Evaluation of Thermal Versus Plasma-Assisted ALD Al₂O₃ as Passivation for InAlN/AlN/GaN HEMTs

摘要

AlO films deposited by thermal and plasma-assisted atomic layer deposition (ALD) were evaluated as passivation layers for InAlN/AlN/GaN HEMTs. As a reference, a comparison was made with the more conventional plasma enhanced chemical vapor deposition deposited SiN passivation. The difference in sheet charge density, threshold voltage, f and f was moderate for the three samples. The gate leakage current differed by several orders of magnitude, in favor of AlO passivation, regardless of the deposition method. Severe current slump was measured for the HEMT passivated by thermal ALD, whereas near-dispersion free operation was observed for the HEMT passivated by plasma-assisted ALD. This had a direct impact on the microwave output power. Large-signal measurements at 3 GHz revealed that HEMTs with AlO passivation exhibited 77% higher output power using plasma-assisted ALD compared with thermal ALD.