Growth behavior and growth rate dependency in LEDs performance for Mg-doped a-plane GaN

Influence of Lateral Growth on the Surface Pit Formation of GaN Heteroepitaxial Film Grown by MOCVD

“…So if it is for an accurate evaluation of dislocation density, chemical wet etching is needed, which could expose the dislocation position clearly. It is interesting to see that (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) semipolar GaN surface is free of pit, different from the a-plane and c-plane sample, in consistent with the literature [24]. Fig.…”

“…In a-plane nonpolar GaN grown with the conventional two-step procedure, the incomplete lateral coalescence of nucleation islands on top of the fine crystals in the buffer would cause large inverted pyramid pits on the surface [13 -16, 26 -28], particularly under the growth condition of high V/III ratio. From the kinetic Wulff plot, it could be observed that under relative high V/III ratio, the ratio between lateral growth rate of the inclined facets {10-11} and vertical growth rate of (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) facet is low, so that island coalescence of a-plane GaN is slow and inclined facets remain, resulting in the pit. Under low V/III ratio, the lateral vs. vertical growth velocity ratio is high, so that growth front along the inclined facet direction would gradually change back to the epitaxial orientation to fill up the pit.…”

“…The undoped GaN samples were grown with lowtemperature GaN buffer layers by metal organic chemical vapor deposition (MOCVD) using a two-step growth procedure. The c-plane (0001) GaN was grown on c-plane sapphire substrate, the a-plane (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) GaN was grown on r-plane sapphire substrate, and the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) semipolar GaN was grown on m-plane sapphire substrate. Triethylgallium (TEG) and NH3 were used as the Ga source and N source, respectively, and H2 was used as a carrier gas.…”

The Same Formation Mechanism of Surface Pits for both a- and c-plane GaN

“…In addition to dislocation mediation, kinetic effect is also critical in determining the surface morphology of a heteroepitaxial film [5,6,8,11,12]. The kinetic process of island coalescence may produce surface pits for a-plane GaN, as well as c-plane GaN.…”

“…However, when the growth orientation deviated from the c-axis [0001], structural defects increased [4], and attaining smooth surface became difficult. Large surface pit is one of themorphological imperfections that frequently encountered in a-plane(1120) GaN growth [5][6][7].It refers to the inverted triangular pyramid pits that bound by one vertical (0001 � ) and two inclined{101 � 1}facets [8]or,in some studies, pentagonal shapes composed of{101 � 2 � }, {202 � 1}, and {112 � 2} facets [9,10]. Reducing the V/III ratio could eliminate these defects; therefore, most researchers considered them as a result of incomplete island coalescence [5,6,[8][9][10][11][12], which was due to the increased vertical growth of the (1120) facet and decreased lateral growth rate of the inclined facets, such as {101 � 1} and (0001 � ) [6,8].…”