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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

Fundamental idea of the newly developed AlN crystal growth apparatus.(a) Calculated ΔG of the reaction Al + 1/2N2 → AlN and for comparison, the reaction Al + NH3 → AlN + 3/2 H2. Negative ΔG values indicate that both are spontaneous. (b) Schematic of the growth apparatus design in which direct nitridation of the Al source is avoided as Ar gas transfers Al vapor to the growth zone. (c) Photograph of the growth apparatus in operation.
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f1: Fundamental idea of the newly developed AlN crystal growth apparatus.(a) Calculated ΔG of the reaction Al + 1/2N2 → AlN and for comparison, the reaction Al + NH3 → AlN + 3/2 H2. Negative ΔG values indicate that both are spontaneous. (b) Schematic of the growth apparatus design in which direct nitridation of the Al source is avoided as Ar gas transfers Al vapor to the growth zone. (c) Photograph of the growth apparatus in operation.

Mentions: A simple thermodynamic calculation on the standard Gibbs free energy change (ΔG) suggests that the reaction Al + 1/2N2 → AlN may occur at a reasonable temperature; Fig. 1a shows the calculated result at 100 kPa as well as the ΔG for the more common reaction Al + NH3 → AlN + 3/2H2. (The enthalpy and entropy values for the calculations are from ref. 31.) Because a more negative ΔG indicates a higher reactivity, the reaction Al + NH3 → AlN + 3/2 H2 has a higher reactivity than the reaction Al + 1/2N2 → AlN. However, it should be noted that ΔG for the latter is also negative, indicating that a spontaneous reaction between Al and N2 occurs near 1500 °C at 100 kPa. If AlN single crystals can be grown using the reaction Al + 1/2N2 → AlN, many benefits should be realized, including an environmentally friendly process without hazardous species (which leads to the exclusion of a detoxifying apparatus), absence of side products, and cost effectiveness.


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)

Fundamental idea of the newly developed AlN crystal growth apparatus.(a) Calculated ΔG of the reaction Al + 1/2N2 → AlN and for comparison, the reaction Al + NH3 → AlN + 3/2 H2. Negative ΔG values indicate that both are spontaneous. (b) Schematic of the growth apparatus design in which direct nitridation of the Al source is avoided as Ar gas transfers Al vapor to the growth zone. (c) Photograph of the growth apparatus in operation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Fundamental idea of the newly developed AlN crystal growth apparatus.(a) Calculated ΔG of the reaction Al + 1/2N2 → AlN and for comparison, the reaction Al + NH3 → AlN + 3/2 H2. Negative ΔG values indicate that both are spontaneous. (b) Schematic of the growth apparatus design in which direct nitridation of the Al source is avoided as Ar gas transfers Al vapor to the growth zone. (c) Photograph of the growth apparatus in operation.
Mentions: A simple thermodynamic calculation on the standard Gibbs free energy change (ΔG) suggests that the reaction Al + 1/2N2 → AlN may occur at a reasonable temperature; Fig. 1a shows the calculated result at 100 kPa as well as the ΔG for the more common reaction Al + NH3 → AlN + 3/2H2. (The enthalpy and entropy values for the calculations are from ref. 31.) Because a more negative ΔG indicates a higher reactivity, the reaction Al + NH3 → AlN + 3/2 H2 has a higher reactivity than the reaction Al + 1/2N2 → AlN. However, it should be noted that ΔG for the latter is also negative, indicating that a spontaneous reaction between Al and N2 occurs near 1500 °C at 100 kPa. If AlN single crystals can be grown using the reaction Al + 1/2N2 → AlN, many benefits should be realized, including an environmentally friendly process without hazardous species (which leads to the exclusion of a detoxifying apparatus), absence of side products, and cost effectiveness.

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