Atomic layer deposition of oxide semiconductor films and their applications in the transparent conductive layers of GaN-based light emitting diodes

• Main Authors: Kuo-Yi Yen, 嚴國藝
• Other Authors: Jyh-Rong Gong
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/28772128445799934264

博士 === 國立中興大學 === 物理學系所 === 101 === In this dissertation, metal oxide films including zinc oxide (ZnO), gallium doped zinc oxide (GZO), indium doped zinc oxide (IZO) and indium oxide (In2O3) were grown by using atomic layer deposition (ALD). Diethylzinc (DEZn), triethylgallium (TEGa), trimethylindium (TMIn) and nitrous oxide (N2O) were employed as the precursors of zinc (Zn), gallium (Ga), indium (In) and oxygen (O) elements in the oxide films. For ALD of ZnO films, it was found that a monolayer-by-monolayer growth regime occurred at 300oC in a range of DEZn flow rates from 5.7 to 8.7μmol/min. Furthermore, the temperature self-limiting process window for the ALD-grown ZnO films was also observed ranging from 290 to 310oC. A deposition mechanism is proposed to explain how saturated growth of ZnO is achieved by using DEZn and N2O. It was also found that ZnO films grown in the self-limiting window all show high optical transparency. Based on self-limiting process regime, GZO and IZO films were prepared by ALD and employed to serve as transparent conducting layers (TCLs) on InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs). According to θ to 2θ X-ray diffraction (XRD) analyses, Ga doping maintain lattice constant of ZnO, but In doping expand lattice constant of ZnO. It was found that N2-annealed GZO-coated and IZO-coated InGaN/GaN MQW LEDs exhibited reduced forward voltage and enhanced light extraction under certain conditions. A forward voltages of 3.1 and 3.18 V at 20 mA were achieved for a 400oC N2-annealed GZO-coated and 600oC N2-annealed IZO-coated InGaN/GaN MQW LEDs having a specific contact resistance of the GZO/p-GaN and IZO/p-GaN contacts being 4.1×10-3 and 8.8×10-3Ω-cm2. Comparing with the same InGaN/GaN MQW LED structure having a commercial-grade indium tin oxide (ITO) TCL, the 400oC N2-annealed GZO-coated InGaN/GaN MQW LED shows an increment of light output power by 15% at 20 mA. It is believed that the enhanced light extraction of the GZO coated InGaN/GaN MQW LED is a consequence of a higher refractive index of GZO than that of ITO. In2O3 films were also grown on (0001) sapphire substrates by ALD. Based on the XRD results, all the In2O3 films were found to show <111> preferred orientation. The In2O3 film deposited on LT-In2O3/(0001)sapphire structure by ALD under certain condition exhibited room temperature (RT) electron concentration and electron mobility of 1.93×1016 cm-3 and 59.6 cm2/V-sec, respectively, with optical transmittance being ~90% in the visible spectra and smooth surface. According to transmission electron microscopy (TEM), twin crystals of In2O3 films exhibit { } twin planes with the atomic displacement being along <111> directions. By an appropriate buffer layer annealing prior to the ALD of an In2O3 film, the twin boundary area of the In2O3 film was reduced.