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

在本计画中，我们提出一种新的元件-铁电闸极高电子迁移率电晶体（F-HEMT），其中二维电子气（2DEG）可借由铁电薄膜的极化来控制。为了实现该器件，我们采用分子束外延（MBE）技术在AlGaAs/GaAs HEMT结构上生长了BaMgF_4铁电薄膜。本项目所用的分子束外延系统由一个岩路室和两个生长室组成，其中一个用于Ga（Al）As生长，另一个用于BaMgF_4生长。首先，我们已经表明，（140）取向的BaMgF_4薄膜可以在高于500 ℃的GaAs衬底上生长。然而，已经发现，当BaMgF_4薄膜生长高于600 ℃时，由于组成元素的相互扩散，2DEG的电子迁移率降低。此外，我们还提出了两步生长法，即先在550 ℃下短时间生长（140）取向的BaMgF_4薄膜，然后在300 ℃下生长非晶BaMgF_4薄膜。对两步法生长的BaMgF_4薄膜进行退火处理，获得了良好的铁电性能和清晰的界面。我们还研究了以Ar/Cl_2为刻蚀气体的BaMgF_4薄膜的干法刻蚀，发现干法刻蚀对薄膜的刻蚀损伤比常规的湿法化学刻蚀小。最后，我们首次制备了BaMgF_4/AlGaAs/GaAsF-HEMT器件，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.