Diluted Magnetic Semiconductor Based Memory Devices

为了评估基于铁磁稀磁半导体（DMS）的存储器件的可行性，对III-V族铁磁DMS的工艺、存储器件结构进行了研究。取得了以下结果。（1）首次采用低温分子束外延（MBE）技术合成了以GaAs为基的Ⅲ-Ⅴ族铁磁DMS（Ga，Mn）As。发现最大Mn摩尔分数为0.071。X射线衍射研究表明，随着Mn摩尔分数的增加，晶格常数增加（Vegard定律）。这种材料可以适合于存储器应用，因为它可以容易地与现有的III-V电路集成。（2）磁化强度和磁输运测量表明，（Ga，Mn）As具有铁磁性，居里温度最高可达110 K，居里温度与Mn的摩尔分数成正比。（3）用InGaAs缓冲层反转（Ga，Mn）As中的应变方向，可以使易磁化轴垂直于样品面。这对于利用反常霍尔效应阅读存储器中存储的信息的存储器应用是非常重要的发现。（4）由临界散射和居里温度确定了铁磁性的起源是RKKY相互作用。（5）发展了存储器制造工艺，并制作了存储器元件，以研究其应用潜力。

In order to asses the feasibility of memory devices based on ferromagnetic diluted magnetic semiconductors (DMS's)'study on III-V based ferromagnetic DMS's, its processing technology, memory devices structures has been carried out. The following results have been obtained.(1)New III-V based ferromagnetic DMS based on GaAs, (Ga, Mn)As, has been synthesized for the first time by low temperature molecular beam epitaxy (MBE). Maximum Mn mole fraction was found to be 0.071. X-ray diffraction study showed increase of lattice constant with increase of Mn mole fraction (vegard's law). This material may be suitable for the memory application since it can be easily integrated with existing III-V circuity.(2)Magnetization as well as magnetotransport measurements showed that (Ga, Mn)As is ferromagnetic ; the highest curie temperature so far obtained was 110K.Curie temperature is proportional to Mn mole fraction below 0.05.(3)Reversing the strain direction in (Ga, Mn)As by using InGaAs buffer layrs, it was shown that the easy axis can be made perpendicular to the sample plane. This is very important finding for the memory application using anomalous Hall effect for reading the information stored in memory.(4)From critical scattering and Curie temperature, it was found that the origin of ferromagnetism is RKKY interaction.(5)Processing technology for memory fabrication has been developed and memory elements were fabricated to study its potential for applicaitons.