Growth and characterization of nonpolar (10-10) ZnO transparent conductive oxide on semipolar (11–22) GaN-based light-emitting diodes

• Polarity control of ZnO film grown in m-/c-sapphire and semipolar GaN template.
• Achievement of high quality nonpolar m-plane ZnO flims on semipolar (11–22) GaN template.
• The simultaneous improvements of carrier concentration and mobility in the nonpolar ZnO TCO flims.
• Nonpolar ZnO TCO increases current spreading length and light output power of semipolar GaN-LED.

We have grown thin films of nonpolar m-plane (10-10) ZnO on a semipolar (11–22) GaN template by atomic layer deposition (ALD) at low growth temperatures (<200 °C). The surface morphology of the ZnO film is found to be an arrowhead-like structure, which is a typical surface structure of the semipolar (11–22) GaN films. On increasing the growth temperature of the ZnO films, the concentration and mobility of the charge carriers in the ZnO film are increased. However, the optical transmittance decreases with an increase in the growth temperature. Based on these results, we have fabricated semipolar (11–22) GaN-based light-emitting diodes (LEDs) with nonpolar m-plane ZnO film as a transparent conductive oxide (TCO) to improve the light extraction efficiency. In spite of a decrease in the optical transmittance, the operation voltage of semipolar (11–22) GaN-based LEDs is found to decrease with an increase in the growth temperature, which might be due to the improvements in the electrical properties and current spreading effect, resulting in an increase in the optical output power.

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