Cleaning and growth morphology of GaN and InGaN surfaces

Abstract

The structure and chemistry of clean GaN surfaces and InGaN thin films and nanostructures grown by metal organic vapour pressure epitaxy (MOVPE) has been studied by means of X-ray photoemission spectroscopy, low-energy electron diffraction as well as scanning tunneling microscopy (STM) and transmission electron microscopy. Thermal annealing strongly improves the cleanliness of samples after dry nitrogen transfer and related exposure to residual oxygen. Nitrogen plasma assisted cleaning is shown to successfully further remove carbon contaminations, while Ga deposition with subsequent desorption to is shown to be superior for an enhanced reduction of surface oxygen. Using STM, the surface morphology has been studied in dependence on major growth parameters at various stages of InGaN MOVPE growth. The formation of nano-islands is reported for different growth conditions. By means of microphotoluminescence measurements, we find samples to show strong photoluminescence from quantum-dot-like structures, however, the corresponding growth front is found to be rather flat throughout InGaN deposition. This leads to the conclusion that the formation of quantum dots does not proceed in a Stranski-Krastanov-like fashion but most likely during overgrowth.Scanning tunneling micrograph and height profile of 3.9 nm InGaN grown by MOVPE at 700 8C, after growth interruption and 1 min post-growth annealing at the growth temperature. The surface exhibits a two-dimensional islands morphology.

Surface oxidation of GaN(0001): Nitrogen plasma-assisted cleaning for ultrahigh vacuum applications

“…19 In conclusion, this technique seems very promising for cleaning procedures in technological semiconductor processing, as well as for surface science experiments where a high chemical purity and a high structural quality is required. As has been reported recently, thin GaN layers grown on such plasma-cleaned GaN templates show a surface morphology as expected for homoepitaxial GaN growth carried out using standard molecular beam epitaxy.…”

“…In recent publications, [17][18][19] we were able to show that, both on c-plane as well as on a-plane GaN, nitrogen plasma assisted cleaning is able to remove carbon and oxygen contaminants to a very large extent. In this report, we focus on the dependence on conditions such as substrate temperature and duration of the treatment.…”

“…The large area STM image in Fig. 19 From their position at the end of step edges, the dark spots are identified as surficial intersections of screw or mixed-type dislocations.…”

“…Among various in-situ cleaning methods of GaN templates, apart from the common degassing/annealing under UHV, Ga deposition and re-evaporation, [14][15][16][17][18][19] sputtering with nitrogen 15,[20][21][22] or other 22,23 ions, or thermal annealing in ammonia (NH 3 ) 8,15,21,24,25 have been reported as very effective for the removal of surface contamination. In a few cases, plasma assisted cleaning has also been employed, where GaN surface was exposed to N 2 , 11,[17][18][19][26][27][28][29] H 2 , 27,30 or BCl 3 /Cl 2 (Refs.…”

Non‐polar group‐III nitride semiconductor surfaces

“…Furthermore, even the storage in dry nitrogen environment leads to a remarkable contamination of both polar [80] and non-polar (1120) [81] surfaces of GaN with oxygen and carbon. Even after extensive cleaning processes under Ga and N exposure the oxygen and carbon contaminations are not removed completely, but are reduced significantly [81].…”