We demonstrate a self-assembling method for growing semiconductor quantum dots into ordered lattices. The quantum dot nucleation and positioning into lattices was achieved using a periodic subsurface stressor lattice. Three different two-dimensional (2D) square lattices are demonstrated. The unit cell dimensions, orientation, and the number of quantum dots in the basis are tunable. We find that the 2D lattice can be replicated at periodic intervals along the growth direction to form a three-dimensional (3D) lattice of quantum dots.

Articles you may be interested inLow density of self-assembled InAs quantum dots grown by solid-source molecular beam epitaxy on InP (001) The role of arsine in the self-assembled growth of In As ∕ Ga As quantum dots by metal organic chemical vapor deposition An experimental approach has been developed to control the formation of InAs self-assembled islands. A lithographically defined mesa lattice on the surface was used to control the growth kinetics and island nucleation. Two distinct island formation regimes were observed from InAs islands grown on patterned GaAs ͑100͒ substrates. In the case of direct growth on patterned substrates, a type I islanding was observed, in which all the islands formed between mesas. Incorporating a stressor layer into the regrowth on the patterned substrate yielded a type island nucleation, where all the islands nucleated on top of the mesas. The possible mechanisms involved in the long range ordering and positioning of islands are discussed.

This article concerns the microstructure of self-assembled ErAs islands embedded in GaAs. The material is grown by molecular beam epitaxy. The nucleation of ErAs on GaAs occurs in an island growth mode leading to spontaneous formation of nanometer-sized islands. Several layers of ErAs islands separated by GaAs can be stacked on top of each other to form a superlattice. A series of such samples were grown with different depositions of ErAs at a growth temperature of 535°C. The microstructure of these samples was investigated by x-ray diffraction and transmission electron microscopy. We find that initially isolated ErAs islands with a diameter of 2 nm are nucleated. With increasing ErAs deposition, these islands branch out and form extended structures. The samples are coherent in growth directions for ErAs depositions up to 1.8 monolayers. At higher ErAs depositions defects are incorporated into the GaAs matrix.

No abstract

Ferroelectric random access memory (FeRAM) is an attractive candidate technology for embedded nonvolatile memory, especially in applications where low power and high program speed are important. Market introduction of high-density FeRAM is, however, lagging behind standard complementary metal-oxide semiconductor (CMOS) because of the difficult integration technology. This paper discusses the major integration issues for high-density FeRAM, based on SrBi2Ta2O9 (strontium bismuth tantalate or SBT), in relation to the fabrication of our stacked cell structure. We have worked in the previous years on the development of SBT-FeRAM integration technology, based on a so-called pseudo-three-dimensional (3D) cell, with a capacitor that can be scaled from quasi two-dimensional towards a true three-dimensional capacitor where the sidewalls will importantly contribute to the signal. In the first phase of our integration development, we integrated our FeRAM cell in a 0.35μm CMOS technology. In a second phase, then, possibility of scaling of our cell is demonstrated in 0.18μm technology. The excellent electrical and reliability properties of the small integrated ferroelectric capacitors prove the feasibility of the technology, while the verification of the potential 3D effect confirms the basic scaling potential of our concept beyond that of the single-mask capacitor. The paper outlines the different material and technological challenges, and working solutions are demonstrated. While some issues are specific to our own cell, many are applicable to different stacked FeRAM cell concepts, or will become more general concerns when more developments are moving into 3D structures.