| 1. |
- Monemar, Bo, et al.
(författare)
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Radiative recombination in In0.15Ga0.85N/GaN multiple quantum well structures
- 1999
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Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 4:16
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of the radiative recombination in In0.15Ga0.85N/GaN multiple quantum well samples, where the conditions of growth of the InGaN quantum layers were varied in terms of growth temperature (< 800 degrees C) and donor doping. The photoluminescence peak position varies strongly (over a range as large as 0.3 eV) with delay time after pulsed excitation, but also with donor doping and with excitation intensity. The peak position is mainly determined by the Stark effect induced by the piezoelectric field. In addition potential fluctuations, originating from segregation effects in the InGaN material, from interface roughness, and the strain fluctuations related to these phenomena, play an important role, and largely determine the width of the emission. These potential fluctuations may be as large as 0.2 eV in the present samples, and appear to be important for all studied growth temperatures for the InGaN layers. Screening effects from donor electrons and excited electron-hole pairs are important, and account for a large part of the spectral shift with donor doping (an upward shift of the photoluminescence peak up to 0.2 eV is observed for a Si donor density of 2 x 10(18) cm(-3) in the well), with excitation intensity and with delay time after pulsed excitation (also shifts up to 0.2 eV). We suggest a two-dimensional model for electron- and donor screening in this case, which is in reasonable agreement with the observed data, if rather strong localization potentials of short range (of the order 100 Angstrom) are present. The possibility that excitons as well as shallow donors are impact ionized by electrons in the rather strong lateral potential fluctuations present at this In composition is discussed.
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| 2. |
- da Silva, AF, et al.
(författare)
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Impurity resistivity of the double-donor system Si : P,Bi
- 1999
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 60:23, s. 15824-15828
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Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity of the shallow double-donor system Si:P,Bi, prepared by ion implantation, was investigated in the temperature range from 1.7 to 300 K. Good agreement was obtained between the measured resistivities and resistivities calculated by a generalized Drude approach for the same temperatures and dopant concentrations. The critical impurity concentration for the metal-nonmetal transition for the double-doped Si:P,Bi system was found to lie between the critical concentrations of the two single-doped systems, Si:P and Si:Bi. [S0163-1829(99)11747-8].
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| 3. |
- Persson, C, et al.
(författare)
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Doping-induced effects on the band structure in n-type 3C-, 2H-, 4H-, 6H-SiC, and Si
- 1999
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 60:24, s. 16479-16493
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Tidskriftsartikel (refereegranskat)abstract
- Doping-induced energy shifts of the lowest conduction band and the uppermost valence band have been calculated for n-type 3 C-, 2H-, 4H-, 6H-SiC, and Si. We present the resulting narrowing of the fundamental band gap and of the optical band gap as functions of donor concentration. The effects on the curvature of the lowest conduction band have been investigated in detail for 3C- and 6H-SiC and, moreover, the effective electron masses in the vicinity of the conduction-band minimum have been calculated for,all five materials. The calculations go beyond the common parabolic treatments of the ground-state energy dispersion by using energy dispersion and overlap integrals from band structure calculations. The nonparabolic valence-band curvatures especially strongly influence the self-energies, but also the double-well minimum of 6H-SiC has effects on the self-energies and the resulting band curvatures. By comparing the total energy of the electron gas with the total energy of electrons in a nonmetal phase, we estimate the critical Mott concentration for the metal-nonmetal transition. The utilized method is based on a zero-temperature formalism within the random phase approximation with local field correction according to Hubbard. [S0163-1829(99)12647-X].
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