Three‐step growth method for high quality AlN epilayers

Nakarmi, M. L.; Cai, Bo; Lin, J. Y.; Jiang, H. X.

doi:10.1002/pssa.201127475

Cited by 27 publications

(14 citation statements)

References 28 publications

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“…(c). Thus, the total dislocation density is comparable to those of some recent studies where the AlN layers were grown on sapphire substrates at temperatures above 1300 °C by taking into account the thickness difference .…”

Section: Resultssupporting

confidence: 80%

“…In addition to the ELO and PALE, high‐temperature growth above 1200 °C has been employed independently or collectively with the ELO and PALE to achieve low dislocation density and smooth surface morphology by metalorganic chemical vapor deposition (MOCVD), where the mobility of Al atoms on the epitaxial surface is enhanced at high temperatures . However, there are concerns regarding the high‐temperature growth.…”

Section: Introductionmentioning

confidence: 99%

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Growth of high‐quality AlN layers on sapphire substrates at relatively low temperatures by metalorganic chemical vapor deposition

Wang

Xie

et al. 2015

Physica Status Solidi (b)

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We report a three‐step method to grow high‐quality AlN heteroepitaxial layers on sapphire substrates at relatively low temperatures by metalorganic chemical vapor deposition (MOCVD) without the use of epitaxial lateral overgrowth (ELO) or pulse atomic layer epitaxy (PALE) method. The three‐layer AlN structure comprises a 15‐nm thick buffer layer, a 50‐nm thick intermediate layer, and a 3.4‐µm thick template layer grown at 930, 1130, and 1100 °C sequentially on the c‐plane sapphire substrate. The resulting AlN layer had smooth surface with well‐defined terraces and low root‐mean square (RMS) roughnesses of 0.50 and 0.07 nm for 20 × 20 and 1 × 1 µm2 atomic force microscopy (AFM) scans. Band‐edge emission was observed at 208 nm by room temperature (RT) photoluminescence (PL) measurements. The total threading dislocation density was 2.5 × 109/cm2 as determined by transmission electron microscopy (TEM), which is comparable to those of some AlN layers recently grown at significantly higher temperatures. Growth evolution was studied and correlated to the TEM results. The residual impurity concentrations were comparable to those of AlN layers grown at higher temperatures, i.e., 1200–1600 °C. This study demonstrates the high quality AlN layers on sapphire substrates can be grown at achievable temperatures for most of the modern MOCVD systems.

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Section: Resultssupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Growth of high‐quality AlN layers on sapphire substrates at relatively low temperatures by metalorganic chemical vapor deposition

Wang

Xie

et al. 2015

Physica Status Solidi (b)

View full text Add to dashboard Cite

show abstract

“…In addition to the ELO and PALE, high-temperature growth above 1200 1C has been employed independently or jointly with the ELO and PALE to achieve low dislocation density and smooth surface morphology by metalorganic chemical vapor deposition (MOCVD), in that the mobility of Al atoms on the epitaxial surface is enhanced at high temperature [10][11][12][13][14][15][16][17]. However, there are some concerns regarding high-temperature growth.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of the crystalline quality of AlN layer grown on sapphire substrates by metalorganic chemical vapor deposition

Wei

Wang

et al. 2015

Journal of Crystal Growth

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a b s t r a c tWe studied temperature dependence of crystalline quality of AlN layers at 1050-1250 1C with a fine increment step of around 18 1C. The AlN layers were grown on c-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD) and characterized by X-ray diffraction (XRD) ω-scans and atomic force microscopy (AFM). At 1050-1068 1C, the templates exhibited poor quality with surface pits and higher XRD (002) and (102) full-width at half-maximum (FWHM) because of insufficient Al atom mobility. At 1086 1C, the surface became smooth suggesting sufficient Al atom mobility. Above 1086 1C, the (102) FWHM and thus edge dislocation density increased with temperatures which may be attributed to the shorter growth mode transition from three-dimension (3D) to twodimension (2D). Above 1212 1C, surface macro-steps were formed due to the longer diffusion length of Al atoms than the expected step terrace width. The edge dislocation density increased rapidly above 1212 1C, indicating this temperature may be a threshold above which the impact of the transition from 3D to 2D is more significant. The (002) FWHM and thus screw dislocation density were insensitive to the temperature change. This study suggests that high-quality AlN/sapphire templates may be potentially achieved at temperatures as low as 1086 1C which is accessible by most of the III-nitride MOCVD systems.

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“…The structure firstly comprised an AlN template layer deposited directly on the sapphire substrate with a thickness of 3.5 m. To achieve lasing from the MQW active region grown on sapphire substrates, the use of a high-quality AlN/sapphire template was necessary to reduce the dislocation density in the active region and thus improve gain therein. In this work, the total dislocation density of the template layer was 2.5×10 9 /cm 2 as determined by cross-sectional transmission-electron microscopy (TEM), which represents one of the lowest dislocation densities reported for planar AlN/sapphire templates [6][7][8][9]. The root-mean-square (RMS) surface roughness is less than 0.10 nm and 0.12 nm determined by 1×1 m 2 and 5×5 m 2 AFM measurement, which is comparable to bulk AlN substrates [10].…”

mentioning

confidence: 79%

Optically pumped low-threshold UV lasers

Detchprohm

Liu

et al. 2015

2015 IEEE Summer Topicals Meeting Series (SUM)

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Recently, low-threshold optically-pumped DUV lasers containing AlGaN-based multiple-quantum wells (MQWs) have been demonstrated by homoepitaxial growth on c-plane bulk AlN substrates [1][2][3][4][5]. The bulk AlN substrates were used in these studies due to low-dislocation density and reduction of the lattice mismatch and thermal expansion difference between the AlN substrate and Al-rich AlGaN epitaxial layers, thus leading to high-quality active regions with relatively low-dislocation density. However, because of high cost, smaller area, and impurity absorption of the bulk AlN substrates today, it is much more desirable to grow DUV lasers on the vastly available and lower-cost sapphire substrates.In this work, we report optically-pumped AlGaN-based MQW DUV lasers grown on (0001) sapphire substrates by metalorganic chemical vapor deposition (MOCVD). Lasing at 249 nm ( the 249-nm laser ) with low pumping-power threshold was demonstrated in an edge-emission configuration at room temperature (RT). X-ray diffraction (XRD), atomic-force microscopy (AFM), scanning-electron microscopy (SEM) and powerdependent photoluminescence (PL) measurements were carried out to investigate crystalline quality of the lasers and stimulated emission characteristics.The entire epitaxial AlGaN MQW laser structure was grown on one two-inch diameter c-plane sapphire -pressure MOCVD reactor with a close-coupled showerhead configuration. The structure firstly comprised an AlN template layer deposited directly on the sapphire substrate with a thickness of 3.5 m. To achieve lasing from the MQW active region grown on sapphire substrates, the use of a high-quality AlN/sapphire template was necessary to reduce the dislocation density in the active region and thus improve gain therein. In this work, the total dislocation density of the template layer was 2.5×10 9 /cm 2 as determined by cross-sectional transmission-electron microscopy (TEM), which represents one of the lowest dislocation densities reported for planar AlN/sapphire templates [6-9]. The root-mean-square (RMS) surface roughness is less than 0.10 nm and 0.12 nm determined by 1×1 m 2 and 5×5 m 2 AFM measurement, which is comparable to bulk AlN substrates [10]. Thus the AlN template layer used herein provided a very smooth surface for subsequent growth of AlGaN-based laser structures.Subsequently, an AlxGa1-xN grading waveguide layer, five periods of 2.0-nm-Al0.66Ga0.34N / 4.8-nm-Al0.83Ga0.17N MQWs designed for laser emission at around 250 nm and a thin Al0.83Ga0.17N cap layer for surface passivation and carrier confinement were grown on the AlN template layer sequentially. The growth conditions, composition and thickness of these AlGaN-based layers were optimized to improve gain and enhance optical confinement in the active region and thus reduce threshold. As shown in the asymmetric (105) reciprocal space mapping (RSM) by XRD in Figure 1(a), all the epitaxial layers were pseudomorphically grown and thus fully strained, which retained the high quality of the AlN template layer. Not shown...

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Three‐step growth method for high quality AlN epilayers

Cited by 27 publications

References 28 publications

Growth of high‐quality AlN layers on sapphire substrates at relatively low temperatures by metalorganic chemical vapor deposition

Growth of high‐quality AlN layers on sapphire substrates at relatively low temperatures by metalorganic chemical vapor deposition

Temperature dependence of the crystalline quality of AlN layer grown on sapphire substrates by metalorganic chemical vapor deposition

Optically pumped low-threshold UV lasers

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