Masataka Higashiwaki

Self-organized GaAs quantum-wire lasers grown on (775)B-oriented GaAs substrates by molecular beam epitaxy

Self-organized GaAs/(GaAs)4(AlAs)2 quantum-wire (QWR) lasers were grown on (775)B-oriented GaAs substrates by molecular-beam epitaxy. The QWRs were naturally formed at thick parts in the GaAs/(GaAs)4(AlAs)2 quantum well with a corrugated AlAs-on-GaAs upper interface and a flat GaAs-on-AlAs lower interface. The density of the QWRs was as high as 8×106u200acm−1. Stripe-geometry lasers with the self-organized (775)B GaAs/(GaAs)4(AlAs)2 QWRs as an active region oscillated at 20u200a°C with threshold current densities of about 3u200akA/cm2 for uncoated mirrors.

Highly uniform and high-density GaAs/(GaAs)4(AlAs)2 quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy

Extremely uniform and high-density GaAs/(GaAs)4(AlAs)2 quantum wires (QWRs) were self-organized in a thin GaAs/(GaAs)4(AlAs)2 quantum well grown on a (775)B GaAs substrate with a regularly corrugated AlAs–on–GaAs interface and a flat GaAs–on–AlAs interface by molecular beam epitaxy. A strong photoluminescence (PL) peak at λ=692 nm from the GaAs/ (GaAs)4(AlAs)2 QWRs showed large polarization anisotropy [P=(I∥−I⊥)/(I∥+I⊥)=0.19]. A full width at half-maximum of the PL peak from the QWRs was as small as 15 meV at 14 K, which is smaller than those of any self-organized GaAs/AlGaAs QWRs reported so far. Density of the QWRs ( 8×105 QWRs/cm) is the same as the highest ever reported. These results indicate that the QWRs grown on the (775)B GaAs substrate meet requirements for applications to QWR lasers (high uniformity, high density, high optical quality, and simple fabrication process).

Low temperature etching of GaAs substrates and improved morphology of GaAs grown by metalorganic molecular beam epitaxy using trisdimethylaminoarsenic and triethylgallium

Metalorganic molecular beam etching of a GaAs surface is observed at temperatures as low as 370 o C, for the first time, when the GaAs surface is exposed to TDMAAs (trisdimethylaminoarsenic) only. At this low temperature, not only the oxide layer is removed, but a smoothening of the surface also occurs. At higher temperatures (≥480 o C), however, this reaction of GaAs with TDMAAs is responsible for a roughening of the (100) GaAs surface, forming (411)A micro-facets. At low V/III beam pressure ratios (≤0.5), smooth surfaces as well as good optical and electrical properties are obtained for GaAs layers grown even at high temperatures (550≤T sub ≤ 650 o C). TDMAAs proves to be an extremely efficient arsenic source which can supply enough As even for a small V/III ratio of 0.25, and provides high GaAs growth-rates up to 2 μm/h for a TDMAAs flux of 0.15 SCCM and TEG of 0.4 SCCM

High fT 50-nm-Gate InAlAs/InGaAs High Electron Mobility Transistors Lattice-Matched to InP Substrates

We fabricated 50-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates using a conventional process under low temperatures below 300°C, and measured DC and RF performance. The measured cutoff frequency fT of our 50-nm-gate HEMT is 362 GHz, which is the highest value ever reported for any transistor, and is much higher than the values reported for previous 50-nm-gate lattice-matched HEMTs. The excellent RF performance of our HEMTs might result from the low-temperature fabrication process.

High f/sub T/ 50-nm-gate lattice-matched InAlAs/InGaAs HEMTs

We fabricated 50-nm-gate lattice-matched InAlAs/InGaAs High Electron Mobility Transistors (HEMTs) using a conventional process under low temperatures below 300/spl deg/C, and measured DC and RF performance. The measured cutoff frequency f/sub T/ of our 50-nm-gate HEMT is 362 GHz, which is much higher than those in previous works, and the highest value ever reported for any transistor. The excellent RF performance might result from the low-temperature fabrication process.

In0.15Ga0.85As/GaAs quantum wire structures grown on (5 5 3)B GaAs substrates by molecular beam epitaxy

Abstract Self-organized In0.15Ga0.85As quantum wires (QWRs) were formed in an In0.15Ga0.85As quantum well (QW) with GaAs barrier layers grown on a (5xa05xa03)B-oriented GaAs substrate by molecular beam epitaxy. The QW has a regularly corrugated interface to the upper GaAs barrier (a lateral period of about 20xa0nm and a vertical amplitude of about 1.5xa0nm) and a rather flat interface to the lower GaAs barrier. A very narrow photoluminescence peak from the QWRs was observed at a wavelength of 864xa0nm at 15xa0K. The PL peak showed strong polarization dependence [the polarization degree P ue606 (I ‖ −I ⊥ )/(I ‖ +I ⊥ )=0.25] at 15xa0K, indicating high one dimensionality of the (5xa05xa03)B QWRs. The full-width at half-maximum (FWHM) of the PL peak was as small as 8.4 meV (15xa0K) which is, to our knowledge, the smallest PL-FWHM reported so far for self-organized QWRs.

GaAs/(GaAs)4(AlAs)2 quantum wire lasers grown on (7 7 5)B-oriented GaAs substrates by molecular beam epitaxy

Abstract Stripe-geometry lasers with high-density GaAs/(GaAs) 4 (AlAs) 2 quantum wires (QWRs) as an active region were grown on (7xa07xa05)B-oriented GaAs substrates by molecular beam epitaxy. The (7xa07xa05)B QWRs were naturally formed at thick parts in a GaAs/(GaAs) 4 (AlAs) 2 quantum well with a corrugated AlAs-on-GaAs upper interface and a flat GaAs-on-AlAs lower interface. The (7xa07xa05)B QWR lasers with a high one-dimensionality exhibited threshold current densities of 1.9xa0kA/cm 2 at 20°C for a cavity length of 1xa0mm, which were about 35% lower than those of conventional QW lasers simultaneously grown on (1xa00xa00) GaAs substrates. Moreover, they showed a 30% higher characteristic temperature in the range of 20–80°C than the (1xa00xa00) QW lasers.

High-density GaAs/(GaAs)2(AlAs)2 quantum wires naturally formed on (7 7 5)B-oriented GaAs substrates by molecular beam epitaxy

GaAs/(GaAs) 2 (AlAs) 2 quantum wires (QWRs) were naturally formed in a thin GaAs/(GaAs) 2 (AlAs) 2 quantum well (QW) with a regularly corrugated AlAs/GaAs upper interface (a period of 12 nm) and a flat GaAs/AlAs lower interface grown on (775)B-oriented GaAs substrates by molecular beam epitaxy. The QWRs were formed side by side with an extremely high density of 8 x 10 5 QWRs/cm, which is the same to that of the previous GaAs/AlAs QWRs grown on the (775)B substrate (the highest density of QWRs ever reported [8]). A photoluminescence from the QWRs formed in the QW with an average well width (L w ) of 2.1 nm, which have a cross section of about 12 x 2 nm 2 , showed a strong polarization dependence (the polarization degree P = [(I∥ - I⊥)/(I∥ + I⊥)] = 0.21). The polarization degree is about twice as large as that of the previous GaAs/AlAs QWRs with an average L w of 3.3 nm grown on the (775)B substrate. This improvement of the polarization degree is mainly due to the further reduced QW width, which results in an improved one-dimensional confinement of carriers in the present QWRs.

DC and RF Performance of 50 nm Gate Pseudomorphic In0.7Ga0.3As/In0.52Al0.48As High Electron Mobility Transistors Grown on (411)A-Oriented InP Substrates by Molecular-Beam Epitaxy

In this paper, we report on the material and device characteristics of pseudomorphic In0.7Ga0.3As/In0.52Al0.48As high electron mobility transistors (HEMTs) grown on a (411)A-oriented InP substrate by molecular-beam epitaxy. The electron Hall mobility in the (411)A HEMT was 2.5 times higher at 15 K and 1.3 times higher even at room temperature than that in a HEMT grown on a conventional (100) InP substrate. The (411)A HEMTs with 50 nm gates provided excellent DC and RF device characteristics.The maximum transconductance was as high as 1.1 S/mm, and the cutoff frequency reached 355 GHz.

High-density In 0.14 Ga 0.86 As/(GaAs) 5 (AlAs) 5 quantum wires naturally formed on (775)B-oriented GaAs substrates by molecular beam epitaxy

Abstract In 0.14 Ga 0.86 As/(GaAs) 5 (AlAs) 5 Quantum Wires (QWRs) were naturally formed in a thin In 0.14 Ga 0.86 As/(GaAs) 5 (AlAs) 5 Quantum Well (QW) with a regularly corrugated AlAs/In 0.14 Ga 0.86 As upper interface (a period of about 40 nm) and a flat In 0.14 Ga 0.86 As/AlAs lower interface grown on (775)B-oriented GaAs substrates by molecular beam epitaxy. The QWRs were formed side by side with a high density of 2.5×10 5 QWRs cm −1 . A photoluminescence from the QWRs formed in the QW with an average well width of 2.2 nm, which have a cross section of about 40×4 nm 2 , showed a strong polarization dependence [the polarization degree P =( I ‖ − I ⊥ )/( I ‖ + I ⊥ )=0.19], indicating good one-dimensionality of those QWRs. Full width at half maximum of the PL peak from the In 0.14 Ga 0.86 As/(GaAs) 5 (AlAs) 5 QWRs was as small as 17 meV at 14 K, which is smaller than any of other naturally synthesized QWRs reported so far.