Byounggu Jo

Optical stability of shape-engineered InAs/InAlGaAs quantum dots

The optical properties of shape-engineered InAs/InAlGaAs quantum dots (SEQDs) were investigated by temperature-dependent and excitation-power-dependent photoluminescence (PL) spectroscopy and compared with those of the conventionally grown InAs QDs (CQDs). The emission wavelength of the InAs/InAlGaAs SEQDs at 240 K was redshifted by 18 nm from that at 15 K, which was relatively smaller than that of the InAs CQDs (97 nm). The PL yield at 240 K was reduced to 1/86 and 1/65 of that measured at 15 K for the InAs CQDs and the InAs/InAlGaAs SEQDs, respectively. The emission wavelength for the InAs CQDs was blueshifted by 76 nm with increasing excitation power from 0.56 to 188 mW, compared to only by 7 nm for the InAs/InAlGaAs SEQDs. These results indicated that the InAs/InAlGaAs SEQDs were optically more stable than the InAs CQDs mainly due to the enhancement of the carrier confinement in the vertical direction and the improvement in the size uniformity.

Carrier repopulation process for spatially-ordered InAs/InAlGaAs quantum dots

From the transmission electron microscope image, the seven-stacked InAs/InAlGaAs QDs on an InP substrate were spatially ordered instead of usual on-top vertical alignment. The increasing rate of the QD size became almost saturated by increasing the number of layers. The photoluminescence (PL) intensity for the seven-stacked InAs/InAlGaAs QDs was decreased up to 60K and remained almost stable at the temperature range from 60 to 220K. And then, the intensity was again drastically decreased with further increasing temperature. The emission peak was first red-shifted at the ratio of 0.446 meV/K from 20 to 60K. However, the degree of the red-shift in the emission peak from 60 to 220K was decreased at the negligibly small ratio of 0.028 meV/K. Above 220K, the emission peak was again significantly decreased at the ratio of 0.323 meV/K. While increasing the temperature, the carrier lifetimes obtained from the PL decay profiles for the seven-stacked QDs initially enhanced and then, almost stable at a certain tempe...

Optical Characteristics of Multi-Stacked InAs/InAlGaAs Quantum Dots

Self-assembled InAs/InAlGaAs quantum dots (QDs) grown on an InP (001) substrate have been investigated by using photoluminescence (PL) and time-resolved PL measurements. The single layer (QD1) and seven stacks (QD2) of InAs/InAlGaAs QDs grown by the conventional S-K growth mode were used. The PL peak at 10 K was 1,320 nm for both QD1 and QD2. As the temperature increases from 10 to 300 K, the PL peaks for QD1 and QD2 were red-shifted in the amount of 178 and 264 nm, respectively. For QD1, the PL decay increased with increasing emission wavelength from 1,216 to 1,320 nm, reaching a maximum decay time of 1.49 ns at 1,320 nm, and then decreased as the emission wavelength was increased further. However, the PL decay time for QD2 decreased continuously from 1.83 to 1.22 ns as the emission wavelength was increased from 1,130 to 1,600 nm, respectively. These PL and TRPL results for QD2 can be explained by the large variation in the QD size with stacking number caused by the phase separation of InAlGaAs.

High-power continuous-wave operation of InP-based InAs quantum-dot laser with dot-in-a-well structure and strain-modulating layer

We report continuous-wave (CW) operation of an InAs/InGaAsP quantum-dot (QD) heterostructure laser diode (LD) with an output power of 1.1?W at room temperature. This is the first observation on the laser output over 1?W from InAs QD-LDs fabricated on InP substrates. Also, the high-power lasing emission was successfully achieved at up to 60??C. The improvement in the lasing characteristics can be attributed to enhancement in modal gain of QD-LDs because of the increase in spatial carrier confinement around localized QD states by using a dot-in-a-well structure and a thin GaAs strain-modulating layer.

Optical Properties of InAs Quantum Dots Grown by Changing Arsenic Interruption Time

The optical properties of InAs quantum dots (QDs) grown on GaAs substrates grown by molecular beam epitaxy have been studied using photoluminescence (PL) and time-resolved PL measurements. InAs QDs were grown using an arsenic interruption growth (AIG) technique, in which the As flux was periodically interrupted by a closed As shutter during InAs QDs growth. In this study, the shutter of As source was periodically opened and closed for 1 (S1), 2 (S2), or 3 s (S3). For comparison, an InAs QD sample (S0) without As interruption was grown in a pure GaAs matrix for 20 s. The PL intensity of InAs QD samples grown by AIG technique is stronger than that of the reference sample (S0). While the PL peaks of S1 and S2 are redshifted compared to that of S0, the PL peak of S3 is blueshifted from that of S0. The increase of the PL intensity for the InAs QDs grown by AIG technique can be explained by the reduced InAs clusters, the increased QD density, the improved QD uniformity, and the improved aspect ratio (height/length). The redshift (blueshift) of the PL peak for S1 (S3) compared with that for S0 is attributed to the increase (decrease) in the QD average length compared to the average length of S0. The PL intensity, PL peak position, and PL decay time have been investigated as functions of temperature and emission wavelength. S2 shows no InAs clusters, the increased InAs QD density, the improved QD uniformity, and the improved QD aspect ratio. S2 also shows the strongest PL intensity and the longest PL decay time. These results indicate that the size (shape), density, and uniformity of InAs QDs can be controlled by using AIG technique. Therefore the emission wavelength and luminescence properties of InAs/GaAs QDs can also be controlled.