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Abstract This mini‐review explores the evolution of image sensors, essential electronic components increasingly integrated into daily life. Traditional manufacturing methods for image sensors and photodetectors, employing high carbon footprint techniques like thermal evaporation and chemical vapor deposition, are being replaced by environmentally conscious solution processing. Organic and Colloidal Quantum Dot‐based image sensors emerge as promising candidates, aligning with the shift toward solution‐based device integration. This review provides insights into the working principles of photodetectors and image sensors, summarizing relevant materials and fabrication approaches. Additionally, it delves into the detailed exploration of pixelated patterning techniques and their potential applications in the realm of solution‐processed image sensor fabrication.

Stripped-back representative VCSEL devices with a simple fabrication process that very closely approaches the performance of standard BCB-planarised devices have been produced. These VCSEL Quick Fabrication (VQF) devices achieve threshold currents only 0.3 mA higher than that of a standard device produced from the same material. The predictability of standard performance from VQF performance is also robustly assessed in terms of temperature effects to account for the observed disparities. These VQF devices are then processed across a 6-inch (152 mm) wafer and the resulting device-level characteristics are mapped. From this, it is apparent that there is an approximately radial decrease in oxide aperture diameter from centre to edge, found to be driven by the strain-induced wafer bow. After corrections, a residual spatial variation across the wafer remains, which, in conjunction with temperature dependent measurements, is shown to be a result of epi-material variation. By observation at 50 °C, that is, at a temperature closely resembling that of intended application, the residual centre-to-edge variation in threshold current density is found to be only 0.2 kA/cm2, compared to 1.3 kA/cm2 when observing the room temperature variation of devices of nominally equivalent active volumes.

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.

The etch rate of AlGaInP-based laser structures and selectivity, with respect to SiO2, are reported as a function of inductively coupled plasma (ICP) process parameters for a BCl3/Cl2 etch chemistry. At room temperature InCl3, a reaction product of In in this environment, is involatile, whereas the products of etching SiO2 are relatively volatile resulting in low selectivity (∼4:1). Temperature is the most important variable for improving etch rate and selectivity. At 190 C it is possible to obtain an etch rate up to 0.7 m min−1 and a selectivity as high as 17:1. It is shown that increasing the ICP power increases the etch rate of AlGaInP but decreases the selectivity, whereas increased reactive ion etching (RIE) power results in improved etch rate and selectivity. The etch rate is also found to be higher at lower chamber pressures although again with little or no change in selectivity. These results are consistent with an AlGaInP etch rate that is dependent on both dc bias and ion flux, in contrast to a SiO2 etch mechanism that is relatively independent of dc bias but strongly dependent on ion flux. With total gas flow kept constant the etch rate and selectivity are found to increase with the fraction of Cl2 present. The addition of Ar to the gas mix does increase the etch rate, reaching a maximum at around 70% Ar, but without any significant effect on selectivity. [ABSTRACT FROM AUTHOR]