Numerical Investigation on the Carrier Transport Characteristics of AlGaN Deep-UV Light-Emitting Diodes

On the p-AlGaN/n-AlGaN/p-AlGaN Current Spreading Layer for AlGaN-based Deep Ultraviolet Light-Emitting Diodes

“…Investigations into the device physics are conducted by using APSYS [ 28 ]. The energy band offset ratio between the conduction band offset and the valence band offset for the AlGaN/AlGaN heterojunction is set to 50:50 [ 29 ].…”

Manipulation of Si Doping Concentration for Modification of the Electric Field and Carrier Injection for AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes

“…Firstly, the polarization level was set to 40% [18]. The Auger recombination coefficient was set to 1.0 × 10 −30 cm 6 s −1 [19] and the Shockley-Read-Hall (SRH) recombination lifetime in the MQWs was assumed to be 10 ns [19]. The energy band offset ratio for Al x Ga 1-x N/Al y Ga 1−y N heterojunction was set to 50/50 [20].The electron effective mass for the AlGaN material was obtained by conducting linear extrapolation between the electron effective mass for the AlN material and the electron effective mass for the GaN material [21], and the calculated values for the effective electron mass were consistent with the report in Ref.…”

On the Hole Injection for III-Nitride Based Deep Ultraviolet Light-Emitting Diodes

“…The valence band discontinuity at the p-AlGaN/p-GaN heterojunction hinders the hole injection. Kuo et al suggest the stair-cased (p-AlGaN) n /p-GaN heterojunction to facilitate the hole transport [ 68 ]. Here, the AlN composition for the stair-cased (p-AlGaN) n /p-GaN heterojunction decreases along the [0001] growth orientation and n represents the total number of the stair-cased p-AlGaN layers.…”

“…For In x Ga 1− x N/GaN based visible LEDs, it has been widely admitted that the holes are strongly accumulated in the quantum well close to the p-EBL side [ 11 ]. However, the hole distribution across the active region shows different spatial profiles for III-nitride based DUV LEDs according to reports by different groups [ 24 , 68 , 72 , 81 , 82 , 83 , 84 ], e.g., the highest hole concentration is not always found in the quantum well closest to the p-EBL [ 68 , 82 ]. Tsai et al attribute the interesting observations to the reduced valence band offset for the Al x Ga 1− x N/Al y Ga 1− y N ( x < y ) based quantum wells, which therefore is beneficial for the hole transport across the MQW region [ 82 ], i.e., the valence band offset is 0.185 eV for the Al 0.55 Ga 0.45 N/Al 0.72 Ga 0.28 N quantum wells of Tsai et al and 0.210 eV for the In 0.15 Ga 0.85 N/GaN quantum wells with the ~450 nm emission wavelength [ 11 ], respectively.…”

“…Tsai et al attribute the interesting observations to the reduced valence band offset for the Al x Ga 1− x N/Al y Ga 1− y N ( x < y ) based quantum wells, which therefore is beneficial for the hole transport across the MQW region [ 82 ], i.e., the valence band offset is 0.185 eV for the Al 0.55 Ga 0.45 N/Al 0.72 Ga 0.28 N quantum wells of Tsai et al and 0.210 eV for the In 0.15 Ga 0.85 N/GaN quantum wells with the ~450 nm emission wavelength [ 11 ], respectively. Till now, various conduction band offset/valence band offset ratios ( ΔE C / ΔE V ) are assumed when calculating the carrier transport within the Al x Ga 1− x N/Al y Ga 1− y N ( x < y ) based quantum wells, e.g., 70/30 [ 81 , 83 , 84 , 85 ], 65/35 [ 68 , 82 ] and 50/50 [ 24 , 72 ]. We agree to the point proposed by Tsai et al, since we find that the hole concentration in quantum well closest to the p-EBL becomes high if the ΔE C /ΔE V of 50/50 is adopted.…”