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

Abstract

The epitaxial growth of transparent p‐AlGaN‐based ultraviolet‐A (UVA), light‐emitting diodes (LEDs) may solve the problems of UVA light absorption through the GaN buffers and p‐GaN contact layers at (326–341 nm)‐band emission, respectively. Herein, first, an idea of conventional n‐AlGaN buffer layer (BL) and n‐AlGaN electron source layer (ESL) for the suppression of threading dislocation density (TDD) and enhancement of internal quantum efficiency (IQE) of UVA emitters, using low‐pressure metalorganic vapor‐phase epitaxy (LP‐MOVPE) is attempted. As a result, the total‐TDDs is reduced from ≈ 3 × 109 cm−2 to ≈ 1 × 109 cm−2 in the n‐AlGaN ESL of a 326 nm‐band UVA multiquantum‐wells (MQWs), and IQE is also improved from 30% to 52% at room temperature (RT). Second, an idea of Si‐doped n‐AlGaN Superlattices (SLs)‐based BL, using LP‐MOVPE is challenged. Subsequently, a record IQE of 56% at RT and high crystal quality in 341 nm‐band UVA MQWs are observed. Finally, using a well thickness ≈ 2 nm in SLs‐based UVA MQWs, the light power and external quantum efficiency (EQE), respectively, are remarkably enhanced from 3.5 mW and 0.5% to 7.5 mW and 1.4% on wafer in 341 nm‐Band UVA LED. The perspective for the improvements of UVA emitter's performances is also discussed.

Low contact resistance and high breakdown voltage of AlGaN/GaN HEMT grown on silicon using both AlN/GaN superlattice and Al0.07Ga0.93N back barrier layer

“…Li et al utilized an AlGaN/GaN SL as an electron blocking layer in LED structures to suppress leakage current and enhance heterostructure uniformity [14]. Replacement of conventional n-AlGaN buffer layers with n-AlGaN SL-based buffer layers in UV-A emitters resulted in an improved perfomance, evidenced by a reduction in the full width at half maximum of the x-ray crocking curves [15] and the achievement of a record internal quantum efficiency of 56% at room temperature [16]. The strain-management properties of the InGaN/GaN SL layer were exploited to reduce the potential for shunt resistance pathways and promote carrier separation, and this enhanced solar cell performance by minimizing defect formation and phase separation in the high indium content layer [17].…”