研究目的
To develop normally-off AlGaN/GaN heterojunction metal-insulator-semiconductor field-effect transistors with a gate-first process using p-GaN cap layers and SiNx dielectrics, and to achieve low-temperature ohmic contact to avoid gate degradation.
研究成果
The low-temperature ohmic contact process with ICP assistance successfully achieved a contact resistance of 1.45 Ω·mm. Fabricated normally-off AlGaN/GaN HJMISFETs with SiNx insulator and gate-first process showed a threshold voltage of 2.0 V, field-effect mobility of 1500 cm2V-1s-1, and suppressed gate leakage current. This approach alleviates gate degradation from high-temperature annealing in gate-first processes.
研究不足
The contact resistance and sheet resistance are higher than conventional values, possibly due to thin AlGaN barrier and surface damage. The gate length is long (94 μm), leading to low transconductance. Off-state breakdown voltage has relatively high leakage current at small gate-drain distances. Interface defects in SiNx/p-GaN may cause current collapse and hysteresis.
1：Experimental Design and Method Selection:
The study uses a gate-first fabrication process for normally-off AlGaN/GaN HJMISFETs with p-GaN cap layers and SiNx dielectrics. A low-temperature ohmic contact technique is developed to prevent gate degradation during annealing.
2：Sample Selection and Data Sources:
AlGaN/GaN heteroepitaxial structures grown on Si substrates by metal organic chemical vapor deposition (MOCVD) are used.
3：List of Experimental Equipment and Materials:
Equipment includes ICP dry etching system, PECVD for SiNx deposition, magnetron sputtering for metal deposition, and SEM for imaging. Materials include TiN/Ni gate stack, Ti/Al/Ti/Au ohmic metal stack, SiNx dielectric, and p-GaN layers.
4：Experimental Procedures and Operational Workflow:
Steps involve wafer cleaning, device isolation by ICP etching, SiNx deposition and annealing, gate metal deposition, self-aligned gate formation via wet and dry etching, ICP treatment for ohmic contact, ohmic metal deposition, and low-temperature annealing.
5：Data Analysis Methods:
Performance is evaluated using I-V characteristics, TLM measurements for contact and sheet resistance, transfer characteristics for threshold voltage and mobility, and gate leakage current analysis.
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