Diffusion-controlled formation mechanism of dual-phase structure during Al induced crystallization of SiGe

Abstract

Aluminum induced crystallization of amorphous SiGe at low temperature is studied and a dual-phase stacked structure with different compositions emerges when the annealing temperature is higher than a critical value. This behavior is very sensitive to the oxidization state of the interlayer. A model based on energetics is proposed to elucidate this temperature dependent behavior. Thermodynamically, it can be ascribed to the competition between grain-boundary-mediated and interface-mediated crystallization and kinetically, it stems from the different diffusion rates of Si and Ge. The results are useful to the design and fabrication of high-efficiency solar cells.

Epitaxial growth of single-crystalline silicon–germanium on silicon by aluminium-assisted crystallization

“…To further understand the mechanism of the epitaxial growth of single-crystalline Si x Ge 1-x on Si using Al film in this work, and how this might differ from those previously reported, such as the AIC of semiconductors on foreign substrates [8][9][10][11][12][13][14][15] and polycrystalline SiGe alloy from Ge/Al/Si via AIC [20], the microstructure of the incompletely crystallized 350°C annealed sample as revealed by XRD analyses and Raman spectroscopy was investigated by TEM and EDS. Figure 4 shows the cross-sectional TEM image of the 350°C annealed sample.…”

“…The aluminium-induced crystallization (AIC) of Si, Ge and SiGe on foreign substrates has been extensively studied by several groups to obtain polycrystalline material at low temperature [8][9][10][11][12][13][14][15]. The AIC process of a semiconductor on a foreign substrate can be divided into four steps: (i) dissociation of amorphous semiconductor material in the Al layer; (ii) diffusion of the semiconductor material solute within the Al layer; (iii) nucleation of the semiconductor material in the Al layer; and (iv) semiconductor grain growth through continuous incorporation of the diffusing semiconductor material.…”

- Introduction to Metal-Induced Crystallization

“…It is not surprising that the high-angle Al GBs can also be wetted by a-SiGe alloy, which is indeed supported by the corresponding thermodynamic model calculation (see Fig. 2.11a) [17]. Accordingly, the critical thicknesses for initiation of crystallization of a-SiGe at the wetted <Al> GBs and at the <Al>|{SiGe} interface have been calculated quantitatively as a function of temperature T by applying Eqs.…”

“…Very recently, the thermodynamic model calculations have also been applied to metal (Al)-induced crystallization of amorphous semiconductor alloy (a-SiGe) [17]. As discussed in Section 2.3.1, high-angle Al GBs can be wetted by both a-Si and a-Ge (see Fig.…”

“…Amorphous semiconductors such as silicon and germanium can crystallize at a temperature much lower than their "bulk" crystallization temperatures when they are put in direct contact with a metal, such as Al [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], Au [18][19][20][21][22], Ag [23][24][25], Ni [26][27][28][29][30][31][32][33], Cu [34][35][36], and Pd [37,38]. This phenomenon, which was firstly observed more than 40 years ago for amorphous germanium [39], is now commonly referred to as metal-induced crystallization (MIC) [40][41][42][43].…”