The research of Pure, Single Crystal Ge Nanodot Arrays Process
Date Issued
2015
Date
2015
Author(s)
Liao, Ting-Wei
Abstract
Ge nanodots (NDs) have novel electrical and optical properties, as well as for their compatibility with Si complementary metal - oxide - semiconductor (MOS) technology. Therefore, the fabrication technology of Ge NDs have been investigated extensively. Although these approaches have illustrated the capability of fabricating highly crystalline Ge NDs, a severe problem still exists regarding the intermixing of Si and Ge due to the high temperature of the annealing treatment, which may degrade the performance and decrease the efficiency of the Ge ND devices. In addition, the uniformity of the Ge NDs needs to be further improved for practical applications. In this paper, to solve these problems of the intermixing, uniformity and random nucleation of the Ge NDs. A sandwich structure comprising a SiO2 capping layer, amorphous Ge NDs (a-Ge NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet (UV) excimer laser. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si–Ge intermixing. The two dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters, the NDs exhibit excellent size uniformity and arrangement, and the area density is about 3.9 × 109 cm-2. The degree of crystallinity of the NDs was determined from their Raman spectra and verified using high-resolution transmission electron microscopy (HR-TEM). Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm-1 at 300.7 cm-1, which is close to that of the original Ge wafer (where the FWHM is 4.0 cm-1and the peak position is at 300.7 cm-1). In addition, it is worth noting that no Si–Ge intermixing signal was observed from the Raman spectrum of the crystallized Ge NDs. The high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities. Therefore, these results reconfirm that the processed Ge ND is a single crystal without any impurities. In this paper, the novel method is developed for fabricating an array of pure, single crystal Ge NDs at room temperature. Moreover, it have the opportunity to improve the performance of electronic or optoelectronic device.
Subjects
single crystal
pure
Germanium
nanodots
sandwich structure
capping layer
pit-patterned
excimer laser
Type
thesis
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