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

该方案的科学目标是开发和测试基于铟铝镓氮化物材料的人造半导体非线性光学材料和半导体量子级联激光器。与以往用于制造量子级联激光器和人造半导体非线性光学材料的材料相比，铟-铝-镓-氮化物材料体系具有根本的优势。特别是，与以前在其他材料系统中展示的半导体激光器不同，工作在太赫兹光谱范围(频率范围为1-10太赫兹)的铟-铝-氮化镓半导体激光器预计能够在室温下工作。室温太赫兹半导体激光器将对在此频率范围内运行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型的非线性超材料，用于在响应时间低于1皮秒的光纤通信设备所使用的波长下运行。两名研究生将在项目过程中接受培训。两位首席研究员还将继续每年参加国家科学基金会本科生研究经验项目和他们所在机构的各种K-12外展活动。技术说明。该方案的目的是开发基于应变补偿的InGaN/AlGaN/GaN异质结的子带间光电器件，用于工作在电磁光谱的短波红外(波长1.4-3微米)和太赫兹(波长30-300微米)区域。目前的子带间器件依赖于具有相对较低的导带偏移量(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红外下工作，并将太赫兹量子级联激光器的工作温度限制在低温下。为了克服上述问题，人们已经研究了生长在c平面衬底上的GaN/AlGaN异质结。GaN基材料系统的导带偏移量大于2 eV，光学声子能量约为90 meV。然而，应变相关的压电场使得在生长在c平面衬底上的实际器件中几乎不可能产生所需的子带间带结构。此外，受应变限制的相对较小的异质结厚度，以及异质结中较差的光场限制，阻碍了以前报道的器件中有效的光-物质相互作用。所提出的在m平面GaN衬底上生长的AlInGaN异质结不受应变感应场的影响，使得可靠的子带间能带结构设计成为可能。应变补偿将被用来克服材料生长中的临界厚度约束。异质结将被进一步加工成双金属等离子体腔，使用光电化学刻蚀去除衬底，以实现高效的光-物质集成。两种类型的子带间器件将被研究：双金属波导太赫兹准分子激光器和工作在通信光谱范围内的子带间非线性亚表面。前者代表了一条在太赫兹光谱范围内开发第一台室温电泵半导体激光器的可行途径，而后者则提供了一条开发短波红外线具有巨大非线性响应的子带间亚表面的途径。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.