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

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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.