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Chemical characterization of extra layers at the interfaces in MOCVD InGaP/GaAs junctions by electron beam methods.

Frigeri C, Shakhmin AA, Vinokurov DA, Zamoryanskaya MV - Nanoscale Res Lett (2011)

Bottom Line: A CL emission peak different from that of the QW was detected.By using HAADF, it is found that the GaAs QW does not exist any longer, being replaced by extra interlayer(s) that are different from GaAs and InGaP because of atomic rearrangements at the interface.The nature and composition of the interlayer(s) are determined by HAADF.

View Article: PubMed Central - HTML - PubMed

Affiliation: CNR-IMEM Institute, Parco Area delle Scienze 37/A, 43010 Parma, Italy. frigeri@imem.cnr.it.

ABSTRACT
Electron beam methods, such as cathodoluminescence (CL) that is based on an electron-probe microanalyser, and (200) dark field and high angle annular dark field (HAADF) in a scanning transmission electron microscope, are used to study the deterioration of interfaces in InGaP/GaAs system with the GaAs QW on top of InGaP. A CL emission peak different from that of the QW was detected. By using HAADF, it is found that the GaAs QW does not exist any longer, being replaced by extra interlayer(s) that are different from GaAs and InGaP because of atomic rearrangements at the interface. The nature and composition of the interlayer(s) are determined by HAADF. Such changes of the nominal GaAs QW can account for the emission observed by CL.

No MeSH data available.


Related in: MedlinePlus

Choice of the exponent n. Calculated HAADF intensity ratios between the three inner standards, taken two by two, for n = 1.7 (black dash and dot line, dark lozenges) and n = 2 (blue solid line, blue circles) as compared to the relevant experimental ratios (red solid line, red squares). Within experimental errors, exponent n = 2 fits very well to the experiment.
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Figure 5: Choice of the exponent n. Calculated HAADF intensity ratios between the three inner standards, taken two by two, for n = 1.7 (black dash and dot line, dark lozenges) and n = 2 (blue solid line, blue circles) as compared to the relevant experimental ratios (red solid line, red squares). Within experimental errors, exponent n = 2 fits very well to the experiment.

Mentions: The HAADF image is formed by collecting the incoherently scattered electrons at high angles [17,18]. Single atoms scatter incoherently, and the image intensity is the sum of the individual atomic scattering contributions [19]. The higher the atomic number Z, the larger the scattering angle is. The HAADF intensity turns out to be proportional to Zn, with n = 2 [17,18,20], so that a more direct evaluation of the composition is possible. Such dependence could also take other values for the exponent n, i.e. 1.7 <n < 2 [20]. Here it is assumed that n = 2. This choice stems from the fact that only the exponent 2 can fully account for our experimental ratios of the intensities of every couple of layers of known composition in the structures (GaAs substrate/buffer, In0.51Ga0.49P, Al0.26Ga0.74As, taken as two by two) as shown in Figure 5, where the calculated HAADF intensity ratios for the two extreme cases of n = 1.7 and n = 2 are compared with the experimental ratios. The best agreement between the calculated rations and those of the experiment is obtained for n = 2.


Chemical characterization of extra layers at the interfaces in MOCVD InGaP/GaAs junctions by electron beam methods.

Frigeri C, Shakhmin AA, Vinokurov DA, Zamoryanskaya MV - Nanoscale Res Lett (2011)

Choice of the exponent n. Calculated HAADF intensity ratios between the three inner standards, taken two by two, for n = 1.7 (black dash and dot line, dark lozenges) and n = 2 (blue solid line, blue circles) as compared to the relevant experimental ratios (red solid line, red squares). Within experimental errors, exponent n = 2 fits very well to the experiment.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211250&req=5

Figure 5: Choice of the exponent n. Calculated HAADF intensity ratios between the three inner standards, taken two by two, for n = 1.7 (black dash and dot line, dark lozenges) and n = 2 (blue solid line, blue circles) as compared to the relevant experimental ratios (red solid line, red squares). Within experimental errors, exponent n = 2 fits very well to the experiment.
Mentions: The HAADF image is formed by collecting the incoherently scattered electrons at high angles [17,18]. Single atoms scatter incoherently, and the image intensity is the sum of the individual atomic scattering contributions [19]. The higher the atomic number Z, the larger the scattering angle is. The HAADF intensity turns out to be proportional to Zn, with n = 2 [17,18,20], so that a more direct evaluation of the composition is possible. Such dependence could also take other values for the exponent n, i.e. 1.7 <n < 2 [20]. Here it is assumed that n = 2. This choice stems from the fact that only the exponent 2 can fully account for our experimental ratios of the intensities of every couple of layers of known composition in the structures (GaAs substrate/buffer, In0.51Ga0.49P, Al0.26Ga0.74As, taken as two by two) as shown in Figure 5, where the calculated HAADF intensity ratios for the two extreme cases of n = 1.7 and n = 2 are compared with the experimental ratios. The best agreement between the calculated rations and those of the experiment is obtained for n = 2.

Bottom Line: A CL emission peak different from that of the QW was detected.By using HAADF, it is found that the GaAs QW does not exist any longer, being replaced by extra interlayer(s) that are different from GaAs and InGaP because of atomic rearrangements at the interface.The nature and composition of the interlayer(s) are determined by HAADF.

View Article: PubMed Central - HTML - PubMed

Affiliation: CNR-IMEM Institute, Parco Area delle Scienze 37/A, 43010 Parma, Italy. frigeri@imem.cnr.it.

ABSTRACT
Electron beam methods, such as cathodoluminescence (CL) that is based on an electron-probe microanalyser, and (200) dark field and high angle annular dark field (HAADF) in a scanning transmission electron microscope, are used to study the deterioration of interfaces in InGaP/GaAs system with the GaAs QW on top of InGaP. A CL emission peak different from that of the QW was detected. By using HAADF, it is found that the GaAs QW does not exist any longer, being replaced by extra interlayer(s) that are different from GaAs and InGaP because of atomic rearrangements at the interface. The nature and composition of the interlayer(s) are determined by HAADF. Such changes of the nominal GaAs QW can account for the emission observed by CL.

No MeSH data available.


Related in: MedlinePlus