Design and fabrication of high electron mobility transistor devices with gallium nitride-based

Abstract

Gallium nitride (GaN) and its family of materials (including GaN, InN, AlN and their alloys) are known as the third generation of semiconductor, which has important applications in optoelectronics and microelectronics. In the structure of GaN-based high electron mobility transistor (HEMT) device, there is a relatively large conduction band offset in the AlGaN/GaN heterojunction structure, and it can produce a strong spontaneous and piezoelectric polarization effect in the vicinity of the heterojunction, which can also accumulate high concentrations of two-dimensional electron gas (2DEG) under the condition of no need of intentionally doping at the interface. The surface of Heterojunction AlGaN/GaN interface will form a 2DEG channel, and the 2DEG in potential well is controlled by the gate voltage, also the 2DEG layer is very close to the surface, which is sensitive to the state of the surface. When the surface state changes, it can cause a change in the 2DEG density, thus the concentration of 2DEG can be adjusted by changing the surface states, thereby changing the current between the source and drain. GaN-based HEMT serves as a gate control device, which has a high concentration of 2DEG and is sensitive to the surface state at the AlGaN/GaN heterojunction. According to the basic structure and advantages of the GaN-based HEMT device, the ferroelectric thin film PZT is deposited on the metal gate serving as a light sensitive layer. When the light is incident on the gate, the photo-sensing layer PZT generates the photovoltaic effect, which causes the surface charge of the photosensitive layer to change, and also causes the 2DEG to change, so the input current changes. In this paper, firstly, a new “M/F/M/S” structure is proposed by introducing a photosensitive material PZT on a GaN-based HEMT gate electrode and combining the PZT of a ferroelectric thin film with photovoltaic effect. Secondly, the HEMT device is fabricated on the AlGaN/GaN epitaxial wafer of sapphire substrate, and the photosensitive unit PZT is prepared on the gate, and thus the HEMT device with photosensitive is realized. Finally, the carrier concentration in the channel is regulated by the photovoltaic effect of PZT and 365 nm UV and visible light are detected through changing the source-drain current. The comparative tests under the conditions with and without a photosensitive gate HEMT device show that when the voltage Vgs is smaller, the saturation drain-source current Ids measured under the irradiation of visible light in the former condition is not reduced compared with that in the latter condition, and the increment of Ids measured in the former condition is 5.2 mA larger than in the latter condition. Therefore it can be seen that the PZT can act on the gate GaN-based HEMT device under the irradiation of visible and ultraviolet light and adjust the channel current.