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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

(a) (200) DF TEM image of the sample and (b) intensity profile across it along the negative growth direction. In (a), the nominal GaAs QW is the dark stripe between InGaP and AlGaAs and corresponds to the downward peak between InGaP and AlGaAs in (b). The profile (b) clearly shows that it exhibits a contrast darker than the GaAs substrate/buffer (at the right-hand side). (c) High-magnification (200) DF image of the GaAs QW. The image has been treated with Adobe Photoshop to improve the visibility of the extra layer in proximity of the GaAs-on-InGaP interface.
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Figure 2: (a) (200) DF TEM image of the sample and (b) intensity profile across it along the negative growth direction. In (a), the nominal GaAs QW is the dark stripe between InGaP and AlGaAs and corresponds to the downward peak between InGaP and AlGaAs in (b). The profile (b) clearly shows that it exhibits a contrast darker than the GaAs substrate/buffer (at the right-hand side). (c) High-magnification (200) DF image of the GaAs QW. The image has been treated with Adobe Photoshop to improve the visibility of the extra layer in proximity of the GaAs-on-InGaP interface.

Mentions: To check the reason for such anomalous emission, TEM (200) DF and STEM-HAADF were applied. Figure 2 shows the (200) DF TEM image of the sample. The nominal GaAs QW layer is the dark stripe between InGaP and AlGaAs. It exhibits a contrast darker than the GaAs substrate/buffer as seen in Figure 2b. This suggests that this layer is not GaAs. Figure 2c shows the high-magnification image of the nominal QW showing two different contrasts inside it in agreement with the profile of Figure 2b, confirming that the nominal QW is made up of two sublayers, as could also be concluded from Figure 2b. As the images were acquired in thin areas of the TEM specimen, the kinematical approximation is used, according to which the (200) DF intensity I200 is proportional to , with F200 as the structure factor of the (200) diffraction that depends on the atomic scattering factors f of the elements in the III-V compound as it is F200 = 4(fIII - fV) [14-16]. To evaluate composition, the DF contrast function C200, which is defined as the ratio between the (200) DF intensity diffracted by a given layer of general form AxB1-xCyD1-y and that diffracted by GaAs, is used. An alloy looks darker than GaAs when C200 is <1. C200 depends on the square of the composition as does [14-16] because fIII and fV have to be introduced in proportion to the relative composition of the element they refer to.


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)

(a) (200) DF TEM image of the sample and (b) intensity profile across it along the negative growth direction. In (a), the nominal GaAs QW is the dark stripe between InGaP and AlGaAs and corresponds to the downward peak between InGaP and AlGaAs in (b). The profile (b) clearly shows that it exhibits a contrast darker than the GaAs substrate/buffer (at the right-hand side). (c) High-magnification (200) DF image of the GaAs QW. The image has been treated with Adobe Photoshop to improve the visibility of the extra layer in proximity of the GaAs-on-InGaP interface.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: (a) (200) DF TEM image of the sample and (b) intensity profile across it along the negative growth direction. In (a), the nominal GaAs QW is the dark stripe between InGaP and AlGaAs and corresponds to the downward peak between InGaP and AlGaAs in (b). The profile (b) clearly shows that it exhibits a contrast darker than the GaAs substrate/buffer (at the right-hand side). (c) High-magnification (200) DF image of the GaAs QW. The image has been treated with Adobe Photoshop to improve the visibility of the extra layer in proximity of the GaAs-on-InGaP interface.
Mentions: To check the reason for such anomalous emission, TEM (200) DF and STEM-HAADF were applied. Figure 2 shows the (200) DF TEM image of the sample. The nominal GaAs QW layer is the dark stripe between InGaP and AlGaAs. It exhibits a contrast darker than the GaAs substrate/buffer as seen in Figure 2b. This suggests that this layer is not GaAs. Figure 2c shows the high-magnification image of the nominal QW showing two different contrasts inside it in agreement with the profile of Figure 2b, confirming that the nominal QW is made up of two sublayers, as could also be concluded from Figure 2b. As the images were acquired in thin areas of the TEM specimen, the kinematical approximation is used, according to which the (200) DF intensity I200 is proportional to , with F200 as the structure factor of the (200) diffraction that depends on the atomic scattering factors f of the elements in the III-V compound as it is F200 = 4(fIII - fV) [14-16]. To evaluate composition, the DF contrast function C200, which is defined as the ratio between the (200) DF intensity diffracted by a given layer of general form AxB1-xCyD1-y and that diffracted by GaAs, is used. An alloy looks darker than GaAs when C200 is <1. C200 depends on the square of the composition as does [14-16] because fIII and fV have to be introduced in proportion to the relative composition of the element they refer to.

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