研究目的
To investigate band alignment in AlGaN/GaN HEMT devices using scanning photocurrent microscopy (SPCM) with UV and visible laser sources, and to quantify the conduction band offset of the semiconductor-metal contacts.
研究成果
The study successfully investigated electronic band alignment in AlGaN/GaN HEMT devices using SPCM, revealing a switching behavior in photocurrent polarity with gate bias and confirming ohmic contact formation. The conduction band offset was measured as 2.1 eV on average, providing valuable insights for optimizing wide-bandgap device performance. This approach is a powerful tool for characterizing localized electronic states in nanoscale devices.
研究不足
The use of UV laser can induce persistent photocurrent effects, which may obscure analysis and require offset current removal. The method is specific to light-sensitive devices and may not be easily applicable to non-optically active materials. Device performance could be affected by UV-induced modifications.
1：Experimental Design and Method Selection:
SPCM was used with UV (355 nm) and visible (532 nm) laser sources to study electronic band alignment in AlGaN/GaN HEMT devices. The method allows non-destructive and non-contact measurement of photoelectrical properties.
2：Sample Selection and Data Sources:
AlGaN/GaN HEMT devices with a 2DEG layer were fabricated on sapphire substrates using metal-organic chemical vapor deposition. Devices had varying channel widths (2–10 μm) and a fixed channel length of 20 μm.
3：List of Experimental Equipment and Materials:
Focused lasers (wavelengths 355 nm and 532 nm), e-beam evaporation system for electrode deposition (Ti/Al/Ni/Au for ohmic contacts, Ni/Al for Schottky gate), annealing equipment, and SPCM setup for scanning and signal monitoring.
4：Experimental Procedures and Operational Workflow:
Lasers were scanned over the samples while monitoring photo-induced signals as a function of position and gate bias. Measurements were taken at different gate voltages and drain-source voltages to observe photocurrent responses and switching behaviors.
5：Data Analysis Methods:
Photocurrent signals were analyzed to determine flat-band voltage, band offset, and gate efficiency. Subthreshold voltage swing was calculated from DC gate response data to derive gate efficiency.
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