Growth of Ge quantum dots on Si(100)-(2×1) by pulsed laser deposition

Abstract

Self-assembled germanium quantum dots ͑QDs͒ were grown on Si͑100͒-͑2 ϫ 1͒ by pulsed laser deposition. In situ reflection-high energy electron diffraction ͑RHEED͒ and postdeposition atomic force microscopy are used to study the growth of the QDs. Several films of different thicknesses were grown at a substrate temperature of 400°C using a Q-switched Nd:yttrium aluminum garnet laser ͑ = 1064 nm, 40 ns pulse width, 23 J / cm 2 fluence, and 10 Hz repetition rate͒. At low film thicknesses, hut clusters that are faceted by different planes, depending on their height, are observed after the completion of the wetting layer. With increasing film thickness, the size of the clusters grows and they gradually lose their facetation and become more rounded. With further thickness increase, the shape of these clusters becomes domelike with some pyramids observed among the majority of domes. The effect of the laser fluence on the morphology of the grown clusters was studied. The cluster density was found to increase dramatically while the average cluster size decreased with the increase in the laser fluence. For a laser fluence of 70 J / cm 2 , dome-shaped clusters that are smaller than the large huts formed at 23 J / cm 2 were observed. At a substrate temperature of 150°C, misoriented three-dimensional ͑3D͒ clusters are formed producing only a RHEED background. At 400 and 500°C, huts and a lower density of domes are formed, respectively. Above 600°C, 3D clusters are formed on top of a discontinuous textured layer.

Nanosecond laser ablation and deposition of Ge films

“…Also shown are the morphology of a nano-sized droplet, and the cross section analysis gave a very small aspect ratio of <0.1. The morphology of nano-sized droplet resembled to those of the quantum dot grown by PLD using the same laser wavelength, reported elsewhere [5,6], but the growth mode is believed to be rather different in our case as the current deposition condition did not favor the Stranski-Krastanov growth. Furthermore, the droplets were detected on both Si and GaAs substrates.…”

“…The condensation of the high energetic species is capable of metastable material growth even at room temperature such as growing diamond-like carbon from graphite. For Ge, a range of amorphous to crystalline films have been deposited by pulsed laser deposition (PLD): amorphous Ge films which can be denser and less stressed than those by thermal evaporation [1], films which are denser, more homogeneous and stable than e-beam deposited films [2], films with optical and structural properties comparable to those deposited by magnetron sputtering [2,3], films that evolved in a similar homoepitaxial growth as in molecular beam epitaxy when deposited at low laser fluence [4], and also Ge quantum dot on Si via Stranski-Krastanov growth [5,6].…”

Nonthermal laser-induced formation of crystalline Ge quantum dots on Si(100)

“…For PLD of Ge on Si͑100͒ without laser excitation of the substrate, the Ge RHEED transmission diffraction patterns only show for samples grown above ϳ400°C. 18 The appearance of RHEED transmission diffraction patterns indicates the formation of crystalline Ge QD, which starts by the formation of hut clusters that are faceted by different planes, depending on the cluster height. 18 For samples grown at substrate temperatures lower than ϳ400°C, the intensity of the Si͑100͒-͑2 ϫ 1͒ RHEED spots decays continuously with deposition time until they completely disappear, resulting in a diffuse pattern, after a given thickness that increases with the substrate temperature.…”

“…Before being loaded into the UHV chamber, the Si͑100͒ substrates ͑dimensions of 3.5Ϯ 0.5ϫ 10Ϯ 0.5 mm 2 , p-type boron doped, resistivity 0.060-0.075 ⍀ cm͒ were cleaned by chemical etching using a modification to the Shiraki method, as described previously. 18 The Ge target was a 2 in. disk, 0.5 mm thick undoped n-type with a resistivity of 45-58.7 ⍀ cm.…”

“…16 The facetation of the huts and domes depends on the deposition technique as well as the deposition conditions. 17,18 Development of low temperature growth methods is of much interest in semiconductor fabrication. Lowering the epitaxial growth temperature is a key parameter to suppress the introduction of defects such as dislocations and staking faults.…”