| Budget Amount *help |
¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2003: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2002: ¥600,000 (Direct Cost: ¥600,000)
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| Research Abstract |
Quantum confined states of the In_<0.53>Ga_<0.47>As/In_<0.52>Al_<0.48>As multi-quantum well structures (MQWs) fabricated with molecular beam epitaxy equipment (MBE) were studied using the photocurrent spectroscopy and the optical transmission spectroscopy.
The optical current spectra of three kinds of undoped MQWs structures, which had different well width (each well width 5, 9.4, 20nm), showed steplike structure and optical interband transitions were observed clearly. In the careful analysis using two or more photocurrent spectra and the difference of those obtained by applying bias voltage, allowed interband transitions having same quantum numbers and forbidden interband transitions having different quantum numbers were assigned between conduction subband and valence subband and eigen-energies of these subbands had been determined. By fitting the experimental eigen-energies of the subbands to the envelope function approximation, and band offset and effective mass of hole, and electron
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to a normal direction to the MQWs layers are determined. It depended for electron effective mass on the energy of corresponding conduction subband. When it assumes that electron effective-mass changes gently to energy and this mass at the bottom of a conduction well was 0.041m_0 as much as as the effective mass at the bandedge end of bulk, the energy dependability of subband with the small number or low eigen-energy can also fully be taken into consideration, and electron effective mass can be expressed with the secondary function of energy. Electron effective mass was increased from 0.041m_0 to 0.08m_0.
Also in the optical transmission spectroscopy to a undoped MQWs structure and two kinds of modulation-doped MQWs, structure with 10 nm well width, these spectra became steplike and allowed interband transitions were observed. About the modulation-doped specimens (1.5x10^<12> cm^<-2> 0.5x10^<12> cm^<-2>) the interband transitions between both ground states which were lower than Fermi Level were not observed by band filling effect of the electric charge within the MQWs structure. There is almost no temperature dependability in the steplike structure of the spectra measured at the temperature of 100K-330K, and the changes of transition energies were only dependent on the band gap energy of a well layer. Moreover, the, spectra of the absorption coefficient by integration of each wave function have expressed the optical transmission spectra.
The eigen-energy and the interbnad transition energy, which were calculated with the Poisson equation of an electric charge distribution and envelope function approximation model using physical-properties parameters, such as effective mass, well agreed with an photocurrent and optical transmission experiment and the quantification of the wave function and effective mass were able to perform on the In_<0.53>Ga_<0.47>As/In_<0.52>Al_<0.48>As MQWs. Less
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