Pendeo-Epitaxy - A New Approach for Lateral Growth of Gallium Nitride Structures

Abstract

A new process route for lateral growth of nearly defect free GaN structures via Pendeoepitaxy 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 SiO 2 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.

Pendeo-Epitaxy versus Lateral Epitaxial Overgrowth of GaN: A Comparative Study via Finite Element Analysis

“…The development of the side facet morphology as a function of the growth time and the temperature led us to the hypothesis that lateral growth should occur even without a SiO 2 mask or any supporting material. This alternative approach, pendeo-epitaxy (PE) (from latin pendeo, meaning hanging on, suspended from) [10,11], is lateral epitaxy when the selectivity is provided not by the geometry of the windows within the SiO 2 , as in the conventional LEO, but by the etched shape of the underlying seed GaN layer. Thus, when the underlying GaN is etched in elongated columns, with orientation similar to that of the stripes in the SiO 2 , conditions are provided such that the side walls of the columns provide the crystallographic template for the lateral pendeoepitaxial growth of free-standing GaN material ± ± mode A of PE-GaN, see Fig.…”

Microscopic lateral overgrowth by physical vapour transport of GaN on self‐organized diamond‐like carbon masks

“…Using the ELO technique or pendeo-epitaxy [3] it has been shown that dislocation densities can be reduced by up to three orders of magnitude. Lateral overgrowth is mainly performed by metal organic vapour phase epitaxy (MOVPE) or by hydride vapour phase epitaxy (HVPE).…”

Beam induced lateral epitaxy: a new approach for lateral growth in molecular beam epitaxy

“…Recently, reduction of dislocation density has been accomplished by using epitaxial lateral growth from a ridge structure by LPE in InGaAs/GaAs [12,13] and by matalorganic vapor phase epitaxy (MOVPE) in GaN/SiC and GaN/Sapphire [14][15][16][17].…”