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Environmentally friendly method to grow wide-bandgap semiconductor aluminum nitride crystals: Elementary source vapor phase epitaxy.

Wu P, Funato M, Kawakami Y - Sci Rep (2015)

Bottom Line: Herein we propose a novel vapor-phase-epitaxy-based growth method for AlN that does not use toxic materials; the source precursors are elementary aluminum and nitrogen gas.This growth rate is comparable to that by HVPE, and the growth temperature is much lower than that in sublimation.Thus, this study opens up a novel route to achieve environmentally friendly growth of AlN.

View Article: PubMed Central - PubMed

Affiliation: Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan.

ABSTRACT
Aluminum nitride (AlN) has attracted increasing interest as an optoelectronic material in the deep ultraviolet spectral range due to its wide bandgap of 6.0 eV (207 nm wavelength) at room temperature. Because AlN bulk single crystals are ideal device substrates for such applications, the crystal growth of bulky AlN has been extensively studied. Two growth methods seem especially promising: hydride vapor phase epitaxy (HVPE) and sublimation. However, the former requires hazardous gases such as hydrochloric acid and ammonia, while the latter needs extremely high growth temperatures around 2000 °C. Herein we propose a novel vapor-phase-epitaxy-based growth method for AlN that does not use toxic materials; the source precursors are elementary aluminum and nitrogen gas. To prepare our AlN, we constructed a new growth apparatus, which realizes growth of AlN single crystals at a rate of ~18 μm/h at 1550 °C using argon as the source transfer via the simple reaction Al + 1/2N2 → AlN. This growth rate is comparable to that by HVPE, and the growth temperature is much lower than that in sublimation. Thus, this study opens up a novel route to achieve environmentally friendly growth of AlN.

No MeSH data available.


Related in: MedlinePlus

Structural properties of AlN grown from Al and N2.(a) Growth rate as a function of the V/III ratio at 1550 °C. Maximum growth rate is ~18 μm/h when the V/III ratio is ~2200. (b) Cross-sectional SEM image of the 18-μm-thick AlN layer. (c) Surface optical microscopy image of the same AlN shown in (b) without cracks, which greatly differs from AlN on SiC grown in this study as well as MOVPE AlN on sapphire. (d,e) Close-up images of the AlN/sapphire and AlN/SiC interfaces, respectively. Both use the same scale. Voids form only at the AlN/sapphire interface.
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f3: Structural properties of AlN grown from Al and N2.(a) Growth rate as a function of the V/III ratio at 1550 °C. Maximum growth rate is ~18 μm/h when the V/III ratio is ~2200. (b) Cross-sectional SEM image of the 18-μm-thick AlN layer. (c) Surface optical microscopy image of the same AlN shown in (b) without cracks, which greatly differs from AlN on SiC grown in this study as well as MOVPE AlN on sapphire. (d,e) Close-up images of the AlN/sapphire and AlN/SiC interfaces, respectively. Both use the same scale. Voids form only at the AlN/sapphire interface.

Mentions: To grow AlN, the source raw materials were Al powder (purity = 99.99%) and N2 gas, while the substrates were sapphire(0001) unless stated. Typical source zone temperature and growth pressure were 1400 °C and 10 kPa, respectively, which were determined in the manner described in Methods. Growth optimization was performed for the growth zone temperature and the molar flow ratio of N2 to Al, which is referred to as the V/III ratio in this letter. The optimized growth zone temperature was 1550 °C (Supplementary information). It is noteworthy that the optimal growth temperature in this study is much lower than that in sublimation (~2000 °C). To adjust the V/III ratio, the Al flow rate was changed under a constant N2 flow rate of 3 standard l/min. Figure 3a plots the growth rate at the optimal growth temperature of 1550 °C as a function of the V/III ratio. Very low V/III ratios tend to form AlN whiskers, which slows the film growth rate. This trend is consistent with GaN MOVPE, in which a low V/III ratio reduces the driving force for growth and promotes nanowire formation33. Additionally, V/III ratios greater than 2500 decrease the growth rate simply because the Al flow rate that contributes to growth is reduced (see the upper axis of Fig. 3a). Therefore, in terms of the growth rate, the optimal V/III ratio in this study is ~2200.


Environmentally friendly method to grow wide-bandgap semiconductor aluminum nitride crystals: Elementary source vapor phase epitaxy.

Wu P, Funato M, Kawakami Y - Sci Rep (2015)

Structural properties of AlN grown from Al and N2.(a) Growth rate as a function of the V/III ratio at 1550 °C. Maximum growth rate is ~18 μm/h when the V/III ratio is ~2200. (b) Cross-sectional SEM image of the 18-μm-thick AlN layer. (c) Surface optical microscopy image of the same AlN shown in (b) without cracks, which greatly differs from AlN on SiC grown in this study as well as MOVPE AlN on sapphire. (d,e) Close-up images of the AlN/sapphire and AlN/SiC interfaces, respectively. Both use the same scale. Voids form only at the AlN/sapphire interface.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663762&req=5

f3: Structural properties of AlN grown from Al and N2.(a) Growth rate as a function of the V/III ratio at 1550 °C. Maximum growth rate is ~18 μm/h when the V/III ratio is ~2200. (b) Cross-sectional SEM image of the 18-μm-thick AlN layer. (c) Surface optical microscopy image of the same AlN shown in (b) without cracks, which greatly differs from AlN on SiC grown in this study as well as MOVPE AlN on sapphire. (d,e) Close-up images of the AlN/sapphire and AlN/SiC interfaces, respectively. Both use the same scale. Voids form only at the AlN/sapphire interface.
Mentions: To grow AlN, the source raw materials were Al powder (purity = 99.99%) and N2 gas, while the substrates were sapphire(0001) unless stated. Typical source zone temperature and growth pressure were 1400 °C and 10 kPa, respectively, which were determined in the manner described in Methods. Growth optimization was performed for the growth zone temperature and the molar flow ratio of N2 to Al, which is referred to as the V/III ratio in this letter. The optimized growth zone temperature was 1550 °C (Supplementary information). It is noteworthy that the optimal growth temperature in this study is much lower than that in sublimation (~2000 °C). To adjust the V/III ratio, the Al flow rate was changed under a constant N2 flow rate of 3 standard l/min. Figure 3a plots the growth rate at the optimal growth temperature of 1550 °C as a function of the V/III ratio. Very low V/III ratios tend to form AlN whiskers, which slows the film growth rate. This trend is consistent with GaN MOVPE, in which a low V/III ratio reduces the driving force for growth and promotes nanowire formation33. Additionally, V/III ratios greater than 2500 decrease the growth rate simply because the Al flow rate that contributes to growth is reduced (see the upper axis of Fig. 3a). Therefore, in terms of the growth rate, the optimal V/III ratio in this study is ~2200.

Bottom Line: Herein we propose a novel vapor-phase-epitaxy-based growth method for AlN that does not use toxic materials; the source precursors are elementary aluminum and nitrogen gas.This growth rate is comparable to that by HVPE, and the growth temperature is much lower than that in sublimation.Thus, this study opens up a novel route to achieve environmentally friendly growth of AlN.

View Article: PubMed Central - PubMed

Affiliation: Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan.

ABSTRACT
Aluminum nitride (AlN) has attracted increasing interest as an optoelectronic material in the deep ultraviolet spectral range due to its wide bandgap of 6.0 eV (207 nm wavelength) at room temperature. Because AlN bulk single crystals are ideal device substrates for such applications, the crystal growth of bulky AlN has been extensively studied. Two growth methods seem especially promising: hydride vapor phase epitaxy (HVPE) and sublimation. However, the former requires hazardous gases such as hydrochloric acid and ammonia, while the latter needs extremely high growth temperatures around 2000 °C. Herein we propose a novel vapor-phase-epitaxy-based growth method for AlN that does not use toxic materials; the source precursors are elementary aluminum and nitrogen gas. To prepare our AlN, we constructed a new growth apparatus, which realizes growth of AlN single crystals at a rate of ~18 μm/h at 1550 °C using argon as the source transfer via the simple reaction Al + 1/2N2 → AlN. This growth rate is comparable to that by HVPE, and the growth temperature is much lower than that in sublimation. Thus, this study opens up a novel route to achieve environmentally friendly growth of AlN.

No MeSH data available.


Related in: MedlinePlus