Development of natural habit of large free‐nucleated AlN single crystals

Abstract

Well-shaped freestanding crystals of aluminum nitride up to 25 mm in length have been grown in tungsten crucibles using physical vapor transport (PVT) method. The platelet crystals exhibit characteristic asymmetric habit with largest flat being a pseudo-facet build by alternating (101 0) facets. Pronounced true facets are Al-terminated (0001) and adjacent {101 2} facets, with one of them growing much larger than others. The analysis of formation history of freestanding AlN crystals made it possible to explain their habit, very unusual for wurtzite-type structure. Growth of freestanding AlN starts from a long needle formed along the [11 2 0] direction at lower temperature of 1900 -2000 °C and continues by needle expansion and thickening along mainly [0001] direction, leading to asymmetric platelet. In such geometry only one extended (101 2) facet can be developed.

Seeded growth of AlN bulk crystals in m- and c-orientation

“…It has a similar lattice parameter and thermal expansion coefficient to that of high Al content AlGaN, which is needed for the active layers in these devices. Progress has been made in bulk crystal growth of AlN, and limited quantities of primarily c-plane (0 0 0 1) single crystal AlN wafers are currently available for research [1][2][3][4][5][6][7].…”

Initial growth stage in PVT growth of AlN on SiC substrates: Influence of Al2O3

“…As a consequence of its close physical, chemical and structural nature to aluminum gallium nitride (AlGaN) from which epilayers are employed in this field, aluminum nitride (AlN) is an excellent candidate as a III-nitride substrate material [2]. Recently, we reported on freestanding AlN crystals, large enough for wafering, grown by PVT technique [3]. Still there are some major problems that need to be solved such as stability of crucible materials at high growth temperatures, anisotropic growth rates varying at different temperatures, and difficulties of seeding due to oxygen contamination of source material.…”

Growth of AlN single crystalline boules

“…On the outer rim of the free-standing boule, m and r-facets usually appeared. These facets were also observed in free-standing crystals, spontaneously nucleated on the crucible wall [9,10], reflecting their stability and suitability for growth. Seeded growth along similar orientations has also been demonstrated [2].…”