New model in analysing the degradation for III-V lasers on Si

Researchers in UCL, Chinese Academy of Sciences, Cardiff University and Zhejiang University have collaborated and derived a theoretical analysis and modelling of degradation for III–V lasers on Si. InAs/GaAs quantum-dot (QD) lasers offer a promising method to realise Si-based on-chip light sources. However, the monolithic integration of III–V materials on Si introduces a high density of threading dislocations (TDs), which limits the performance of such a laser device in terms of device lifetime. Here, the UK and Chinese researchers propose a kinetic model including a degradation term and a saturation term to simulate the degradation process caused by the TDs in the early stage of laser operation. By using a rate equation model, the researchers calculate the current density in the wetting layer, where the TDs concentrate.

The researchers compare the rate of degradation of QD lasers with different cavity lengths and of quantum-well lasers, where both are directly grown on Si substrates, by varying the fitting parameters in the calculation of current densities in the kinetic model.

The study reveals the longer the laser cavity, the lower the rate of degradation.  Ignoring the effects of other defect reactions except TD-induced reactions, the simulations show that quantum well (QW) lasers are more severely affected than QD lasers. The study is the first theoretical approach to assess the rate of degradation caused by TDs for QD and QW laser in the early operation stage and hence further enhances the understanding of performance of QD lasers as the lasers age in the stage that the internal optical loss increases significantly.

The study was published in August 2022 in Journal of Physics D: Applied Physics -

• Liu J, Tang M, Deng H, Shutts S, Wang L, Smowton P, Jin C, Chen S, Seeds A and Liu H (2022). "Theoretical analysis and modelling of degradation for III–V lasers on Si", Journal of Physics D: Applied Physics, 55 404006. DOI: 10.1088/1361-6463/ac83d3