Power improvement of the InGaN/GaN LED

Indium Tin Oxide (ITO) has been used as transparent contacts for various optical devices for many years. Recent success in nitride-based LEDs has also been reported [1, 2]. The normalized transmittance of Ni(5nm)/Au(5nm) film was around 74% at the wavelength of 450nm, which is much less than ITO films. With different ITO deposition rates, the transmittance spectra and electrical properties of the ITO films were investigated. After post annealing, the transmittance can reach as high as 98% at a specific wavelength. ITO transmittance-peak wavelength was found to shift with different e-beam deposition rate. Furthermore, we find that the refractive index (n) decreases with increasing deposition rate. Based on data, ITO thin film with transmittance >95% in violet and blue wavelength can be achieved by corresponding designated deposition rates. Output powers of violet and blue LEDs with ITO as p-current-spreading layer were increased. Even higher external quantum efficiency could be achieved by applying various p-contact current spreading mask designs. Based on previous results in group, InGaN/GaN multiple quantum well LEDs grown on Stripe Patterned Sapphire Substrate (SPSS) was found to have higher output power compared with the conventional growth method [3]. This phenomenon was further investigated in this research. InGaN/GaN Blue LED with wavelength around 460nm grown on Shallow Island Patterned Sapphire Substrate (SIPSS) was proven to produce better performance than conventional growth method. LEDs grown on patterned wafers could result in higher output power, lower threshold-voltage, and less leakage. The phenomenal was attributing to the good GaN crystal quality grown at patterned regions of sapphire. Detailed study about this issue could be found in the latter part of this thesis