Pendeo-Epitaxy - A New Approach for Lateral Growth of Gallium Nitride Structures
- PDF / 259,674 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 14 Downloads / 127 Views
ABSTRACT A new process route for lateral growth of nearly defect free GaN structures via Pendeo−
epitaxy is discussed. Lateral growth of GaN films suspended from {112 0} side walls of [0001] oriented GaN columns into and over adjacent etched wells has been achieved via MOVPE technique without the use of, or contact with, a supporting mask or substrate. Pendeo-epitaxy is proposed as the descriptive term for this growth technique. Selective growth was achieved using −
process parameters that promote lateral growth of the {11 2 0} planes of GaN and disallow nucleation of this phase on the exposed SiC substrate. Thus, the selectivity is provided by tailoring the shape of the underlying GaN layer itself consisting of a sequence of alternating trenches and columns, instead of selective growth through openings in SiO2 or SiN x mask, as in the conventional lateral epitaxial overgrowth (LEO). Two modes of initiation of the pendeo-epitaxial GaN growth via MOVPE were observed: −
Mode A - promoting the lateral growth of the {112 0} side facets into the wells faster than the vertical growth of the (0001) top facets; and Mode B - enabling the top (0001) faces to grow initially faster followed by the pendeo-epitaxial growth over the wells from the newly formed −
{112 0} side facets. Four-to-five order decrease in the dislocation density was observed via transmission electron microscopy (TEM) in the pendeo-epitaxial GaN relative to that in the GaN columns. TEM observations revealed that in pendeo-epitaxial GaN films the dislocations do not propagate laterally from the GaN columns when the structure grows laterally from the sidewalls into and over the trenches. Scanning electron microscopy (SEM) studies revealed that the coalesced regions are either defect-free or sometimes exhibit voids. Above these voids the PEGaN layer is usually defect free. INTRODUCTION Recent studies on selected area growth (SAG) and lateral epitaxial overgrowth (LEO) of GaN structures on 6H-SiC [1-6] and Sapphire [7-10] have shown that the laterally overgrown regions have four-to-five orders of magnitude lower densities of dislocations compared to the regions of vertical growth. During the selective growth the GaN structure grows vertically and
Downloaded from https://www.cambridge.org/core. IP address: 46.161.63.135, on 18 Mar 2019 at 05:48:35, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300002581
laterally at the same time, but the vertical growth dominates during the growth from the windows in SiO2 (i.e. the growth rate of (0001) planes of GaN is higher than the growth rate of the GaN side facets), while the lateral growth dominates during the GaN growth over the SiO2 (i.e. the growth rate of the GaN side facets is higher than the growth rate of the (0001) planes). Thus, the reduction in the defect density is associated with the change in the growth direction from vertical during the initial stages of growth from the openings in the SiO2, to lateral over the SiO2 in
Data Loading...
