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Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

Shih HY, Shiojiri M, Chen CH, Yu SF, Ko CT, Yang JR, Lin RM, Chen MJ - Sci Rep (2015)

Bottom Line: Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition.This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2).In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan.

ABSTRACT
High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2). In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

No MeSH data available.


Related in: MedlinePlus

HRTEM images.(a,e) HRTEM images of the PDA-treated ALD compliant BL and sapphire substrate without the overlying GaN epilayer (a) and with the overlying GaN epilayer (e) grown by MOCVD. (b–d) FFT diffractograms of the areas enclosed in the upper and the bottom regions of the ALD compliant BL, and the sapphire in (a), respectively. (f,j) HRTEM images of the PDA-treated MOCVD NL and sapphire substrate without the overlying GaN epilayer (f) and with the overlying GaN epilayer (j) grown by MOCVD. A TD is indicated in (j), which was taken by a condition so as to excite exclusively the 0002 reflections and off any hki0 reflections of GaN. (g–i) FFT diffractograms of the areas enclosed in the upper and the bottom regions of the MOCVD NL, and the sapphire in (f), respectively. (k,l) show schematic diagrams of the ALD compliant BL and MOCVD NL, respectively.
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f3: HRTEM images.(a,e) HRTEM images of the PDA-treated ALD compliant BL and sapphire substrate without the overlying GaN epilayer (a) and with the overlying GaN epilayer (e) grown by MOCVD. (b–d) FFT diffractograms of the areas enclosed in the upper and the bottom regions of the ALD compliant BL, and the sapphire in (a), respectively. (f,j) HRTEM images of the PDA-treated MOCVD NL and sapphire substrate without the overlying GaN epilayer (f) and with the overlying GaN epilayer (j) grown by MOCVD. A TD is indicated in (j), which was taken by a condition so as to excite exclusively the 0002 reflections and off any hki0 reflections of GaN. (g–i) FFT diffractograms of the areas enclosed in the upper and the bottom regions of the MOCVD NL, and the sapphire in (f), respectively. (k,l) show schematic diagrams of the ALD compliant BL and MOCVD NL, respectively.

Mentions: Figure 3(a) displays a high-resolution transmission electron microscopy (HRTEM) image of the cross section including the ALD compliant BL and sapphire substrate. The fast Fourier transform (FFT) diffractograms shown in Fig. 3(b–d) refer to the areas enclosed in the upper region of the ALD compliant BL, the bottom region of the ALD compliant BL, and the sapphire substrate, respectively. The diffractograms in Fig. 3(b,d) show that a single crystal of GaN with the wurtzite structure grew with the following epitaxial relation with respect to the substrate: [0001] GaN // [0001] sapphire and . As shown in Fig. 1(a), the as-deposited GaN is composed of fine grains exhibiting the diffuse (0002) XRD peak. The coalescence and recrystallization of the fine grains caused by the PDA treatment lead to a nearly perfect single crystal with a strong (0002) XRD peak. Figure 3(e) shows an HRTEM image of the overlying GaN epilayer, the ALD compliant BL and sapphire substrate in the InGaN/GaN LED structure. As shown in Fig. 3(a,e), the lattice distortion can be observed in the BL, but it is only within ~10 nm from the interface. An influence of the substrate lattice is seen in this region near the interface where the GaN lattice is heavily distorted, which is clearly recognized by comparing the FFT diffractograms shown in Fig. 3(b,c). This heavily distorted GaN may absorb the misfit dislocations generated by the large lattice mismatch and thus prevent these dislocations from propagating into the overlying GaN epilayer, as shown schematically in Fig. 3(k). As a result, the strain caused by lattice misfit is relaxed within this heavily distorted region, leading to the near strain-free ALD compliant BL as revealed by the PL and Raman spectroscopy shown in Figs 1(b) and 2(a).


Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

Shih HY, Shiojiri M, Chen CH, Yu SF, Ko CT, Yang JR, Lin RM, Chen MJ - Sci Rep (2015)

HRTEM images.(a,e) HRTEM images of the PDA-treated ALD compliant BL and sapphire substrate without the overlying GaN epilayer (a) and with the overlying GaN epilayer (e) grown by MOCVD. (b–d) FFT diffractograms of the areas enclosed in the upper and the bottom regions of the ALD compliant BL, and the sapphire in (a), respectively. (f,j) HRTEM images of the PDA-treated MOCVD NL and sapphire substrate without the overlying GaN epilayer (f) and with the overlying GaN epilayer (j) grown by MOCVD. A TD is indicated in (j), which was taken by a condition so as to excite exclusively the 0002 reflections and off any hki0 reflections of GaN. (g–i) FFT diffractograms of the areas enclosed in the upper and the bottom regions of the MOCVD NL, and the sapphire in (f), respectively. (k,l) show schematic diagrams of the ALD compliant BL and MOCVD NL, respectively.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4556983&req=5

f3: HRTEM images.(a,e) HRTEM images of the PDA-treated ALD compliant BL and sapphire substrate without the overlying GaN epilayer (a) and with the overlying GaN epilayer (e) grown by MOCVD. (b–d) FFT diffractograms of the areas enclosed in the upper and the bottom regions of the ALD compliant BL, and the sapphire in (a), respectively. (f,j) HRTEM images of the PDA-treated MOCVD NL and sapphire substrate without the overlying GaN epilayer (f) and with the overlying GaN epilayer (j) grown by MOCVD. A TD is indicated in (j), which was taken by a condition so as to excite exclusively the 0002 reflections and off any hki0 reflections of GaN. (g–i) FFT diffractograms of the areas enclosed in the upper and the bottom regions of the MOCVD NL, and the sapphire in (f), respectively. (k,l) show schematic diagrams of the ALD compliant BL and MOCVD NL, respectively.
Mentions: Figure 3(a) displays a high-resolution transmission electron microscopy (HRTEM) image of the cross section including the ALD compliant BL and sapphire substrate. The fast Fourier transform (FFT) diffractograms shown in Fig. 3(b–d) refer to the areas enclosed in the upper region of the ALD compliant BL, the bottom region of the ALD compliant BL, and the sapphire substrate, respectively. The diffractograms in Fig. 3(b,d) show that a single crystal of GaN with the wurtzite structure grew with the following epitaxial relation with respect to the substrate: [0001] GaN // [0001] sapphire and . As shown in Fig. 1(a), the as-deposited GaN is composed of fine grains exhibiting the diffuse (0002) XRD peak. The coalescence and recrystallization of the fine grains caused by the PDA treatment lead to a nearly perfect single crystal with a strong (0002) XRD peak. Figure 3(e) shows an HRTEM image of the overlying GaN epilayer, the ALD compliant BL and sapphire substrate in the InGaN/GaN LED structure. As shown in Fig. 3(a,e), the lattice distortion can be observed in the BL, but it is only within ~10 nm from the interface. An influence of the substrate lattice is seen in this region near the interface where the GaN lattice is heavily distorted, which is clearly recognized by comparing the FFT diffractograms shown in Fig. 3(b,c). This heavily distorted GaN may absorb the misfit dislocations generated by the large lattice mismatch and thus prevent these dislocations from propagating into the overlying GaN epilayer, as shown schematically in Fig. 3(k). As a result, the strain caused by lattice misfit is relaxed within this heavily distorted region, leading to the near strain-free ALD compliant BL as revealed by the PL and Raman spectroscopy shown in Figs 1(b) and 2(a).

Bottom Line: Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition.This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2).In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan.

ABSTRACT
High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2). In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

No MeSH data available.


Related in: MedlinePlus