Electrical and optical analysis on effects of low-temperature-grown p-AlGaAs cladding layer in all-MOCVD InAs/GaAs quantum dot laser diodes

Abstract

In this work, we investigate how low-temperature growth of the p-AlGaAs cladding layer affects the structural and device characteristics of all-metal-organic chemical vapor deposition (MOCVD)-grown InAs/GaAs quantum dot laser diodes (QDLDs) operating in the O-band. While reduced-temperature p-AlGaAs growth is required to suppress degradation of the strained dots-in-a-well (DWELL) active region, its direct device-level impact has remained insufficiently clarified. Here, we show that, although dislocation-related morphology is shown in the p-AlGaAs cladding, the underlying DWELL active region remains largely preserved. Cross-sectional transmission electron microscopy and etch-dependent photoluminescence measurements further indicated that the structural non-uniformity was mainly confined to the upper cladding rather than associated with irreversible active-region degradation. Electrical current-component analysis showed that the bulk injection path was only weakly affected and that the surface-related current contribution was negligible. Based on these results, 1.5-mm-cavity shallow-ridge devices were fabricated and evaluated under continuous-wave operation. After high-reflectivity coating, the threshold current decreased from 125.5 to 65.5 mA and the slope efficiency increased from 0.084 to 0.128 W/A. The device also exhibited a lasing linewidth of 6.8 MHz and relatively low near-threshold relative intensity noise. These results show that low-temperature p-AlGaAs cladding growth can be used to realize all-MOCVD-grown InAs/GaAs QDLDs without imposing a severe electrical or optical degradation.