Ge quantum dot arrays grown by ultrahigh vacuum molecular-beam epitaxy on the Si(001) surface: nucleation, morphology, and CMOS compatibility

Abstract

Issues of morphology, nucleation, and growth of Ge cluster arrays deposited by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface are considered. Difference in nucleation of quantum dots during Ge deposition at low (≲600°C) and high (≳600°C) temperatures is studied by high resolution scanning tunneling microscopy. The atomic models of growth of both species of Ge huts--pyramids and wedges-- are proposed. The growth cycle of Ge QD arrays at low temperatures is explored. A problem of lowering of the array formation temperature is discussed with the focus on CMOS compatibility of the entire process; a special attention is paid upon approaches to reduction of treatment temperature during the Si(001) surface pre-growth cleaning, which is at once a key and the highest-temperature phase of the Ge/Si(001) quantum dot dense array formation process. The temperature of the Si clean surface preparation, the final high-temperature step of which is, as a rule, carried out directly in the MBE chamber just before the structure deposition, determines the compatibility of formation process of Ge-QD-array based devices with the CMOS manufacturing cycle. Silicon surface hydrogenation at the final stage of its wet chemical etching during the preliminary cleaning is proposed as a possible way of efficient reduction of the Si wafer pre-growth annealing temperature.

On atomic structure of Ge huts growing on the Ge/Si(001) wetting layer

“…There are two possible models of processes which, in principal, may describe the growth of huts. 17 The first one implies that the cluster growth goes on due to uniform attachment of Ge atoms to all cluster facets (we refer to this model as a model of uniform growth). 17 This means that the width of a cluster in all <110> directions increases by the value of two elementary translations (or in total by four elementary translations along each <110> axis) after each step of completion of the cluster facets (Fig.…”

“…Experiments were carried out using a specially built setup 16,17 consisting of a UHV MBE vessel (Riber EVA 32) connected with a UHV STM chamber (GPI 300) 24 . Details of the pre-growth treatments of Si wafers, which included chemical etching and oxide removal by short high-temperature annealing (T ∼ 900℃), can be found in our previous articles cited in Refs.…”

“…23 We have demonstrated that both pyramids and wedges grow in height conserving the width and the atomic structure of their apexes (the topmost (001) terraces). 4,6,17 This phenomenon also requires comprehension and adequate description: up to date, we have only hinted at such description in our recent articles. [15][16][17] An aim of this article is to propose physical processes on WL and cluster facets, and their structural schemes, on the basis of the previously performed STM studies, which could give adequate interpretation on atomic level to the experimentally observed evolution of each species of hut clusters during their growth setting the direction of thought for explanation of the presently incomprehensible phenomenon of simultaneous appearance of two types of hut nuclei on Ge/Si(001) WL which give rise to two mutually independent species of huts.…”

“…Our recent experimental explorations 6,[15][16][17][18][19]21 carried out on atomic level by high-resolution STM have demonstrated fine details of hut nucleation and its evolution during the growth which however have not been sufficiently interpreted thus far and presented in terms of structural schematics and drawings which would be helpful for further theoretical calculations and numerical simulations. For example, we have discovered the phenomenon of simultaneous appearance of two types of nuclei 15,19 which are composed by 16 dimers and different only in symmetry-a separate nucleus for each species of huts-on tops of Ge WL M × N patches 22 of 4-monolayer 18 (ML) height (Fig.…”

“…However, only a few of these works studied this issue on atomic level. [15][16][17][18][19] Investigations carried out on atomic-level were mainly devoted to the structure of the {105} facets, for which an initially proposed simple model based on paired dimers 1 (the so called PD model) was eventually replaced by a model considering step rebonding as a source of the facet stability 20 (the latter one is usually referred to as the RS model), rather than to nucleation of the clusters or their in-height or longitudinal growth.…”