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3D sensing is being widely adopted in consumer, industrial and automotive markets. As an illumination source, VCSELs provide a combination of high efficiency, miniaturized packaging, fast pulse rise times and minimal spectral shift with temperature. This paper will describe advances in VCSEL technology that address the requirements of 3D sensing and LiDAR applications. 3D Sensing based on structured light requires power efficient VCSELs with a narrow beam divergence, compatible with the optics that produce a spot pattern in the far field. Time of Flight or LiDAR also requires high power efficiency, as well as fast rise times for good resolution in the 3rd dimension. For consumer applications, compactness of the illumination module is important, while all versions of 3D sensing benefit from the VCSEL’s narrow spectrum and low spectral shift with temperature. In this paper we will describe recent advances in VCSEL technology that enable improvements in 3D sensing systems. This includes efficiency improvements (greater than 60% power conversion efficiency), multi-junction VCSEL designs (up to 5 junctions in a device), and flip-chip back-side emitting VCSELs that enable miniaturization of illumination modules and large-scale addressability. In addition, we will describe module level integration of illumination sources, particularly for Time of Flight (TOF) and LiDAR applications, that incorporate VCSEL, driver, monitor diode, eye safety measures and optics.

We report scanning tunneling microscopy and spectroscopy (STM and STS) studies of graphene formed from a nitrogen-seeded SiC( 000 1 ¯ ) surface. STM indicates that much of the graphene consists of wide flat plateaus with hexagonal features bounded by pleats and regions with disordered character. Nitrogen impurities are not observed in the epitaxial graphene layers. STS measurements on this surface show peaks corresponding to Landau levels associated with pseudo-magnetic fields as high as 1000 T. The energy distribution of Landau levels is consistent with an electronic model employing a finite bandgap.

International audience; A wide band gap semiconducting form of graphene can be produced by growing a buckled form of graphene from a SiC(0001) surface randomly seeded with nitrogen. In this work, we show that the disorder observed in this form of graphene can be substantially reduced by pre-patterning the nitrogen seeded SiC surface into trenches. The result of the patterning is highly improved film thickness variations, orientational epitaxy, domain size, and electronic structure. The ordering induced by this patterned growth offers a way to take advantage of the extremely high mobilities and switching speeds in C-face graphene devices while having the thickness uniformity and fabrication scalability normally only achievable for graphene grown on the SiC(0001) Si-face

All carbon electronics based on graphene has been an elusive goal. For more than a decade, the inability to produce significant band-gaps in this material has prevented the development of semiconducting graphene. While chemical functionalization was thought to be a route to semiconducting graphene, disorder in the chemical adsorbates, leading to low mobilities, have proved to be a hurdle in its production. We demonstrate a new approach to produce semiconducting graphene that uses a small concentration of covalently bonded surface nitrogen, not as a means to functionalize graphene, but instead as a way to constrain and bend graphene. We demonstrate that a submonolayer concentration of nitrogen on SiC is sufficient to pin epitaxial graphene to the SiC interface as it grows, causing the graphene to buckle. The resulting 3-dimensional modulation of the graphene opens a band-gap greater than 0.7eV in the otherwise continuous metallic graphene sheet.

We utilize ultrafast time-resolved terahertz (THz) spectroscopy as a direct, sensitive, and non-contact all-optical probe to investigate the hot-carrier relaxation and cooling dynamics of buckled epitaxial graphene. This special form of graphene is grown epitaxially on nitrogen-seeded single-crystal silicon carbide (SiC( 0001¯)) substrates by thermal decomposition of Si atoms. The pre-deposited interfacial nitrogen atoms pin the first graphene layer to the SiC substrate, and cause it and subsequent graphene layers to buckle into nanoscale folds, which opens an energy gap of up to ∼0.7 eV. We observe a remarkable increase of up to two orders of magnitude in the relaxation rate of the THz carrier dynamics of this semiconducting form of epitaxial graphene relative to pristine epitaxial graphene, which we attribute to a large enhancement of the optical-phonon-mediated carrier cooling and recombination over a wide range of electron temperatures due to the finite bandgap. Our results suggest that the introduced...