The investigation of selective pre-pattern free self-assembled Ge nano-dot formed by excimer laser annealing
© Lee and Chen; licensee Springer. 2012
Received: 30 November 2011
Accepted: 30 March 2012
Published: 18 June 2012
Localized Ge nano-dot formation by laser treatment was investigated and discussed in terms of strain distribution. The advantage of this technique is patterning localization of nano-dots without selective epitaxial growth, reducing costs and improving throughput. Self-assembled Ge nano-dots produced by excimer laser annealing statistically distributed dot density and size dependent on laser energy. Improvement in the crystallization quality of the dots was also studied, and a strain analysis was undertaken.
Self-assembled Ge quantum dots and well arrangements have attracted a lot of attention due to their ability of being integrated into silicon-based optoelectronic and nano-electronic devices [1, 2]. One of the motivations behind these efforts is to form devices and functions that take advantage of quantum confinement effects for electronic and optical applications, such as light emitting diodes, tunneling diodes, detectors, etc. [3, 4], where Ge quantum dots were formed by ultra-high vacuum chemical vapor deposition (UHV-CVD). Recently, the Ge dots multilayer solar cell made by molecular beam epitaxy was reported . Another motivation is to find cost-effective methods for forming nanoscale devices without using expensive lithography techniques. Among the different ways in producing quantum dots [6–8], excimer laser annealing (ELA) to induce self-assembled Ge islands is an innovative technique. ELA has been widely used in low temperature poly-Si thin film-transistor processes for flat panel display products . One of the characteristics of laser annealing is a shallow absorption depth, which avoids heating of layers underneath, due to the high absorption coefficient of semiconductor material in the UV laser wavelength range . An advantage of laser annealing is the determination of dot localization on the surface. By contrast, dot patterning is difficult to directly use conventional chemical vapor deposition processes, except for selective epitaxial growth (SEG) over pre-patterned samples. Weizman et al. reported the formation of a ripple structure to hillock structure by single laser pulse with silicon-germanium (Si1−xGex), 0.3 < x < 0.7 . In this work, we propose nominal pure Ge re-crystallization and self-assembly into dots by excimer laser irradiation, and discuss the resulting improvement in Ge crystallization quality. We also study the relationship between dot volume and beam energy.
Results and discussions
The selective pre-pattern free self-assembly of Ge nano-dots was demonstrated, and discussed as a function of laser energy. The advantage of this technique is patterning localization without SEG, reducing cost and improving throughput. Self-assembled Ge nano-dots were produced by excimer laser annealing, and the statistical distribution of dot density and size was collected for different laser energy. Improvement in crystallization quality of Ge dots was studied, and a strain analysis was carried out.
The authors are very grateful for the UHV-CVD support from Prof. C. W. Liu, Graduate Institute of Electronics Engineering, National Taiwan University, funding support by National Science Council, (NSC 98-2221-E-003-020-MY3, 101-2221-E-003-019), and National Taiwan Normal University (NTNU100-D-01), and experimental support by Display Technology Center (DTC), Industrial Technology Research Institute (ITRI), Taiwan.
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