Seminarium Fizyki Ciała Stałego

Maruska and Tietjen did the first GaN growth by using hydride vapor phase epitaxy in 1969. Since their first GaN growth, a lot of breakthroughs have been achieved for the crystal growth of GaN and InGaN, conductivity control of p-type GaN, and the device structures of LED and laser diodes. Then finally, first high efficient blue LEDs were invented in 1993 [1]. The first white LED was also developed using the blue LED and YAG phosphor by Nichia Chemical Ind., in 1996. Since first high efficient blue LEDs grown on sapphire were invented in 1993, these blue and white LEDs have been used for all kinds of applications, such as back light of LCD display, general lighting and others. I name these LEDs grown on sapphire and SiC substrate as 1stgeneration LEDs. These LEDs have been operated at a low current density due to an efficiency droop caused by a high dislocation density and Auger recombination. Recently, high efficient violet LEDs have been developed using GaN substrates by Soraa Inc., [2]. It is called GaN on GaN LED. These high efficient violet LEDs grown on GaN substrates are called as 2nd generation LEDs because white LEDs made by using the violet LED grown on GaN substrates have superior characteristics in the view of the wavelength stability, efficiency droop, white color quality with a high CRI and the low peak intensity of the blue light which disrupt the circadian cycle. The high efficient blue LEDs with a wall-pug efficiency of more than 70% were developed by UCSB group using the TJ recently [3]. I like to talk about the latest results of the TJ blue LEDs and laser diodes.

References

[1] S. Nakamura, T. Mukai, and M. Senoh,”Candera-class high-brightness InGaN/AlGaN double-heterostructure blue-light-emitting diodes,” Appl. Phys. Lett., vol. 64, 1994, pp. 1687-1689

[2] C.A. Hurni, A. D. David, M.J. Cich, R. I. Aldaz, B. Ellis, K. Huang, A. Tyagi, R. A. DeLille, M. D. Craven, F. M. Steranka and M. R. Krames,”BulkGaN flip-chip violet light-emitting diodes with optimized efficiency for high-power operation.” Appl. Phys. Lett., vol. 106, 2015, 031101

[3] B.P. Yonkee, E.C. Young, S.P. DenBaars, S. Nakamura and J. S. Speck, Apply. Phys. Lett., 109, 191104 (2016), “Silver free III-nitride flip chip LED with wall plug efficiency over 70% utilizing GaN tunnel junction”