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

本课题的科学目标是开发和测试基于铟铝氮化镓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。与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相比，铟-铝-氮化镓材料系统具有根本的优势。特别是，在太赫兹光谱范围内工作的铟铝氮化镓半导体激光器（频率在1-10太赫兹范围内）有望在室温下工作，这与以前在其他材料系统中演示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。铟铝氮化镓材料也有望创造一种新的非线性超材料，用于光纤通信设备使用的波长，响应时间低于1皮秒。两名研究生将在课程期间接受培训。两位主要研究人员还将继续每年参加国家科学基金会本科项目的研究经验和各自机构的各种K-12外展活动。技术描述。本提案的目标是开发基于应变补偿的InGaN/AlGaN/GaN异质结构的子带间光电器件，该器件生长在非极性m平面GaN衬底上，用于在短波红外（波长范围在1.4-3微米）和太赫兹（波长范围在30-300微米）区域的电磁波谱中工作。目前的子带间器件依赖于相对较低的导带偏移（1 eV）和较低的纵向光学声子能量（~30-40 meV）的材料，这分别阻止了子带间器件在短波长的红外中工作，并限制了太赫兹量子级联激光器在低温下的工作。为了克服上述问题，在c平面衬底上生长GaN/AlGaN异质结构已经进行了研究。氮化镓基材料系统提供超过2 eV的导带偏移，光学声子能量为~90 meV。然而，应变相关的压电场使得在c平面衬底上生长的实际器件几乎不可能产生所需的子带间带结构。此外，相对较小的异质结构厚度，受应变的限制，以及异质结构中较差的光场约束，阻碍了先前报道的器件中有效的光物质相互作用。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。将研究两种类型的子带间器件：双金属波导太赫兹qcl和用于电信频谱范围的子带间非线性超表面。前一种器件代表了在太赫兹光谱范围内开发第一台室温电泵浦半导体激光器的可行途径，而后一种器件为开发具有短波红外巨大非线性响应的亚带间超表面提供了途径。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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.