Microstructure investigation of semi-polar (11-22) GaN overgrown on differently designed micro-rod array templates

Taking advantage of electron diffraction based measurements, in a scanning electron microscope, can deliver non-destructive and quantitative information on extended defects in semiconductor thin films. In this work, we have studied a (11-22) semi-polar GaN thin film overgrown on regularly arrayed GaN micro-rod array templates grown by metal organic vapour phase epitaxy. We were able to optimise the diffraction conditions to image and quantify basal plane stacking faults (BSFs) and threading dislocations (TDs) using electron channelling contrast imaging (ECCI). Clusters of BSFs and TDs were observed with the same periodicity as the underlying micro-rod array template. The average BSF and TD densities were estimated to be ≈4 × 104 cm−1 and ≈5 × 108 cm−2, respectively. The contrast seen for BSFs in ECCI is similar to that observed for plan-view transmission electron microscopy images, with the only difference being the former acquiring the backscattered electrons and the latter collecting the transmitted electrons. Our present work shows the capability of ECCI for quantifying extended defects in semi-polar nitrides and represents a real step forward for optimising the growth conditions in these materials.

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“…This is consistent with our previous plan view TEM studies 39 (data not shown here) which reveal the average TD density to be %4.2 Â 10 8 cm…”

Section: à2supporting

confidence: 93%

“…39 We have used a similar approach for imaging and maximising the contrast for BSFs in our samples. The ECCI shown in Fig.…”

Section: B Imaging Of Bsfs In (11-22) Ganmentioning

confidence: 99%

Imaging basal plane stacking faults and dislocations in (11-22) GaN using electron channelling contrast imaging

Naresh-Kumar

Thomson

Zhang

et al. 2018

Journal of Applied Physics

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“…A series of semi-polar AlGaN layers with different AlN concentrations were deposited on GaN overgrown on microrod templates. For the GaN microrod template a high temperature AlN buffer was grown on m -plane sapphire substrates followed by a 400 nm thick GaN layer 35 , which was processed into regularly-arrayed microrods of 4 μ m diameter and pitch using a standard photolithography technique and dry-etching processes 8 , 36 . The microrod array was overgrown with semi-polar GaN until the GaN layer was nearly-but not fully-coalesced at a thickness of approximately 2.1 μ m at which point the growth of about 2.7 μ m thick semi-polar AlGaN was initiated.…”

Section: Experimental Methodsmentioning

confidence: 99%

Spatially-resolved optical and structural properties of semi-polar $$\mathrm{(11}\bar{2}\mathrm{2)}$$ Al x Ga1−x N with x up to 0.56

Bruckbauer

Naresh-Kumar

et al. 2017

Sci Rep

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Pushing the emission wavelength of efficient ultraviolet (UV) emitters further into the deep-UV requires material with high crystal quality, while also reducing the detrimental effects of built-in electric fields. Crack-free semi-polar AlxGa1−xN epilayers with AlN contents up to x = 0.56 and high crystal quality were achieved using an overgrowth method employing GaN microrods on m-sapphire. Two dominant emission peaks were identified using cathodoluminescence hyperspectral imaging. The longer wavelength peak originates near and around chevron-shaped features, whose density is greatly increased for higher contents. The emission from the majority of the surface is dominated by the shorter wavelength peak, influenced by the presence of basal-plane stacking faults (BSFs). Due to the overgrowth technique BSFs are bunched up in parallel stripes where the lower wavelength peak is broadened and hence appears slightly redshifted compared with the higher quality regions in-between. Additionally, the density of threading dislocations in these region is one order of magnitude lower compared with areas affected by BSFs as ascertained by electron channelling contrast imaging. Overall, the luminescence properties of semi-polar AlGaN epilayers are strongly influenced by the overgrowth method, which shows that reducing the density of extended defects improves the optical performance of high AlN content AlGaN structures.

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“…Previously, we developed a cost-effective approach for the overgrowth of (11–22) semi-polar GaN on m-plane sapphire by using regularly arrayed micro-rod templates, leading to substantial improvement in crystal quality. By using the semi-polar GaN templates, we have achieved high performance light emitting diodes (LEDs) with longer emission wavelengths such as green and amber 12 – 15 . We further extend this approach to the overgrowth of non-polar (11–20) GaN on r-plane sapphire, aiming to significantly improve the overall performance of non-polar GaN including crystal quality and strain situation that is a typical issue for GaN grown on large lattice-mismatched substrates.…”

Section: Introductionmentioning

confidence: 99%

“…The diameter of each micro-rod is 2.5 µm. It is well-known that the overgrowth of semi- or non- polar GaN along the [0001] direction, i.e., c direction, leads to being defect-free, while the overgrowth along the opposite direction (i.e., -c direction) allows defects to effectively penetrate to any overlying layers 13 – 15 . Therefore, it is essential to ensure that the growth along the c direction is dominant and that the growth along the -c direction can be effectively suppressed.…”

Section: Introductionmentioning

confidence: 99%

Overgrowth and strain investigation of (11–20) non-polar GaN on patterned templates on sapphire

Jiu

Gong

Wang

2018

Sci Rep

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Non-polar (11–20) GaN with significantly improved crystal quality has been achieved by means of overgrowth on regularly arrayed micro-rod templates on sapphire in comparison with standard non-polar GaN grown without any patterning processes on sapphire. Our overgrown GaN shows massively reduced linewidth of X-ray rocking curves with typical values of 270 arcsec along the [0001] direction and 380 arcsec along the [1–100] direction, which are among the best reports. Detailed X-ray measurements have been performed in order to investigate strain relaxation and in-plane strain distribution. The study has been compared with the standard non-polar GaN grown without any patterning processes and an extra non-polar GaN sample overgrown on a standard stripe-patterned template. The standard non-polar GaN grown without involving any patterning processes typically exhibits highly anisotropic in-plane strain distribution, while the overgrown GaN on our regularly arrayed micro-rod templates shows a highly isotropic in-plane strain distribution. Between them is the overgrown non-polar GaN on the stripe-patterned template. The results presented demonstrate the major advantages of using our regularly arrayed micro-rod templates for the overgrowth of non-polar GaN, leading to both high crystal quality and isotropic in-plane strain distribution, which is important for the further growth of any device structures.

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Microstructure investigation of semi-polar (11-22) GaN overgrown on differently designed micro-rod array templates

Cited by 18 publications

References 19 publications

Imaging basal plane stacking faults and dislocations in (11-22) GaN using electron channelling contrast imaging

Imaging basal plane stacking faults and dislocations in (11-22) GaN using electron channelling contrast imaging

Spatially-resolved optical and structural properties of semi-polar $$\mathrm{(11}\bar{2}\mathrm{2)}$$ Al x Ga1−x N with x up to 0.56

Overgrowth and strain investigation of (11–20) non-polar GaN on patterned templates on sapphire

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