Wire-length dependences of In-place polarization anisotropy in GaInAsP/InP quantum-wire (Q-wire) structures
fabricated by dry-etching and regrowth processes were investigated using a photo luminescence (PL) measurement. The
reduction of polarization anisotropy of Q-wires is expected in the shorter Q-Wires. A strain-compensated GaInAsP/InP
single-quantum-well initial wafer was prepared by an organometallic-vapor-phase-epitaxy (OMVPE) system. Using
electron beam lithography, Ti-mask lift-off, CH4/H2 reactive-ion-etching and OMVPE regrowth processes, various
lengths (L) of the Q-wires were realized for wire-widths (W) of 11-, 14- and 18 nm. The Q-wires were measured the
polarization property in normal and parallel to wire-length direction at room temperature. As a result, stronger
polarization anisotropy was observed in narrower Q-Wires and reduced in shorter length of Q-Wires. Furthermore,
polarization anisotropy of strained Q-Wires was predicted by taking in account of the dipole moment interaction between
conduction and heavy-hole subbands optical transition. A 5-nm narrowed wire-width calculation results shows a good
agreement with experimental results. This could be considered that a strain distribution in the Q-Wire induced the energy
band deformation at the edge of the Q-Wire, which reduced the effective wire-width to much narrower than the actual
size observed by an SEM image.
In order to realize low damage fine structuring processes for the low-dimensional quantum structures, we investigated a
process for reducing the degradations of optical properties, which was induced during a reactive-ion-etching (RIE)
process with CH4/H2 gas mixture in the quantum-well (QW) structures. Quantitative studies of optical degradation were
carried out by photoluminescence (PL) and electroluminescence (EL) measurements. We introduced a thicker upper
optical confinement layer (OCL) to protect the QWs from the RIE-plasma. In practical, for the PL measurement, twotypes
of strain-compensated single-quantum-well (SC-SQW) structures were prepared for 40-nm-thick- and 80-nmthick-
upper OCL wafers and covered by 20-nm-thick SiO2. After the samples were exposed to CH4/H2-RIE for 5-
minutes, a relatively stronger suppression of integral PL intensity as well as a spectral broadening was observed in the
sample with 40-nm-thick OCL, while those did not change in the sample with 80-nm-thick OCL. For the EL
measurements, using two types of SC-DQW structures, samples were exposed to CH4/H2-RIE plasma for 5-minute and
then re-grown for other layers to form high-mesa stripe laser structures (Ws=1.5μm). As a result, the spontaneous
emission efficiency of the lasers with 80-nm-thick OCL was almost 2 times higher than that of the lasers with 40-nmthick
OCL. In addition, a lower threshold current as well as a higher differential quantum efficiency was obtained for the
lasers with 80-nm-thick OCL , while that in lasers with 40-nm-thick OCL indicated poor efficiency and a slightly higher
threshold.
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