We present a procedure whereby a sheet of donor atoms is incorporated in (100) Si during molecular beam epitaxial growth, Analysis by secondary ion mass spectroscopy and transmission electron microscopy shows that the width of such 8-function doping layers is only a few lattice planes. Tunneling spectroscopy and transport measurements give evidence for quantum confinement of the electronic charge in the layer and thus confirm the narrow width.For a number of Si device applications an extremely sharp and high density doping profile is required. In principle such a sharply defined doping layer can be achieved with molecular beam epitaxial (MBE) growth ofSi. The problem is that for Sb or Ga densities in the 10 20 em -3 range there are significant surface segregation and a low rate of incorporation into the growing Si crystal, At the typical growth temperature of -700 °C the dopants are carried along the surface of the growing crystal. The doping profile is significantly broadened. 1To overcome this difficulty two procedures have been reported in the literature. In Ref 2 the co-evaporation of a layer of Si and dopant at room temperature followed by solid phase epitaxy has been employed. Reference 3 introduces secondary ion implantation, whereby a negative potential ( -500 V) is applied to the substrate and the dopant is incorporated by knock-on from Si ions. Doping spikes of _10 19 em
We present results on deconvolution of molecular beam epitaxy (MBEkgrown boron profiles in Si and SiGe that are of crucial importance for Si/SiGe heterojunction bipolar transistors (HBTs). They are based on the assump tions of linearity and homogeneity of the measurement. We determine experimentally the physical limits of these assumptions by investigating sequences of boron spikes in Si and SiGe. The deconvolution is performed by Fourier transformation into the k-domain, preceded by a physically motivated least-squares fitting of the measurement data. In this way, the high-frequency noise contributions are eliminated to a great extent without producing a systematic broadening. The numerical evaluation of the SIMS profiles is extremely fast in comparison to forward techniques and the numerical error is shown to be small. We discuss the deconvoluted SIMS profiles of MBEgrown boron spikes in Si and SiGe after annealing. Our method is suited to give information about the dopant outdiffusion from th SiGe layer in the case of HBTs.
Highly doped (∼1018 to 1021cm−3) polycrystalline Si1-xGex films, crystallized from amorphous (a) state at relative low temperatures, are prospective materials in a variety of applications, such as liquid-crystal displays, solar cells and integrated thermoelectric sensors on large-area glass substrates. Since the nature of the grains in the crystallized film defines properties such as carrier mobility, the nucleation and growth process of the a-SiGe films is of fundamental interest. We have studied the crystallization of undoped and highly doped (B or Ga) amorphous SiGe films. The films were deposited by RFCVD or molecular beam on oxidized (001)Si and for TEM study on cleaved NaCl. The incubation time and grain growth rate were studied by means of in situ TEM using a heating stage. The crystallization process in undoped SiGe followed Avrami relationship. An average grain size between 0.1 and 2μm was observed. However, the highly p-doped (with B or Ga) SiGe films crystallized to a stable nanocrystalline structure (grain size <10nm). The process of the a-SiGe crystallization is explained on the basis of self-diffusion. During the first stage, the nucleation of crystals is accompanied with nonequilibrium vacancy generation at the amorphous/crystalline interface. During the second stage, the growth of crystals takes place by vacancy outdiffusion which is hindered by B and Ga interaction with vacancies.
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