Properties of the RF Sputter Deposited n-ZnO Thin-Film and the n-ZnO/p-GaN heterojunction LED

Abstract

Abstract The ZnO thin films were grown on GaN template substrates by RF magnetron sputtering at different RF powersand n-ZnO/p-GaN heterojunction LEDs were fabricated to investigate the effect of the RF power on the characteristics of then-ZnO/p-GaN LEDs. For the growth of the ZnO thin films, the substrate temperature was kept constant at 200 o C and the RFpower was varied within the range of 200 to 500 W at different growth times to deposit films of 100 nm thick. The electrical,optical and structural properties of ZnO thin films were investigated by ellipsometry, X-ray diffraction (XRD), atomic forcemicroscopy (AFM), photoluminescence (PL) and by assessing the Hall effect. The characteristics of the n-ZnO/p-GaN LEDswere evaluated by current-voltage (I-V) and electroluminescence (EL) measurements. ZnO thin films were grown with apreferred c-axis orientation along the (0002) plane. The XRD peaks shifted to low angles and the surface roughness becamenon-uniform with an increase in the RF power. Also, the PL emission peak was red-shifted. The carrier density and the mobilitydecreased with the RF power. For the n-ZnO/ p-GaN LED, the forward current at 20 V decreased and the threshold voltageincreased with the RF power. The EL emission peak was observed at approximately 435 nm and the luminescence intensitydecreased. Consequently, the crystallinity of the ZnO thin films grown with RF sputtering powers were improved. However,excess Zn affected the structural, electrical and optical properties of the ZnO thin films when the optimal RF power wasexceeded. This excess RF power will degrade the characteristics of light emitting devices.Key wordsZnO, GaN, RF sputtering, heterojunction, LED.