ABSTRACT
So far, most GaN-based layers are grown heteroepitaxially on foreign substrates,suchassapphire,SiC,orsilicon.Inspiteofaremarkableprogressin thegrowthofhigh-qualitygroupIII-nitrides,theepitaxialˆlmsarefarfrom beingperfectascomparedtolattice-matchedstructuresintheconventional III-Vheterosystems,suchas(In,Ga,Al)As/InPorthenearlylattice-matched AlGaAs/GaAs. Large bulk single-crystal GaN substrates are not really availableyetand,therefore,alarge-scalehomoepitaxialgrowthofGaN/GaN willnotbepossibleinthenearfuture.Therefore,apartfromlaserapplications,heteroepitaxialgrowthwilldominatetheGaNgrowthinthenear future.Withallheterosubstrates,thelargelatticemismatchleadstoahigh dislocation density of the order of 1010 cm−3 or higher near the interface. In addition,inthecaseofGaNonSi,thelargedifferenceinthelinearthermal expansioncoefˆcientsleadstostrongcrackingproblems.Toagreatextent,
CONTENTS
10.1Introduction ................................................................................................ 401 10.2 Crystal Structure and Mosaicity..............................................................402
