Seeded growth of boron arsenide single crystals with high thermal conductivity

Abstract

Materials with high thermal conductivities are crucial to effectively cooling high-power-density electronic and optoelectronic devices. Recently, zinc-blende boron arsenide (BAs) has been predicted to have a very high thermal conductivity of over 2000 W m À1 K À1 at room temperature by first-principles calculations, rendering it a close competitor for diamond which holds the highest thermal conductivity among bulk materials. Experimental demonstration, however, has proved extremely challenging, especially in the preparation of large high quality single crystals. Although BAs crystals have been previously grown by chemical vapor transport (CVT), the growth process relies on spontaneous nucleation and results in small crystals with multiple grains and various defects. Here, we report a controllable CVT synthesis of large single BAs crystals (400-600 lm) by using carefully selected tiny BAs single crystals as seeds. We have obtained BAs single crystals with a thermal conductivity of 351 6 21 W m À1 K À1 at room temperature, which is almost twice as conductive as previously reported BAs crystals. Further improvement along this direction is very likely.

Boron isotope effect on the thermal conductivity of boron arsenide single crystals

“…In the mixed This expression provides a good approximation to the positions of the sharp peaks in Figure 2B. In boron mixed isotope samples with prevailing 11 B content, there also exists isotope disorder that relaxes the Raman selection rules, such that 10 Electronic Raman scattering has been observed also in a number of BAs samples. ERS produces a scattering background and Fano lineshape of the Raman peaks in BAs [11].…”

“…Details of the CVT growth process can be found in previous reports [25,26]. 10 BAs and 11 BAs single crystals with dimensions of 2.0 x 1.0 x 0.1 mm 3 were obtained within a two-week growth time, as shown in Figure 1A and 1B, respectively. The transparency and dark reddish color of the single crystals clearly show that their RT band gap is around 1.78 eV, which matches recent calculations [16][17][18].…”

“…Early experimental efforts showed BAs samples with relatively low but promising k values [9,10] and the later developments delivered BAs with k values [11][12][13] as high as the theoretically predicted k ~1300 W m -1 K -1 at RT when four-phonon scattering is taken into consideration [14,15]. BAs k value is smaller than that of natural diamond (2290 W m -1 K -4 1 ) [4], but still much higher than that of any other reported bulk material.…”

“…Varying B isotopes in BAs changes the acoustic phonon dispersion and phonon velocities negligibly little. The two stable B-isotopes, 10 B and 11 B, affect only the optical phonons. Under the three-phonon scattering mechanism, the RT k of isotopically pure BAs ( pure BAs) is more than 3100 W m -1 K -1 [6,7], nearly 50% higher than that of nat BAs under the same assumption.…”

“…We expect these results will help to clarify the influence of isotopes on the thermal properties of BAs single crystals. 6 Results and discussion 10 B (boron powder, ≥96% atomic 10 B, crystalline, particle size: from 0.425 mm to 4.75 mm, 99.9% metals basis, Alfa Aesar), 11 B (boron powder, ≥96% atomic 11 B, crystalline, particle size: less than 0.15 mm, 99.9% metals basis, Alfa Aesar), and nat B (boron powder, crystalline, particle size: from 0.425 mm to 4.75 mm, 99.9999% metals basis, Alfa Aesar) were used as different boron sources. Manually mixed B powders of 20% 10 B and 80% 11 B (denoted 10 B0.2 11 B0.8), and 50% 10 B and 50% 11 B (denoted 10 B0.5 11 B0.5) were also prepared as boron sources for comparison with results obtained from natural B.…”