Progress in nitride semiconductor electronic devices

Abstract

A nitride wide-bandgap semiconductor is an excellent choice to realize large-power, high-frequency, high-voltage, high-temperature, and radiation-resistive electronic devices. The mainstream structure of a nitride electronic device is a high electron mobility transistor (HEMT) based on a gallium nitride (GaN) heterostructure. The HEMT devices utilize a two-dimensional electron gas (2DEG) with a high electrical conductivity to realize a powerful current-driving capability and simultaneously maintain the high breakdown field of nitride materials. In recent years, GaN HEMTs have been developed very rapidly for promising applications in microwave power amplification and power electronics. Nitride growth on silicon carbide (SiC) substrates, device surface passivation (generally using a silicon nitride dielectric), and the utilization of a field plate (FP) structure have increased the power density of GaN HEMTs to greater than 40 W/mm at 4 GHz. Further, recessed insulating gate HEMT technology has helped to realize a power added efficiency (PAE) of 73% at 4 GHz. In addition, aggressive vertical and lateral downscaling has achieved a power density of 1.8 W/mm and PAE = 21% at 94 GHz, a cutoff frequency ( f T) of 454 GHz, and a maximum oscillation frequency ( f max) of 582 GHz. For GaN power electronic devices, an off-state breakdown voltage ( V BR) of 10.4 kV and a power figure of merit ( V BR2/ R on, where R on is the specific on-resistance) of 2100 MV2/(Ω cm2) have been realized for depletion-mode GaN HEMTs through current leakage control with various technologies such as a highly resistive Al(Ga)N back barrier, an insulating gate, an FP or more, and aluminum nitride (AlN) passivation. Some enhancement- mode GaN HEMT device structures including metal-oxide-semiconductor-(MOS-) channel HEMTs, a gate injection transistor (GIT), and p-GaN gate HEMTs have also exhibited promising high-voltage switching characteristics. A threshold voltage ( V th) of 2.0 V and V BR=1.7 kV have been reported for MOS-channel HEMTs along with a power figure of merit of 1613 MV2/(Ω cm2) for p-GaN gate HEMTs. On the basis of a review of the progress in GaN-based microwave/millimeter-wave power devices and high-efficiency power electronic devices, some obstacles hindering the further development of nitride electronic devices, mainly related to the fundamental device physics, the fabrication of nitride materials with a low defect density, the thermal management and the device reliability of GaN HEMTs, etc., are analyzed, and potential solutions are proposed.