Takuya Sano

Electronic band structures of GaInAsP/InP vertically stacked multiple quantum wires with strain-compensating barriers

Energy-band structures of compressively strained GaInAsP/InP quantum wires fabricated by etching and regrowth method have been calculated using an 8 band k⋅p theory including strain relaxation. The effects of strain-compensating barriers and vertically stacking multiple wire layers on band structures are investigated. It is found that due to the dependence of strain relaxation on the amount of strain compensation in barrier regions and on the number of wire layers in the vertical stack, unlike strained quantum films, the energy-band structures of strained quantum wires are dependent on these factors. Experimentally observed wire-width dependence of the large energy blueshift in vertically stacked multiple quantum-wire structures is accurately explained using our calculations without any fitting parameter. Additional broadening in the emission spectra due to vertically stacking multiple quantum wires is found to be negligible. Our results show that strain compensation in barrier layers may be used effectiv...

GaInAsP/InP Partially Strain-Compensated Multiple-Quantum-Wire Lasers Fabricated by Dry Etching and Regrowth Processes

This paper reports the structural properties and lasing characteristics of GaInAsP/InP multiple-quantum-wire lasers fabricated by electron beam lithography, CH4/H2-reactive ion etching and organometallic vapor-phase-epitaxial regrowth. Good size distributions of multiple-quantum-wire structures (wire widths of 18 nm and 27 nm in a period of 80 nm) have been obtained with standard deviations less than ±2 nm. We have confirmed that low-damage etched/regrown interfaces of quantum-wire structures can be realized by using a partially strain-compensated quantum-well structure. Threshold current densities of 5-quantum-well wirelike lasers (wire widths of 43 nm and 70 nm) were found to be lower than that of the quantum-film laser, fabricated from the same initial wafer, due to a volume effect at temperatures up to 85°C. Finally, room temperature (RT)-continuous wave (CW) operation of multiple-quantum-wire lasers (wire width of 23 nm in a period of 80 nm, 5-stacked quantum-wires) was achieved, and the good reliability of this quantum-wire laser was demonstrated for the first time by means of lifetime measurement under the RT-CW condition.

Low-damage etched/regrown interface of strain-compensated GaInAsP/InP quantum-wire laser fabricated by CH4/H2 dry etching and regrowth

GaInAsP/InP strain-compensated five-layered quantum-wire lasers with the wire width of 23 nm were fabricated by electron-beam lithography, CH4/H2-reactive ion etching and organometallic vapor-phase-epitaxial regrowth, and the quality of the etched/regrown interface was evaluated from the spontaneous emission efficiency dependence on the active region width in comparison with that of unetched quantum-well lasers. As a result, the product of the surface recombination velocity and the carrier lifetime at the etched/regrown interface was estimated to be less than 3 nm at room temperature. Finally, no noticeable degradation in the spontaneous emission efficiency of this quantum-wire laser was observed within measurement temperature from 25 °C to 85 °C.

Room Temperature-Continuous Wave Operation of GaInAsP/InP Multiple-Quantum-Wire Lasers by Dry Etching and Regrowth Method

Room temperature (RT)-continuous wave (CW) operation of GaInAsP/InP quantum-wire lasers fabricated by electron beam lithography, CH4/H2-reactive ion etching and organometallic vapor-phase-epitaxial regrowth was realized for the first time. The threshold current density of 802 A/cm2 and differential quantum efficiency of 36% were obtained for a device with strain-compensated 5-layered quantum-wires with the wire width of 23 nm in the period of 80 nm, the stripe width of 15 µm and the cavity length of 1.15 mm. From lifetime measurement under RT-CW condition, no noticeable degradation in light output was observed even after more than 3,200 h.

Multiple-quantum-wire structures with good size uniformity fabricated by CH4/H2 dry etching and organometallic vapor-phase-epitaxial regrowth

GaInAsP/InP multiple-quantum-wire structures with wire widths of 18 nm and 27 nm in the period of 80 nm were fabricated by electron beam lithography, CH4/H2-reactive ion etching and organometallic vapor-phase-epitaxial regrowth. Size distributions of these quantum-wire structures were measured by scanning electron microscope and the standard deviation was obtained to be less than ±2 nm. From EL spectra at 103 K, the full-width at half maximum of these quantum-wire structures was found comparable to that of the quantum-film structure fabricated from the same initial wafer.

Anomalous in-plane polarization dependence of optical gain in compressively strained GaInAsP-InP quantum-wire lasers

In-plane polarization anisotropy of optical gain in compressively strained GaInAsP-InP quantum wire (Q-wire) lasers including elastic strain relaxation induced band mixing is studied. The interaction between two-dimensional (2-D) quantum confinement and elastic strain relaxation effects is found to be complex depending qualitatively also on the wire width. Additional valence band mixing due to strain relaxation has a strong influence on the polarization dependence of optical gain. In the absence of elastic strain relaxation, gain is the maximum for tranverse electric (TE) polarization with the electric field parallel to the wire axis (TE/sub /spl par//), in agreement with the existing theory. On the other hand, when strain relaxation is strong, contrary to the existing theory, valence band mixing causes the gain to be the maximum in TE polarization with the electric field normal to the wire axis (TE/sub /spl perp//). Moreover, Q-wire lasers without suppression of strain relaxation are more likely to exhibit ground-state lasing for TE/sub /spl perp// polarization. These results suggest that in the presence of strong strain relaxation, a laser cavity parallel to the wire axis would provide higher gain. Therefore, the appropriate orientation of the laser cavity in strained GaInAsP-InP Q-wire lasers should be decided after carefully studying the polarization dependence of gain. Our calculation also shows that strong strain relaxation causes in-plane polarization anisotropy to show complex, nonmonotonic dependence on the wire width. Consequently, in such structures, in-plane polarization anisotropy may not be regarded as a direct measure of 2-D confinement effects.

GaInAsP/InP Strain-Compensated Quantum-Wire Lasers Fabricated by CH4/H2 Dry Etching and Organometallic Vapor-Phase-Epitaxial Regrowth.

1.5-µm-wavelength GaInAsP/InP strain-compensated 5-layered quantum-wire lasers with the wire width of 23 nm in the period of 80 nm were realized by electron beam lithography, CH4/H2-reactive ion etching and organometallic vapor-phase-epitaxial regrowth. The energy blue shift at the peak wavelength was observed to be 38 meV, which was much larger than the calculated value, and the spontaneous emission spectral width was almost constant at temperatures between 103 K and 263 K, indicating a lateral quantum confinement effect. While the threshold current density was about 50% higher than that of a 5-quantum-well laser fabricated from the same initial wafer, the differential quantum efficiency was almost the same as that of the 5-quantum-well laser up to 85°C.

Large blue shift in GaInAsP/InP vertically-stacked multiple-quantum-wire lasers by dry etching and regrowth processes

GaInAsP/InP partially strain-compensated multiple-quantum-wire lasers with the wire widths of 18 nm and 27 nm in the period of 80 nm were fabricated by electron beam lithography, CH/sub 4//H/sub 2/-reactive ion etching and organometallic vapor-phase-epitaxial regrowth. Size distributions of these quantum-wire structures were measured by scanning electron microscope and the standard deviation was obtained to be less than /spl plusmn/ 2 nm. From EL spectra of various wire widths lasers, a larger energy blue shift than that from a simple analysis model was observed, which can be attributed to residual compressive strain between the active region and surrounding InP layer.

1.5 /spl mu/m wavelength GaInAsP/InP 5-layered quantum-wire lasers fabricated by CH/sub 4//H/sub 2/ dry etching and regrowth

We report on the lasing properties of SC 5-layered Q-wire lasers with wire width of 23 nm. The spontaneous emission efficiency below the threshold was almost comparable to that of the Q-film lasers up to 85 C, that revealed low-damage property of the etched/regrown interfaces.

GaInAsP/InP multiple-quantum-wire lasers with narrow (14 nm) quantum-wire structure

GaInAsP/InP strain-compensated 5-stacked compressively strained quantum-wire lasers with the wire width of 14 nm in the period of 80 nm were realized by electron beam lithography, CH/sub 4//H/sub 2/-reactive ion etching and two-step organometallic vapor-phase-epitaxial growth. By adopting completely strain-compensating barriers, a smaller energy blue shift at the peak wavelength in spontaneous emission spectra was obtained than that in the case of partial strain-compensation, indicating the suppression of strain relaxation in the active regions and the surrounding InP layers. A lateral quantum confinement effect could be observed via sharper shape of the spontaneous emission spectrum than that of quantum-film lasers in the higher transition energy region. Threshold current density of 1.46 kA/cm/sup 2/ and differential quantum efficiency of 39% were also obtained under a pulsed condition at room temperature.