Periodic Reporting for period 1 - NOVEL (Nanoscale Vertical Cavity Surface Emitting Laser and its Arrays)
Reporting period: 2018-01-01 to 2019-12-31
To address these bottlenecks and realize high-performance semiconductor light sources with CW operated current injection at room temperature, flexible and precise control of photonic confinement with a high Q-factor cavity is essential. For this purpose, lithographically defined laser diodes are introduced in which the vertical-cavity, transverse optical confinement, and electrical confinement were enabled by epitaxial growth and lithography. The objectives of this project were based on using a lithographically defined laser concept to develop a novel growth and fabrication process for GaAs-based nanoscale vertical emitting lasers (NOVEL). NOVEL employed a buried electrical- and optical-confinement method to scale the transverse cavity size down to 500 nm diameter. We have designed laser epitaxial structures, developed fabrication and characterization methods for NOVEL devices. Additionally, we established NOVEL array architectures to obtain significantly increased laser beam quality and brightness for applications in 3D sensing and LiDARs.
The fundamental optical properties and versatile advantages of NOVEL cavity structures were analyzed using numerical modeling techniques. Using this cavity approach, we investigated the effect of size on the quality factor (Q-factor) for both micro-scale and sub-wavelength sizes. The limits of emission wavelength tuning with lateral size control were analyzed. We extended the modeling study to large sizes to explore the large emission apertures in order to obtain a high-power single-mode operation.
The results are expected to have a strong impact in academia, industry, and society as it opens a way for a completely new approach enabling novel photonic technologies. The NOVEL devices, with their fundamentally new capabilities, hold special promise in a wide range of multi-disciplinary areas such as optical communication, computer science, on-chip nanophotonics, and LiDARs.
1) Precise control of photonic confinement for high-performance semiconductor light sources
The ability to control the photonic confinement within an optical cavity is a key element for the development of high-performance semiconductor light sources. The researcher developed a new type of optical cavity with micro- and nano-scale dimensions by employing the concept of the lithographically defined cavity (Li-cavity). The optical properties and versatile advantages of the Li-cavity were analyzed in detail with numerical simulation of practical vertical-cavity design. Numerical simulations were implemented by using the Finite Difference Time Domain (FDTD) method. It was demonstrated that i) high Q-factor is possible even for sub-wavelength size cavities based on all epitaxial GaAs/AlAs structures; ii) The Li-cavity design features large resonance wavelength tuning of with high Q-factor by adjusting its transverse size, which makes them highly appealing for wavelength-tunable light sources; iii) precise control of transverse photonic confinement provides large emission apertures to operate in single optical mode enabling high-power single-mode light sources.
2) Fabrication of micro- and nano-scale semiconductor lights sources as single emitters and arrays
The researcher performed epitaxial design, fabrication, and characterization of NOVEL structures. In order to understand the current blocking characteristics, various epitaxial design parameters have been investigated for carrier confinement. The designed vertical cavity structures were grown and characterized using spectral analysis of the epitaxial structure. Structure with a designed resonance wavelength at ~975 nm was achieved. Different current blocking techniques were studied using various dopant and annealing conditions. The carrier profile measurements were carried out using the electrochemical capacitance (ECV) profiling technique.
To investigate the optical characteristics, we developed NOVELs using e-beam lithography for sizes ranging from 0.5um to 5um. Distributed Bragg mirror (DBR) structures were formed and characterized for the top mirror of the cavity. Established characterization setup allows optical pumping of the single emitters and arrays, then emitted light is collected for concurrent analysis of output power, emission spectra, and near-field profile.