Blue luminescence from ultrathin GaAs layers embedded in AlAs
Our investigations focus on low-temperature luminescence experiments on a set of type-II GaAs/AlAs multiple-quantum-well (MQW) samples grown by low-pressure metal-organic vapor-phase epitaxy. The layered structures consists of 50 periods of either 2 monolayers (ML), 4, 5, 6, or 7 ML GaAs embedded in 28 ML AlAs. For (001) GaAs substrates, 6 degrees misoriented towards the nearest (111) plane of group-V atoms, monolayer steps at the AlAs/GaAs interfaces with regular terrace widths (2.7 nm) can be seen by high-resolution transmission-electron microscopy. In the photoluminescence spectra of these MQW samples, type-I luminescence is found to be dominant even at room temperature. The peak wavelength of the type-I emission depends strongly on the GaAs layer thickness; it ranges from about 620-440 nm. The intense type-I emission seems to be connected with the interface peculiarities. Our astonishing observation might be explained as follows: (i) The perfect interface structure pl events the loss of photoexcited carriers from GaAs layers to the surrounding AlAs materials, i.e., the energy loss by optical-phonon scattering is reduced. (ii) For our well thicknesses two-dimensional (2D) phonons must be coupled with 3D electrons leading also to a reduction of the electron-phonon interaction. (iii) The regular interface steps should favor a coherent interaction (quantum interferences) of excitons and/or electrons confined in the GaAs wells with energetically resonant continuum states of the AlAs barriers. The experimentally observed optical transition energies of the type-I and type-II recombination are compared with model calculations applying an effective-mass approach and empirical tight-binding Green's-function scheme.
WOS:A1997XV00700009
1997
56
8
R4329
R4332
Univ leipzig, fac chem, d-04103 leipzig, germany. swiss fed inst technol, dept phys, ph ecublens, ch-1015 lausanne, switzerland. Schwabe, R, UNIV LEIPZIG, FAC PHYS, LINNESTR 3-5, D-04103 LEIPZIG, GERMANY.
ISI Document Delivery No.: XV007
Cited Reference Count: 15
Cited References:
BOSIO C, 1988, PHYS REV B, V38, P3263
DAWSON P, 1990, SEMICOND SCI TECH, V5, P54
DIVENTRA M, 1997, PHYS REV B, V55, P13148
FELDMANN J, 1989, PHYS REV LETT, V62, P1892
FU LP, 1995, PHYS REV B, V51, P17630
ISHIBASHI A, 1986, P 18 INT C PHYS SEM, V2, P1365
MAAREF M, 1992, PHYS STATUS SOLIDI B, V170, P637
MADER KA, 1992, P INT M OPT EXC CONF, P341
MADER KA, 1992, THESIS SWISS FED I T
MASCHKE K, 1992, PHYS REV LETT, V67, P2646
MEYNADIER MH, 1988, PHYS REV LETT, V60, P1338
MOORE KJ, 1989, SPECTROSCOPY SEMICON, P293
NUNNENKAMP J, 1990, TECH DIG, V6, P94
OELGART G, 1994, PHYS REV B, V49, P10456
PLANEL R, 1993, J PHYS IV, V3, P159
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