Samiul Hasan1,Mohi Uddin Jewel1,Stavros Karakalos1,Mikhail Gaevski2,Iftikhar Ahmad1
University of South Carolina1,CVD Equipment Corporation2
Samiul Hasan1,Mohi Uddin Jewel1,Stavros Karakalos1,Mikhail Gaevski2,Iftikhar Ahmad1
University of South Carolina1,CVD Equipment Corporation2
Aluminum nitride (AlN) is a III-Nitride material with the largest bandgap (6.2 eV) for any semiconductor material that has the native substrate; in addition, it has high thermal, chemical, and mechanical stability. AlN has a very high Baliga figure-of-merit (BFOM) that spurred its continued applications in high power high-temperature devices. The high-quality AlN films have been grown using the metal-organic chemical vapor deposition (MOCVD) technique in hydrogen (H<sub>2</sub>) and recently in the nitrogen (N<sub>2</sub>) reaction environment. Thus, a comparative spectroscopic study is warranted to gain an in-depth understanding of AlN material growth.<br/>Here we report a comparative spectroscopic study on the MOCVD grown AlN thin film on basal plane sapphire (Al<sub>2</sub>O<sub>3</sub>) substrates in H<sub>2</sub> and N<sub>2</sub> reaction environments. It has been previously reported that the H<sub>2</sub> environment encourages early coalescence of the AlN epitaxial layers leading to cracking of the films at smaller thicknesses. To achieve similar thickness (~3.0 µm) of AlN films, for comparison in this study, insertion of low-temperature layer technique was adopted to avoid the surface cracks in H<sub>2</sub> environment. The impact of reaction gas environment on the AlN epilayers was characterized using high-resolution x-ray diffraction (HR-XRD), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), secondary ion mass spectroscopy (SIMS), cathodoluminescence (CL), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The study showed that AlN layers have better crystalline quality with significantly lower stress in a N<sub>2</sub> gas environment than grown in a H<sub>2</sub> gas environment. On the other hand, comparative results from various spectroscopic methods have shown that AlN films grown in an H<sub>2</sub> gas environment have lesser impurities like carbon, oxygen, hydrogen while retaining close to the ideal Al:N stoichiometric ratio. This presentation will discuss the possible mechanisms that influenced the structural quality and impurity incorporation for two different reaction environments to grow AlN epilayers in the MOCVD system on sapphire substrates.