本文選題：AlGaN/GaN + Al　； 參考：《天津大學》2015年碩士論文

【摘要】：由于AlGaN/GaN異質結材料在高頻、高能電子器件中具有廣闊的應用前景,所以近幾十年來該材料受到了人們的廣泛關注。理論上,通過提高勢壘層AlGaN中Al的含量可以提高載流子的濃度,然而這樣會增加AlGaN和GaN之間的晶格失配,進而使霍爾遷移率降低。為了解決此問題,Kuzmí等人提出利用Al In N代替AlGaN作為勢壘層,當其中In的成分為18%時,AlInN與GaN可以實現(xiàn)完美晶格匹配。本文利用MOCVD的方法制備了高質量的AlGaN/GaN、AlInN/AlN/GaN和AlInN/GaN/AlN/GaN異質結樣品,系統(tǒng)地研究了它們的磁輸運性質。測量了AlGaN/GaN和AlIn N/AlN/GaN兩個樣品不同溫度下(2-270 K)的載流子濃度和霍爾遷移率,在整個溫區(qū)范圍內Al InN/AlN/GaN中二維電子氣的濃度都要高于AlGaN/GaN中二維電子氣的濃度,然而AlGaN/GaN異質結中電子卻擁有更高的霍爾遷移率和更低的方塊電阻。在兩者的磁電阻中都觀察到了SdH(Shubnikov-de Haas oscillations)振蕩現(xiàn)象,然而Al GaN/GaN中的振蕩明顯比AlInN/AlN/GaN樣品中的振蕩強,表明在AlGaN/GaN異質結中電子具有更高的量子遷移率。通過SdH振蕩的FFT(Fast Fourier Transformation)變換譜,可以知道兩個樣品中的電子均只占據(jù)最低的能級并且可以得到二維電子氣的濃度,利用這種方法得到的載流子濃度和霍爾測量得到的值基本一致,表明兩個樣品中不存在平行電導。2 K下,霍爾遷移率和量子遷移率的比值都遠大于1,說明在低溫下,電子受到的主要散射是小角散射,散射源可能來自勢壘層中的電離雜質等。從Al InN/AlN/GaN和Al InN/GaN/AlN/GaN兩個樣品的AFM圖像可以觀察到GaN插入層的存在有效地降低了樣品的粗糙度。同時,GaN插入層增大了二維電子氣波函數(shù)與AlInN勢壘層之間的距離,從而降低了二維電子氣波函數(shù)進入勢壘層的可能性,進而降低了合金無序散射對電子的散射作用。這樣使得AlInN/GaN/AlN/GaN在保持了較高的載流子濃度的前提下,大幅度地提高了載流子的霍爾遷移率,從而降低了樣品中的方塊電阻,使得AlInN/GaN/AlN/GaN的電輸運性質整體得到了提升。此外,GaN插入層明顯增強了SdH振蕩,這是由于GaN插入層削弱了界面粗糙度、合金無序和電離雜質等對電子的散射作用,使得AlInN/GaN/AlN/GaN樣品中電子擁有更高的量子遷移率。
[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 鉚 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.
【學位授予單位】：天津大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TN304.2

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