Maximising 1.3-μm InAs QD gain for photonic integrated circuit light sources

InAs quantum dot (QD) materials emitting in the O-band are of interest as amplifiers and comb sources and more generally as laser light sources in photonic integrated circuits. The advantages, such as tolerance to defects and fast gain recovery time, are well understood but it is also well known that the QD ground state gain can limit device performance. Here we describe the use of direct n-doping of the QD together with modulation p-doping (co-doping) as one approach to increase the gain and improve threshold current density and threshold current density temperature dependence. We also consider design implementations to maximise the effectiveness of the QD material gain. Threshold current density in 1 mm long QD lasers with as-cleaved and uncoated facets can be effectively halved at both 27°C and 97°C when using co-doping, compared to the undoped case, leading to lasing above 200°C even for simple Fabry-Pérot lasers with uncoated, as-cleaved facets.