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Abstract
In recent years, InGaN-based light emitting diodes (LEDs) covering the blue and green spectral regions have emerged into widespread use. However, due to fundamental material issues related to InGaN, achieving yellow and red emissions from InGaN-based structures have presented a unique challenge.
The optimum growth conditions for the metal organic chemical vapor deposition (MOCVD) growth of a series of InGaN-based multiple quantum well (MQW) devices that emit over a wide spectral range are developed. Despite the challenges involved with the growth of mOaN-based structures, we were able to grow InGaN/GaN MQW LEDs covering the spectral region from blue to amber (— 600 nm). The data presented in this dissertation represents the longest reported emission wavelengths for Al-free InGaN/GaN MQW LEDs grown by MOCVD. The dependence of the emission properties of these monochromatic devices on several parameters is studied. These parameters include the growth rate, growth temperature, quantum well width, and p-type capping layer growth conditions. Additionally, white electroluminescence is demonstrated through the proper mixing of complementary wavelengths. Moreover, the structural, electrical and optical characteristics of these devices are discussed. A mathematical model for the different parameters affecting the emission wavelength of InGaN/GaN LEDs is presented. The thickness dependence of strain relaxation in lnGai.N/GaN is studied for single and multiple quantum well structures. Then, the dependence of the onset of relaxation of MQWs on the number of quantum wells, and the different relaxation mechanisms involved in strain relaxation process are discussed.
Nearly lattice-matched grown mOaN based p-i-n photodiodes detecting in the 365—500 am range with tunable peak responsivity tailored by the i-layer properties are developed. The novelty of our study is to grow high quality i-mOaN layers that can avoid the problems associated with the growth of thick InGaN layers. This has been achieved by growing the iInGaN layer on a lattice matched n-mOaN layer and capping it with InGaN p-type capping layer instead of a GaN one. This approach has proven to circumvent some of the growth problems and offers better quality i-layer where optical detection is taking place. The effect of the lattice matched i- and n-InGaN layers on the device performance is studied. The effects of InN content and i-layer thickness on photodiode properties and performance are discussed. The obtained peak responsivity wavelength ranging between 416 and 466 nm is the longest reported for Ill-N photodiodes.