AVS 49th International Symposium
    Electronic Materials and Devices Tuesday Sessions
       Session EL+SC-TuM

Paper EL+SC-TuM7
Interdiffusion, Alloying, and Defect Formation at GaN-Sapphire Interfaces

Tuesday, November 5, 2002, 10:20 am, Room C-107

Session: Heterojunctions
Presenter: X.L. Sun, The Ohio State University
Authors: X.L. Sun, The Ohio State University
S.T. Bradley, The Ohio State University
G.H. Jessen, The Ohio State University
L.J. Brillson, The Ohio State University
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The chemical and electronic structure at GaN/sapphire interfaces has a major influence on the electronic quality of epitaxial GaN films. In particular, degenerate doping usually occur near hydride vapor phase epitaxy (HVPE) grown GaN/sapphire interfaces that can affect lateral transport in overgrown devices. Near the interface, impurity diffusion, alloying, and related defect formation can occur at the high (1150°C) growth temperatures that is important to understand and control. We have used Auger electron (AES) and cathodoluminescence (CLS) spectroscopies in a UHV scanning electron microscope (SEM) to probe the chemical and electronic features at the HVPE GaN/sapphire interface in cross section in a nanometer scale. Specimens were cleaved and Ar sputtered in UHV to prepare clean interfaces with well-defined AES, CLS, and secondary electron images. AES images reveal dramatic evidence for diffusion of O from sapphire typically decreasing exponentially ~ 1 µm into GaN from 60% to the detection limit of < 1% surface coverage. The AES O intensity line profile mirrors corresponding SIMS O depth profiles and a donor level CLS emission vs. depth normal to the interface found in similar samples. Conversely, N with plateau concentrations of ~5 % extend ~ 2 µm into the sapphire and correspond spatially to a 3.8 eV defect emission attributed to Al-N-O complexes. While Ga exhibits no strong diffusion, interface Al decreases from 10% to < 1% over ~1 µm into the GaN and support evidence for AlGaN alloy formation, based on ~3.6 eV CLS emission above the GaN band gap at the buried interface. Depending on surface pretreatment and growth conditions, such interfaces can be abrupt to < 200 nm or can exhibit interdiffusion on a micron scale. These results illustrate a new approach to probe chemical and electronic interactions at semiconductor heterojunctions and reveal that both interdiffusion and alloying can occur and lead to extrinsic electronic effects.