Kun Zhou

Abstract Current laser-based display and lighting applications are invariably using blue laser diodes (LDs) grown on free-standing GaN substrates, which are costly and smaller in size compared with other substrate materials. 1–3 Utilizing less expensive and large-diameter Si substrates for hetero-epitaxial growth of indium gallium nitride/gallium nitride (InGaN/GaN) multiple quantum well (MQW) structure can substantially reduce the cost of blue LDs and boost their applications. To obtain a high crystalline quality crack-free GaN thin film on Si for the subsequent growth of a blue laser structure, a hand-shaking structure was formed by inserting Al-composition step down-graded AlN/Al x Ga 1−x N buffer layers between GaN and Si substrate. Thermal degradation in InGaN/GaN blue MQWs was successfully suppressed with indium-rich clusters eliminated by introducing hydrogen during the growth of GaN quantum barriers (QBs) and lowering the growth temperature for the p-type AlGaN/GaN superlattice optical cladding layer. A continuous-wave (CW) electrically pumped InGaN/GaN quantum well (QW) blue (450 nm) LD grown on Si was successfully demonstrated at room temperature (RT) with a threshold current density of 7.8 kA/cm 2 .

Local InGaN quantum well (QW) decomposition and resultant inhomogeneous luminescence in green laser diode (LD) epitaxial structures are investigated using micro-photoluminescence, Z-contrast scanning transmission electron microscopy, and high-resolution transmission electron microscopy. The local InGaN QW decomposition is found to happen during p-type layer growth due to too high thermal budget and may initiate at the InGaN/GaN QW upper interface probably due to the formation of In-rich InGaN clusters there. Reducing thermal budget and optimizing InGaN/GaN QW growth suppress the local InGaN QW decomposition, and green LD structures with homogeneous luminescence and bright electroluminescence (EL) intensity are obtained.