Scanning force microscopy studies of GaAs films grown on offcut Ge substrates

Research of surface morphology in Ga(In)As epilayers on Ge grown by MOVPE for multi-junction solar cells

“…In this work, we have studied the effect of the growth temperature, the V/III ratio, and two-step temperature growth, even though further information about these dependencies are discussed in Refs. [7,12,[15][16][17][18][19]. It is worth noting that our results are in opposition to these reports [7,15,16].…”

Anti-phase domain-free growth of GaAs on offcut (001) Ge wafers by molecular beam epitaxy with suppressed Ge outdiffusion

“…23 The strain fields associated with these misfits produce characteristic crosshatching surface undulations along in-plane <110> directions which are clearly observable via AFM and which also are faintly visible via Nomarski phase contrast optical microscopy. 11,24 We have found that for thick films, the observable crosshatching surface undulations strongly correlate with very minimal or non-existent APD disorder as characterized by TEM. Since the crosshatch results from aggregates of long misfit segments which in turn result from glide of threading dislocations over long distances, this relationship between crosshatch and APD disorder indicates that the APDs block dislocation glide.…”

“…These microscopy studies are detailed in separate publications. 11,20 We have consistently observed that a high temperature anneal (~640°C) of the epitaxial Ge surface is necessary to grow APD-free GaAs on Ge. In sharp contrast, annealing the epitaxial Ge at lower temperatures (350 or 560°C) always resulted in high APD densities as observed by both RHEED and TEM.…”

“…Growth directly onto the Ge wafer without a Ge buffer layer produces unpredictable and typically poor results with the observation of rough surfaces by AFM 11 and high APD densities as observed by TEM. In-situ AES indicated a high concentration of carbon (few atomic percent) is present at the initial Ge wafer surface after the usual thermal cleaning step and that the use of the Ge buffer layer effectively buries the carbon, resulting in a clean, smooth starting surface for subsequent GaAs nucleation.…”

Anti-phase domain-free GaAs on Ge substrates grown by molecular beam epitaxy for space solar cell applications

“…Surface roughening due to high APD densities has been confirmed by atomic force microscopy (AFM) measurements of these films. [9] APD's can lead to surface rms roughness of order tens of nm, while our 2.5 pm thick APD-free films have AFMmeasured rms roughness -1 nm averaged over 40 pm2 areas, [8,9] which is similar to the roughness of homoepitaxial MBE-grown GaAs films. Fig 5. [I101 RHEED diffraction patterns during GaAs nucleation.…”