We studied the cluster size distribution of dislocation-free InAs͞GaAs self-assembled quantum dots obtained by the Stranski-Krastanow mode of molecular beam epitaxy. The same scaling function was obtained over a wide range of dot density. The scaling function indicated that the cluster size fluctuation, normalized by the average size, is constant for all the quantum dot densities studied. The resemblance of the scaling function to that of the submonolayer homoepitaxial growth implies that the strain is not the essential factor determining the cluster size distribution of quantum dots.[S0031-9007(98)05602-6] PACS numbers: 68.55. 61.43.Hv, 82.20.Mj The growth of lattice-mismatch semiconductor systems such as Ge͞Si and InAs͞GaAs has been known to produce a dotlike structure by the Stranski-Krastanow (SK) mode. Recently this growth mode, especially of InAs͞GaAs dots (known as "self-assembled quantum dots" [1]) has drawn much attention as a method to obtain quantum dots which are damage-free and fabrication-free. Now practical applications of quantum dots are seriously sought for, and efforts are being made in fabricating quantum dot lasers with predicted high performance such as a high characteristic temperature and a low threshold current. However, the current InAs quantum dots have a problem in size uniformity which is commonly about 610%, and is insufficient for laser applications. It is intriguing to know if this common size fluctuation is essential or accidental.Not to mention practical applications, the scaling property of two-dimensional (2D) island size distribution is known for submonolayer coverage. According to the scaling assumption [2,3], the island distribution is given byHere N s is the number of islands (normalized by the number of lattice sites) which contain s atoms, u is the fractional surface coverage, ͗s͘ is the average number of atoms in an island, and f͑x͒ is the scaling function, which depends only on s͗͞s͘. This scaling assumption was confirmed experimentally in Fe homoepitaxy [4] and InAs͞ GaAs heteroepitaxy [5].It is interesting to know if something similar to Eq. (1) holds for three-dimensional (3D) island growth by the SK mode, especially because it was reported [6] that the total island density r shows a power law as a function of the coverage expressed as r r 0 ͑u 2 u c ͒ a (2) for u from 1.5 to 1.9 monolayer (ML), where r 0 is the proportionality coefficient, u c is the critical coverage (1.5 ML), and the critical exponent a is 1.76. Equation (2) implies the presence of the scaling region and consequently the scaling function.In this Letter, we present the 3D island size scaling which holds for a quite wide range of the total density of the dislocation-free InAs͞GaAs islands by the SK mode.The growth was done by the Riber 2300 molecular beam epitaxy (MBE) system on a nominally flat GaAs (001) substrate. After the growth of the GaAs buffer layer at a substrate temperature of 600 ± C, growth was interrupted for 3-5 min, to decrease the temperature to 490 ± C to obtain a c͑4 3 4͒ surf...

PACS. 68.18.+p Langmuir-Blodgett films, 46.50.+a Fracture mechanics, fatigue and cracks, 81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture and failure,

No abstract

A multilayer structure consisting of 20 layers of InAs self-assembled quantum dots was grown by molecular beam epitaxy and observed by transmission electron microscopy. The positions of quantum dots in a quantum-dot layer were not correlated with those in the lower quantum-dot layer because of the thick (70 nm) GaAs spacer layer. Threading dislocations were observed, which originated from large strain-relaxed (incoherent) InAs islands in a quantum-dot layer. The dislocations were 30° dislocations in the [112] and [112] directions, and were generated by a misfit between large InAs islands and a GaAs overlayer.

No abstract