Laytec Tool Plays Key Role In VCSEL Research
EpiCurve TT metrology helps reveal and control AlInN strain and alloy compositions
Last year, scientists from Meijo University and the R&D division of Stanley Electric in Japan demonstrated high-efficiency and high-power operation for blue GaN-based VCSELs with AlInN /GaN distributed Bragg reflectors (DBRs). They published the results in Applied Science.
These AlInN /GaN DBRs are used at the front (emitting) side of the VCSEL that emits through the GaN substrate and is completed by a second, dielectric DBR at the VCSEL's back-side. Hence, perfect lattice match of the AlInN in the front DBR is essential for enabling extremely low-defect InGaN layers in the active zone of the device that is grown on top of the AlInN /GaN DBRs.
Now, the German metrology company Laytec has reported that a paper in the Journal of Crystal Growth by scientists from Meijo University shows the power of its EpiCurve TT metrology tool in revealing and controlling the AlInN strain and alloy compositions at accuracy levels of XRD already during growth of the epitaxial layers.
The team developed a model for in-situ wafer curvature values of AlInN/GaN distributed Bragg reflectors (DBRs) and determined InN mole fractions in the DBRs with the model. In order to develop the model, they experimentally investigated contributions of substrate temperature ramping and a GaN growth to changes in the in-situ curvature values during the AlInN/GaN DBR growth.
They found that an increase of curvature changes at the substrate temperature ramping steps was explained by an increase of the total epitaxial layer thicknesses. Another finding was that strain in the GaN layers at the GaN layer growth steps was almost zero. Finally, they determined the InN mole fractions in the AlInN layers by using the model, showing excellent agreements with the values estimated from ex-situ X-ray diffraction measurements. The model reveals not only the entire in-situ curvature change profile but also the InN mole fraction under the precisely lattice-matched condition of AlInN/GaN DBRs.
'High-Power GaN-Based Vertical-Cavity Surface-Emitting Lasers with AlInN/GaN Distributed Bragg Reflectors' by Masaru Kuramoto et al; Appl. Sci. 2019, 9(3), 416