High-power hybrid GaN-based green laser diodes with ITO cladding layer

Green laser diodes(LDs)still perform worst among the visible and near-infrared spectrum range,which is called the"green gap."Poor performance of green LDs is mainly related to the p-type Al Ga N cladding layer,which on one hand imposes large thermal budget on In Ga N quantum wells(QWs)during epitaxial growth,and on the other hand has poor electrical property especially when low growth temperature has to be used.We demonstrate in this work that a hybrid LD structure with an indium tin oxide(ITO)p-cladding layer can achieve threshold current density as low as 1.6 k A∕cm^2,which is only one third of that of the conventional LD structure.The improvement is attributed to two benefits that are enabled by the ITO cladding layer.One is the reduced thermal budget imposed on QWs by reducing p-Al Ga N layer thickness,and the other is the increasing hole concentration since a low Al content p-Al Ga N cladding layer can be used in hybrid LD structures.Moreover,the slope efficiency is increased by 25%and the operation voltage is reduced by 0.6 V for hybrid green LDs.As a result,a 400 m W high-power green LD has been obtained.These results indicate that a hybrid LD structure can pave the way toward high-performance green LDs.

Reduced threshold current density of GaN-based green laser diode by applying polarization doping p-cladding layer

Absorption induced by activated magnesium(Mg)in a p-type layer contributes considerable optical internal loss in Ga Nbased laser diodes(LDs).An LD structure with a distributed polarization doping(DPD)p-cladding layer(CL)without intentional Mg doping was designed and fabricated.The influence of the anti-waveguide structure on optical confinement was studied by optical simulation.The threshold current density,slope efficiency of LDs with DPD p-CL,and Mg-doped CL,respectively,were compared.It was found that LDs with DPD p-CL showed lower threshold current density but reduced slope efficiency,which were caused by decreasing internal loss and hole injection,respectively.

Epitaxial growth of 2.5-μm quaternary AlInGaN for n-cladding layer in GaN-based green laser diodes

The ridge morphology,which is related to random atomic step meandering,appears in thick AlInGaN films grown by metal organic chemical vapor deposition on both GaN templates and free-standing GaN substrates;this can be primarily attributed to the in-plane compressive strain in the thick layer.Therefore,a 2.5-μm Al 0.08 In 0.0123 GaN film with a slightly tensive strain was grown,with a regular and smooth step-flow morphology;the root mean square deviation of the film(with a size of 5μm×5μm)was 0.56 nm.