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Fabrication and characterization of GaN-based light-emitting diodes without pre-activation of p-type GaN.

Hu XL, Wang H, Zhang XC - Nanoscale Res Lett (2015)

Bottom Line: During the fabrication process, a 100-nm-thick indium tin oxide film was served as the p-type contact layer and annealed at 500°C in N2 ambient for 20 min to increase its transparency as well as to activate the p-type GaN.We discussed the mechanism of activation of p-type GaN at 500°C in N2 ambient.Furthermore, x-ray photoemission spectroscopy examinations were carried out to study the improved electrical performances of the LEDs without pre-activation of p-type GaN.

View Article: PubMed Central - PubMed

Affiliation: Engineering Research Center for Optoelectronics of Guangdong Province, School of Physics and Optoelectronics, South China University of Technology, Guangzhou, Guangdong 510640 China.

ABSTRACT
We fabricated GaN-based light-emitting diodes (LEDs) without pre-activation of p-type GaN. During the fabrication process, a 100-nm-thick indium tin oxide film was served as the p-type contact layer and annealed at 500°C in N2 ambient for 20 min to increase its transparency as well as to activate the p-type GaN. The electrical measurements showed that the LEDs were featured by a lower forward voltage and higher wall-plug efficiency in comparison with LEDs using pre-activation of p-type GaN. We discussed the mechanism of activation of p-type GaN at 500°C in N2 ambient. Furthermore, x-ray photoemission spectroscopy examinations were carried out to study the improved electrical performances of the LEDs without pre-activation of p-type GaN.

No MeSH data available.


Output power and WPE versus injection current for LED samples A, B, and C, respectively.
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Fig3: Output power and WPE versus injection current for LED samples A, B, and C, respectively.

Mentions: The light output power as a function of injection current for LED samples A, B, and C is shown in Figure 3. It is found that the light output power of LED sample A (21.8 mW) is much lower than that of LED sample B (24.5 mW) and LED sample C (24.6 mW). We believe that the defects, which were generated during the high-temperature thermal annealing process, increased the non-radiative recombination and ultimately lead to a decrease of output power, and this is consist with the results in PL measurements. It is also shown that the WPE of LED samples A, B, and C is 32.0%, 36.9%, and 38.2% at an operating current of 20 mA, respectively. Therefore, the WPE of LED sample C is 19.4% higher than that of LED sample A. The decrease in the WPE for LED sample A is due to the lower light output power and the higher forward voltage. In addition, the WPE of LED sample C demonstrated a 3.5% improvement in comparison with that of LED sample B, which is mainly attributed to the lower forward voltage of LED sample C. The Hall effect and x-ray photoemission spectroscopy (XPS) measurements were carried out in the following experiment to explain the improved performance for LED sample C. In order to clarify the mechanism of activation of p-type GaN at a relatively low temperature of 500°C in N2 ambient, p-type GaN epitaxial wafers without MQWs active region were grown by MOCVD as follows: The epitaxial layers were done by sequentially depositing of a 30-nm-thick low-temperature GaN nucleation layer, a 2.0-μm-thick undoped GaN layer, a 0.6-μm-thick p-type GaN layer, and a 2.0-nm-thick InGaN strained layer on sapphire substrates. X-ray rocking curves showed that the full width at half maximums of the wafers was 299 arcsec for (0002) symmetric plane, indicating a good quality of the p-type GaN layers [21]. A 100-nm-thick ITO film was evaporated on the p-type GaN epitaxial layers by the electron beam evaporator. The sample was then annealed at 500°C in N2 ambient for 20 min and finally cleaned in hot ITO acid etching solution for 20 min to remove the ITO film. The sample was marked as sample D. For sample E, the same annealing process was carried out but without depositing ITO film. Subsequently, the two samples were cut into 0.6 cm × 0.6 cm and rinsed in boiling aqua regia for 10 min to remove the native oxides. Finally, Ni/Au dots were evaporated on the surface to form electrical contacts in Vander Pauw geometry for Hall effect measurements [14]. The samples were annealed at 500°C in O2 ambient for only 30 s to form ohmic contacts. The short-time annealing process would have fewer influences on the result of the pre-annealing of the samples.Figure 3


Fabrication and characterization of GaN-based light-emitting diodes without pre-activation of p-type GaN.

Hu XL, Wang H, Zhang XC - Nanoscale Res Lett (2015)

Output power and WPE versus injection current for LED samples A, B, and C, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385135&req=5

Fig3: Output power and WPE versus injection current for LED samples A, B, and C, respectively.
Mentions: The light output power as a function of injection current for LED samples A, B, and C is shown in Figure 3. It is found that the light output power of LED sample A (21.8 mW) is much lower than that of LED sample B (24.5 mW) and LED sample C (24.6 mW). We believe that the defects, which were generated during the high-temperature thermal annealing process, increased the non-radiative recombination and ultimately lead to a decrease of output power, and this is consist with the results in PL measurements. It is also shown that the WPE of LED samples A, B, and C is 32.0%, 36.9%, and 38.2% at an operating current of 20 mA, respectively. Therefore, the WPE of LED sample C is 19.4% higher than that of LED sample A. The decrease in the WPE for LED sample A is due to the lower light output power and the higher forward voltage. In addition, the WPE of LED sample C demonstrated a 3.5% improvement in comparison with that of LED sample B, which is mainly attributed to the lower forward voltage of LED sample C. The Hall effect and x-ray photoemission spectroscopy (XPS) measurements were carried out in the following experiment to explain the improved performance for LED sample C. In order to clarify the mechanism of activation of p-type GaN at a relatively low temperature of 500°C in N2 ambient, p-type GaN epitaxial wafers without MQWs active region were grown by MOCVD as follows: The epitaxial layers were done by sequentially depositing of a 30-nm-thick low-temperature GaN nucleation layer, a 2.0-μm-thick undoped GaN layer, a 0.6-μm-thick p-type GaN layer, and a 2.0-nm-thick InGaN strained layer on sapphire substrates. X-ray rocking curves showed that the full width at half maximums of the wafers was 299 arcsec for (0002) symmetric plane, indicating a good quality of the p-type GaN layers [21]. A 100-nm-thick ITO film was evaporated on the p-type GaN epitaxial layers by the electron beam evaporator. The sample was then annealed at 500°C in N2 ambient for 20 min and finally cleaned in hot ITO acid etching solution for 20 min to remove the ITO film. The sample was marked as sample D. For sample E, the same annealing process was carried out but without depositing ITO film. Subsequently, the two samples were cut into 0.6 cm × 0.6 cm and rinsed in boiling aqua regia for 10 min to remove the native oxides. Finally, Ni/Au dots were evaporated on the surface to form electrical contacts in Vander Pauw geometry for Hall effect measurements [14]. The samples were annealed at 500°C in O2 ambient for only 30 s to form ohmic contacts. The short-time annealing process would have fewer influences on the result of the pre-annealing of the samples.Figure 3

Bottom Line: During the fabrication process, a 100-nm-thick indium tin oxide film was served as the p-type contact layer and annealed at 500°C in N2 ambient for 20 min to increase its transparency as well as to activate the p-type GaN.We discussed the mechanism of activation of p-type GaN at 500°C in N2 ambient.Furthermore, x-ray photoemission spectroscopy examinations were carried out to study the improved electrical performances of the LEDs without pre-activation of p-type GaN.

View Article: PubMed Central - PubMed

Affiliation: Engineering Research Center for Optoelectronics of Guangdong Province, School of Physics and Optoelectronics, South China University of Technology, Guangzhou, Guangdong 510640 China.

ABSTRACT
We fabricated GaN-based light-emitting diodes (LEDs) without pre-activation of p-type GaN. During the fabrication process, a 100-nm-thick indium tin oxide film was served as the p-type contact layer and annealed at 500°C in N2 ambient for 20 min to increase its transparency as well as to activate the p-type GaN. The electrical measurements showed that the LEDs were featured by a lower forward voltage and higher wall-plug efficiency in comparison with LEDs using pre-activation of p-type GaN. We discussed the mechanism of activation of p-type GaN at 500°C in N2 ambient. Furthermore, x-ray photoemission spectroscopy examinations were carried out to study the improved electrical performances of the LEDs without pre-activation of p-type GaN.

No MeSH data available.