Abstract
The impact of a face-to-face annealed sputtered AlN/sapphire (FFA Sp-AlN) template with threading-dislocation densities (TDDs) of 2 × 108 cm−2 and an n-type AlGaN (n-AlGaN) underlayer on optical properties of AlGaN multiple quantum wells (MQWs) with an ultraviolet C (UVC) emission is investigated comprehensively. For comparison of the FFA Sp-AlN template with low TDDs, a conventional MOVPE (metalorganic vapor phase epitaxially)-grown AlN/sapphire (MOVPE-AlN) template with TDDs of 1 × 109 cm−2 was prepared. Consequently, cathodoluminescence (CL), temperature-dependent photoluminescence (PL), and time-resolved PL (TR-PL) measurements verified that both the FFA Sp-AlN template and n-AlGaN underlayer are indispensable for obtaining MQWs with high internal quantum efficiencies, which decrease the TDDs and point defect (PD) densities. Our results revealed that 10-period quantum wells (10QWs)/n-AlGaN/AlN grown on the FFA Sp-AlN template exhibit a lower dark spot density in CL panchromatic intensity maps, a higher integrated emission intensity ratio from the temperature-dependent PL (from 15 to 300 K), and a longer nonradiative lifetime from the TR-PL measurements at 300 K compared with those grown on the MOVPE-AlN template. Moreover, we found that the optical properties of 10QWs/AlN in FFA Sp-AlN and MOVPE-AlN templates do not exhibit a significant difference because of the existence of numerous PDs. Our experimental results demonstrate the favorable impact of the FFA Sp-AlN template for low-TDDs and the n-AlGaN underlayer for low-PDs, which holds promise for highly efficient AlGaN deep-ultraviolet light-emitting devices.
Highlights
AlGaN based light-emitting devices have developed rapidly1–3 and gained popularity in the medical, environmental, and industrial applications, such as sterilization and water purification systems
Our results revealed that 10-period quantum wells (10QWs)/n-AlGaN/AlN grown on the FFA Sp-AlN template exhibit a lower dark spot density in CL panchromatic intensity maps, a higher integrated emission intensity ratio from the temperature-dependent PL, and a longer nonradiative lifetime from the time-resolved PL (TR-PL) measurements at 300 K compared with those grown on the metalorganic vapor phase epitaxially (MOVPE)-AlN template
We demonstrated the internal quantum efficiency (IQE) improvement of 10QWs/nAlGaN/AlN on the FFA Sp-AlN template using the results of CL, temperature-dependent PL, and TR-PL measurements
Summary
Scitation.org/journal/adv known as one of the major nonradiative recombination centers (NRCs). For AlGaN MQWs, the IQEs are usually estimated by the excitation-power-density-dependent photoluminescence (PL) at room temperature (RT) based on the well-known Shockley-ReadHall (SRH) recombination, temperature-dependent PL with an assumption of IQE being 100% at low temperatures, and a combination of both.. For AlGaN MQWs, the IQEs are usually estimated by the excitation-power-density-dependent photoluminescence (PL) at room temperature (RT) based on the well-known Shockley-ReadHall (SRH) recombination, temperature-dependent PL with an assumption of IQE being 100% at low temperatures, and a combination of both.14,18,19 These methods are convenient and frequently used, the IQE estimation of the AlGaN-MQWs is not simple because of the influence of the saturable SRH recombination centers and Auger recombination.. We investigate the optical properties of AlGaN MQWs on the FFA Sp-AlN template to understand the origin of EQE improvements in AlGaN LEDs on FFA Sp-AlN, and we compare the results with that on the MOVPE-AlN. As for the MOVPE regrowth structures, in addition to 10 periods quantum wells (10QWs) directly grown on AlN (10QWs/AlN), 10QWs/n-type AlGaN (n-AlGaN)/AlN were grown to assimilate the condition of LED structures and check the impact of n-AlGaN underlayers
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