At the 2024 CS MANTECH conference, Kevin presents his work on using anti-phase coatings to achieve high-power, single-mode, single-polarization performance in VCSELs.
Kevin Presents Polarization-Control Research at CS MANTECH 2024
Category: Publications
Robert Presents TI-QCS Research at CS MANTECH 2024
At the 2024 CS MANTECH conference, Robert presents his work finding unique device physics in his transistor injected quantum cascade structure (TI-QCS).
Ultra-sensitive current bistability and light switching in a resonant tunneling superlattice transistor
Bistability in the current–voltage characteristics of semiconductor superlattices and quantum cascade laser structures has the potential for wide-ranging applications, particularly in sensing systems. However, the interdependency of applied bias and current injection in conventional two-terminal structures has led to complications in analysis and rendered the bistability phenomenon difficult to implement in practical applications. Here, we report a new kind of electronic bistability coupled to optical switching in a resonant tunneling bipolar superlattice transistor. This bistability manifests as sharp discontinuities in the collector current with extremely small variations of the applied voltage, which arise from unstable tunneling transmission across the hetero-barrier between the two-dimensional electron gas (2DEG) at the edge of the transistor base and the collector superlattice structure. The electronic transitions between high and low quantum mechanical transmissions are demonstrated to be caused by self-consistent variations of the internal electric field at the heterointerface between the 2DEG and the superlattice. They are also present in the base current of the three-terminal device and result in sharp switching of near-infrared spontaneous light emission output from an interband radiative recombination process with a peak emission wavelength of 1.58 m. A comprehensive quantum mechanical theoretical model accounting for the self-consistent bistable tunneling transmission is in quantitative agreement with the experimental data. The measured peak transconductance sensitivity value of 6000 mS can be used in the highly sensitive detector and non-linear device applications.
Kevin Presents Mode-Control Research at CS MANTECH
At the 2023 CS MANTECH conference, Kevin presents his work on using anti-phase coatings to achieve high-power, single-mode performance in VCSELs.
Leah Presents Integration Work at CS International
At the 2023 CS International Conference in Brussels, Belgium, Leah gave an invited talk on her work making heterogeneously integrated VCSELs on silicon. These VCSELs integrated via epitaxial transfer have improved thermal performances compared to non-integrated counterparts.
Robert, Kevin, and Leah Present at the Engineering Research Fair
Robert Kaufman, Kevin Pikul, and Leah Espenhahn present a high-level view on the research conducted within the group at the 2023 Engineering Research Fair. Over the course of two hours, 74 undergraduate students show interest in the group and the research being performed.
Laser Islands: Illinois Researcher Leah Espenhahn Shows How to Fully Integrate VCSELs on Silicon
Leah Espenhahn, Kevin Pikul, and Prof. Dallesasse are interviewed about their article published in Compound Semiconductor. They explore the topics of VCSELs and III-V/Si integration via epitaxial transfer.
Compound Semiconductor Article
Achieving high-power single-mode operation in vertical-cavity surface-emitting lasers via scalable, higher-order mode suppression techniques
Achieving high-power single-mode operation in Vertical-Cavity Surface-Emitting Lasers (VCSELs) has received renewed interest due to performance needs driven by facial recognition and 3D imaging in mobile telephones. Two distinct mode control methods that rely on exploiting the spatial field distribution of optical transverse modes to achieve high-power single-mode operation in VCSELs will be discussed. The first method uses a surface-deposited optical coating of multilayer SiO2/TiO2 or single-layer silicon to achieve single-mode emission. The capability to pattern these layers in a wafer-scale process makes this method attractive for high-volume manufacturing. The second method utilizes impurity-induced layer disordering (IID) to selectively intermix the top distributed Bragg reflector (DBR) in a VCSEL, thereby creating a mirror whose reflectivity spatially varies across the aperture. Using these techniques, single-mode output power in excess of 10 mW has been demonstrated with side-mode suppression ratios in excess of 35 db.
Impact of Diffusion Profile on the Modulation Response of Single-Mode Disorder-Defined VCSELs
The impact of diffusion profile shaping through the use of tensilely and compressively strained diffusion masks on the modulation response of single-mode vertical-cavity surface-emitting lasers (VCSELs) using disorder-defined apertures is investigated. VCSELs designed for high-power single-fundamental-mode emission through the use apertures defined via impurity-induced disordering (IID) in conjunction with a standard oxide-confinement process are characterized to extract high-frequency optical cavity parameters across oxide aperture and diffusion mask strain variations. The 3-dB small-signal bandwidth is maintained for a 7.68 mW single-mode 850 nm VCSEL with an oxide aperture of 13 μm using a tensilely strained diffusion mask relative to a non-disordered multimode device of the same oxide aperture. A large K-factor reduction is also observed, from 0.248 ns to 0.045 ns, indicating that damping and photon lifetimes within the cavity of VCSELs employing disorder-defined apertures are substantially reduced. Performance implications to data communication applications are discussed.
IEEE Photonics Technology Letters Article Link
Impact of Diffusion Mask Strain on Impurity-Induced Disordered VCSELs Designed for Single-Fundamental-Mode Operation
The strain of diffusion masks utilized for impurity-induced disordering is demonstrated to control the curvature of the diffusion front, and therefore disordering front, of the disordered distributed Bragg reflector (DBR) aperture. As a result, the disordered apertures formed under strain conditions varying from compressive to tensile are shown to significantly impact the electro-optical performance and spectral characteristics of impurity-induced disordered (IID) VCSELs designed for single-fundamental-mode operation. An investigation and analysis of the electro-optical performance and spectral characteristics of IID-VCSELs as a result of varying diffusion mask strain is presented.
