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Three techniques for improving gain in InAs quantum dot lasers are examined. Silicon photonics is a promising solution for meeting increasing global data bandwidth demands. However, silicon itself is a poor emitter due to its indirect bandgap. One potential candidate for light sources for on-chip devices is the monolithic growth of III-V quantum dot materials onto silicon, however, III-V quantum dot materials exhibit reduced gain due to the differences in the population of electron and hole states and ultimately because of the difference in electron and hole effective masses. P-type modulation doping is a well-established strategy for improving gain in InAs quantum dot lasers on both native GaAs and silicon substrates. The doping density and positioning is optimised for a given wafer design, and ground state lasing at room temperature for a 400um lasing cavity is demonstrated, in addition to reduced sensitivity of threshold current to temperature. Optimized p-type modulation doping is compared to a relatively new approach to enhancing gain – direct n-type doping of the quantum dots. It is found to improve the gain in low loss operation, unlike p-type modulation doping. However, direct n-type doping detrimentally showed increased threshold current dependence compared with p-type modulation doping and decreased the maximum temperature at which ground state lasing could be attained. A novel third method is investigated in which both p-type modulation doping and direct n-type doping are applied to a device simultaneously, referred to as co-doping. Co-doping reduced the threshold current density from 245 A/cm^2 to 132 A/cm^2 at 27C and 731 A/cm^2 to 312 A/cm^2 at 97C, compared to undoped devices. The reduction was greater than for either individual doping strategy alone. Co-doping also retained the beneficial reduction in the sensitivity of the threshold current density to temperature provided by the p-type modulation doping.

Three techniques for improving gain in InAs quantum dot lasers are examined. Silicon photonics is a promising solution for meeting increasing global data bandwidth demands. However, silicon itself is a poor emitter due to its indirect bandgap. One potential candidate for light sources for on-chip devices is the monolithic growth of III-V quantum dot materials onto silicon, however, III-V quantum dot materials exhibit reduced gain due to the differences in the population of electron and hole states and ultimately because of the difference in electron and hole effective masses. P-type modulation doping is a well-established strategy for improving gain in InAs quantum dot lasers on both native GaAs and silicon substrates. The doping density and positioning is optimised for a given wafer design, and ground state lasing at room temperature for a 400um lasing cavity is demonstrated, in addition to reduced sensitivity of threshold current to temperature. Optimized p-type modulation doping is compared to a relatively new approach to enhancing gain – direct n-type doping of the quantum dots. It is found to improve the gain in low loss operation, unlike p-type modulation doping. However, direct n-type doping detrimentally showed increased threshold current dependence compared with p-type modulation doping and decreased the maximum temperature at which ground state lasing could be attained. A novel third method is investigated in which both p-type modulation doping and direct n-type doping are applied to a device simultaneously, referred to as co-doping. Co-doping reduced the threshold current density from 245 A/cm^2 to 132 A/cm^2 at 27C and 731 A/cm^2 to 312 A/cm^2 at 97C, compared to undoped devices. The reduction was greater than for either individual doping strategy alone. Co-doping also retained the beneficial reduction in the sensitivity of the threshold current density to temperature provided by the p-type modulation doping.

The quantum confined Stark effect in InAs/InGaAs QDs using an undoped and p-modulation doped active region was investigated. Doping potentially offers more than a 3x increase in figure of merit modulator performance up to 100 C.

The performance of O-band InAs/GaAs quantum-dot (QD) lasers grown by molecular beam epitaxy with three different doping strategies are investigated in a temperature range 17 °C – 97 °C. We demonstrate lasers with a reduced threshold current using direct n-doping (during the dot formation) in the active region compared lasers with a nominally undoped active region. We explain results using calculations of the dot and wetting layer potentials and the electron and hole energy levels.

A semi-empirical model is compared with measurements to establish limiting factors in the performance of p-modulation doped InAs quantum dot (QD) lasers. Fitted absorption spectra allow identification of supposed factors and comparison of multiple samples isolates their origin, providing insights for future laser design.

In this work, the feasibility of a monolithically integrated laser and electroabsorption modulator based on the same active quantum dot epistructure is studied. The net modal gain and the absorption in the modulator were measured using the segmented contact method from 25 °C to 125 °C. The maximum of the net modal gain active region of the laser decreases from 10 cm -1 at 25 °C to 3.9 cm -1 at 125 °C. The non-optimized maximum extinction ratio of the modulator, 4.1 dB·mm -1 , is almost constant until 25 °C. The wavelengths at which the net modal gain and the change in absorption are maximum shifts with temperature by 0.04 eV.