Temperature-dependent surface current measurements were performed to analyze the mechanism of surface conductance of AlGaN/GaN channel high-electron-mobility transistors by utilizing process-optimized double gate structures. Different temperatures and electric field dependence have been found in surface current measurements. At low electric field, the mechanism of surface conductance is considered to be two-dimensional variable range hopping. At elevated electric field, the Frenkel–Poole trap assisted emission governs the main surface electrons transportation. The extracted energy barrier height of electrons emitting from trapped state near Fermi energy level into a threading dislocations-related continuum state is 0.38 eV. SiN passivation reduces the surface leakage current by two order of magnitude and nearly 4 orders of magnitude at low and high electric fields, respectively. SiN also suppresses the Frenkel–Poole conductance at high temperature by improving the surface states of AlGaN/GaN. A surface treatment process has been introduced to further suppress the surface leakage current at high temperature and high field, which results in a decrease in surface current of almost 3 orders of magnitude at 476 K.
We present a detailed analysis of trap states in InAlN/AlN/GaN double-channel high electron mobility transistors grown by pulsed metal organic chemical vapor deposition. By frequency dependent conductance measurements, trap densities and time constants at both InAlN/AlN/GaN interfaces were determined. Two types of traps, with a high density of up to ∼1014 cm−2 eV−1, were observed existing at the higher InAlN/AlN/GaN interface. On the other hand, the density dramatically decreased to ∼1012 cm−2 eV−1 for traps located at lower InAlN/AlN/GaN interface on which a low-temperature grown GaN (LT-GaN) layer was deposited. Additionally, photo-assisted capacitance-voltage measurements were performed to estimate deep-level defects, yielding a low density of 1.79 × 1011 cm−2 acting as negative fixed charges at the LT-GaN and lower InAlN interface.
By comparing the Schottky diodes of different area and perimeter, reverse gate leakage current of AlGaN/GaN high mobility transistors (HEMT) at gate bias beyond threshold voltage is studied. It is revealed that reverse current consists of area-related and perimeter-related current. An analytical model of electric field calculation is proposed to obtain the average electric field around the gate edge at high revers bias and estimate the effective range of edge leakage current. When the reverse bias increases, the increment of electric field is around the gate edge of a distance of ΔL, and perimeter-related gate edge current keeps increasing. By using the calculated electric field and the temperature-dependent current-voltage measurements, the edge gate leakage current mechanism is found to be Fowler-Nordheim tunneling at gate bias bellows -15V caused by the lateral extended depletion region induced barrier thinning. Effective range of edge current of Schottky diodes is about hundred to several hundred nano-meters, and is different in different shapes of Schottky diodes.
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