UCLA

Al-based materials, specifically aluminum oxide (Al₂O₃), aluminum nitride (AlN) and lithium aluminosilicate (Li_xAl_ySi_zO) were synthesized via atomic layer deposition (ALD) and investigated for their applications in power electronics and miniaturized Li-ion batteries.

Al₂O₃ and AlN films were deposited on two substrates, silicon carbide (SiC) and gallium nitride (GaN) based heterostructures, AlGaN/GaN, to compare their electrical performances as alternative dielectrics for wide bandgap semiconductor based power devices. Amorphous Al₂O₃ was deposited at 195-200 ^oC at a rate of 0.75-1 �/cycle. The film exhibited a dielectric constant of 9 and a leakage current of 10^-3 A/cm² at 8 MV/cm on SiC. When it was applied on AlGaN/GaN, the Al₂O₃ passivation resulted in an increased sheet carrier density but a dramatic decrease in the mobility compared to those of a clean AlGaN/GaN substrate. Crystalline AlN was deposited at 540 ^oC with a rate of 1.5 �/cycle. The AlN film demonstrated a dielectric constant of 8.3 and a leakage current density of 10^-3 A/cm² at 4.3 MV/cm on SiC. When AlN was applied on AlGaN/GaN, an increased carrier density was observed while the mobility was at 1130 cm²/V-s, similar to that of a clean AlGaN/GaN. The electrical properties of synthesized AlN were promising and comparable to those of MBE or sputtering synthesized AlN, confirming the promise of ALD for synthesizing AlN. Due to their material properties, Al₂O₃ is preferred choice for preventing gate leakage current on SiC, whereas AlN demonstrated superior capability of passivating AlGaN/GaN.

Stoichiometric LiAlSiO₄ was realized at 290 ^oC with a rate of ~23 �/global cycle, in which one global cycle sequence represented 10(Al-O)-6(Li-O)-4(Si-O) ALD cycles. As-deposited films were amorphous, pin-hole free, as confirmed by electrochemical testing in ferrocene, and conformal over 3D nanowires. The ionic conductivity of Li_xAl_ySi_zO films was 10^-9-10^-7 S/cm and the activation energy was 0.34-0.98 eV, both correlated to cation contents in the films. After rapid thermal annealing at 900 ^oC, the as-deposited LiAlSiO₄ films crystallized into epitaxial β-LiAlSiO₄ on Si (001) with a relationship of β-LiAlSiO4 (1 2bar 1 0) || Si (100) and β-LiAlSiO₄ (1 0 1bar 0) || Si (001). The application of the LiAlSiO₄ film on tin dioxide (SnO₂) NWs showed that the film possessed a high ionic conductivity, which suppressed the formation of metallic Sn particles, showing the capability of Li_xAl_ySi_zO films to serve as electrolytes and surface modification layers in 3D Li-ion microbatteries.