Utilization of silicon optical coatings for transverse-mode suppression in high-power oxide-confined vertical-cavity surface-emitting lasers

Engineering of the electric-field standing-wave pattern of oxide-confined vertical-cavity surface-emitting lasers (VCSELs) via a scalable, high-refractive-index silicon optical coating is demonstrated to achieve high-power, single-transverse-mode emission. The electron-beam deposition of a thin silicon film atop a standard VCSEL structure reduces the amplitude of the electric-field standing wave over the quantum well gain region, raising the threshold modal gain. Patterning the coating into the shape of an annulus increases the threshold modal gain in the periphery of the VCSEL aperture overlapping with the higher-order transverse modes while leaving the central region unaffected. This patterning creates a radially dependent threshold modal gain profile, suppressing higher-order modes and encouraging operation in a single-fundamental mode. High-power continuous-wave single-mode emission with an output power of 7.43 mW in 850 nm AlGaAs-based VCSELs with silicon coatings is demonstrated, as well as submillamp threshold currents, thermal rollover delay, and a side-mode suppression ratio exceeding 30 dB for single-fundamental-mode operation at room temperature.

https://www.doi.org/10.1063/5.0260091

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.

https://doi.org/10.1063/5.0190385