GaN-基半导体异质结的磁输运性质研究

发布时间：2018-06-24 23:46

本文选题：AlGaN/GaN + Al　；参考：《天津大学》2015年硕士论文

【摘要】：由于AlGaN/GaN异质结材料在高频、高能电子器件中具有广阔的应用前景,所以近几十年来该材料受到了人们的广泛关注。理论上,通过提高势垒层AlGaN中Al的含量可以提高载流子的浓度,然而这样会增加AlGaN和GaN之间的晶格失配,进而使霍尔迁移率降低。为了解决此问题,Kuzmí等人提出利用Al In N代替AlGaN作为势垒层,当其中In的成分为18%时,AlInN与GaN可以实现完美晶格匹配。本文利用MOCVD的方法制备了高质量的AlGaN/GaN、AlInN/AlN/GaN和AlInN/GaN/AlN/GaN异质结样品,系统地研究了它们的磁输运性质。测量了AlGaN/GaN和AlIn N/AlN/GaN两个样品不同温度下(2-270 K)的载流子浓度和霍尔迁移率,在整个温区范围内Al InN/AlN/GaN中二维电子气的浓度都要高于AlGaN/GaN中二维电子气的浓度,然而AlGaN/GaN异质结中电子却拥有更高的霍尔迁移率和更低的方块电阻。在两者的磁电阻中都观察到了SdH(Shubnikov-de Haas oscillations)振荡现象,然而Al GaN/GaN中的振荡明显比AlInN/AlN/GaN样品中的振荡强,表明在AlGaN/GaN异质结中电子具有更高的量子迁移率。通过SdH振荡的FFT(Fast Fourier Transformation)变换谱,可以知道两个样品中的电子均只占据最低的能级并且可以得到二维电子气的浓度,利用这种方法得到的载流子浓度和霍尔测量得到的值基本一致,表明两个样品中不存在平行电导。2 K下,霍尔迁移率和量子迁移率的比值都远大于1,说明在低温下,电子受到的主要散射是小角散射,散射源可能来自势垒层中的电离杂质等。从Al InN/AlN/GaN和Al InN/GaN/AlN/GaN两个样品的AFM图像可以观察到GaN插入层的存在有效地降低了样品的粗糙度。同时,GaN插入层增大了二维电子气波函数与AlInN势垒层之间的距离,从而降低了二维电子气波函数进入势垒层的可能性,进而降低了合金无序散射对电子的散射作用。这样使得AlInN/GaN/AlN/GaN在保持了较高的载流子浓度的前提下,大幅度地提高了载流子的霍尔迁移率,从而降低了样品中的方块电阻,使得AlInN/GaN/AlN/GaN的电输运性质整体得到了提升。此外,GaN插入层明显增强了SdH振荡,这是由于GaN插入层削弱了界面粗糙度、合金无序和电离杂质等对电子的散射作用,使得AlInN/GaN/AlN/GaN样品中电子拥有更高的量子迁移率。
[Abstract]:AlGaN / gan heterojunction materials have wide application prospects in high-frequency and high-energy electronic devices, so in recent decades, this material has been paid more and more attention. Theoretically, the concentration of carriers can be increased by increasing the Al content in AlGaN, however, the lattice mismatch between AlGaN and gan will be increased, and the Hall mobility will be reduced. In order to solve this problem, Kuzm 铆 proposed to replace AlGaN with AlGaN as barrier layer. When the composition of in is 18 layers, AlInN and gan can achieve perfect lattice matching. In this paper, high quality AlGaN / gan / AlInN / AlN / gan and AlInN / gan / AlN / gan heterostructures have been prepared by MOCVD, and their magnetic transport properties have been studied systematically. The carrier concentration and Hall mobility at different temperatures (2-270K) of AlGaN / GaN and AlInN / AlN- / gan samples were measured. In the whole temperature range, the concentration of two-dimensional electron gas in Al InN / AlN / gan was higher than that in AlGaN / AlN / gan, and the concentration of two-dimensional electron gas in AlGaN / AlN / gan was higher than that in AlGaN / AlN / gan. However, the electrons in Algan / gan heterojunction have higher Hall mobility and lower square resistance. The SdH (Shubnikov-de Haas oscillations) oscillation is observed in both magnetoresistance, but the oscillation in Al gan / gan is stronger than that in AlInN / AlN / gan, indicating that the electron has higher quantum mobility in AlGaN / gan heterojunction. By using the FFT (Fast Fourier Transformation) transform spectrum of the SdH oscillation, it can be known that the electrons in the two samples only occupy the lowest energy level and the concentration of the two-dimensional electron gas can be obtained. The carrier concentration obtained by this method is basically the same as that obtained by Hall measurement. It is shown that there is no parallel conductance at 2.2K, the ratio of Hall mobility to quantum mobility is far greater than 1, which indicates that at low temperature, the main scattering of electrons is small angle scattering, and the scattering source may come from the ionization impurities in the barrier layer. From the AFM images of Al InN / AlN / gan and Al InN / gan / AlN / gan, we can see that the existence of gan intercalation layer can effectively reduce the roughness of the samples. At the same time, the insertion layer increases the distance between the two-dimensional electron wave function and the AlInN barrier layer, thus reducing the possibility of the two-dimensional electron gas wave function entering the barrier layer, and thus reducing the scattering effect of the alloy random scattering on the electron. This makes AlInN / gan / AlN / gan keep a high carrier concentration, greatly increases the Hall mobility of the carriers, reduces the square resistance in the sample, and improves the electrical transport properties of AlInN / gan / AlN / gan as a whole. In addition, the SdH oscillation is enhanced obviously by the insertion layer of gan, which is due to the weakening of the interface roughness, the disorder of the alloy and the scattering of electrons by the ionization impurity, which makes the electrons in AlInN / gan / AlN / gan samples have higher quantum mobility.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN304.2

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