Active region doping strategies in O-band InAs/GaAs quantum-dot lasers

Abstract

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 400µm 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 245Acm −2 to 132Acm −2 at 27 • C and 731Acm −2 to 312Acm −2 at 97 • C, 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.