Understanding the Pyramidal Growth of GaN

Abstract

By a combination of conventional, HREM and CBED TEM experiments we have studied wurtzite GaN layers grown by Metal-Organic Chemical Vapour Deposition (MOCVD) on (0001)Al2O3. We experimentally determine the structure of the macroscopic hexagonal pyramids that are visible at the surface of the layers when no optimised buffer is introduced. These pyramids look like hexagonal volcanoes with one hexagonal microscopic chimney (up to 75nm wide) at their core. The crystal inside the chimney is a pure GaN crystal with a polarity opposed to the one of the neighbouring material : the GaN layers grown on (0001)Al2O3 are everywhere Ga-terminated except in the chimneys where they are N-terminated. Some of the N-terminated chimneys grow faster and form macroscopic hexagonal pyramids. Chimneys bounded by Inversion Domains Boundaries (IDBs) originate from steps at the surface of the substrate and may be suppressed by an adapted buffer layer.

Planar defects in ZnO thin films deposited on optical fibers and flat substrates

“…For example they can lie on the ͗1100͘ or on the ͗1120͘ planes instead of the (0001) plane. When a planar defect has only a translation character and does not lie on the basal plane as it is the case for a stacking fault, it has been called a translation domain boundary 32 or a double positioned boundary 35 in other studies. Dislocations were also observed for the coated fiber and flat substrate samples.…”

“…Due to the low processing temperatures used for ZnO thin film growth and the tendency for the wurtzite structure to allow the formation of stacking faults and IDB, it is likely that these types of planar defects will be produced during thin film deposition. Concerning wurtzite films, recently a lot of results have been obtained on the microstructure and defects of GaN films deposited epitaxially onto various substrates [32][33][34][35] due to the optoelectronic applications associated with the GaN layer. In all cases dislocations are observed.…”

Initial Growth Prismatic Domains in Cyclotron Assisted MBE of GaN/SiC

“…Similar defects in AlN grown on SiC have also been identified as prismatic stacking faults for which an atomic model was given [8] [9]. Such defects are also presumed to limit inversion domains [10]. Recently, a third kind of defects named nanopipes has been observed in GaN grown on sapphire by OMVPE [11], and they have been characterized as open core screw dislocations [12].…”

Study of Thin films Polarity of Group III Nitrides

“…The primary focus of our investigations was the absolute polarity determination and correlations between the polarity and extended defects present in the GaN films grown on sapphire. The polarity of the layers was traditionally determined by convergent beam electron diffraction (CBED) [2][3][4] and multiple dark field transmission electron microscopy (TEM) techniques [5][6]. However, CBED method can only be applied for perfect crystals of considerable volume, while the GaN films often contain thin (of the order of 10 nm in diameter) pipe-like domains.…”