GaN-Schichten

Rissfreie dicke GaN-Schichten konnten mittels Hydrid-Gasphasen- Epitaxie (HVPE) sowohl auf exakt als auch auf leicht fehlorientierten GaN-Al2O3 Templat-Strukturen abgeschieden werden. Ein dramatischer Unterschied in der Oberflaechenqualitaet konnte auf die Fehlorientierung der Substrate zurueckgefuehrt werden. Spiegelglatte Schichten konnten auf leicht fehlorientierten Wafern erzielt werden, waehrend auf exakt orientierten Substraten die Ausbildung von pyramidenfoermigen Strukturen und insgesamt raueren Oberflaechen beobachtet wurden. HVPE-Schichten mit einer so ausgezeichneten Oberflaechenmorphologie koennen voraussichtlich ohne die sonst notwendigen Polier-Zwischenschritte als Substrate fuer anschliessende Epitaxie-Prozesse verwendet werden.

WO 2006119927 A1 UPAB: 20070112 NOVELTY - Production of a III-N substrate containing element(s) of group III involves: depositing III-N layer having thickness of greater than or equal to 40 microns by epitaxial growth, onto thin III-N layer of template on foreign substrate having slight intentional misorientation with respect to next crystallographic lattice plane of its surface onto which the III-N layer is deposited; or depositing layer under predetermined N/III ratio and reactor pressure, such that towards end of growth the N/III ratio and/or pressure in reactor is lowered, relative to predetermined ratio and/or pressure. DETAILED DESCRIPTION - Production of a III-N substrate containing element(s) of group III involves: depositing III-N layer having thickness of (greater than or equal to40, preferably greater than 100) microns, onto thin III-N layer of template on foreign substrate having slight intentional misorientation (0.1 - 2, preferably 0.1 - less than 1, especially 0.3 - 0.6)degrees, with respect to next crystallographic lattice plane of its surface onto which the III-N layer is deposited; or depositing layer by epitaxial growth under predetermined N/III ratio and reactor pressure, such that towards end of growth the N/III ratio and/or pressure in reactor is lowered, relative to predetermined ratio and/or pressure. The reduction of the N/III ratio, and/or reactor pressure is performed to (50 - 5)% of the predetermined N/III ratio, and/or to (65 - 25)% of the predetermined pressure, respectively; in the final stage (preferably in last 60 minutes, especially in last 30 minutes) of the epitaxial growth process. The epitaxial growth is preformed by hydride vapour phase epitaxy (HVPE). INDEPENDENT CLAIMS are included for: (a) epitaxial growth for producing a thick III-N layer having a thickness of greater than 40 mm involving: depositing the layer above foreign substrate having a misorientation of 0.1 - 2degrees; (b) a substrate (S1) comprising: a III-N layer having a surface roughness of 50 nm and a thickness of (40, preferably 100, especially 150) mm, at least on one side; and (c) a semiconductor device comprising: a foreign substrate having a misorientation of 0.1 - 2degrees, with at least one III-N layer provided on at least one of its surfaces. USE - For production of a III-N substrate containing element(s) of group III, used in a semiconductor device (claimed). ADVANTAGE - The method provides thick III-N layers capable of growing with a (0001)- or C-plane surface, and exhibiting improved surface properties, and are suitable as substrate for further epitaxial growth steps. The epitaxial growth performed on a template whose foreign substrate has a slight miscut with respect to the next crystallographic lattice plane of its surface above which epitaxial growth occurs, with a thin first III-N layer deposited on it, results in thick III-N layers of greater than or equal to40 microns thickness with very smooth surface morphology, without the requirement of additional steps like high temperature annealing (e.g. at a temperature of greater than or equal to1200degreesC for greater than or equal to1 hour) etching and/or polishing of the initial first III-N layer; as compared to the prior art methods that involve production of template on a foreign substrate with exact orientation and without miscut, which provide deposition of a thin III-N layer with smooth surface morphology of the thin layer, while allowing further growth of thick layers with microscopically rough surfaces often covered with a high density of hexagonal pyramids. The surface morphology of the substrate can also be significantly improved by lowering the N/III ratio and/or reactor pressure in the last part of the epitaxial growth process by the hydride vapour phase epitaxy (HVPE), even without using exact substrates without the miscut.