S. Nagao's scientific contributions
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Publications (9)
The phonon bottleneck effect is studied in InAs/GaInP quantum dots (QDs). The time-resolved photoluminescence spectra from the lowest (n=1) and second lowest (n=2) exciton states in QDs are measured in the temperature range of 5–200K. We find that the rise time of the n=1 level is about 500ps when the excitation energy is in resonance with the n=2...
The improvement of the characteristic temperature is one of the superior performances that are expected to QD-LD. However, the temperature characteristic has deteriorated at room temperature. As one of the cause, the thermal escape of the carrier from QD to wetting layer or matrix is considered. The (Al1-xGax)0.5In0.5P/InAs system has large band-di...
We studied the growth of self-assembled InAs quantum dots (QDs) on GaInP using solid source molecular beam epitaxy (MBE) with the aim of reducing the thermionic escape of bound carriers by burying the QDs in large bandgap materials such as GaInP. The density and size of QDs were measured by atomic force microscopy (AFM). This showed that InAs QDs w...
We have found that a large number of dislocation loops of interstitial type are introduced in the active region of (Al)GaInP strained triple quantum wells (STQW) lasers by the effect of laser operation. These loops were always generated in the lasers, the driving current of which increased gradually as operating time increased. We have shown that t...
We have studied the effect of oxygen incorporation into AlGaInP on carrier recombination in GaInP/AlGaInP double heterostructures (DH) grown by MBE using a solid phosphorus valved cell. It was found that photoluminescence efficiency and interfacial recombination velocity of the DH were determined by residual oxygen concentration in the AlGaInP laye...
We have performed high-pressure and time-resolved photoluminescence (PL) measurements on GaP/AlP/GaP quantum wells with AlP well width of 1 to 8 monolayers at liquid helium temperature. Experimental results show that the lowest confined electron states in the AlP wells are almost pure X states, and the high efficiency of the luminescence is due to...
We have studied time-resolved photoluminescence (PL) of type-II GaP/AlP/GaP quantum wells with different well widths and acquired detailed information concerning the mechanisms of the radiative recombination. At low temperatures, the PL spectra consist mainly of a no-phonon line. The decay of the no-phonon line was slow and nonexponential. The deca...
We have studied both continuous-wave and time-resolved photoluminescence from type-II GaP/AlP/GaP quantum wells with thickness of 1, 2, 3, 5, and 8 monolayers. Highly efficient no-phonon luminescence was observed at low temperatures, indicating long-lived temporal behavior. Photoluminescence results indicated that the lowest confined electron state...
GaAs quantum wires (QWIs) buried on a V-shaped groove were successfully fabricated by the selective-area in-situ gas etching and regrowth processes in the metalorganic vapor phase epitaxy (MOVPE) reactor. The V-shaped groove formation by in-situ HCl gas etching and the behavior of selective growth in the V-groove were investigated. From the detail...
Citations
... Note that combination of two different 2D semiconductor to form superlattices or heterostructures, the intrinsic band offset, 38 and built-in layer-thickness 43 due to different stacked order play important roles to tune the bandgap values. 44,45 The former usually leads to lower bandgap than the bandgap of homogenous 2D semiconductor, 17,42 while the later can lead to varying of bandgap values 46 though it is generally uncontrollable in experiment. ...
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... This is significantly lower than the critical thickness of $1.6 ML for initialising InAs/GaAs QD growth via the Stranski-Krastanov (SK) mode. In general, the large clusters with irregular shapes are defective [19][20][21]. The formation of defective clusters can be explained by the aggregation of QDs due to the diffusion of In atoms from the InGaP buffer layer to the InAs QDs [22][23][24]. ...
... Another critical issue is the growth of QDs with proper size and composition so as to produce a transition energy of the order of 1.24 eV between the valence band (or hole ground state) and their electronic ground state level and, consequently, of 0.71 eV between the electronic ground state of the QDs and the barrier conduction band. In the case of InAs QDs on InGaP, the control of their composition can be critical due to the intermixing between As and P at the interface [13]. ...
... The first model has a function IðtÞ / ð1 þ 2CtÞ Àb , which accounts for the distribution of the C-X mixing amplitude at the random heterointerface. The model describes the luminescence dynamics of type-II short-period superlattices 24,25 and quantum wires. 26 The second model is a stretched exponential function IðtÞ / e Àðt=sÞ b , which accounts for distributed lifetimes in strongly inhomogeneous systems. ...
... Recently, the efficient two-step photon absorption has been theoretically predicted by inserting closely stacked InAs QDs into a high-bandgap InGaP matrix [15]. In addition, this material system is well known for its strong phonon bottleneck effect at low temperature due to the large confinement for carriers [16]. Well aligned In 0.4 Ga 0.6 As/GaAs QDs were grown in InGaP matrix, which form a larger energy separation between the QD ground state and the conduction band edge in comparison to conventional InAs/ GaAs QDs [17]. ...
