CAREER: Short-Wavelength Vertical-Cavity Surface-Emitting Laser Arrays Using Nonpolar and Semipolar GaN

该学院早期职业发展(CALEAR)计划奖项的研究目标是展示第一个具有稳定和可预测的光偏振的短波长(蓝绿)垂直腔面发射激光器(VCSEL)阵列。该方法将使用一种创新的制造工艺来解决GaN基材料的问题，这些问题以前限制了短波长VCSEL的输出功率、波长范围和功能。VCSEL中阻碍光偏振系统控制的根本挑战将通过新的材料生长工艺来克服。具有稳定和可预测的光偏振的短波长垂直腔面发射激光器的实现将使其在高密度光学数据存储、高分辨率打印、照明、显示器、投影仪、微型原子钟和化学/生物传感等方面具有独特的应用，而这些应用是传统的边缘发射激光器不容易实现的。为了解决各种需要更高功率光发射器的偏振敏感应用，这些设备将形成偏振钉扎阵列。教育和宣传部分的目的是提高人们对科学、技术、工程和数学(STEM)学科的兴趣，并培养本科生和K-12年级的科学素养。这些活动的重点是与代表性不足的学生合作，包括美洲原住民、西班牙裔和女性。具体的教育目标是与西南印度理工学院在教育和外展项目上合作，继续为代表不足的人群和当地K-12教师开展指导活动，并开发光电设备制造技术的本科生/研究生课程。氮化镓(GaN)的非极性和半极性取向的独特材料特性将与一种新的倒装芯片制造方案相结合，从而实现第一个极化钉扎GaN基VCSEL阵列和第一个半极性GaN基绿色VCSEL。这种新的制作方案利用带隙选择性光电化学刻蚀去除生长衬底，实现了高反射介质分布布拉格反射镜，并提供了对腔长的精细控制。非极性和半极性GaN平台具有大的和高度各向异性的光学增益，为实现短波长GaN基VCSEL的偏振钉扎提供了一种简单的方法。当这些方法组合在一起时，可以实现适用于偏振敏感光学系统的蓝色和绿色VCSEL阵列，并提供比单个VCSEL高出数量级的输出功率。初始目标为10×10元非极性蓝色VCSEL阵列输出功率50 mW。对非极性和半极性垂直腔面发射激光器的深入研究将产生关于偏振钉扎与能带结构、高阶模、增益腔共振偏移量和工作条件之间的关系的新的基础知识。将用共聚焦显微镜研究单个器件和阵列的偏振、光谱纯度和噪声特性，并与材料和器件特性相关联。最后，首次研究了半极性GaN的带隙选择光电化学刻蚀，可能会揭示新的基本材料现象，并可应用于其他半极性发光器件。

The research objective of this Faculty Early Career Development (CAREER) Program award is to demonstrate the first short-wavelength (blue and green) vertical-cavity surface-emitting laser (VCSEL) arrays with stable and predictable light polarization. The approach will use an innovative fabrication process to address issues with GaN-based materials that have previously limited the output power, wavelength range, and functionality of short-wavelength VCSELs. Fundamental challenges that have prevented systematic control of light polarization in VCSELs will be overcome with novel materials growth processes. The realization of short-wavelength VCSELs with stable and predictable light polarization will enable unique applications in high-density optical data storage, high-resolution printing, lighting, displays, projectors, miniature atomic clocks, and chemical/biological sensing that are not easily accomplished with conventional edge-emitting lasers. To address a variety of polarization-sensitive applications that require higher-power light emitters, the devices will be formed into polarization-pinned arrays. The educational and outreach components are aimed at promoting interest in science, technology, engineering, and mathematics (STEM) disciplines and developing scientific literacy at the undergraduate and K-12 levels. These activities are focused on working with underrepresented students, including Native Americans, Hispanics, and women. Specific educational objectives are to collaborate with the Southwestern Indian Polytechnic Institute on an education and outreach program, continue mentoring activities for underrepresented populations and local K-12 teachers, and develop a combined undergraduate/graduate course in fabrication techniques for optoelectronic devices. The unique material properties of nonpolar and semipolar orientations of Gallium nitride (GaN) will be combined with a novel flip-chip fabrication scheme to enable the first polarization-pinned GaN-based VCSEL arrays and the first semipolar GaN-based green VCSELs. The novel fabrication scheme utilizes band-gap-selective photoelectrochemical etching to remove the growth substrate, enable high-reflectance dielectric distributed Bragg reflector mirrors, and provide fine control of the cavity length. The nonpolar and semipolar GaN platform exhibits large and highly anisotropic optical gain, which provides a simple method to achieve polarization pinning in short wavelength GaN-based VCSELs. When combined, these approaches enable blue and green VCSEL arrays that are applicable to polarization-sensitive optical systems and provide orders-of-magnitude higher output powers than single VCSELs. An output power of 50 mW from a 10x10 element nonpolar blue VCSEL array is set as an initial target. The thorough study of nonpolar and semipolar VCSELs will generate new fundamental knowledge about the correlations between polarization-pinning with band structure, higher-order modes, gain-cavity resonance offset, and operating conditions. The polarization, spectral purity, and noise properties of individual devices as well as arrays will be investigated with confocal microscopy and correlated to the material and device properties. Finally, the first investigation of band-gap-selective photoelectrochemical etching on semipolar GaN may reveal new fundamental materials phenomena and be applicable to other semipolar light-emitting devices.