Abstract
A systematic analysis of the performance of VCSELs, fabricated with a decreasing number of structural elements, is used to assess the complexity of fabrication (and therefore time) required to obtain sufficient information on epitaxial wafer suitability. Initially, sub-mA threshold current VCSEL devices are produced on AlGaAs-based material, designed for 940 nm emission, using processing methods widely employed in industry. From there, stripped-back Quick Fabrication (QF) devices, based on a bridge-mesa design, are fabricated and this negates the need for benzocyclcobutane (BCB) planarisation. Devices are produced with three variations on the QF design, to characterise the impact on laser performance from removing time-consuming process steps, including wet thermal oxidation and mechanical lapping used to reduce substrate thickness. An increase in threshold current of 1.5 mA for oxidised QF devices, relative to the standard VCSELs, and a further increase of 1.9 mA for unoxidised QF devices are observed, which is a result of leakage current. The tuning of the emission wavelength with current increases by ~0.1 nm/mA for a VCSEL with a 16 μm diameter mesa when the substrate is unlapped, which is ascribed to the increased thermal resistance. Generally, relative to the standard VCSELs, the QF methods employed do not significantly impact the threshold lasing wavelength and the differences in mean wavelengths of the device types that are observed are attributed to variation in cavity resonance with spatial position across the wafer, as determined by photovoltage spectroscopy measurements.
Highlights
Introduction published maps and institutional affilVertical cavity surface emitting lasers (VCSELs) have become ubiquitous in recent years due to their use as light sources in a wide range of applications from 3D imaging to optical fibre data transmission and, with the emerging technology of LiDAR, the market is rapidly expanding [1,2,3,4]
We considered the relative change in performance for Quick Fabrication (QF) bridge-mesa devices without an oxide aperture, resulting in a 54% reduction in fabrication time relative to the standard VCSELs
We found that the Quick Fabrication bridge-mesa
Summary
Vertical cavity surface emitting lasers (VCSELs) have become ubiquitous in recent years due to their use as light sources in a wide range of applications from 3D imaging to optical fibre data transmission and, with the emerging technology of LiDAR, the market is rapidly expanding [1,2,3,4] This expansion has led wafer manufacturers to scale up production to larger substrates; currently 6-inch (152 mm) [5] and beyond [6], whilst work is being done to maximise the uniformity over individual wafers, as well as between wafers from the same and separate growth runs. Destructive techniques such as capacitance-voltage measurements on etched iations.
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