The development of Low-Gain Avalanche Detectors (LGADs) that make controlled use of impact ionization has led to an advancement in the use of silicon diode detectors in particle detection, particularly in the arena of ultrafast (~10 ps) timing. For what are today considered to be “conventional” LGADs, the high fields needed to induce the impact ionization process lead to breakdown between the separated n-p junctions that are used to simultaneously deplete the sensors and establish the readout segmentation. As a result, working devices have included a Junction Termination Extension (JTE) that provide electrostatic isolation between neighboring implants, but at a cost of introducing a dead region between the sensor segments that is insensitive to the deposited charge from an incident particle. The width of this dead region is 50 µm or more, making conventional LGAD sensors inefficient for granularity scales much below 1mm. On the other hand, demands from the particle physics (4D tracking) and photon science (high frame-rate X-Ray imaging) communities call for granularity at the 50 µm scale. Thus, there is great interest in overcoming the current granularity limits of LGAD sensors. There are several ideas, under various levels of development, that have been proposed to circumvent the JTE limitAC-coupled (“AC-LGAD”) LGADs eliminate the need for the JTE by making use of a completely planar (non-segmented) junction structure, and then establish the granularity entirely through the electrode structure, which is AC-coupled to the planar device through a thin layer of insulator. Since charge is not collected directly by the electrodes, there is a point-spread function that relates the signal location to the pad (electrode) response that is a property of the effective AC network formed by the highly doped gain layer just below the insulating layer and the electrode structure. Prototype devices exhibit good response and timing characteristics.Inverse (“ILGAD”) LGADs also eliminate the need for the JTE by making use of a planar junction structure. In this case, the electrode structure is placed on the side of the device opposite the junction. Prototypes with appealing signal characteristics have yet to be produced. In addition, the manufacture of these devices requires processing on both sides of the sensor, which is significantly more difficult than the single-sided processes used for conventional and AC LGADs.Trench-isolated (“TI-LGAD”) LGADs attempt to replace the JTE with a physical trench etched around the edge of the detector segment, which is then filled with insulator. This approach is very new, and its proponents hope to be able to use it to reduce the dead area between segments to as little as 5 µm. First prototypes are just recently available and are under study. Much work remains to be done to show that this approach will produce a stable sensor, and to see how small the dead region can be made.

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Methods for monitoring device operating conditions and current are shifting towards the use of optical measurements, which are are less susceptible to electromagnetic noise. Existing light emission techniques utilize complex components, like laser diodes and photodiodes, to measure device current, rendering such techniques expensive to implement.

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The inventors have developed a scalable laser aperture that emits light perpendicular to the surface. The aperture can, in principal, scale to arbitrarily large sizes, offering a universal architecture for systems in need of small, intermediate, or high power. The technology is based on photonic crystal apertures, nanostructured apertures that exhibit a quasi-linear dispersion at the center of the Brillouin zone together with a mode-dependent loss controlled by the cavity boundaries, modes, and crystal truncation. Open Dirac cavities protect the fundamental mode and couple higher order modes to lossy bands of the photonic structure. The technology was developed with an open-Dirac electromagnetic aperture, known as a Berkeley Surface Emitting Laser (BKSEL).  The inventors demonstrate a subtle cavity-mode-dependent scaling of losses. For cavities with a quadratic dispersion, detuned from the Dirac singularity, the complex frequencies converge towards each other based on cavity size. While the convergence of the real parts of cavity modes towards each other is delayed, going quickly to zero, the normalized complex free-spectral range converge towards a constant solely governed by the loss rate of Bloch bands. The inventors show that this unique scaling of the complex frequency of cavity modes in open-Dirac electromagnetic apertures guarantees single-mode operation of large cavities. The technology demonstrates scaled up single-mode lasing, and confirmed from far-field measurements. By eliminating limits on electromagnetic aperture size, the technology will enable groundbreaking applications for devices of all sizes, operating at any power level. BACKGROUND Single aperture cavities are bounded by higher order transverse modes, fundamentally limiting the power emitted by single-mode lasers, as well as the brightness of quantum light sources. Electromagnetic apertures support cavity modes that rapidly become arbitrarily close with the size of the aperture. The free-spectral range of existing electromagnetic apertures goes to zero when the size of the aperture increases. As a result, scale-invariant apertures or lasers has remained elusive until now.  Surface-emitting lasers have advantages in scalability over commercially widespread vertical-cavity surface-emitting lasers (VCSELs). When a photonic crystal is truncated to a finite cavity, the continuous bands break up into discrete cavity modes. These higher order modes compete with the fundamental lasing mode and the device becomes more susceptible to multimode lasing response as the cavity size increases. 

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