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

Abstract

Aluminium gallium nitride (AlGaN)‐based ultraviolet‐B light‐emitting diodes (UVB LEDs) are expected to offer smart size, wider choice of UVB light emission in the wavelengths range of 280 nm > λ > 320 nm, and low cost as well as low power consumption compared with other UV light sources including toxic mercury UV‐lamps. The hole‐tunneling from p‐AlGaN side of UVB LED into the multi‐quantum‐wells (MQWs) is strongly dependent on the thickness (TFB) and Al‐contents of undoped (ud)‐AlGaN final barrier (FB). Herein, the photoluminescence (PL) efficiency from MQWs of the UVB LED devices is investigated and compared with the electroluminescence (EL) spectra as a function of TFB. Subsequently, the dependence of PL efficiency, external quantum efficiency (EQE), and light output power on the TFB of UVB LEDs is attempted, using the same growth condition for all samples except variation in TFB. When TFB is set to 6–7 nm, improvements in the EQE and light output power, respectively, from 4.3% and 7 mW to the high values of 5.6% and 17 mW in emission band of 295–300 nm under continuous‐wave (cw) at room temperature (RT) are achieved.

Highly Transparent p‐AlGaN‐Based (326–341 nm)‐Band Ultraviolet‐A Light‐Emitting Diodes on AlN Templates: Recent Advances and Perspectives

“…[ 6,18,19 ] The possibility of broadening of EL emission or double peak emission might be attributed to several potential reasons, such 3D growth mode, alloy fluctuation, and high TDs. [ 20–30 ] However, theoretical calculations suggest that the AlGaN system is completely miscible, [ 29 ] enabling Al x Ga 1– x N epilayers to be grown with Al content from x = 0 to 1. AlGaN phase separation in the AlGaN has been reported by Cremades et al [ 30 ] On the other hand, Marques et al investigated the thermodynamic properties of the AlGaN alloys and indicated that most of the nitride alloy systems can have strong indications of a miscibility gap, except AlGaN.…”

“…[ 49 ] We found that the relaxation condition in the n‐AlGaN ESL underneath the MQWs does influence the piezoelectricity in the MQWs. Therefore, in this article we followed the same direction of UVB emitters [ 23,49 ] for UVA emitters too to enhance the EQE up to 6.5%. [ 49 ] In the next part, some review and recent advances in the SLs‐based UVA MQWs and LEDs are given.…”

“…[ 18,19 ] This was calibrated to measure the luminous flux for accurate values of light output power measurement in the UVA and UVB LEDs. [ 6,18,19,23 ] The performances of UVA LED devices were evaluated at RT under both continuous‐wave (CW)—as well as under pulse—operation on wafer. [ 6,18,19,23,49 ] In the next section, results achieved so far were deeply discussed in sequential manner for two types of the UVA emitters including UVA LEDs.…”

“…[ 20,22 ] The issues of TDs suppression in the pure p‐AlGaN‐based UVB LEDs at 300–310 nm were successfully mitigated. [ 6,23,24 ] However, such values of LM ≈ 2.6% can still give rise to localized energy states or even 3D growth modes or kinetic separation as well as vertically propagating TDs in the AlGaN‐based UVA MQWs. [ 18–21,25–30 ] Previously, TDs`s annihilation, TD's bending, and 90° reorientation in the n‐AlGaN BL were attempted by different researchers on filtering effect of superlattices (SLs) in LEDs.…”

“…[ 40–43 ] To suppress the total‐threading dislocation densities (total‐TDDs), 3D growth mode or localized energy state in the UVA MQW region, we have only one choice to make an incredibly good crystal quality of n‐AlGaN ESL underneath the MQWs, shown in Figure 1A. [ 18,19,23,24,31–35 ]…”