We report on the epi-design and characterisation of VCSELs for atomic sensors, including miniaturised clocks and magnetometers. To understand how epi-design impacts device performance and separate this from effects of growth and fabrication, we employ techniques to study the interplay between optically-active gain medium and the cavity-resonance. We experimentally determine the net modal-gain spectrum of VCSEL material using a single-pass stripe-length method covering the range of pumping and hence gain requirements of VCSELs. This is compared to photovoltage spectroscopic measurements, which are used to determine the quantum well transition energies and cavity resonance, aiding further optimisation of device design.
Development of a quick fabrication (QF) method for commercial wafer characterisation based on rapid feedback of VCSEL performance. We report on the design of the fabrication process including the systematic removal of time-consuming steps of planarization, oxidation and substrate lapping, and the associated impact on device performance and yield. We show comparable performance of the oxide-confined QF etched trench VCSELs and full process devices and we show that unoxidised devices behave as large aperture oxidised devices. Further, we demonstrate similar performance of substrate-lapped and -unlapped VCSELs between 1.0-1.2 Ith with a difference in current tuning typically 0.064nm/mA.
High-volume low-cost production of vertical cavity surface emitting lasers (VCSELs) will allow their exploitation in new commodity markets. We report the successful scaling up from research level fabrication to produce oxide confined VCSELs across a whole 150mm wafer. On-wafer light-current-voltage (L-I-V) and spectral measurements are analyzed to determine the cross-wafer variations in threshold current, threshold current densities and emission wavelength, which is compared with reflectivity measurements taken immediately after growth. We examine the dependence of VCSEL performance on fabrication parameters over a range of device dimensions to assess whether variation arises from non-uniformity of the epitaxial material or wafer processing.
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