Collaborative Research: Analysis of Defects and Their Causes in Bulk Aluminum Nitride Crystals – Jharna Chaudhuri, Texas Tech University, Lubbock, TX DMR High Resolution Transmission Electron Microscopy Study of Thermal Oxidation of Single Crystalline AlN interface Objective: HRTEM study was performed to determine the phases, quality and thickness of the oxide layers on AlN, and also the nature of defects produced in AlN during the oxidation process. Oxidation was performed at 800 °C for 2 hours and 1000 °C for 2, 4 and 6 hours. Results: The oxide layer thickness was only 40 nm for oxidation at 800 °C for 2 hours and varied from 200 to 600 nm for oxidation at 1000 °C from 2 to 6 hours. The oxide was amorphous when formed by oxidation for 2 hours at both 800 °C and 1000 °C, whereas a partly crystalline α-Al 2 O 3 layer with γ-Al 2 O 3 on the surface formed for oxidation for 4 to 6 h at 1000 °C. Also the thickness of the amorphous layer was quite uniform but that of partly crystalline layer was non-uniform. The waviness and non-uniform thickness of the partly crystalline oxide layer as well as the existence of the γ-Al 2 O 3 at the surface suggest that the amorphous oxide layer transformed to stable α-Al 2 O 3 through γ-Al 2 O 3 for longer oxidation time. During the transition from amorphous oxide layer to γ- alumina, there is a nonuniform transition along the AlN surface, i. e., the newly formed γ- alumina does not uniformly cover the entire AlN surface and hence a waviness occurs. A high density of defects occurred in the AlN at the oxide/nitride interface for oxidation at 800 °C only but not at 1000 °C. This could be a consequence of equilibrium reached throughout the nitride due to the rapid diffusion of the nitrogen and aluminum interstitials at a high temperature, but not at a low temperature. Significance: This research has demonstrated for the first time defects and structures produced during the oxidation of single crystal AlN. The results obtained will be useful in the fabrication of high quality dielectric Al 2 O 3 thin films. This basic materials research opens up new opportunities for making field effect transistors, and other electronic and optical devices. Figure 1. (a) Bright field high resolution transmission electron microscopy (HRTEM) image, from AlN oxidized at 1000°C for 2 hours, indicating a uniform thickness of the oxide layer. (b) HRTEM of the same sample at much higher magnification indicating the oxide layer as amorphous. (c) Bright field HRTEM image, from AlN oxidized at 1000°C for 6 hours. The oxide layer is mostly α-Al 2 O 3 at the interior and a mixture of α-Al 2 O 3 and γ-Al 2 O 3 at the surface, and also the thickness of the oxide layer is nonuniform. (d) HRTEM of the same sample shown in Figure 1 (c) at much higher magnification indicating mostly crystalline epitaxial oxide layer. AlN crystal is free of defects in both samples. (a)(b) (c)(d)

Collaborative Research: Analysis of Defects and Their Causes in Bulk Aluminum Nitride Crystals – Jharna Chaudhuri, Texas Tech University, Lubbock, TX NSF Grant # DMR Broader Impact One Ph. D., one MS and two undergraduate (one female) students involved in this research are advancing their education by discovery through experiments they design and perform, through training on sophisticated instrumentation, and application of state-of-the-art modeling techniques. Members of my group participated in Go Girl Engineering Fair and Science It’s a Girl Thing (SIGT). The Go Girl Engineering fair was an engineering fair held exclusively for 6th-8th grade girls at Frenship Intermediate School, Lubbock, Texas. The event had a great turnout with about 60 girls from each of the three grades. The girls were received recommendations to attend the fair based on their grades in math and science. There were seven tables setup like stations that each group of 6 to 8 girls would rotate around every thirty minutes. We described our research and let the girls construct a ScN crystal structure. SIGT was one afternoon workshop during summer held at Texas Tech campus in which six women sophomore and junior high school students participated. we described our research, showed them the scanning and transmission electron microscopes, helped them to construct the crystal structure model of ScN and edge dislocation. The girls took home with them the crystal models and a SEM image of an enlarged mosquito eye. Figure 1. Middle school women students making a crystal model of ScN under the supervision of undergraduate research student Jamie Armstrong (standing). Figure 2. High school women student participants of the work shop science it’s a girl thing (SIGT) with PI Jharna Chaudhuri (at the back) and her Ph. D. student Luke Nyakiti (at the front showing a scanning electron microscope). Figure 3. Undergraduate research student Ryan Breighner explaining the defects and their causes in semiconductors to the participants of SIGT using a poster.