Initial stages of molecular-beam epitaxy growth of GaN on 6H-SiC(0001)

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Lu, J. ; Haworth, L. ; Westwood, David ; Macdonald, John Emyr (2001)

We studied the atomic H etching of 6H-SiC substrates and the initial stages of GaN/6H-SiC molecular-beam epitaxy growth. Atomic H etched 6H-SiC(0001)Si and (000math)C surfaces show a (√×√)−R30° and a (1×1) reconstruction respectively, with 0.7±0.2 monolayers of remnant O on both surfaces. GaN/6H-SiC(0001)Si growth is initiated by the formation of islands that develop into flat-top terraces through coalescence. Growth steps of one or integer numbers of the GaN atomic bilayer height are observed. GaN grown on 6H-SiC(000math)C is rougher with islands of irregular shape. X-ray photoemission spectroscopy studies show that Si 2p and C 1s photoelectron inelastic mean free paths in GaN are 22±1 and 20±1 Å, respectively.
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    coalescence. At 110 Å @Fig. 2~d!#, the surface grew flatter with larger coalesced islands. After 1100 Å GaN had been grown ~Fig. 3!, large hexagonal terraces with growth steps of ;2.5 Å or multiples of 2.5 Å in height were observed consistent with the height of one or an integer number of GaN bilayers. In contrast, GaN grown on ( 000¯1 ) C is rougher and consists of islands with irregular shape. The growth steps were not observed.

    The polarities of the two samples were determined by chemical etching using a 20% KOH aqueous solution for 5 min at room temperature.12 The etching resulted in little change on the morphology of the film grown on ( 0001) Si , whereas considerable morphology change was observed for the film grown on ( 000¯1 ) C . According to Ref. 12, the film grown on ( 0001) Si and ( 000¯1 ) C are assigned to Ga and N polarity, respectively.

    In conclusion, 6H-SiC prepared by in situ atomic H etching at 650 °C exhibits a weak ( ) 3 ) ) 2 R 30° and a ( 1 3 1 ) RHEED pattern for ( 0001) Si and ( 000¯1 ) C face, respectively, with a remnant O coverage of ; 0.76 0.2 monolayers for both faces. XPS studies show that the inelastic mean free path for Si 2 p and C 1 s photoemissions in GaN are 226 1 and 206 1 Å , respectively. The GaN/6HSiC~0001!Si MBE growth is initiated by the formation of islands following 0.6 Å of two-dimensional growth. Further growth results in coalescence of the islands at ;25 Å. The flat-top shaped islands and flat terraces with growth steps of one or integer number of GaN atomic bilayer height are ob-

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