Study On High κ Dielectric Stack Gate AlGaN/GaN MOS-HEMT Characteristics

Higher requirements for the high-frequency power devices has been brought up by the rapid development of wireless communication technology in order to meet the fast and stable data exchange requirement in mobile Internet era. As the representative of the third generation of semiconductor material, Gallium nitride(Ga N) has a large band gap, high carrier mobility and good thermal conductivity, which makes it an ideal material for the high-frequency power devices. All these excellent properties mentioned above make up the inherent shortcomings of Si and Ga As, which are the representative of the first and second generations of the semiconductor materials separately. Due to its promising potential in high-frequency application, Ga N is extensively investigated in recent years.The low turn-on voltage of Schottky junction limits the use of traditional HEMT in high-temperature high-power devices. However, the introduction of MOS-HEMT broaden the application of the device by suppressing the gate leakage current and improving the breakdown voltage. As the power density increases, the device temperature may increase. Increased temperature may affect the device reliability. As the oxide thickness is reduced and the electric field is increased, gate oxides are closer to breakdown and oxide integrity may be more difficult to maintain. In addition, direct tunneling of carriers through the oxide may be more likely to occur. Increased electric fields may also increase the chances of hot-electron effects, which are discussed later in this paper.The realization and optimization of the high κ dielectric stack gate Al Ga N/Ga N MOS-HEMT are studied in this paper. Based on the theoretical analysis, the effects of structure difference and process parameters variation on the characteristics of the device are studied and optimized using an new simulation model.In order to reveal the advantages and disadvantages of HEMT and MOS-HEMT, the characteristics of gate leakage currents of two structures are investigated by comparing the DC curves. Then, compared with single gate dielectric structure, the properties of the stack gate is studied in deep submicron level. A large number of simulation analyses are performed by ISE software. The effects of different barrier layer doping concentration, ratio of Al in Al Ga N, the kinds and different thicknesses of the gate dielectric material on the 2DEG density and carrier mobility are analyzed. Finally, the characteristics of the side gate structure device is studied comparing with the symmetry structure, especially on carrier mobility and the peak of electric field in the channel.The MOS-HEMT structure indeed serves as a good solution to solve the problem of the rapidly increasing gate leakage current when the applied gate voltage is close to the turn-on voltage of the Schottky junction. However, some problems accompany with the introduction of the MOS-HEMT structure are the weakening gate control capability and the decline of transconductance. Further research found that the introduction of the high κ stack gate structure makes a significant improvement on the gate control capability and transconductance characteristics. The 2DEG density in channel is increased with the increasing of doping concentration and Al ratio in the Al Ga N barrier layer, but the carrier mobility acts as an reverse tendency. Therefore, the characteristics of the device can be optimized only at suitable doping concentration and Al ratio.For side gate device, the simulation results of the basic characteristics by the ISE software indicate that the peak of electric filed intensity drops 10% compared with the symmetrical structure. The problem of the decrease of carrier mobility in high electric field is relieved. The drain saturation current is enhanced by 31% under the same gate and drain voltage. So all the improved properties mentioned above lead to an significant improvement in the DC characteristics of the side gate device.