Degradation of III–V Quantum Dot Lasers Grown Directly on Silicon Substrates

Abstract

Initial age-related degradation mechanisms for InAs quantum dot lasers grown on silicon substrates emitting at 1.3 µm are investigated. The rate of degradation is observed to increase for devices operated at higher carrier densities and is therefore dependent on gain requirement or cavity length. While carrier localization in quantum dots minimizes degradation, an increase in the number of defects in the early stages of aging can increase the internal optical-loss that can initiate rapid degradation of laser performance due to the rise in threshold carrier density. Population of the two-dimensional states is considered the major factor for determining the rate of degradation, which can be significant for lasers requiring high threshold carrier densities. This is demonstrated by operating lasers of different cavity lengths with a constant current and measuring the change in threshold current at regular intervals. A segmented-contact device, which can be used to measure the modal absorption and also operate as a laser, is used to determine how the internal optical-loss changes in the early stages of degradation. Structures grown on silicon show an increase in internal optical loss, whereas the same structure grown on GaAs shows no signs of increase in internal optical loss when operated under the same conditions.

Optical gain and absorption of 1.55 μm InAs quantum dash lasers on silicon substrate

“…Over the past few years, considerable progress has been made to achieve epitaxial growth of 1.3 μm QD lasers directly grown on Si, with in-depth research into optical properties and device reliability. [1][2][3][4] These lasers comprise of InAs QDs incorporated into layers of GaAs-based alloys which have ~4% lattice mismatch to Si. It is highly desirable to access the 1.55 μm lasing wavelength range to meet growing demands in siliconphotonics for long-haul optical communication and sensing technologies.…”

Electrically injected 164µm emitting In065Ga035As 3-QW laser diodes grown on mismatched substrates by MOVPE

“…9. The observed blue-shift may stem from a different potential profile of the QW active region on the Si substrate, carrier band-filling due to the higher threshold current density, and/or the potentially higher internal optical loss by a higher defect density [25]. Fig.…”

“…It must be noted that a significantly smaller slope efficiency was obtained from the device grown on Si substrate (η slope = 26.5mW/A), while those from the devices on either InP substrate or GaAs substrate were η slope = 174mW/A and η slope = 130mW/A, respectively. This observation can be indicative of a higher internal optical loss within the laser cavity, as a results of a higher defect density [25] and/or a significantly lower injection efficiency above the threshold, which can be greatly affected by the carrier leakage rate [26]. The carrier leakage rate can be, then, sensitive to the operation temperature, due to the nature of thermionic process.…”

Addressing the Optical Degradation of 1.3 μm Quantum Dot Lasers through Subthreshold Characterization

“…Based on these considerations, and on the experimental results in, , the optical degradation of QD LDs has to be modeled by considering a reduction in the injection efficiency. This reduction can be ascribed to the increase in carrier losses within the DWELL, which is mainly driven by the increase of defects close to the InGaAs well, ,,, which are responsible of enhancing the carrier losses affecting the QD reservoir (Figure ). According to previous investigations, the origin of the defects contributing to the increase in SRH recombination could be related to point defects participating to the recombination enhanced growth of pre-existent misfit dislocations, , such as As Ga or V As , , or, in general, to the extended defects themselves.…”