High Mobility III-V Semiconductor Devices with Gate Dielectrics and Passivation Layers Grown by Atomic Layer Deposition
This dissertation focuses on the applications of atomic layer deposition (ALD) to high mobility III-V semiconductor devices. The first study is an in situ ALD-based interface passivation technique using ALD diethylzinc (DEZ) treatment on n-type and p-type In₀․₅₃Ga₀․₄₇As substrate. The capacitance-voltage (C-V) characteristics of metal-oxide-semiconductor capacitors (MOSCAPs) were studied for a variety of ALD DEZ treatment cycles, different measurement temperatures, and different thickness of ALD-grown high-k gate insulators. The reasons for the presence of inversion-like C-V characteristics shown on n-type substrates are discussed. In addition to ALD DEZ passivation, two alternative ALD-based interface passivation techniques were studied. Furthermore, inversion-type enhancement-mode n-channel and p-channel In₀․₅₃Ga₀․₄₇As metal-oxide-semiconductor field-effect transistors (MOSFETs) were demonstrated using in situ ALD DEZ-based interface passivation techniques. The second part of this dissertation is the fabrication and characterization of AlGaN/GaN MIS-HEMTs. Silicon nitride (SiNₓ), grown by low-temperature hollow cathode plasma-enhanced ALD (PEALD), served as a gate dielectric and a surface passivation layer for MIS-HEMTs. Extensive characterization of the devices was done by high-resolution transmission electron microscopy (HRTEM), current-voltage (I-V) measurement, C-V measurement, gate bias stress measurement, and pulsed I-V measurement. The SiNₓ/GaN MIS-HEMTs not only showed a crystalline interfacial layer in the HRTEM images of gate stack, but also demonstrated excellent threshold voltage stability and a mitigated current collapse. Clearly, the effective passivation of surface/interface defects (e.g., nitrogen vacancies and dangling bonds) by the crystalline interfacial layer and the low bulk trap density of PEALD SiNx are highly beneficial to the reliability of GaN devices. The last part of this dissertation mainly focuses on the electrical characteristics of AlGaN/GaN heterostructure with ALD-grown epitaxial ZnO cap layer. Theoretically, it was predicted that the piezoelectric polarization of epitaxial ZnO cap layer should have a direction opposite to that in the underlying AlGaN/GaN substrate. As a result, resembling the effect of an InGaN cap layer, a ZnO cap layer may deplete the two-dimensional electron gas (2DEG) near the AlGaN/GaN interface. Experimentally, HRTEM confirmed the epitaxial growth of single-crystalline ZnO cap layer on AlGaN/GaN heterostructure by thermal ALD at 300 °C. The Ids-Vg transfer curve and C-V curve showed a significant positive shift (~1 V) for devices with an O₃-based epitaxial ZnO cap layer, compared to those of Schottky gate devices and devices with a highly conductive H₂O-based epitaxial ZnO cap layer.