Web Growth of Semiconductors

Abstract

A novel process for growth of diamond-lattice semiconductors is described, and a model is proposed for the growth mechanism. For germanium the process yields extended thin flat sheets, typically 1 cm wide and 0.1 mm thick, of good crystalline quality and relatively flat {111} surfaces. The sheet, or web, freezes from a liquid film drawn up by surface tension between two coplanar dendrites which originate from a single seed and are grown from the melt simultaneously with the sheet. Resistivity throughout the sheet is quite uniform. Etching of germanium webs shows them to be essentially dislocation-free and does not reveal any microsegregation of impurities. Silicon and indium antimonide have also been grown in this manner. The proposed model postulates that although the dendrites at either side of the web grow beneath the melt surface in usual dendritic fashion, the faces of the web itself normally have no extension below the melt surface. The exterior contact angle between the solid and liquid surfaces is less than 180° but greater than the equilibrium contact angle which would be observed if the flat faces extended beneath the melt surface. In spite of this the grown faces are plane and vertical, thickening of the web being restricted by difficulty of nucleation. In this respect the predictions of this model are significantly different than for Čzochralski or floating-zone growth. Extensive experimental observations, including deliberately produced irregularities, verify the predictions of the model.

Growth mechanism of the Si⟨110⟩faceted dendrite

“…Regarding the former, it is well known that the ͗112͘ dendrite is bounded by ͕111͖ planes and that it contains parallel twins. [8][9][10][11][12][13][14][15][16][17][18][19][20] To investigate the structural features of the ͗110͘ dendrite, we analyzed its crystallographic orientation ͑Fig. 4͒.…”

“…It was also shown that the preferential growth directions of Si faceted dendrites are ͗112͘ and ͗110͘. 18 Such features of faceted dendrites can be applied in technologies for growing thin Si ribbon crystals 13,14 and polycrystalline Si ingots 21,22 for solar cells. A growth mechanism for the dendrite preferentially grown along the ͗112͘ direction, hereafter referred to as a ͗112͘ dendrite, was first proposed in 1960.…”

Growth Mechanism of Si-Faceted Dendrites

“…In particular, twin-related dendrites of Si or Ge, which are the so-called ''faceted dendrites,'' have attracted much attention from both scientific and technological viewpoints due to their unique crystal structures. The surface of the dendrite is bounded by f111g habit planes, and at least two parallel twins exist at the center of the dendrite [1][2][3][4][5][6][7][8][9][10][11][12]. It is also known that the growth rate of a faceted dendrite is larger than equiaxed grains [12,13].…”

“…It is also known that the growth rate of a faceted dendrite is larger than equiaxed grains [12,13]. Such features can be applied in technologies for growing thin Si ribbon crystals [6,7] and polycrystalline Si ingots [13] for solar cells. The growth model of faceted dendrites was proposed in 1960 [3,4].…”

Grain Growth in the Melt

“…The features of a faceted dendrite are different from dendrites of metallic alloys in terms of the following[19][20][21][22][23][24][25][26][27]:…”