@article{24d79fa0ac81484eb315a709c86c5178,
title = "InGaN/GaN multiple-quantum-well light-emitting diodes grown on Si(111) substrates with ZrB 2(0001) buffer layers",
abstract = "Multiple-quantum-well light-emitting diode (LED) structures of InGaN/GaN were grown by metalorganic chemical vapor deposition on Si(111) substrates via ZrB 2(0001) buffer layers and a GaN template comprising composite Al xGa 1-xN (where x lies in the range from 0 to 1) transition layers to minimize cracking due to thermal expansion mismatch between Si and GaN. Photoluminescence and electroluminescence results from the LED structures compared favorably with similar measurements obtained on identical LED structures grown on sapphire substrates. However, in spite of all the precautions taken, cracking was still present in the LED structures. Scanning electron microscopy and transmission electron microscopy in plan-view and cross-section geometries were conducted on the LED structures to examine the presence and the influence of various defects such as microvoids, micropipes, and threading dislocations on the mechanism of cracking. Our results suggest that the crack network propagates from microvoids on the surface of the LED structure. The formation of microvoids appears to originate from imperfections in the epitaxial ZrB 2(0001) buffer layer.",
author = "Blake, {Adam H.} and Derek Caselli and Christopher Durot and Jason Mueller and Eduardo Parra and Joseph Gilgen and Allison Boley and David Smith and Tsong, {Ignatius S T} and Roberts, {John C.} and Edwin Piner and Kevin Linthicum and Cook, {James W.} and Koleske, {Daniel D.} and Crawford, {Mary H.} and Fischer, {Arthur J.}",
note = "Funding Information: This work was supported by the National Science Foundation Partnership for Innovation program grant number 0438400. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy{\textquoteright}s National Nuclear Security Administration under contract DE-AC04-94AL85000. We also acknowledge use of facilities within the John M. Cowley Center for High Resolution Electron Microscopy at Arizona State University. FIG. 1. (Color) Schematic diagram of the In 0.13 Ga 0.87 N/GaN MQW LED structure grown by MOCVD on a Si(111) substrate at Sandia National Laboratories. Included in the substrate is a 30-nm thick ZrB 2 (0001) buffer layer grown by GSMBE at Arizona State University (ASU). The GaN template fabricated by Nitronex Corporation is the transition layer comprising GaN, AlGaN, and AlN to prevent crack formation by accommodating the stresses arising from thermal expansion mismatch between the III-nitride film and Si substrate. FIG. 2. (Color) Photoluminescence (PL) spectra from MQW LED structures grown on substrates of sapphire (red); Si(111) with ZrB 2 buffer layer and Nitronix GaN template (green); and Si with the Nitronix GaN template but without the ZrB 2 buffer layer (blue) labeled as “Control” sample. The absolute PL intensity is shown as a function of wavelength for each sample. FIG. 3. (Color) Electroluminescence (EL) spectra from MQW LED structures grown on substrates of sapphire (red), GaN/Si control sample (black), and GaN/ZrB 2 /Si (blue). The normalized EL intensities are shown as a function of wavelength. FIG. 4. (Color) Optical-microscopy images (upper row) and EL images (lower row) taken from the Mg-doped p -type GaN on the topside of MQW LED structures grown on the substrates of sapphire, GaN/ZrB 2 /Si, and GaN/Si (control). The probes for electrical injection are visible in the optical images on the upper row. Note the difference in color of the EL emission in the control sample, reflecting the shift toward higher wavelengths, i.e., from purple to blue, for the spectral peak position in this sample as shown in Fig. 3 . FIG. 5. (Color) Optical-microscopy image of the top surface of the MQW LED grown on GaN/ZrB 2 /Si substrate showing the formation of an extensive crack network. Microvoids or micropits of varying sizes in the form of dark spots are visible throughout the image. FIG. 6. Scanning electron microscopy (SEM) image of a microvoid showing a classic crack pattern propagating from the corners of the microvoid. FIG. 7. Cross-sectional transmission electron microscopy (XTEM) image of the entire MQW LED structure grown on GaN/ZrB 2 /Si substrate. Most of the threading dislocations are concentrated in the 1-μm thick GaN-template transition layer grown by Nitronex immediately above the ZrB 2 buffer layer. The threading dislocation density in the MQW region is in the range of 10 9 –10 10 cm −2 . No micropipes are observed in any of the XTEM images. FIG. 8. High resolution XTEM image showing disruption caused by threading dislocation through the 5× MQW of In 0.13 Ga 0.87 N. FIG. 9. XTEM images of different segments of the 30-nm thick ZrB 2 (0001) buffer layer showing imperfections in epitaxy of the layer. FIG. 10. Time-lapsed images taken in the Nova 200 FIB/SEM showing sections of the LED structure ion-milled as a function of time. (a) A microvoid on the LED surface is selected at the center of the plan-view SEM image. (b) A section of the LED in the vicinity of the microvoid is revealed after ion milling for 1 h with the focused ion beam (FIB). (c) The same LED section after further ion-milling for 9 min. The profile of the microvoid and certain distinctive features at the substrate interface directly below the microvoid are clearly visible in images (b) and (c). FIG. 11. (Color) (a) SEM image showing the depression created by the material removed by the FIB after ion-milling the LED structure for 1 h at the vicinity of the microvoid shown in Fig. 10(a) . (b) Magnified image of dotted outline in the LED section shown in image (a). (c) and (d) are composition scans taken at the locations of arrows (c) and (d) shown in image (b). The distance scales in (c) and (d) represent the lengths of arrows shown in image (b). ",
year = "2012",
month = feb,
day = "1",
doi = "10.1063/1.3684557",
language = "English (US)",
volume = "111",
journal = "Journal of Applied Physics",
issn = "0021-8979",
publisher = "American Institute of Physics Publising LLC",
number = "3",
}