Collaborative Research: Intersubband transitions and devices in non-polar strain-compensated InGaN/AlGaN

该提案的科学目标是开发和测试基于铟铝镓氮化物材料的人工半导体非线性光学材料和半导体量子级联激光器。铟-铝-镓-氮化物材料系统比以前用于制造量子级联激光器和人工半导体非线性光学材料的材料具有根本优势。特别是，在太赫兹光谱范围（1-10 THz范围内的频率）内工作的氮化铟铝镓半导体激光器预计能够在室温下工作，这与先前在其他材料系统中证明的半导体激光器不同。室温太赫兹半导体激光器将对在该频率范围内工作的仪器产生重大的变革性影响。氮化铟铝镓材料也有望创造一种新型的非线性超材料，用于在光纤电信设备使用的波长下工作，响应时间低于1皮秒。两名研究生将在该计划的过程中进行培训。两位主要研究人员还将继续每年参加国家科学基金会的本科生项目研究经验，以及他们所在机构的各种K-12外联活动。技术说明。该提议的目的是开发基于生长在非极性m-平面GaN衬底上的应变补偿InGaN/AlGaN/GaN异质结构的子带间光电器件，用于在电磁波谱的短波长红外（波长在1.4-3微米范围内）和太赫兹（波长在30-300微米范围内）区域中操作。当前的子带间器件依赖于具有相对低的导带偏移（leV）和低的纵向光学声子能量（~30-40 meV）的材料，这分别防止子带间器件在短波长红外中操作，并将太赫兹量子级联激光器的操作限制在低温温度。先前已经研究了在c面衬底上生长的GaN/AlGaN异质结构以克服上述问题。GaN基材料系统提供超过2 eV的导带偏移，并具有约90 meV的光学声子能量。然而，应变相关的压电场使得它几乎不可能产生所需的子带间能带结构在实际的c-平面衬底上生长的设备。此外，相对较小的异质结构厚度，受应变的限制，以及异质结构中的光场限制较差，阻碍了先前报道的器件中的有效光-物质相互作用。所提出的m-平面GaN衬底上的AlInGaN异质结构不受应变诱导场的影响，使得可靠的子带间能带结构设计成为可能。应变补偿将用于克服材料生长中的临界厚度限制。异质结构将被进一步加工成双金属等离子体腔，使用光电化学蚀刻去除衬底，以实现有效的光物质集成。两种类型的子带间设备将被调查：双金属波导太赫兹QCL和子带间非线性超表面的电信光谱范围内的操作。前一种器件代表了一条可行的途径，可以开发出第一种在太赫兹光谱范围内的室温电泵浦半导体激光器，而后一种器件提供了用于开发具有巨大非线性响应的子带间元表面的路径，该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

The scientific objective of this proposal is to develop and test artificial semiconductor nonlinear optical materials and semiconductor quantum cascade lasers based on indium-aluminum-gallium-nitride materials. The indium-aluminum-gallium-nitride materials system has fundamental advantages over the materials that were previously used for making quantum cascade lasers and artificial semiconductor nonlinear optical materials. In particular, indium-aluminum-gallium-nitride semiconductor lasers operating in the terahertz spectral range (frequencies in the range of 1-10 THz) are expected to be able to operate at room temperature, unlike semiconductor lasers previously demonstrated in other materials systems. Room-temperature terahertz semiconductor lasers will have a major transformative impact on the instrumentation operating in this frequency range. Indium-aluminum-gallium-nitride materials are also expected to enable the creation of a novel kind of nonlinear metamaterials for operation at the wavelengths used by fiber-optics telecommunication equipment with sub-1-picosecond response time. Two graduate students will be trained during the course of the program. The two principal investigators will also continue their annual participation in the National Science Foundation research experience for undergraduate program and in various K-12 outreach activities at their institutions. Technical Description. The objective of this proposal is to develop intersubband optoelectronic devices based on strain-compensated InGaN/AlGaN/GaN heterostructures grown on non-polar m-plane GaN substrates for operation in the short-wavelength infrared (wavelengths in the range 1.4-3 microns) and terahertz (wavelengths in the range 30-300 microns) regions of the electromagnetic spectrum. Current intersubband devices rely on materials with relatively low conduction band offsets (1 eV) and low longitudinal optical phonon energies (~30-40 meV) that, respectively, prevent intersubband devices from operating in the short-wavelength infrared and limit the operation of terahertz quantum cascade lasers to cryogenic temperatures. GaN/AlGaN heterostructures grown on c-plane substrates have been previously investigated to overcome the abovementioned problems. GaN-based materials system offers conduction band offsets over 2 eV and have optical phonon energies of ~90 meV. However, strain-dependent piezo-electric fields make it virtually impossible to produce desired intersubband bandstructure in practical devices grown on c-plane substrates. Additionally, relatively small heterostructure thickness, limited by strain, and poor optical field confinement in the heterostructure prevented efficient light-matter interaction in devices reported previously. The proposed AlInGaN heterostructures on m-plane GaN substrates are free from strain-induced fields making reliable intersubband bandstructure design possible. Strain-compensation will be used to overcome critical thickness constrains in materials growth. The heterostructures will be further processed into double-metal plasmonic cavities using photoelectrochemical etching for substrate removal to enable efficient light-matter integration. Two types of intersubband devices will be investigated: double-metal waveguide THz QCLs and intersubband nonlinear metasurfaces for operation in the telecommunication spectral range. The former devices represent a viable path towards developing the first room-temperature electrically pumped semiconductor lasers in the THz spectral range, while the latter devices offer a path for developing intersubband metasurfaces with a giant nonlinear response for short-wavelength infrared.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.