| 1. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Electronic Properties of Ga(In)NAs Alloys
- 2001
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Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- A brief review on the present knowledge of the electronic properties of the Ga(In)NAs ternary and quaternary alloys is given mainly from an experimental perspective. The discussion is focused on Ga(In)NAs with low N composition (< 10 %), where a large amount of experimental work has been done. Important fundamental electronic properties of the material system are analyzed with the emphasis on the nature of the giant band gap bowing in the alloy and nitrogen-induced modifications of the electronic structure of the conduction band. The current knowledge of the key material parameters, relevant for the device applications, such as electron effective mass, recombination processes and band alignment in Ga(In)NAs/GaAs heterostructures, is also reviewed.
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| 2. |
- Goldys, EM, et al.
(författare)
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Characterization of red emission in nominally undoped hydride vapor phase epitaxy GaN
- 2001
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Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 6:1, s. art. no.-1
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Tidskriftsartikel (refereegranskat)abstract
- We report characterization of the red emission band in hydride vapor phase epitaxial GaN using cathodoluminescence spectroscopy and imaging and time-resolved photoluminescence. The observed properties of the emission are consistent with recombination of excitons bound at close donor-acceptor pairs. The time evolution of the emission signal during electron beam irradiation supports the association of the red emission with charged centres.
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| 3. |
- Monemar, Bo, et al.
(författare)
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Photoluminescence in n-doped In0.1Ga0.9N/In0.01Ga0.99N multiple quantum wells
- 2002
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Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 7:7, s. 1-
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Tidskriftsartikel (refereegranskat)abstract
- In0.1Ga0.9N/In0.01Ga0.99N multiple quantum wells (MQWs) with heavily Si-doped barriers, grown with Metal Organic Vapor Phase Epitaxy (MOVPE) at about 800(0)C, have been studied in detail with optical spectroscopy. Such structures are shown to be very sensitive to a near surface depletion field, and if no additional layer is grown on top of the MQW structure the optical spectra from the individual QWs are expected to be drastically different. For a sample with 3 near surface QWs and Si-doped barriers, only the QW most distant from the surface is observed in photoluminescence (PL). The strong surface depletion field is suggested to explain these results, so that the QWs closer to the surface cannot hold the photo-excited carriers. A similar effect of the strong depletion field is found in an LED structure where the MQW is positioned at the highly doped n-side of the pn-junction. The internal polarization induced electric field in the QWs is also rather strong, and incompletely screened by carriers transferred from the doped barriers. The observed PL emission for this QW is of localized exciton character, consistent with the temperature dependence of peak position and PL decay time. The excitonic lineshape of 35-40 meV in the QW PL is explained as caused by a combination of random alloy fluctuations and interface roughness, the corresponding localization potentials are also responsible for the localization of the excitons in the low temperature range (
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| 4. |
- 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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| 5. |
- Petersson, A, et al.
(författare)
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Compositional variation of AlGaN epitaxial films on 6H-SiC substrates determined by cathodoluminescence.
- 2002
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Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 7:5
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Tidskriftsartikel (refereegranskat)abstract
- High quality epitaxial films of A(l)xGa(1-x)N, grown on SiC substrates, were investigated using spatially resolved cathodoluminescence (CL), scanning electron microscopy, and atomic force microscopy. A variation in the observed peak energy position of the CL was related to alloy fluctuations. CL was used to reveal relative alloy fluctuations of approximately 1% on a sub-micrometer scale, with a precision difficult to surpass with other available techniques. By correlating data from the different techniques, a model was derived. The main feature of it is an alloy fluctuation on the micrometer scale, seeded during the initial growth and extending through the epitaxial film. These alloy fluctuations seems to be related to terrace steps ( approximate to5 nm in height), formed preferentially at scratches on the SiC surface. This investigation indicates that the initial growth of epitaxial films is critical and structures formed at the beginning of the growth tend to persist throughout the growth. Further, a strain gradient from the SiC interface extending towards the surface, was observed.
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| 6. |
- Torres, V.J.B., et al.
(författare)
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Theoretical studies of hydrogen passivated substitutional magnesium acceptor in wurzite GaN
- 1997
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Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- Infrared measurements on wurzite GaN codoped with Mg and H reveal strong absorption at 3125 cm-1, Theorectical work provides strong evidence for the H being antibonding to N. We have performed an ab-initio study of Mg-H complexes in wurzite GaN, using the Local Density Approximation on a large H-terminated cluster MgHGa25N26H42. We have investigated the physical properties of three neutral configurations along the c direction. In all configurations Mg sits in a gallium substitutional site. H is then located in the Mg-N bond centre (BC), in the antibonding site on nitrogen side (ABN) or in the antibonding position on magnesium side (AB Mg). We found the lowest total energy configuration is hydrogen in the antibonding on the nitrogen site. The stretch mode in this configuration is calculated at 3277 cm-1 which agrees with experiment and previous LDA calculations and we predict an unreported infra red active wag mode at 1311 cm-1. The experimental isotopic shift with D is well reproduced. The BC and ABMg configurations are 0.5 and 3.7eV higher, producing local modes at 3645 and 2144cm-1, respectively. No wag modes appear for the BC and ABMg configurations.
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