Room-temperature continuous-wave electrically pumped InGaN/GaN quantum well blue laser diode directly grown on Si

Yi Sun,Xiaojuan Sun,Dabing Li,Masao Ikeda,Jianping Liu,Meixin Feng,Shuming Zhang,Zengcheng Li,Yu Zhou,Liqun Zhang,Qian Sun,Hui Yang,Deyao Li,Kun Zhou

doi:10.1038/s41377-018-0008-y

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/AlxGa1−xN 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/cm2.

Highlights

Current laser-based display and lighting applications are invariably using blue laser diodes (LDs) grown on freestanding 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
Most InGaN/GaN QW blue LDs are homo-epitaxially grown on expensive 2-inch free-standing GaN substrates[3], which leads to LDs costing orders of magnitude higher than lightemitting diodes (LEDs) grown on hetero-epitaxial substrates
By replacing costly and small-size GaN free-standing substrates with costeffective and large-diameter Si substrates, the cost of InGaN/GaN QW blue LDs can be reduced to the same level as LEDs, which will lead to further applications of LDs

Summary

Tensile stress

AlGaN-containing optical cladding layers on GaN induces additional tensile stress. defect control and stress engineering are critical for the realization of electrically pumped InGaN/GaN LDs grown on a Si substrate[10]. Growing an InGaN/GaN QW blue LD structure on a Si substrate is more challenging: the longer the emission wavelength, the smaller the difference in refractive index between III-nitride materials[18]. Both the In composition in the InGaN waveguide layers and the Al composition in the AlGaN optical cladding layers must be increased to obtain a sufficient optical confinement for the realization of blue lasing[19]. According to scanning transmission electron microscopy (STEM) cross-sectional images (Fig. 3), sharp interfaces for the individual layers indicated a high quality for the as-grown blue LD structure on Si. On the other hand, a longer lasing wavelength means a higher In composition in the MQWs, and threshold current density often increases dramatically with the In composition in MQWs20, especially when the dislocation density is relatively high (~5 × 108 cm−2). It is generally believed that the precipitation of metallic indium and void formation originate from the decomposition of a fraction of indium-rich

AlGaN Buffer layers AIN Si substrate

Findings

Coating Facet