Gallium Arsenide based photonic crystal surface emitting lasers

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Photonic crystal surface emitting lasers (PCSELs) are an emerging class of semiconductor laser which incorporate a 2D photonic crystal into a semiconductor laser structure to provide large area 2D feedback and surface emission. These devices have a number of desirable properties, chief of which is the ability to achieve high quality, high power emission through scaling of device size. In this thesis, the design, fabrication, and characterisation of GaAs based PCSELs is discussed, with the aim of improving the quality and manufacturability of these devices. Additionally, the characteristics of coherent PCSEL arrays are analysed, a possible route to very high brightness semiconductor lasers.

Initially, optimal design properties of square lattice, circular atom PCSELs are determined through optical waveguide and photonic bandstructure modelling. It is shown that increased 1D and 2D coupling strength, a measure of the strength of feedback in a device, is achieved in a PCSEL which utilises a void/semiconductor photonic crystal contrast as opposed to all-semiconductor contrast, contradicting the previous study on all-semiconductor devices. Optimal photonic crystal design parameters are then determined for a prospective PCSEL
structure.

Informed by these modelling results, the growth, fabrication, and characterisation of 1070 nm GaAs based PCSELs is discussed. Four PCSEL devices with varying void geometries in the photonic crystal are analysed, utilising transmission electron microscopy imaging of each device. It is shown how the position and size of a void in the photonic crystal region affects the threshold and slope efficiency of a PCSEL, and the results are compared to simulation, the first time a study of this kind has been carried out to the best of my knowledge. It will be shown how improved void geometries result in strong coupling strengths, and how this improved coupling strength leads to lower threshold, more efficient devices. The photonic bandstructure of the best performing device is mapped and analysed to determine photonic crystal coupling strength, and the lasing band of this device is identified.

The power efficiency benefits of PCSEL arrays are then investigated. Coherent PCSEL arrays offer the possibility of realising a very high brightness laser diode through large area scaling of PCSEL power, but are still in their infancy. It this thesis, it is shown that that for two and three element PCSEL arrays, with electrically driven waveguide regions, that utilisation of an array structure results in increased device efficiency compared to devices operating individually. The improved efficiency is attributed to the reduction of in-plane cavity losses of the PCSELs when the waveguide regions are in transparency. The results obtained are then compared to expected values and show strong agreement. The coherence of the two and three element arrays is also discussed.

Finally, a method for the in-line non-destructive characterisation of PCSELs at the point of photonic crystal etch is outlined. It is shown that a simple photoluminescence measurement provides information on the fill factor and height of the etched photonic crystal structure prior to regrowth, without the need of any advanced microscopy techniques. It is discussed how this method could be applied in an industrial context, improving the manufacturability
of PCSELs.
Date of AwardDec 2021
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsEngineering & Physical Sciences Research Council
SupervisorRichard Hogg (Supervisor), David Childs (Supervisor) & Robert Pollard (Supervisor)

Keywords

  • PCSEL
  • photonic crystal
  • laser
  • laser diode

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