Growth and characterization of InGaN-based light-emitting diodes on patterned sapphire substrates

陳詠升

W.K. Wang, D.S. Wuu, S.H. Lin, S.Y. Huang, K.S. Wen, R.H. Horng

Journal of Physics and Chemistry of Solids 69 (2008) 714–718

Outline

• Introduction• Experimental details• Results and discussion• Conclusions• References

Introduction

• High dislocation density will influence the device characteristics,such as device lifetime, electron mobility, and the quantum efficiency of radiative recombination.

• In this work, we propose a new approach for growing a high-quality GaN film using the patterned sapphire substrates (PSSs) with different depth of grooves (Dg). This technique eliminates the dislocations and increases the emitted light extraction efficiency.

Experimental details

Schematic diagram of the LED structure grown on grooved sapphire substrate. The atomic-force-microscopy micrograph shows the patterned substrate after dry etching.

1.0μm0.5 μm0 μm

Results and discussion

Cross-section TEM image of GaN epilayer grown on (a)conventional sapphire substrate and (b) patterned sapphire substrate(Dg =1.0 mm).

X-ray rocking curves of (0 0 0 2) reflections for GaN grown on PSS with different etching depths (Dg =0, 0.5, 1.0 μm).

Output power as a function of injection current for PSS InGaN LEDs with different etching depths (Dg =0, 0.5, 1.0 μm).

Trace-Pro simulated ray extraction ratio of PSS LEDs with various Dg values.

Reliability test of relative luminous intensity of PSS InGaN LEDs with different etching depths (Dg = 0, 0.5, 1.0 μm).

Light output patterns of the PSS LEDs with various groove depths. The forward current was driven at 20 mA.

PSS LED (Dg =1.0 μ m) (22%) conventional LED (28%)

Conclusions

• As much as 33% increased light emission intensity of the PSS LED was obtained at a forward current of 20 mA.

• The output power and external quantum efficiency of the PSS LED at 20mA were measured to be 7.1mW and 10.1%

• From the TEM study, the use of PSS was confirmed to be an efficient way to reduce the TDs in the GaN microstructure.

References

• Y.D. Wang, K.Y. Zang, S.J. Chua, S. Tripathy, H.L. Zhou, C.G.Fonstad, Improvement of microstructural and optical properties of GaN layer on sapphire by nanoscale lateral epitaxial overgrowth,Appl. Phys. Lett. 88 (2006) 211908.

• W.K. Wang, D.S. Wuu, S.H. Lin, P. Han, R.H. Horng, T.C. Hsu,D.T.C. Huo, M.J. Jou, Y.H. Yu, A. Lin, Efficiency improvement of near-ultraviolet InGaN LEDs using patterned sapphire substrates,IEEE J. Quantum Electron. 41 (2005) 1403–1408.