Investigation of V/III ratio dependencies for optimizing AlN growth during reduced parasitic reaction in metalorganic vapor phase epitaxy

Abstract

AlGaN-based ultraviolet (UV) light-emitting diodes (LEDs) are expected to have various applications, including sensing and printing, and light with ultraviolet-C (UVC) wavelengths has a virus inactivation effect. The metalorganic vapor phase epitaxy (MOVPE) method has been used to fabricate LED devices with film control and impurity doping. However, to achieve high luminous efficiency, highly crystalline aluminum nitride (AlN) must be grown in the underlying layer. Although high temperatures are required to grow high-quality AlN for strong migration at the surface, there is a trade-off in the high temperature promoting parasitic reactions. These parasitic reactions are more dominant at a high V/III ratio with more raw material in the case of using the conventional MOVPE. Here, we used jet stream gas flow MOVPE to investigate the effect of V/III ratio dependencies in optimizing AlN growth and without affecting parasitic reaction conditions. As a result, trends of typical AlN crystal growth at V/III-ratio dependencies were obtained. AlN is more stable at a higher V/III ratio of 1000, exhibiting a double atomic step surface, and the crystal orientation is further improved at 1700 °C compared to that at a lower V/III ratio.

Influence of pressure on AlN thick films prepared by epitaxial lateral overgrowth through hydride vapor phase epitaxy

“…4(a), a large-step bunching morphology is observed with the grain stretching along [11−20] AlN and flowing in [10−10] AlN . 43,44 Due to the diffusion of threading dislocations, the stretching of AlN grains is interrupted and numerous unmerged holes appear, resulting in a large surface roughness of 5.73 nm. 45 The threading dislocation density is approximately 1.7 × 10 8 cm −2 based on the density of unmerged holes, which is consistent with the EPD in Fig.…”

Improved light extraction efficiency of AlGaN DUV light emitting diodes using Al/MgF2-based highly reflective film

“…In contrast to that of InGaN-based LEDs, the growth of Alrich hetero-structures on sapphire requires high temperatures (T > 1200 • C) to break Al-N bonds, overcoming the obstacles posed by the large difference between the thermal expansion coefficient of sapphire and AlN [9][10][11]. Moreover, the chips should be annealed at 1700 • C to reduce the defect densities of AlGaN and achieve ohmic contact [12,13]. The strong UV absorbance in the p-contact layer comprising GaN [14], the tremendous amount of heat released at short wavelengths [15] and the limits of optical polarisation in AlGaN [16,17] are detrimental to their performance.…”