Epitaxial GaN films by hyperthermal ion-beam nitridation of Ga droplets

Abstract

Epitaxial GaN film formation on bare 6H-SiC(0001) substrates via the process of transformation of Ga droplets into a thin GaN film by applying hyperthermal nitrogen ions is investigated. Pre-deposited Ga atoms in well defined amounts form large droplets on the substrate surface which are subsequently nitridated at a substrate temperature of 630?°C by a low-energy nitrogen ion beam from a constricted glow-discharge ion source. The Ga deposition and ion-beam nitridation process steps are monitored in situ by reflection high-energy electron diffraction. Ex situ characterization by x-ray diffraction and reflectivity techniques, Rutherford backscattering spectrometry, and electron microscopy shows that the thickness of the resulting GaN films depends on the various amounts of pre-deposited gallium. The films are epitaxial to the substrate, exhibit a mosaic like, smooth surface topography and consist of coalesced large domains of low defect density. Possible transport mechanisms of reactive nitrogen species during hyperthermal nitridation are discussed and the formation of GaN films by an ion-beam assisted process is explained

Low temperature selective growth of GaN single crystals on pre-patterned Si substrates

“…2d. It is in agreement with [27] where it is hypothesized that the top surface of liquid Ga droplets acts as a major mass transport path for nitrogen species delivered by hyperthermal nitrogen ions which then diffuse to peripheral regions of the droplet-substrate interface. Hence, this interface acts as a collector of nitrogen particles dissolved on the droplet (and of those diffusing towards the interface from the substrate surface around droplets) as schematically depicted in Fig.…”

High-fluence hyperthermal ion irradiation of gallium nitride surfaces at elevated temperatures

“…The findings are in agreement with those of Lai et al [33] who showed with XPS that the stoichiometry at the surface is preserved when irradiating GaN with a 1 keV N 2 + ion beam. It should be noted that nitrogen atoms which are probably sputtered out of the film during the nitrogen ion irradiation process can be permanently filled up with arriving nitrogen ions [16,33]. In contrast, this preservation of surface stoichiometry is not given in the case of Ar ion sputtering of a GaN surface, where preferential sputtering of N atoms leads to a significant decrease of the N/Ga surface concentration ratio [19,20,22,23,[27][28][29][30]33,34].…”

“…The 70 nm thick wurtzitic GaN films were grown in two-dimensional growth mode on super-polished 6H-SiC(0001) substrates at a substrate temperature of 700 • C (for details see Refs. 15,16). These GaN films were then irradiated without interrupting the UHV conditions with hyperthermal nitrogen ions generated by a hollow-anode plasma-beam source, operating with a constricted DC glow-discharge.…”

“…Semiconductors of group-III-nitrides like gallium nitride (GaN) [12] are of great interest because of their applications in electronics and optoelectronics [13,14]. Previous investigations have shown that nitrogen ion energies below 25 eV used in the IBA-MBE technique result in a high crystalline quality of the GaN films and a low defect density in the material [15,16]. There is only a limited number of studies about the interaction processes between low-energy ions with kinetic energies of up to a few keV and GaN , in particular regarding sputtering of GaN.…”

Optimization of ion-atomic beam source for deposition of GaN ultrathin films

“…[7][8][9][10][11][12] Another possibility for low temperature preparation of GaN thin films and nanocrystals is the ion beam assisted deposition IBAD (sometimes called IBA-MBE). [13][14][15] Due to an excess of the energy delivered by ions to the substrate, this method can improve the adhesion of the grown a) mach@fme.vutbr.cz structures and lead to the synthesis of compounds and various metastable phases at temperatures substantially lower than in conventional methods.…”