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ABSTRACT: Electronic states of two-dimensional conduction subbands (CSs) accompanied by complex exciton and impurity states, caused by modulation-doping in InGaAs/InAlAs quantum wells (QWs), were studied by magneto-photoluminescence (MPL) at 1.4 K below 13 Tesla. MPL peak energies of two specimens were analyzed as a function of magnetic field. Up to four or five Landau levels (LLs) in CSs were resolved below the Fermi level. LLs were duty assigned to fit theoretical LL energies in nonparabolic CSs. Experimental LL energy differences in CSs, determined by infrared cyclotron resonance, were larger by about 6 meV than corresponding MPL peak energy difference. The difference was tentatively assigned to the difference in magneto-exciton binding energies, accompanied by LLs in CSs. The difference of binding energy changed like a kink with changing B and was possibly affected by valence band mixing at LLs. The effect of QW structure was discussed in relation to an impurity-related multiple exciton model.
Indium Phosphide and Related Materials Conference, 2002. IPRM. 14th; 02/2002
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ABSTRACT: Energies of interband optical transition in InGaAs/InAlAs multi-quantum well (MQW) structures were studied using one undoped and two n-type modulation-doped specimens grown by MBE. Step-like allowed transitions were observed and identified between 120 K and 330 K. In a 10 nm-thick quantum well (QW), three typical eigen states of the conduction subband (CS) were discriminated in a 0.52 eV range of energy in the QW. Doped and undoped MQW specimens had almost the same transition energies from the valence subband to the CSs. In a highly doped specimen of 1.5×10<sup>12</sup> cm<sup>-2</sup> electrons per QW, the inter-ground-state optical transition was prohibited by the band filling effect. In the low doped specimen of 5×10<sup>11</sup> cm<sup>-2</sup> electrons per QW, however, the same transition below the Fermi energy level was observed at 120 K. Moreover, localized states or an impurity band with an activation energy of 25 meV associated with the ground and the second higher CSs, were observed. No localized state was observed in the undoped ones.
Indium Phosphide and Related Materials Conference, 2002. IPRM. 14th; 02/2002
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ABSTRACT: Interband magneto-photoluminescence (MPL) spectra in n-type InGaAs/InAlAs quantum wells (QWs) lattice-matched to InP were measured between 1.4 and 275 K. From a fan chart of MPL peak energy vs. magnetic field, assignment of Landau levels (LLs) associated with conduction subband (CS) was made consistently. Two series of LL peak energies with different Landau quantum number was subtracted to cancel the effects of complex valence subband states and bandgap renormalization, etc. The energy difference of two CS LL peak series in the MPL fan chart, between Landau quantum number 0 and 1, did not agree with the measured cyclotron resonance (CR) energy or the related theoretical CS LL energy difference. The difference was 6–10 meV at 1.4 K near 10 T. Temperature dependence of the difference of CS LL peak energies was studied and the difference tended to diminish at 175–275 K. The behavior suggested that the quantity was the difference of magneto-exciton binding energy and that the exciton states were merged into LLs at higher temperature. A band parameter, Ep, in nonparabolic band theory was discussed.
Microelectronic Engineering 63:301-307. · 1.56 Impact Factor
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ABSTRACT: Nonparabolic effective masses of conduction electrons were comprehensively studied in two-dimensional InGaAs quantum wells (QWs) deeply confined within InAlAs barriers of the 0.52-eV band offset. Cause of nonparabolicity was attributed not to the penetration of wavefunctions into barriers but to the InGaAs bulk band structure of bandgap energy of 0.74 eV. Band calculations by a Kane's three-level model for narrow-gap semiconductors and a Zawadzki's model under Landau quantization modified for QW confinement were fairly compared with in-plane apparent cyclotron masses of electrons measured in a 10-nm-wide InGaAs QW. Simulation of optical transmittance through complex epitaxial wafer structures fit quite well with cyclotron resonance experiments. Masses normal to the QW plane were also determined from a series of eigen-energies observed in 20-nm-wide InGaAs QW. In-plane nonparabolicity was found to be several times larger than normal nonparabolicity.
Physica B: Condensed Matter.
