A few yield loss issues in AlInGaN-based LED manufacturing are addressed in this paper. V-defects initiated from N-type GaN, multiple quantum well region, and P-type GaN are classified by their size and depth. Their impacts on device performance are discussed and the effective ways to eliminate or reduce V-defects are presented in detail. An approach using multiple composite inter-layers in a highly doped Si-GaN layer to reduce cracks is proposed. Each individual composite inter-layer reduces the stress accumulated from the layer underneath and thus keeping the N-GaN layer free from crack. The composite inter-layer is a pair of InxGa1-xN/GaN thin layers grown at low temperature (LT). Design rules and growth conditions are also discussed. Other issues which may cause yield loss or troublesome in AlInGaN LED manufacturing are briefly touched such as wafer color non-uniformity, bad cut in chip dicing, wavelength and light output correlation at wafer, chip and lamp level.
Variable angle spectroscopic ellipsometry (VASE) and micro Raman scattering have been employed to study the optical anisotropy and optical constants of AlN films grown at high and low temperature (HT and LT). The AlN films were grown by metalorganic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) on c-plane sapphire ((alpha) -Al2O3) substrates, respectively. Anisotropic optical phonon spectra of AlN have been measured along two directions so that the optical axis <c> of AlN is either perpendicular or parallel to the polarization of the incident beam. Nonzero off-diagonal elements Aps and Asp of Jones matrix in the reflection VASE (RVASE) measurements indicate that the <c> of AlN is slightly away from surface normal due to substrate miscut. The ordinary optical constants of both HT AlN have been determined spectroscopic ellipsometry at small angles of incidence so that the extraordinary response is greatly reduced. The film thickness along with the surface overlayer was determined via the VASE data analysis as well.
Generalized variable angle spectroscopic ellipsometry (VASE) and Raman scattering have been employed to study the optical anisotropy of GaN/Sapphire structures. The GaN films were grown hydride vapor phase epitaxy and molecular beam epitaxy on both m-plane and c-plane sapphire ((alpha) -Al2O3) substrates, respectively. Anisotropic optical phonon structure of sapphire have been measured, based on which the optical axis of sapphire substrate has been determined. A 541 cm-1 TO phonon of GaN grown on m-plane sapphire substrate has been discovered experimentally which is due the coupling of A1 and E1 TOs. Optical axis orientation of GaN film on m-sapphire has been fully determined by the anisotropic angular dependence of the coupled TO phonon. Off-diagonal elements Apst and Aspt of transmission VASE (TVASE) are very sensitive parameters related to the optical anisotropy. The optical axis orientation of GaN on m-sapphire has also been accurately determined by TVASE at two special sample positions. The optical anisotropy due to GaN film and sapphire substrate has been successfully separated at 90 degree(s) samples position allowing to study the optical anisotropy of GaN film only.
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