Effect of SiN:H_x passivation layer on the reverse gate leakage current in GaN HEMTs

This paper concentrates on the impact of SiN passivation layer deposited by plasma-enhanced chemical vapor deposition（PECVD） on the Schottky characteristics in GaN high electron mobility transistors（HEMTs）. Three types of SiN layers with different deposition conditions were deposited on GaN HEMTs. Atomic force microscope（AFM）, capacitance-voltage（C-V）, and Fourier transform infrared（FTIR） measurement were used to analyze the surface morphology, the electrical characterization, and the chemical bonding of SiN thin films, respectively. The better surface morphology was achieved from the device with lower gate leakage current. The fixed positive charge Qf was extracted from C-V curves of Al/SiN/Si structures and quite different density of trap states（in the order of magnitude of 1011-1012 cm^（-2）） was observed.It was found that the least trap states were in accordance with the lowest gate leakage current. Furthermore, the chemical bonds and the %H in Si-H and N-H were figured from FTIR measurement, demonstrating an increase in the density of Qf with the increasing %H in N-H. It reveals that the effect of SiN passivation can be improved in GaN-based HEMTs by modulating %H in Si-H and N-H, thus achieving a better Schottky characteristics.

Standing at the Gate

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Study and modeling of the transport mechanism in a Schottky diode on the basis of a GaAs semiinsulator

The current through a metal-semiconductor junction is mainly due to the majority carriers. Three distinctly different mechanisms exist in a Schottky diode： diffusion of the semiconductor carriers in metal, thermionic emission-diffusion （TED） of carriers through a Schottky gate, and a mechanical quantum that pierces a tunnel through the gate. The system was solved by using a coupled Poisson-Boltzmann algorithm. Schottky BH is defined as the difference in energy between the Fermi level and the metal band carrier majority of the metal--semiconductor junction to the semiconductor contacts. The insulating layer converts the MS device in an MIS device and has a strong influence on its current-voltage （I-V） and the parameters ofa Schottky barrier from 3.7 to 15 eV. There are several possible reasons for the error that causes a deviation of the ideal behaviour of Schottky diodes with and without an interracial insulator layer. These include the particular distribution of interface states, the series resis- tance, bias voltage and temperature. The GaAs and its large concentration values of trap centers will participate in an increase in the process ofthermionic electrons and holes, which will in turn act on the I-V characteristic of the diode, and an overflow maximum value [NT = 3 × 10^20] is obtained. The I-V characteristics of Schottky diodes are in the hypothesis of a parabolic summit.