two types of InGaAs multiple quantum wells to realize optical gain for two-color lasing while a single GaAs layer of the (113)B side cavity is a nonlinear medium for efficient DFG. Lasing behavior was clearly observed for two modes under pulsed current conditions at room temperature. We found that intensity relation between two-color lasing was dependent on the pulse duration due to the different temporal profiles of emission intensity. Simultaneous two-color lasing in the device was also confirmed by measuring the sum-frequency generation signal using a beta barium borate crystal.

Compact and room-temperature operable terahertz emitting devices have been proposed using a semiconductor coupled multilayer cavity that consists of two functional cavity layers and three distributed Bragg reflector (DBR) multilayers. Two cavity modes with an optical frequency difference in the terahertz region are realized since two cavities are coupled by the intermediate DBR multilayer. In the proposed device, one cavity is used as the active layer for two-color lasing in the near-infrared region by current injection and the other is used as the second-order nonlinear optical medium for difference-frequency generation of the two-color fundamental laser light. The control of the nonlinear polarization by face-to-face bonding of two epitaxial wafers with different orientations is quite effective to achieve bright terahertz emission from the coupled cavity. In this study, two-color emission by optical excitation was measured for the wafer-bonded GaAs/AlGaAs coupled multilayer cavity containing self-assembled InAs quantum dots (QDs). We found that optical loss at the bonding interface strongly affects the two-color emission characteristics when the bonding was performed in the middle of the intermediate DBR multilayer. The effect was almost eliminated when the bonding position was carefully chosen by considering electric field distributions of the two modes. We also fabricated the current-injection type devices using the wafer-bonded coupled multilayer cavities. An assemble of self-assembled QDs is considered to be desirable as the optical gain medium because of the discrete nature of the electronic states and the relatively wide gain spectrum due to the inhomogeneous size distribution. The gain was, however, insufficient for two-color lasing even when the nine QD layers were used. Substituting two types of InGaAs multiple quantum wells (MQWs) for the QDs, we were able to demonstrate two-color lasing of the device when the gain peaks of MQWs were tuned to the cavity

Current-injection two-color lasing has been demonstrated using a GaAs/AlGaAs coupled multilayer cavity that is a good candidate for novel terahertz-emitting devices based on difference-frequency generation (DFG) inside the structure. The coupled cavity structure was fabricated by the direct wafer bonding of (001)- and (113)B-oriented epitaxial wafers for the efficient DFG of two modes in the (113)B side cavity, and two types of InGaAs multiple quantum wells (MQWs) were introduced only in the (001) side cavity as optical gain materials. The threshold behavior was clearly observed in the current–light output curve even at room temperature. Two-color lasing was successfully observed when the gain peaks of MQWs were considerably tuned to the cavity modes by the operating temperature.

Two-color surface-emitting lasers were fabricated using a GaAs-based coupled multilayer cavity structure grown by molecular beam epitaxy. InGaAs/GaAs multiple quantum wells were introduced only in the upper cavity for two-mode emission in the near-infrared region. Two-color lasing of the device was successfully demonstrated under pulsed current operations at room temperature. We also observed good temporal coherence of the two-color laser light using a Michelson interferometer. A coherent terahertz source is expected when a wafer-bonded coupled cavity consisting of (001) and non-(001) epitaxial films is used for the two-color laser device, in which the difference-frequency generation can be enabled by the second-order nonlinear response in the lower cavity.

GaAs/Ge/GaAs heterostructures were grown on high-index (113)B GaAs substrates by molecular beam epitaxy. Sublattice reversal in GaAs/Ge/GaAs was identified by comparing the anisotropic etching profile of the epitaxial sample with that for reference (113)A and (113)B GaAs substrates. The shape of the resulting mesa for the lower GaAs layer was similar to that for the reference (113)B GaAs substrate, whereas that for the upper GaAs layer was similar to that for the reference (113)A GaAs substrate. An atomic-resolution analysis was also conducted by mapping using energy-dispersive X-ray spectroscopy, whereby the sublattice reversal was directly observed through the atomic arrangements.

Two-color surface-emitting lasers were demonstrated, employing a GaAs/AlGaAs coupled multilayer cavity composed of two cavity layers and three distributed Bragg reflector (DBR) multilayers. InGaAs multiple quantum wells (MQWs) with two different well widths were introduced only in the upper cavity, sandwiched between p-type and n-type DBRs. This current-injection type device exhibited two-color lasing in the near-infrared region under room temperature pulsed conditions. This two-color lasing was obtained when the lower cavity had an optimal thickness relative to the upper cavity thickness and the MQW emission properties.

We fabricated a photoconductive antenna structure utilizing Er-doped InAs quantum dot layers embedded in strain-relaxed In0.35Ga0.65As layers on a GaAs substrate. Mesa-shaped electrodes for the antenna structure were formed by photolithography and wet etching in order to suppress its dark current. We measured the photocurrent with the excitation of ~1.5 µm cw and femtosecond pulse lasers. Compared with the dark current, the photocurrent was clearly observed under both cw and pulse excitation conditions and almost linearly increased with increasing excitation power in a wide range of magnitudes from 10 W/cm2 to 10 MW/cm2 order.

We fabricated the two color surface emitting device of a coupled cavity structure which is applicable to terahertz light source. GaAs/AlGaAs vertical multilayer cavity structures were grown on a (001) and (113)B GaAs substrates and the coupled multilayer cavity structure was fabricated by wafer-bonding of them. The top cavity contains self-assembled InAs quantum dots (QDs) as optical gain materials for two-color emission of cavity-mode lights. The bonding position was optimized for the equivalent intensity of two-color emission. We formed a current injection structure, and two-color emission was observed by current injection, although lasing was not observed.