Development of III-V Materials and Devices for Silicon Photonic Integration
Creators: name: Fitch, Christopher Richard
Publisher: name: University of Surrey
Year: 2023

description: Silicon photonics is expected to enable a wide range of emerging applications. However, its full potential cannot be realised without a silicon compatible laser. While silicon is intrinsically inefficient as a gain medium, direct bandgap III-V based lasers are well established and a number of approaches are being developed for their integration on silicon. Of these, monolithic epitaxial growth on silicon provides the opportunity for high volume and low cost production using existing fabrication infrastructure. Monolithic epitaxial growth raises further challenges associated with the physical differences between III-V materials and silicon. This thesis reports on the investigation of three different novel laser device and material approaches which are being developed to overcome these challenges.<br>
description: <br>
description: Antimonide-based III-V compounds are suitable for growth on silicon because of their ability to accommodate strain and prevent dislocation propagation into the active area. Temperature and pressure dependence experimental data for 1.5 µm GaInSb quantum well lasers on native substrates was analysed to identify the origin of high threshold current densities (471-1092 Acm-2) and temperature sensitivity. Carrier leakage to the barrier and Auger recombination were found to account for &gt; 58% of the current at room temperature. Increasing the barrier aluminium fraction from 0.35 to 0.4 was calculated to reduce leakage by a third. The associated reduction in threshold carrier density would reduce Auger recombination leading to a further reduction in threshold current density and temperature sensitivity.<br>
description: <br>
description: While GaNAsP quantum well lasers, lattice matched to silicon, have been realised at low temperature their threshold current density (1.6 kA cm−2) is much higher than other quantum well lasers on silicon. Improvements may be achieved through improved optical confinement. Spectroscopic ellipsometry was used to measure and model the refractive index of BGaAsP alloys to investigate their suitability for optical confinement (waveguiding). It was found that a refractive index contrast range of ~0.05-0.07 can be achieved between BGaP and BGaAsP in the near infrared. While less than a contrast of ~0.2-0.3 in established material systems such as AlGaAs/GaAs and InGaAsP/InP, it is shown to be sufficient for BGaAsP to provide good optical confinement for GaNAsP quantum well laser waveguide applications. <br>
description: <br>
description: High performance 1.3 µm InAs dot-in-well lasers on silicon were compared to similar devices on GaAs substrates. Threshold current densities of undoped silicon-based devices at room temperature (~200 Acm-2) were 4-5 times higher than those on GaAs. Low temperature and high pressure investigations and modelling identified defect related non-radiative recombination as the most likely reason for the elevated threshold current densities for on-silicon devices which is consistent with higher threading dislocation densities for the silicon-based devices (~ 106-108 cm-2) compared to GaAs-based devices (&lt; 1×103 cm−2). Differences in the temperature characteristics of undoped and p-doped devices were explained in terms of additional electrostatic attraction inhibiting establishment of thermal equilibrium.<br>
description: <br>
description: While the devices and materials investigated in this thesis are being developed for telecoms applications, the methods, analyses and results are also widely applicable and relevant to other material systems, wavelengths and applications.<br>