Performance investigation of GaN-based light-emitting diodes with tiny misorientation of sapphire substrates

Abstract

GaN-based light-emitting diodes (LEDs) grown on c-plane vicinal sapphire substrates are fabricated and characterized. Based on the material quality and electrical properties, the LED with a 0.2 degrees tilt sapphire substrate (device A) exhibits the lowest defect density and high performance, while the LED with a 1.0 degrees tilt sapphire (device D) exhibits the highest one. At 2 mA, the extremely enhanced output power of 23.3% indicates of the reduction of defect-related nonradiative recombination centers in active layers for the device A. At 60 mA, the improved value is up to 45.7%. This is primarily caused by the formation of indium quantum dots in MQW which provides an increased quantum efficiency.

Highly-efficient GaN-based light-emitting diode wafers on La0.3Sr1.7AlTaO6 substrates

“…Additionally, it is known that the FWHM of GaN(0002) is related to the skew dislocation that is formed by the various height of substrates, and the FWHM of GaN(10-12) is respected to the pure edge and mixed dislocations which are generated during the coalescence process among the mis-oriented individual islands242526. The skew dislocation density, and pure edge and mixed dislocation densities in as-grown GaN epi-layer are estimated to be 7.9 × 10 7 , and 8.8 × 10 7  cm −2 , respectively2728. This crystalline quality of GaN-based LEDs grown on LSAT substrates is much better than traditional GaN-based LEDs prepared on sapphire and nanopatterned sapphire substrates2930313233.…”

Breakdown-induced conductive channel for III-nitride light-emitting devices

“…This is called the full breakdown n*–p* LED, where the asterisk represents the reverse breakdown. This is the very general breakdown phenomena in GaN-based LEDs 30 , 36 , 37 . However, after a local breakdown (p*) is formed in the only p-layer under the reverse breakdown voltage of ~60 V, the I – V curve of the n–p* LED represents almost linear properties—like a conductive material—below +3.4 V and then the normal I – V characteristics of an n–p LED above 3.4 V. As a result, the electrical properties of the n–p* LED were modified from an n–p diode to an n–n- or n–i-like structure in the low-voltage region.…”

“…These crystal imperfections lead to not only a high reverse leakage but also an undesirable satellite luminescence, both of which are very different from the behaviour predicted by theory 26 , 27 . Therefore, there have been studies on understanding and improving the reverse breakdown and reverse leakage properties 28 – 36 . However, the reverse leakage current and breakdown mechanisms of GaN-based LEDs are still not clearly understood.…”

Effect of AlN buffer layer thickness on the properties of GaN films grown by pulsed laser deposition

“…When a 30 nm-thick AlN buffer layer is inserted, the FWHM value of GaN(0002) rises to 84.6 arcmin in Sample B and then falls to 31.8 arcmin in Sample C after the AlN buffer layer up to 150 nm. However, no XRCs of GaN (10)(11)(12) are detected in Sample B and Sample C. Since the FWHM value of GaN(0002) is corresponding to screw dislocations generated from the different step heights of the epitaxial base, and the FWHM value of GaN(10-12) is related to pure edge and mixed dislocations formed during the coalescence process among the disoriented individual islands [32,33], the GaN film without AlN buffer layer is suffered less dislocations and obtains better crystalline quality than the ones with AlN buffer layers according to the results mentioned above. Apparently, AlN buffer layer does not show similar effect in enhancing the crystalline quality of GaN film.…”