Nitride-based materials have been reported to be a promising semiconductor for high brightness light-emitting diodes (LED), and high power and high frequency device, due to their direct and wide bandgap (0.6–6.2 eV)[
Journal of Semiconductors, Volume. 43, Issue 7, 072801(2022)
Improving the incorporation of indium component for InGaN-based green LED through inserting photonic crystalline in the GaN layer
We report on the effect of inserted photonic crystalline (Ph-C) in the GaN epitaxial layer on the incorporation of the indium component for the InGaN-based green LED. The adoption of Ph-C in the GaN layer shifted the Raman peak value of E2 mode of GaN to lower frequency and resulted in a tensive stress relief. The stress relief can be attributed to strained lattices restoring in the matrix of Ph-C and the GaN pseudo-epitaxy over the air-void of the Ph-C. Moreover, the HRXRD rocking curves and AFM results show that the insertion of Ph-C also improves the crystal quality. With the inserted Ph-C, the indium component in the multiple quantum wells of the green LED (Ph-C LED) was enhanced. This resulted in a 6-nm red-shift of the peak wavelength. Furthermore, the LOP of the Ph-C LED was enhanced by 10.65% under an injection current of 20 mA.We report on the effect of inserted photonic crystalline (Ph-C) in the GaN epitaxial layer on the incorporation of the indium component for the InGaN-based green LED. The adoption of Ph-C in the GaN layer shifted the Raman peak value of E2 mode of GaN to lower frequency and resulted in a tensive stress relief. The stress relief can be attributed to strained lattices restoring in the matrix of Ph-C and the GaN pseudo-epitaxy over the air-void of the Ph-C. Moreover, the HRXRD rocking curves and AFM results show that the insertion of Ph-C also improves the crystal quality. With the inserted Ph-C, the indium component in the multiple quantum wells of the green LED (Ph-C LED) was enhanced. This resulted in a 6-nm red-shift of the peak wavelength. Furthermore, the LOP of the Ph-C LED was enhanced by 10.65% under an injection current of 20 mA.
Introduction
Nitride-based materials have been reported to be a promising semiconductor for high brightness light-emitting diodes (LED), and high power and high frequency device, due to their direct and wide bandgap (0.6–6.2 eV)[
Many methods have been proposed and employed to relax the stress in the GaN epilayer grown on sapphire substrate, such as by using AlGaN/AlN transition layer[
Experiment
A control sample and a GaN sample introducing Ph-C (Ph-C sample) were grown on c-plane sapphire substrates in a Veeco metal-organic chemical vapor deposition system. First, two GaN/sapphire templates were grown: The sapphire substrates were cleaned at 1015 °C in H2 atmosphere, followed by the growth of GaN buffer layer at temperature of 560 °C (about 30 nm thick); Subsequently, a 2 μm undoped GaN was grown at a temperature of 1150 °C. Then, a 1 μm thick un-doped GaN epilayer was grown directly on the GaN template for the control sample. For the Ph-C sample, the fabrication process started with the spinning of 600 nm thick photoresist on the GaN/sapphire template, followed by the transfer of monolayer of polystyrene sphere on the surface of the photoresist; Subsequently, the UV-exposure was conducted and followed by the inductively coupled plasma (ICP) etching, forming nano-voids with a diameter of about 200 nm and a depth of 400 nm. Then, cleaning of the etched wafer and regrowth of GaN on the Ph-C were conducted with the same growth condition as the control sample. The InGaN-based green LED epitaxial structure was then grown on the two templates. At first, a 200 nm n-GaN layer was grown on the n-GaN/sapphire substrate at 900 °C. Then, an InGaN/GaN MQWs sample consisting of eight pairs of 3.5 nm undoped InGaN wells and 15 nm Si doped GaN barriers was grown. Mg-doped p-AlGaN EBL with a uniform aluminum content of 20% was grown directly on the MQWs. The thickness of the p-AlGaN EBL was 30 nm for both samples. On top of the EBL, a 120-nm thick p-type GaN was grown. Detailed information about the experiment process can be found in the early works of our team[
Results and discussion
A schematic diagram of the fabrication process flow to realize Ph-C sample is shown in
Figure 1.(Color online) Schematic of the fabrication process flow to realize Ph-C sample.
Figure 2.The cross-sectional scanning electron microscope of the Ph-C sample.
Figure 3.(Color online) Atomic force microscopes surface topography of (a) control sample, (b) Ph-C sample, (c) control sample after KOH etching, (d) Ph-C sample after KOH etching.
Raman measurements performed with a laser of excitation wavelength of 514 nm at room temperature is present in the
Figure 4.(Color online) Raman spectra of control sample and Ph-C sample measured at room temperature.
Two reasons may contribute to the strain relief for the Ph-C sample: (1) The strain in the GaN Ph-C was partially relaxed in the ICP process. The stress was relieved in three mechanisms in the ICP process[
Figure 5.(Color online) (a) HRXRD 2θ–ω patterns of the two LED samples. (b) HRXRD (002) rocking curves of the Ph-C sample and the control samples. (c) HRXRD (102) rocking curves of the Ph-C sample and the control samples.
Beside the stress relief, the inserted Ph-C also have an influence on the crystal quality. The AFM results show that the pits were reduced at the surface of the Ph-C sample, which means a reduction of the threading dislocations. To further prove the improvement of the crystal quality, HRXRD rocking curves measurement of GaN for symmetric (002) and asymmetric (102) planes were conducted to confirm the reduction of the dislocations, which is shown in
Figure 6.(Color online) (a) PL spectra of compared LED and Ph-C LED measured at room temperature. (b) EQE of compared LED and Ph-C LED measured under different injection currents. (c) LOP of compared LED and Ph-C LED measured under different injection currents.
Conclusion
In conclusion, we investigated the effect of the inserted Ph-C in the GaN epitaxial layer on the incorporation of indium component for the InGaN-based green LED. The Raman results show that the E2 mode value shifts to the higher value in the Ph-C sample, indicating that the tensive stress was relaxed in the Ph-C sample. HRXRD results showed that the insertion of the Ph-C also reduced the dislocation density which was consistent with the AFM results. The HRXRD results also reveals that the In incorporation in the active region was enhanced for the Ph-C LED, resulting in a 6 nm red-shift of the PL peak wavelength. Moreover, the LOP of the Ph-C LED was enhanced by 10.65% under the injection current of 20 mA.
Get Citation
Copy Citation Text
Yunqi Li, Xinwei Wang, Ning Zhang, Xuecheng Wei, Junxi Wang. Improving the incorporation of indium component for InGaN-based green LED through inserting photonic crystalline in the GaN layer[J]. Journal of Semiconductors, 2022, 43(7): 072801
Category:
Received: Jan. 24, 2022
Accepted: --
Published Online: Jul. 22, 2022
The Author Email: Zhang Ning (zhangn@semi.ac.cn)