Role of hydrogen during Si capping of strained Ge or Si1-xGex hut clusters

Atomic hydrogen (H) is supplied during Si capping (by solid source MBE at 4 00 degrees C) of Ge related islands strained on Si(001). Without H, Si capp ing is known to smooth the initial rough surface caused by the Stranski-Kra stanov Ge growth mode which ensures a partial strain relief at the island c rests. We demonstrate elsewhere that this smoothing takes place by stress m ediated surface migration of Si accumulating in the troughs between the hut -clusters where the misfit is the lowest and by lateral Ge segregation. Sim ilar to a growth temperature lowering which reduces these surface migration s, the effect of H is to maintain the stress induced roughening suppressed by Si, as proven by the persistence of spotty RHEED patterns and by the non -restoration of intensity oscillations. Moreover, the ali recovery of the S i bulk value in the Si cap layer is significantly slower than without H, a consequence of the kinetically blocked Si deposition, particularly on the t op of the partially relaxed hut clusters where it is forced to grow more te nsely strained than without H. As a general learning, the same H adsorption and relevant adatom mobility decrease is able to presently preserve the in itial Ge related 3D growth whereas, for the growth of Ge upon Si, it mainta ins a 2D growth in preventing 3D island formation. In both cases of tensely or compressively strained growths, the H-induced kinetic diffusion length limitation impedes local elastic energy minimizing occurring, without H, by strain relieving adatom migrations. Additionally, the fact that the step d ensity is here essentially unchanged by the growth under H, does not suppor t the use of step involving models to explain the H-surfactant action. (C) 1998 Elsevier Science S.A. All rights reserved.