Preparation of ferroelectric BaMgF_4films on GaAs for the control of two-dimensional electron gas

在本项目中，我们提出了一种新的器件，铁电栅高电子迁移率晶体管（F-HEMT），其中二维电子气（2DEG）可以通过铁电膜的极化来控制。为了实现该器件，我们研究了利用分子束外延（MBE）在AlGaAs/GaAs HEMT结构上生长铁电BaMgF_4薄膜。本工程采用的MBE系统由一个路岩室和两个生长室组成，其中一个用于生长Ga (Al) As，另一个用于生长BaMgF_4。首先，我们证明了（140）取向的BaMgF_4薄膜可以在高于500℃的GaAs衬底上生长。然而，当BaMgF_4薄膜生长在600℃以上时，由于组成元素的相互扩散，2DEG的电子迁移率下降。此外，本文还提出了两步生长法来生长高质量的BaMgF_4薄膜，即在550℃的温度下短时间生长（140）取向的BaMgF_4薄层，然后在300℃的温度下生长非晶BaMgF_4薄膜。对二步法生长的BaMgF_4薄膜进行退火处理，得到了良好的铁电性能和尖锐的界面。我们还研究了以Ar/Cl_2为蚀刻气体的BaMgF_4薄膜的干式蚀刻，发现干式蚀刻对薄膜的蚀刻损伤要小于湿式化学蚀刻。最后，我们首次制备了BaMgF_4/AlGaAs/GaAs f - hemt，并证明了由于BaMgF_4薄膜的铁电性质，该器件具有良好的晶体管特性和非易失性存储功能。

In this project, we have proposed a new device, ferroelectric-gate high electron mobility transistor (F-HEMT), in which two dimensional electron gas (2DEG) can be controlled by the polarization of the ferroelectric film. In order to realize the device, we have investigated the growth of ferroelectric BaMgF_4 thin films on AlGaAs/GaAs HEMT structures using molecular beam epitaxy (MBE). An MBE system used in this project consists of a road-rock chamber and two growth chambers, where one is used for Ga (Al) As growth and the other for BaMgF_4 growht. First, we have shown that the (140) -oriented BaMgF_4 films can be grown on GaAs substrates above 500ﾟC.However, it has been found that electron mobility of 2DEG decreases when the BaMgF_4 film is grown above 600ﾟC,because of the inter-diffusion of the constituent elements. In addition, 2-step growth method has been proposed to grow high quality BaMgF_4 films, where the thin (140) -oriented BaMgF_4 layr is grown at 550ﾟC for a short time followed by the low temperature (300ﾟC) growth of amorphous BaMgF_4 films. Good ferroelectric properties and sharp interfaces have been obtained by annealing the BaMgF_4 films grown by the 2-step method. We have also studied the dry etching of BaMgF_4 thin films using Ar/Cl_2 as etching gases and found that the etching damage is less serious for the film etched by dry-etching process than by the normal wet chemical etching. Finally, we have fabricated BaMgF_4/AlGaAs/GaAs F-HEMTs for the first time and shown that the device has proper transistro characteristics with non-volatile memory function because of the ferroelectric nature of the BaMgF_4 film.