Janipour Mohsen, Misirlioglu I Burc, Sendur Kursat
Faculty of Engineering and Natural Science, Sabanci University, 34956 Istanbul, Turkey.
Materials (Basel). 2019 Jul 29;12(15):2412. doi: 10.3390/ma12152412.
Semiconductor heterostructures are suitable for the design and fabrication of terahertz (THz) plasmonic devices, due to their matching carrier densities. The classical dispersion relations in the current literature are derived for metal plasmonic materials, such as gold and silver, for which a homogeneous dielectric function is valid. Penetration of the electric fields into semiconductors induces locally varying charge densities and a spatially varying dielectric function is expected. While such an occurrence renders tunable THz plasmonics a possibility, it is crucial to understand the conditions under which propagating resonant conditions for the carriers occur, upon incidence of an electromagnetic radiation. In this manuscript, we derive a dispersion relation for a p-n heterojunction and apply the methodology to a GaAs p-n junction, a material of interest for optoelectronic devices. Considering symmetrically doped p- and n-type regions with equal width, the effect of certain parameters (such as doping and voltage bias) on the dispersion curve of the p-n heterojunction were investigated. Keeping in sight the different effective masses and mobilities of the carriers, we were able to obtain the conditions that yield identical dielectric functions for the p- and n-regions. Our results indicated that the p-n GaAs system can sustain propagating resonances and can be used as a layered plasmonic waveguide. The conditions under which this is feasible fall in the frequency region between the transverse optical phonon resonance of GaAs and the traditional cut-off frequency of the diode waveguide. In addition, our results indicated when the excitation was slightly above the phonon resonance frequency, the plasmon propagation attained low-loss characteristics. We also showed that the existence or nonexistence of the depletion zone between the p- and n- interfaces allowed certain plasmon modes to propagate, while others decayed rapidly, pointing out the possibility for a design of selective filters.
由于半导体异质结构具有匹配的载流子密度，因此适用于太赫兹（THz）等离子体器件的设计与制造。当前文献中的经典色散关系是针对金属等离子体材料（如金和银）推导出来的，对于这些材料，均匀的介电函数是有效的。电场穿透半导体时会引起局部变化的电荷密度，预计会出现空间变化的介电函数。虽然这种情况使可调谐太赫兹等离子体成为可能，但了解在电磁辐射入射时载流子发生传播共振的条件至关重要。在本手稿中，我们推导了p-n异质结的色散关系，并将该方法应用于GaAs p-n结，这是一种对光电器件有意义的材料。考虑到对称掺杂且宽度相等的p型和n型区域，研究了某些参数（如掺杂和电压偏置）对p-n异质结色散曲线的影响。考虑到载流子的不同有效质量和迁移率，我们能够获得使p区和n区具有相同介电函数的条件。我们的结果表明，p-n GaAs系统能够维持传播共振，可作为分层等离子体波导使用。这种情况可行的条件落在GaAs的横向光学声子共振频率与二极管波导的传统截止频率之间的频率区域。此外，我们的结果表明，当激发略高于声子共振频率时，等离子体传播具有低损耗特性。我们还表明，p-n界面之间耗尽区的存在与否允许某些等离子体模式传播，而其他模式则迅速衰减，这指出了设计选择性滤波器的可能性。
