Epitaxially grown GaZnO thin films as transparent electrodes for 4H-SiC

In this paper, we investigate the deposition temperature dependent electrical properties of GaZnO thin films grown onto 4H-SiC. GaZnO thin films were deposited by pulsed laser deposition (PLD), at substrate temperatures (Ts) from 250 to 550 °C, on the n-type 4H-SiC (phosphorus doped, -0.019 Ohm-cm). The AFM surface morphology scans are shown in Fig.l. The surface roughness reduction is clearly seen for GaZnO thin films grown at a substrate temperature over 400 °C. Fig.2. shows the x-ray diffraction (XRD) θ-2θ patterns of GaZnO thin films deposited on n-type 4H-SiC (0001). The peaks around 34.4° and at 36.6° correspond to the GaZnO (0002) and 4H-SiC (0004) reflections, respectively. GaZnO thin films exhibit the c-axis preferential orientation perpendicular to the SiC substrate surface, as the surface energy minimization in the hexagonal close-packed plane of GaZnO (0002). Fig.3 shows Auger electron spectroscopy (AES) measurement data for GaZnO thin films deposited at different substrate temperatures, which results in the relative amount of Ga ions as 1.81, 2.02, and 1.77 %, for Ts~ 250, 400, and 550 °C, respectively. The relative amount of Ga ions in GaZnO thin films may affect electrical characteristics in GaZnO thin film, as the surplus Zn ions fill up the interstitial defects and Ga³⁺ ions contributes to effective carrier concentration. Fig. 4 (a) shows room temperature I-V characteristics for GaZnO/4H SiC structures, which exhibits Ohmic-like behavior and the temperature dependent barrier height extractions are shown in Fig.4 (b). As measurement temperature increases, the extracted effective barrier height also slightly increases due possibly to scattering effect.