(Invited) Polarization-Induced Doping in Graded AlGaN Epilayers Grown on AlN Single Crystal Substrates

Abstract

Compositionally graded Al x Ga1-x N epilayers were coherently grown on AlN single crystal substrates by MOCVD, and polarization-induced doping was determined by contactless sheet resistance and capacitance-voltage measurements on unintentionally doped, n-type graded layers; and by temperature-dependent Hall effect measurements on a Mg doped, p-type graded layer. The room-temperature resistivity, hole concentration, and hole mobility of the p-type layer graded from x= 1.0 to x= 0.36 were 1.2 Ωcm, 4.5x1018 cm-3, and 1.2 cm2/Vs, respectively, which represents a significant improvement over traditional, thermally-activated Mg doping in AlGaN alloys.

Influence of Undoped‐AlGaN Final Barrier of MQWs on the Performance of Lateral‐Type UVB LEDs

“…The improved EQE of 5.6% at 20 mA and maximum light output power of 17 mW at 82 mA dc drive measured on bare‐wafer level conditions in Lat‐UVB LED are relatively small, when compared with those obtained from flip‐chip‐based deep ultraviolet light‐emitting diodes (DUV LEDs), using photonic crystal (PhC) in p‐AlGaN (p‐GaN) as well as using lens‐like packaging . Therefore, further improvement in the Lat‐UVB LEDs is expected, by using flip‐chip technology, PhC in p‐AlGaN (p‐GaN), polarization doping, and lens‐like packaging …”

“…These results can further be improved, by promoting the Mg‐atomic activation in the p‐AlGaN HIL and then enhancing to the tunneling probability of hole from p‐AlGaN HIL side including p‐AlGaN MQB‐EBL toward the MQWs of Lat‐UVB LED. The hole concentration up to 2 × 10 15 cm −3 in the p‐AlGaN HIL via special approach of 3D‐hole generation, using polarization doping, is desired. The measurement and detailed investigation of the internal field due to both the SP and PZ polarization in the AlGaN‐based UVB LED devices grown on c‐plan of AlN are also inevitable in the future…”

“…[7,8,42] Therefore, further improvement in the Lat-UVB LEDs is expected, by using flip-chip technology, PhC in p-AlGaN (p-GaN), polarization doping, and lens-like packaging. [32,33,[41][42][43] Last but not the least, the ultimate goal is to develop NB-UVB LED light sources, which are strongly needed for the specific realworld applications, such as those in immunotherapy, for vulgaris treatment, and plant lightning. [1][2][3][4][5][6]8] A small part of the NB-UVB spectrum can be used to treat skin conditions such as psoriasis and eczema.…”

Perspectives on UVC LED: Its Progress and Application

“…Through optimization of the SL period, the AlN crystallinity was systematically improved, and an ultra-low etch pit density was achieved. The relative IQE of 280-nm AlGaN MQWs dramatically increased from 22.8% to 85% when the inserted SL was increased from 0 to 20 periods [53]. On the other hand, p-type conductivity for high-Al-content AlGaN has recently been achieved using distributed-polarization-induced 3D hole gas [53,54].…”

“…The relative IQE of 280-nm AlGaN MQWs dramatically increased from 22.8% to 85% when the inserted SL was increased from 0 to 20 periods [53]. On the other hand, p-type conductivity for high-Al-content AlGaN has recently been achieved using distributed-polarization-induced 3D hole gas [53,54]. The numerous approaches on the improvement of UV LED efficiencies such as the modified quantum barriers were deeply investigated [55,56].…”