Effect of 4μm-thick Buffer as well as 50 relaxed n-AlGaN Electron Injection Layer on thePerformance of 308nm UV-B LED

摘要

Eco-friendly, smart and high-power DUV and UV-B LED light sources on AlN template are strongly demandedfor both medical and agricultural applications, including vitamin D3 production in the human body, immunotherapy, andenriching phytochemicals in the plants. AlN template-based n-AlGaN buffer layer (BL) and n-AlGaN electron injection layer(EIL) require a low dislocation densities (TDDs) and cracks free surface underneath the multiple quantum wells (MQWs) forthe fabrication of LEDs. The crystal structure of AlN template grown on c-(0001)-sapphire substrates was improved using awell-known technique of "ammonia (NH3) pulsed-flow multilayer (ML) growth" in Riken, where FWHM values of the XRCsfor the (0002) and (10-12) planes approximately 200 and 350 arcsec, respectively (TDDs ～5×10~8 cm~(−2)) were achieved. Butstill the growth of Al0.40Ga0.60N BL on AlN template, with x～20.40 Al-content for UV-B emission, can have a lattice mismatch>1.7% and subsequently can generate a huge number of vertically propagating TDDs in the n-AlGaN EIL underneath theMQWs and can deteriorate the internal quantum efficiency (IQE). Hirayama et al. successfully achieved the highest relativeIQE of 86% at 280nm, using InAlGaN MQWs and Wang et al. reported about high relative IQE of 85% in AlGaN MQWsat 280nm grown on AlN template having FWHM values of XRC for (002) and (102), namely 331 and 652arcsec. Shatalovet al. also reported about the relative IQE of 60% in AlGaN MQWs at 278nm grown on AlN templates. But when it comesto x=0.38-42 Al-contents for 295-310nm-band UV-B emission then the TDDs are relatively more challenging. Very recentlywe successfully achieve the relative IQE of 40-50% from the AlGaN UV-B LED using a 1.8μm-thick n-AlGaN BL and 200nmthickn-AlGaN EIL (TDDs ～1.4-1.1×10~9 cm~(−2)) with FWHM values for (102) plan respectively 590 and 579arcsec.