Al-based materials, specifically aluminum oxide (Al2O3), aluminum nitride (AlN) and lithium aluminosilicate (LixAlySizO) 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 LixAlySizO 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 LixAlySizO films to serve as electrolytes and surface modification layers in 3D Li-ion microbatteries.
