Takuma Fuyuki

Long-wavelength emission in photo-pumped GaAs1−xBix laser with low temperature dependence of lasing wavelength

This study demonstrates long-wavelength emission of up to 1204 nm in photo-pumped GaAs1−xBix lasers grown by molecular beam epitaxy under low temperature conditions. The characteristic temperature (T0) between 20 and 80 °C in the GaAs1−xBix lasers with Al0.3Ga0.7As electron blocking layer is approximately 100 K, which is larger than that of the typical 1.3-μm InGaAsP Fabry-Perot laser diodes (FP-LDs; T0 = 66 K). The temperature coefficient of the lasing wavelength is approximately 40% of that of InGaAsP FP-LDs.

Electrically pumped room-temperature operation of GaAs1−xBix laser diodes with low-temperature dependence of oscillation wavelength

Lasing oscillation at wavelengths up to 1045 nm at room temperature has been realized from GaAs1−xBix Fabry–Perot laser diodes (FP-LDs) by electrical injection, and the temperature characteristics of GaAs1−xBix FP-LDs are revealed for the first time. The characteristic temperature T0 of the GaAs0.97Bi0.03 FP-LD in the temperature range between 15 and 40 °C (T0 = 125 K) is similar to that reported for typical 0.98 µm InGaAs/GaAs LDs. The temperature coefficient of the lasing wavelength in GaAs0.97Bi0.03 FP-LDs is reduced to 0.17 nm/K, which is only 45% of that of GaAs FP-LDs.

Deep-Hole Traps in p-Type GaAs1-xBix Grown by Molecular Beam Epitaxy

Deep-level transient spectroscopy measurements reveal deep-hole traps with activation energies of 0.43 and 0.23 eV in p-type GaAs1-xBix samples with x = 1.2 and 3.4%, respectively, grown at 370 °C by molecular beam epitaxy. In spite of low-temperature growth, the deep-level trap concentration is suppressed on the order of 1015 cm-3, suggesting that Bi atoms contribute to the enhancement of migration to prevent the formation of point defects. The possible origin of the hole traps is discussed in connection with arsenic antisite, AsGa, and bismuth antisite, BiGa.

Growth of GaAs1-xBix/AlyGa1-yAs Multi-Quantum-Well Structures

GaAs1-xBix/AlyGa1-yAs (0<x<0.05, 0<y<0.26) multi-quantum-wells (MQWs) have been successfully grown by molecular-beam epitaxy. The intensity oscillation and streaky patterns of in situ reflection high-energy electron diffraction suggested the layer-by-layer growth of GaAs1-xBix/AlyGa1-yAs MQWs. Clear satellite peaks attributed to periodical structures were observed in high-resolution X-ray diffraction measurements. The cross-sectional transmission microscopy images and secondary-ion mass spectrometry depth profile showed that GaAs1-xBix/AlyGa1-yAs MQWs with a smooth interface can be fabricated without distinct segregation.

Localized States in GaAsBi and GaAs/GaAsBi Heterostructures

Deep- and shallow-level defects in device-quality GaAs1−x Bi x (x ≤ 10.9%) are investigated. Despite low-temperature growth, GaAs1−x Bi x emits intense band-edge photoluminescence, and GaAs0.975Bi0.025 shows lasing operation by optical pumping. The deep-level trap density is suppressed on the order of 1015 cm−3 because of a surfactant effect of the Bi atoms. The Bi-induced localized states generated by the interaction between spatially localized Bi states and the valence band of GaAs are continuously located up to ~90 meV from the valence band with a density of ~1 × 1017 cm−3. Despite concerns regarding the degradation of the hole mobility due to scattering at these Bi-induced localized states, the p-type doping masks the contribution of the Bi-induced states to the hole mobility, and a high hole mobility of 200 cm2 V−1 s−1 is achieved. By characterizing the superlattices, (Al)GaAs/GaAs1−x Bi x heterointerfaces have been proven to be smooth without distinct segregation and stable up to 700 °C. While the interface state density of ~9 × 1011 cm−2 eV−1 in a GaAs/GaAs1−x Bi x heterointerface cannot be reduced by annealing, it can be reduced by half by the insertion of a Bi graded layer into the heterointerface, presumably due to the mitigation of the differences in the metallic GaAs1−x Bi x and nonmetallic GaAs surfaces.