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We present a review of semiconductor surface reconstruction. Experimental and theoretical results on atomic geometry, electronic states, phonon modes, and bonding are presented for clean cleaved, clean epitaxially grown, overlayer covered, surfactant mediated epitaxially grown, and defect induced reconstructed semiconductor surfaces. Energetic aspects of reconstructions are discussed using empirical as well as first-principles theoretical approaches.

Effect of the cluster size in modeling the H 2 desorption and dissociative adsorption on Si(001)Using a first-principles pseudopotential method we have studied the adsorption and dissociation of NH 3 , PH 3 , and AsH 3 on the Si͑001͒-͑2ϫ1͒ surface. Apart from the existence of a barrier for the adsorption of the precursor state for arsine, we observe that the global behavior for the chemisorption of the XH 3 molecules considered in this work is as follows: the gas phase XH 3 adsorbs molecularly to the electrophilic surface Si atom and then dissociates into XH 2 and H, bonded to the electrophilic and nucleophilic surface silicon dimer atoms, respectively. The energy barrier, corresponding to a thermal activation, is much smaller than the usual growth temperature, indicating that all three molecules will be observed in their dissociated states at room temperature. All adsorbed systems are characterized by elongated Si-Si dimers that are ͑almost͒ symmetric in the dissociative case but asymmetric in the molecular case. According to our first-principles calculations, all XH 3 and XH 2 systems retain the pyramidal geometry observed for the gas molecules. Our calculated vibrational spectra further support the dissociative model for the XH 3 molecules considered here.