宽禁带III族氮化物极化特性的研究
发布时间：2018-07-24 22:08
【摘要】：以GaN为代表的宽禁带III族氮化物在高能、高频、功率以及光电器件中有重要的应用的价值。由于晶体结构中心不对称,材料中存在着强的自极化效应。基于此,本文主要研究宽禁带III族氮化物的极化特性,以及极化效应在宽禁带III族氮化物基器件中的应用。首先,本文介绍了第一性原理计算方法和理论模型,利用CASTEP软件包基于第一性原理计算,研究了GaN和AlGaN的能带结构以及电子态密度。分析了价电子处在的能级位置。利用DOML软件包基于第一性原理计算,研究了GaN/AlN超晶格中极化效应对电子态密度以及电荷分布的影响。在极化效应的作用下,Ga原子处于价带底的3d态电子跃迁到上价带顶和导带中。在异质结的结面处,出现了正电荷和负电荷堆积现象。通过自洽求解薛定谔方程和泊松方程,研究了极化效应对AlGaN/GaN异质结中二维电子气的作用。无需杂质掺杂,利用极化诱导掺杂获得了浓度为1019cm-3量级的二维电子气。总结了不同Al组分和不同AlGaN薄膜厚度,极化诱导二维电子气浓度和分布变化的规律。深入的研究了极化诱导掺杂提高宽禁带III族氮化物掺杂效率的问题。无需杂质掺杂,沿[0001]晶向方向,线性的增加AlGaN薄膜Al的组分,获得了电子浓度达到1019cm-3量级的n型AlGaN薄膜。无需杂质掺杂,在Si衬底上制备出具有二极管电学特性的极化诱导掺杂的高Al组分AlGaN基PN结。最后运用Silvaco软件中的ATLAS半导体器件仿真器,分析了极化效应对AlGaN基紫外LED发光效率的影响。由极化效应产生的极化电场,导致能带弯曲,电子空穴波函数空间分离,溢出电流增加。对N-face AlGaN基紫外LED的光学特性和辐射光谱进行了研究,并与Ga-face AlGaN基紫外LED对比。在N-face AlGaN紫外LED中引入了阶梯结构的电子注入层。通过分析光谱、电流-输出光功率特性曲线、能带结构图以及载流子辐射复合速率,结果表明相对于Ga-face的紫外LED,N-face的紫外LED具有更好的光学性能,阶梯结构的电子注入层可以有效的降低溢出电流,提高紫外LED的发光效率。
[Abstract]:The wide band gap III nitrides, represented by GaN, have important applications in high energy, high frequency, power and optoelectronic devices. Due to the asymmetry of crystal structure center, there is a strong self-polarization effect in the material. Based on this, the polarization characteristics of wide band gap III group nitride and the application of polarization effect in wide band gap III family nitride based devices are studied in this paper. Firstly, the first principle calculation method and theoretical model are introduced. The energy band structure and electronic density of states of GaN and AlGaN are studied by using CASTEP software package based on first principle calculation. The energy level position of valence electron is analyzed. The effects of polarization on the density of states and charge distribution in GaN/AlN superlattices have been studied by using DOML software package based on first-principles calculations. Under the effect of polarization, the electrons in the 3D states of Ga atoms at the bottom of the valence band transition to the top of the upper valence band and the conduction band. At the junction surface of the heterojunction, positive charge and negative charge stacking appear. By self-consistent solution of Schrodinger equation and Poisson equation, the effect of polarization effect on two-dimensional electron gas in AlGaN/GaN heterojunction is studied. Without impurity doping, two dimensional electron gas with concentration of 1019cm-3 was obtained by polarization induced doping. The changes of concentration and distribution of two-dimensional electron gas induced by polarization with different Al components and different thickness of AlGaN films were summarized. The effect of polarization induced doping on the efficiency of wide band gap III nitride doping was studied. Without impurity doping and along the direction of [0001] crystal direction, the composition of Al in AlGaN thin films was linearly increased, and n-type AlGaN films with electron concentration of 1019cm-3 order were obtained. Polarization-induced doped AlGaN based PN junctions with diode electrical properties were fabricated on Si substrates without impurity doping. Finally, using the ATLAS semiconductor device simulator in Silvaco software, the effect of polarization effect on the luminescence efficiency of AlGaN based UV LED is analyzed. The polarized electric field produced by the polarization effect results in the band bending, the separation of the electron hole wave function in space, and the increase of the overflow current. The optical properties and radiation spectra of N-face AlGaN based UV LED were studied and compared with Ga-face AlGaN based UV LED. An electron injection layer with step structure was introduced into N-face AlGaN UV LED. By analyzing spectrum, current-output optical power characteristic curve, band structure diagram and carrier radiation recombination rate, the results show that the UV LED of Ga-face has better optical performance than the UV LEDN-face of Ga-face. The electron injection layer with step structure can effectively reduce the overflow current and improve the luminescence efficiency of UV LED.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN304
[Abstract]:The wide band gap III nitrides, represented by GaN, have important applications in high energy, high frequency, power and optoelectronic devices. Due to the asymmetry of crystal structure center, there is a strong self-polarization effect in the material. Based on this, the polarization characteristics of wide band gap III group nitride and the application of polarization effect in wide band gap III family nitride based devices are studied in this paper. Firstly, the first principle calculation method and theoretical model are introduced. The energy band structure and electronic density of states of GaN and AlGaN are studied by using CASTEP software package based on first principle calculation. The energy level position of valence electron is analyzed. The effects of polarization on the density of states and charge distribution in GaN/AlN superlattices have been studied by using DOML software package based on first-principles calculations. Under the effect of polarization, the electrons in the 3D states of Ga atoms at the bottom of the valence band transition to the top of the upper valence band and the conduction band. At the junction surface of the heterojunction, positive charge and negative charge stacking appear. By self-consistent solution of Schrodinger equation and Poisson equation, the effect of polarization effect on two-dimensional electron gas in AlGaN/GaN heterojunction is studied. Without impurity doping, two dimensional electron gas with concentration of 1019cm-3 was obtained by polarization induced doping. The changes of concentration and distribution of two-dimensional electron gas induced by polarization with different Al components and different thickness of AlGaN films were summarized. The effect of polarization induced doping on the efficiency of wide band gap III nitride doping was studied. Without impurity doping and along the direction of [0001] crystal direction, the composition of Al in AlGaN thin films was linearly increased, and n-type AlGaN films with electron concentration of 1019cm-3 order were obtained. Polarization-induced doped AlGaN based PN junctions with diode electrical properties were fabricated on Si substrates without impurity doping. Finally, using the ATLAS semiconductor device simulator in Silvaco software, the effect of polarization effect on the luminescence efficiency of AlGaN based UV LED is analyzed. The polarized electric field produced by the polarization effect results in the band bending, the separation of the electron hole wave function in space, and the increase of the overflow current. The optical properties and radiation spectra of N-face AlGaN based UV LED were studied and compared with Ga-face AlGaN based UV LED. An electron injection layer with step structure was introduced into N-face AlGaN UV LED. By analyzing spectrum, current-output optical power characteristic curve, band structure diagram and carrier radiation recombination rate, the results show that the UV LED of Ga-face has better optical performance than the UV LEDN-face of Ga-face. The electron injection layer with step structure can effectively reduce the overflow current and improve the luminescence efficiency of UV LED.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN304
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