Fabricating Ge-on-Si or GaAs-on-Si single photon detectors is nowadays a topic of extreme interest in optoelectronics, since various applications require the use of these heterostructures. Different solutions for light detection have been proposed, but they still have many limitations. In this context, the microSPIRE project, funded by the European Commission Horizon 2020 under the grant agreement no.736969, aims to solve the typical problems of Ge-on-Si epitaxial growth by using a novel deposition approach, termed Vertical Hetero-Epitaxy (VHE). Thanks to this technique, starting from an array of etched pillars in a silicon substrate it is possible to assemble ordered arrays of 3D micro-crystals, ideally free from dislocations. Since the above mentioned devices are vertical structures with tunable height up to tens of µm, a thick absorption region can be implemented in order to have a Photon Detection Efficiency (PDE) which is well beyond the state of the art. This thesis work focuses on a TCAD-assisted design of the first 3D micro-crystals silicon photomultiplier prototype: electrical simulations have been performed in order to determine the proper electric field profile, taking into account the technological limits concerning doping levels, geometry, resolution, etc. In order to merge electrical and optical simulations and compute the PDE in the same simulation environment, a new approach for optical simulations is presented. Additionally, reflections at the air-silicon interface have been studied and an anti-reflection coating solution is discussed. Finally, optical crosstalk has been analyzed: a model considering the 3D shape of each micro-crystal has been developed and a qualitative estimation has been made in order to define how critical this problem could be in a single-photon detector fabricated within such micro-crystals structures. Thanks to vertical hetero-epitaxy, 3D micro-crystals seem very promising structures for high PDE in the near-infrared range (800-1800 nm wavelength), enhanced photon number resolving capability and high fill factor.
Realizzare eterostrutture come Ge-on-Si o GaAs-on-Si è ad oggi uno dei temi più accesi nell’ambito dell’optoelettronica, siccome molteplici applicazioni ne richiedono l’uso. Differenti soluzioni sono state proposte, ma tutte con qualche limite. In questo contesto, il progetto microSPIRE, finanziato dall’Unione Europea nell’ambito del programma Horizon 2020 con grant agreement no.736969, punta a risolvere i problemi tipici della crescita epitassiale Ge-on-Si proponendo un nuovo approccio di deposizione chiamato Vertical Hetero Epitaxy (VHE). Attraverso questa tecnica è possibile ottenere array ordinati di micro cristalli 3D, idealmente privi di dislocazioni. Essendo queste strutture verticali e ad altezza variabile, fino a decine di µm, ci si aspetta che queste raggiungano livelli di Photon Detection Efficiency (PDE) ben aldilà dello stato dell’arte. Questo lavoro di tesi si concentra sul progetto TCAD del primo prototipo di matrice di microcristalli 3D: tenendo in considerazione i livelli di drogaggio ottenibili, sono state svolte delle simulazioni elettriche in modo da determinare il profilo ottimale di campo elettrico. Sono stati analizzati i problemi di questo primo prototipo e sono suggerite delle possibili soluzioni. Un nuovo approccio per effettuare simulazioni ottiche è stato sviluppato, ed i risultati di simulazioni ottiche ed elettriche sono poi utilizzati congiuntamente per il calcolo della PDE. Vengono in seguito considerate le riflessioni all’interfaccia aria-silicio e sono proposte soluzioni con strati antiriflesso. Infine, è affrontato il problema del crosstalk ottico: partendo dai risultati quantitativi di simulazioni dedicate, un’analisi qualitativa è stata condotta per poter capire quanto critico può essere il problema. Grazie all’impiego di strutture ad etero epitassia verticale, i micro-cristalli 3D considerati sembrano molto promettenti sia in termini di alta PDE nel range del vicino infrarosso (lunghezze d’onda comprese tra 800 e 1800 nm), sia per l’elevata photon number resolving capability e per l’alto fill factor.
Electrical and optical design of high-efficiency micro-crystals silicon photomultipliers
ZIROTTI, ANDREA
2018/2019
Abstract
Fabricating Ge-on-Si or GaAs-on-Si single photon detectors is nowadays a topic of extreme interest in optoelectronics, since various applications require the use of these heterostructures. Different solutions for light detection have been proposed, but they still have many limitations. In this context, the microSPIRE project, funded by the European Commission Horizon 2020 under the grant agreement no.736969, aims to solve the typical problems of Ge-on-Si epitaxial growth by using a novel deposition approach, termed Vertical Hetero-Epitaxy (VHE). Thanks to this technique, starting from an array of etched pillars in a silicon substrate it is possible to assemble ordered arrays of 3D micro-crystals, ideally free from dislocations. Since the above mentioned devices are vertical structures with tunable height up to tens of µm, a thick absorption region can be implemented in order to have a Photon Detection Efficiency (PDE) which is well beyond the state of the art. This thesis work focuses on a TCAD-assisted design of the first 3D micro-crystals silicon photomultiplier prototype: electrical simulations have been performed in order to determine the proper electric field profile, taking into account the technological limits concerning doping levels, geometry, resolution, etc. In order to merge electrical and optical simulations and compute the PDE in the same simulation environment, a new approach for optical simulations is presented. Additionally, reflections at the air-silicon interface have been studied and an anti-reflection coating solution is discussed. Finally, optical crosstalk has been analyzed: a model considering the 3D shape of each micro-crystal has been developed and a qualitative estimation has been made in order to define how critical this problem could be in a single-photon detector fabricated within such micro-crystals structures. Thanks to vertical hetero-epitaxy, 3D micro-crystals seem very promising structures for high PDE in the near-infrared range (800-1800 nm wavelength), enhanced photon number resolving capability and high fill factor.| File | Dimensione | Formato | |
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2019_10_Zirotti.pdf
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https://hdl.handle.net/10589/149950