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The effect of oxygen plasma in plasma cleaning equipment on the surface treatment of AlGaN/GaN HEMT:
The wide bandgap semiconductor material gallium nitride (GaN) has become the most researched semiconductor material with its good physical and chemical properties and electrical properties. It is the next generation semiconductor material silicon (Si) and the second generation semiconductor material arsenic ( GaAs), phosphating (GaP), copper phosphide (InP) and other rapidly developed third-generation semiconductor materials.
Compared with most current semiconductor materials, GaN semiconductor materials have a series of excellent physical and chemical properties, such as large forbidden band width, high saturation drift speed of electrons, high thermal conductivity, and good thermal stability. The research focus in the high-tech field.
Although the device performance of AlGaN/GaN HEMTs has been continuously improving, there are still many problems that need to be solved if they are to be truly practical and applied in integrated circuits. Current is one of them.
Plasma cleaning equipment Plasma treatment is a simple and convenient gate surface treatment method that reduces the threshold voltage of the device and increases the on-current of the device. Oxygen plasma is used to oxidize the AIGaN surface of the HEMT device, which increases the Schottky barrier of the device and reduces the voltage of the device. At the same time, the surface treated by oxygen plasma will not introduce new insulating film to affect the device characteristics.
The basic structure of the HEMT is a modulation-doped heterojunction. A 2DEG surface channel is formed at the A1GaN and GaN interface of the AlGaN/GaN HEMT device, and this 2DEG is controlled by the gate voltage.
At zero bias, the edge of the conduction band of GaN is lower than the Fermi level, indicating that there is a large density of 2DEG: when a negative voltage is applied to the gate, the edge of the conduction band of GaN will gradually rise, and the density of 2DEG will decrease. When the negative voltage reaches a certain value Later, the edge of the conduction band of GaN will be higher than the Fermi level, which means that the 2DEG is depleted and the current in the HEMT channel is almost zero. This voltage is called the reading voltage.
The comparison of sample A without oxygen plasma treatment with plasma cleaning equipment and sample B with oxygen plasma treatment shows that the saturation current of sample A without oxygen plasma treatment at Vgs=2V, Vds=10V is about 0.0687A/mm=68.7mA/mm, the saturation current of sample B after oxygen plasma treatment when Vgs=2V, Vds=10V rises to 0.0747A/mm=74.7mA/mm. This result shows that the surface of the device after the oxygen plasma treatment is not damaged, but the saturation current of the device is increased.
The samples after plasma treatment are all higher than those before oxygen plasma treatment. This indicates that the oxygen plasma treatment improves the large transconductance of the device and improves the performance of the device. After the oxygen plasma treatment, the threshold voltage of the HEMT device has a negative shift. Due to the decrease of the threshold voltage, the saturation region current and transconductance of the device are increased, and the experiment is consistent with the theoretical value.
The a of the sample after the oxygen plasma treatment of the plasma cleaning equipment is reduced, and the Va is reduced. Thereby, the saturated conduction current of the device is increased, and the electrical characteristics of the device are improved. Oxygen plasma treatment of the AlGaN surface in the HEMT with appropriate conditions can effectively reduce the device threshold voltage, increase the current in the saturation region of the device, and also increase the large transconductance of the device, which can be effectively used in the preparation and application of high-performance GaN HEMT devices.
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