Planar InAs avalanche photodiodes for infrared sensing : towards a true solid state photomultiplier

• Main Author: White, Benjamin
• Other Authors: Tan, Chee Hing ; David, John
• Published: University of Sheffield 2016
• Subjects: 621.3815
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.696057

Planar InAs avalanche photodiodes (APDs) are reported as low noise, high gain photon detectors operating across the electromagnetic spectrum from 1.5 to 3.5 µm. This work includes a study of post-growth selective area doping techniques in InAs required for forming planar junctions, through to developing the first planar and lateral InAs APDs to realise high gain. Be ion implantation and annealing are developed for selective area P-type doping InAs. An implantation and annealing procedure was optimised to maximise Be activation and recovery, whilst minimising Be diffusion. A planar fabrication procedure was developed and InAs planar photodiodes were characterised with high uniformity and low surface leakage achieving a detectivity of 6.08 × 108 cmHz^-1/2W^-1 at room temperature. InAs APDs were fabricated using a planar fabrication process. The activation energy of the bulk and surface leakage components of the dark current were analysed to determine the dominant leakage mechanisms. Utilising an optimised structure to minimise tunnelling current, a record high gain in excess of 300 was achieved at -26 V at 200 K. The maximum gain was limited by breakdown, and the breakdown mechanism was found to be due to an unusual thermal runaway effect within an electric field hotspot at the planar junction edge. To mitigate the formation of electric field hotspots, planar APDs with guard rings were designed and characterised. Planar APDs with optimised guard ring placements were characterised with lower dark current near breakdown, and an increased breakdown voltage at 200 K compared to unguarded APDs. The gain limitations of InAs APDs utilising a conventional structure are discussed. To overcome such limitations a novel lateral APD structure was proposed. A range of lateral APD structures were simulated to evaluate the evolution of a lateral electric field that may lead to enhanced lateral gain. N-type selective area doping using Si implantation and annealing were developed, and a range of lateral APD structures were fabricated utilising Be and Si implantation and annealing. Lateral APDs were characterised and an optimised structure was identified. Finally a discussion of the recommended work to be carried out on InAs APDs is presented.