缺陷对III族氮化物瞬态光谱的影响及调控研究

The excitation spectra and carrier relaxation properties of carriers in III-nitrides are closely related to the defects, and exploring the effect of defects on their transient spectra is critical to the performance improvement of nitride-based devices. Due to the diversity of defects types and states, the effects and mechanisms of defects on transient spectra are not fully understood, which are extremely unfavorable for the performance improvement and widespread applications of devices. Recently, by tuning the distribution of photo-excited carriers, the characteristics of absorption spectra and carrier lifetime of Mg impurity and intrinsic defects in GaN were distinguished by femtosecond transient spectroscopy. According to this idea, the transient absorption spectra and pump-probe with phase-object are combined experimentally to carry out the qualitative and quantitative relationship between transient absorption and defect states of III-nitrides systematically under different doping and growth conditions. Thus, the carrier capture cross-section, absorption cross-section and refraction volume of the corresponding defect states can be obtained. Simultaneously, by using hybrid density function first-principles calculations, the theoretical interpretation of the experimental results is given. Accordingly, the absorption spectra and carrier lifetime in III-nitrides can be further regulated and improved. Our project will greatly promote the widespread applications of III-nitrides in optoelectronic devices such as light emitting diodes, detectors, and solar energy.

III族氮化物中的激发光谱以及载流子弛豫特性与缺陷密切相关，探究缺陷对其瞬态光谱的影响对氮化物基器件的性能提升至关重要。由于缺陷类型和状态的多样性，目前为止，缺陷对瞬态光谱的影响及机理尚不完全清楚，这对器件的性能改良和广泛应用极为不利。最近，申请人通过调控光生载流子分布，利用飞秒瞬态光谱区分了GaN中镁杂质和本征缺陷态的吸收光谱特性和载流子寿命。据此思路，本项目在实验上拟将瞬态吸收光谱和相位物体泵浦探测结合，系统深入地开展III族氮化物在不同掺杂和生长条件下瞬态吸收光谱与缺陷态之间的定性和定量关系，获得相应缺陷态的载流子俘获截面、吸收截面和折射体积；同时利用杂化密度泛函第一性原理方法对实验结果给出理论解释，据此进一步调控和改良III族氮化物的吸收光谱和载流子寿命。我们的研究将极大促进III族氮化物在发光二极管、探测器以及太阳能等光电子器件中的广泛应用。

以氮化镓与碳化硅为代表的第三代半导体材料已被认为是当今电子产业发展的新动力。但是，在宽禁带半导体中存在的不同杂质和缺陷会严重影响载流子复合和寿命，影响半导体器件的效率。因此，了解缺陷态俘获的载流子动力学对改善器件的性能至关重要。本项目利用飞秒瞬态吸收光谱技术结合半导体的能带和复合理论，在区分不同缺陷态下的载流子复合过程和机制，缺陷和掺杂对能带结构影响、载流子寿命及吸收光谱的调制等方面取得了如下研究成果：. （1）掺杂和缺陷对n型GaN载流子动力学的影响机理及寿命调控。利用在单光子和双子激发下的超快瞬态光谱确定线缺陷和体缺陷的载流子俘获机制，确定了相应的俘获系数，并从实验和理论上实现了不同掺杂和激发条件制对GaN载流子寿命和瞬态吸收光谱的调制。. （2）碳缺陷对GaN光生载流子的超快俘获和复合机制。利用不同泵浦能流下的超快瞬态光谱，区分了电子和空穴的载流子俘获过程，证明了碳缺陷在GaN中两种电荷态的存在，并利用双俘获模型获得了碳不同电荷态对电子和空穴的俘获系数。. （3）不同导电类型碳化硅的超快瞬态吸收光谱研究。利用氮和钒掺杂实现碳化硅的n型掺杂和半绝缘型调控；通过调节飞秒瞬态吸收光谱的激发波长，调控光生载流子分布，区分了碳化硅载流子表面和体缺陷的俘获过程；通过研究瞬态光谱波形的演变推断了表面和缺陷态在能带中的位置；利用全局分析和简化载流子弛豫模型确定并明确解释了各种弛豫复合机制的载流子寿命和对瞬态光谱的影响。. 我们相信上述的研究与成果对宽禁带半导体的缺陷物理学的研究与在未来光电子器件领域中的应用具有重要意义。