氮化镓基感光栅极高电子迁移率晶体管器件设计与制备

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

GaN基高电子迁移率晶体管(HEMT)作为栅控器件,具有AlGaN/GaN异质结处高浓度的二维电子气(2DEG)及对表面态敏感等特性,在栅位置处与感光功能薄膜的结合是光探测器领域重要的研究方向之一.本文首先提出在GaN基HEMT栅电极上引入光敏材料锆钛酸铅(PZT),将具有光伏效应的铁电薄膜PZT与HEMT栅极结合,提出一种新的"金属/铁电薄膜/金属/半导体(M/F/M/S)"结构;然后在以蓝宝石为衬底的AlGaN/GaN外延片上制备感光栅极HEMT器件.最后,通过PZT的光伏效应来调控沟道中的载流子浓度和通过源漏电流的变化来实现对可见光和紫外光的探测.在365 nm紫外光和普通可见光条件下,对比测试有/无感光栅极的HEMT器件,在较小V_(gs)电压时,可见光下测得前者较后者的饱和漏源电流I_(ds)的增幅不下降,紫外光下前者较后者的I_(ds)增幅大5.2 mA,由此可知,感光栅PZT在可见光及紫外光下可作用于栅极GaN基HEMT器件并可调控沟道电流.

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 V（gs） is smaller, the saturation drainsource current I（ds）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 I（ds）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.