Growth and Photoelectric Properties of Graded-Gap Si– Si2

Growth and Photoelectric Properties of Graded-Gap
Si–(Si₂)_{1 – x}(GaP)_x Heterostructures
Abstract—Theoretical grounds for formation of continuous substitutional solid solutions are analyzed taking
into account the generalized moments, the difference in valence, and covalent radii of initial components. On
the basis of these studies, the technology of formation of epitaxial (Si2)1 – x(GaP)x (0 ≤ x ≤ 1) layers on silicon
substrates from the tin solution–melt using forced cooling is developed. The distribution of components over
the thickness of Si–(Si2)1 – x(GaP)x layers, the photosensitivity, and the current–voltage characteristics of the Si–
(Si2)1 – x(GaP)x heterostructures are studied. Analyses of the results of the X-ray studies and photoelectric properties of obtained solid-solution epitaxial layers indicate that the grown graded-gap (Si2)1 – x(GaP)x layers have
a high structural quality
Research in the field of present-day materials science of semiconductors is aimed at production of new semiconductor materials that have high quality and exhibit the improved characteristics compared to those of the materials used currently in photoelectronics. Therefore, the development of technology and then study of properties of obtained new semiconductor materials and solid solutions based on these materials are of utmost importance in this field. In this context, heteroepitaxial deposition of GaP onto Si substrates is of much interest since the lattice parameters of Si and GaP are almost the same, whereas the band gaps are radically different. Substitutional solid solutions of Si and GaP can be formed since the conditions ∆Z = 0 and |∆r| = (rA + rB) – (rC – rD) ≤ 0.1 [1] are satisfied for these solutions (here, Z is the valence and r are the covalent radii of the components).
It was shown for the first time by Alferov et al. [2]
by the example of a (Ge2)1 – x(GeAs)x system that pyrolytic synthesis from gaseous phase can be used to form a continuous sequence of solid solutions. We also previously showed [3] that it is possible to obtain gradedgap (Ge2)1 – x(GeAs)x (0 ≤ x ≤ 1) metastable solid solutions on the Ge and GaAs using a Pb solution–melt as the source. An analysis of solubility of Si and GaP in liquid metallic solvents show that the use of tin as the solvent and a relatively low growth temperature (750–
900°C) are conducive to the formation of (Si2)1 - x(GaP)x solid solutions.
Epitaxial layers with the thickness in the range from 15 to 30 µm had the n-type conductivity. According to the data on the distribution of components over the
thickness obtained using a Cameca electron-probe analyzer, the GaP content in the graded-gap epitaxial (Si2)1 – x(GaP)x layer increases along the growth axis
and is as high as 48% for Ga, 52% for P, and 0% for Si
(Fig. 1a). The raster patterns obtained using a Jeol JSM
5910 LV X-ray microanalyzer (Fig. 1b) show that there
are no macroscopic structural defects and metallic
inclusions of the second phase. The measurement error
was no larger than 2%.