# A Review of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes on Sapphire
## 2 Groups Manufacturing AlGaN-Based DUV-LEDs
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Root of Science Venture** & **Start Up Company** & **Large Company or Alliance Partners** & **Substrate** & **Option** & **Refs.** \\ \hline RP1 & SET1 & Seoul Viosys(R)  & **S**epphire & EM & [24; 25; 26; 27; 28] \\ Univ. South Carolina & Nitek & & & & \\ \hline RP1 & Crystal IS & Asahi Kase(P) & AlN & +R & [17; 29] \\ \hline North Carolina State Univ. & Hexatech & Tokuyama(P) \(\rightarrow\) 3 Stanley(P) & AlN & +HVPE & [18; 20] \\ \hline  & Rayvio & & & & \\ \hline Nagoya Univ. & UV Craftory & Nikkiso(P) +FPG(T) & Sapphire & CHT [13; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40] \\ Meijo Univ. & & & & & \\ \hline RIKEN & & NCK(P) \(\rightarrow\) 3 Dowa(P) & Sapphire & EM & [19; 41; 42; 43; 44; 45] \\  & & Panasonic(P) & Sapphire & & [40; 21; 41; 42; 44; 45] \\ \hline  & & Nichia(P) & Sapphire & & [20; 21; 46] \\ \hline  & & Toyoda Gosel(P) & Sapphire & & \\ \hline FBH2 & UV Photonics & & & & [47; 48; 49] \\  & & & & & \\ \hline  & Siemens AC(P) & & & \\ \hline  & Bioraytron & HPL (T) +Eplieds(T) & Sapphire & & \\ \hline  & LG Innotek(R) & Sapphire & +LLO & [50] \\ \hline  & Samsung(R) & Sapphire & & [51; 52] \\ \hline  & QD Jason(CN) & Sapphire & EM & [53; 54] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of research, development and manufacturing groups of AlGaN-based DUV-LEDs, indicating the substrate type, the growth technique, and related techniques. EM, enhanced migration; CHT, continuous high-temperature growth by metal organic chemical vapor deposition (MOCVD); +HVPE, halide vapor phase epitaxy. +R and +LLO indicate roughening and laser liftoff, used as additional techniques, respectively. following methods. Migration-enhanced MOCVD (MEMCVD) [25], ammonia pulse-flow method [70], and migration-enhanced epitaxy (MEE) [71] are based on a similar concept and their growth temperatures are generally lower than that required for continuous growth [31; 72; 73]. The problem with the EM technique from the industrial viewpoint is its slow growth rate. A growth rate of 0.6 \(\upmu\)m/h [70] has been reported for EM, and the low growth rate is considered to be an intrinsic nature of the atomic-layer-like epitaxy. To overcome the lack of mass transport for AlN growth, CHT growth was attempted by increasing the growth temperature greater than 1300 \({}^{\circ}\)C. The growth rate in this case of continuous growth has been reported to be higher than 5 \(\upmu\)m/h [34; 72], enabling epitaxial lateral overgrowth (ELO) [31; 73], the use of a patterned sapphire substrate (PSS) [39], and the thick AlN growth within a growth time of several hours. However, the problems of CHT growth were a large run-to-run fluctuation of growth machine and a short lifetime of waste parts inside the growth chamber, which must be solved for the mass production of DUV-LEDs. Recently, a new approach to the fabrication of AlN templates on sapphire substrate has been demonstrated [74; 75; 76]. The crystallinity of a thin AlN film as deposited on sapphire by sputtering can be improved by annealing at over 1500 \({}^{\circ}\)C. AlGaN-based NUV- (\(\uplambda\) = 350 nm) and DUV-LEDs (\(\uplambda\) = 268 nm) have been demonstrated [47] using this new AlN templates. Currently, there are three main approaches to fabricating AlN templates on sapphire.