Sapphire substrate off-angle and off-direction dependences on characteristics of AlGaN-based deep ultraviolet light-emitting diodes

Abstract

We investigated dependences of sapphire substrate off-angle from 0.2°to 3.0°and off-direction (a-axis or m-axis) on the device characteristics of the AlGaN quantum-well deep ultraviolet LEDs emitting 280-290 nm. We found that the terrace regions of the LEDs showed a lower threading dislocation density, while the step-edge regions of the LEDs contain more threading dislocations, more Ga, and thicker well widths. The emissions from the terrace regions of the LED with the off-angle were dominant at higher current injection. Finally, the light output power from the LED with the m-axis 1.0°off was the highest among the samples. We then developed a model to explain the above optical properties of our deep ultraviolet LEDs with off-angles.

Detailed analysis of Ga-rich current pathways created in an n-Al0.7Ga0.3N layer grown on an AlN template with dense macrosteps

“…AlGaN-based DUV-LEDs fabricated on an AlN template with dense macrosteps using sapphire substrates with high miscut angles such as 1.0°have been reported to have a higher internal quantum efficiency (IQE) than those on flat AlN templates. [13][14][15][16][17][18] The IQE is considered to be boosted by localized carrier injection through Ga-rich zones, which function as current pathways in an n-AlGaN cladding layer. 19) The carrier localization centers created along the edges of multiple quantum wells (QWs) with high IQE, which are combined with current pathways, may dominate the IQE of the device.…”

Fabrication of AlN templates by high-temperature face-to-face annealing for deep UV LEDs

“…However, in the range where the substrate off-cut angle is relatively large (⩾0.6°), the emission efficiency tends to decrease, although the emission wavelength becomes more uniform as the substrate off-cut angle increases. It is speculated that this phenomenon is due to the deterioration in the crystallinity of the MQWs caused by the step bunching in the underlying AlGaN and MQWs 69) or the increase in the PD density in the MQWs facilitated by the modification of the growth surface morphology such as the reduction of the terrace width 70) with the increase in the substrate off-angle. Thus, optimizing the thickness, composition, and MOVPE growth conditions of the MQWs to match the respective substrate off-cut angle is necessary.…”

Weak metastability of Al x Ga1−x N (x = 13/24, 15/24, 17/24) shown by analyzing AlGaN grown on AlN with dense macrosteps

“…6) Furthermore, cathodoluminescence (CL) with scanning electron microscopy (SEM) from nonflat AlGaN layers (>1 μm) on the AlN by other research groups well agreed with Al n/12 Ga 1−n/12 N metastability (n: integer). [7][8][9] except the result in Ref. 10 obtained from Al 0.5 Ga 0.5 N. Thus, the major trend of generating metastable Al n/12 Ga 1−n/12 N (n = 2-10) was shown.…”