Growth of high-quality InSb films on Si(1 1 1) substrates without buffer layers

Abstract

Molecular beam epitaxial growth of InSb on Si(1 1 1)7×7 surface is performed in the temperature range, 170–400°C. Epitaxial growth is achieved by suitably adjusting the growth rate, In/Sb flux ratio and substrate temperature. For growth temperatures up to 300°C surface morphology and the epitaxial quality of the film improve with temperature, whereas above 300°C, an increase in growth temperature deteriorates the epitaxial growth. Hall measurements reveals that the electron mobility of the film increases with growth temperature and for the film grown at 300°C it is about 2200 cm² V⁻¹ s⁻¹ at RT. Significant improvement in the electrical properties of the film is achieved using a two-step growth procedure, consists of 300 Å thick interface layer growth at 300°C followed by growth at 400°C. The electron mobility of a 1.8 μm thick two-step grown film at RT is 23 000 cm² V⁻¹ s⁻¹. Surface morphology, crystal quality and electrical properties of the grown films are discussed with respect to growth parameters.

Introduction

InSb has the highest electron mobility and the smallest band gap of all known III–V compound semiconductors. Due to these characteristics, InSb based structures are most suitable for applications like infrared detectors, high-speed devises and magnetic sensors. For these applications, amplification and signal processing are usually done using discrete circuits that are physically separated from the InSb sensor array. Integration of InSb with highly matured Si circuitry would enable significant gains in terms of reliability and speed. Moreover, high density of integration allows considerable cost down in the manufacturing process. Several laboratories have reported the successful growth of InSb on GaAs (lattice mismatch≈14.6%) using various deposition techniques like molecular beam epitaxy (MBE) [1], [2] metalorganic magnetron sputtering (MOMS) [3] and metalorganic vapour phase epitaxy (MOVPE) [4].

However, direct growth of InSb on Si substrate is very difficult and much less has been reported in the literature. The only report that we came across about the direct growth of InSb on Si(0 0 1) substrate illustrates the polycrystalline nature of the films [5]. The large lattice mismatch (over 19%), different thermal expansion coefficients and antiphase domain formation (polar on non-polar growth) all create formidable challenges. Several groups have reported the successful growth of InSb on Si by incorporating various buffer layers, such as GaAs [6], AlSb [7], fluoride [8] and Ge [9]. However, buffer layer incorporation may pose serious problems in the materials processing and thus not desired.

We have also come across two reports on the InSb growth on Si substrates with an In-prelayer [10], [11]. However, neither of these reposts detailed the characteristics of this In-prelayer and its role in the InSb growth processes. The earlier report by Chyi et al. [10] used a two-step growth process to grow epitaxial InSb layers on an off-axis Si(0 0 1) substrate covered with a thin In-layer. Here a 500 Å thick interface layer was grown at 380°C followed by InSb growth at 420°C. Later report by Kitabatake et al. [11] used a H-terminated Si(1 1 1) substrate covered with 0.5 nm thick In-layer to initiate the two-step growth of InSb. This growth process resulted in a 3 μm thick InSb film with a room temperature electron mobility of 49 300 cm² V⁻¹ s⁻¹. This report also indicated that growth without the In-prelayer resulted in the formation of a multi-domain InSb film with poor surface morphology. However, crystalline quality of the film grown directly on Si substrate and the role of In-layer in improving the epitaxial quality were not detailed. In this context, it becomes interesting to see the role played by the In-layer at the interface, to improve the crystalline quality. Voigtlander et al. [12] showed that a predeposited In-layer dramatically increases the surface diffusivity of Si atoms (on Si(1 1 1) substrates) whereas Sb working exactly in the opposite way [12]. However, these results are difficult to envisage during the heteroepitaxial growth of InSb on Si(1 1 1) substrates because the present case is far more complex due to the presence of various types of interface reactions namely, Si–In, Si–Sb and In–Sb [13].

Our early studies on the InSb growth on Si(0 0 1) substrate via Si(0 0 1)-In(4×3) surface phase [14], [15] indicated that, significant improvement in the epitaxial quality of the film can be achieved by the incorporation of the In-induced surface phase. We explained that the improvement in the heteroepitaxy is directly related to the geometric structure of the In(4×3) reconstruction [14]. However, InSb growth on Si(1 1 1)-In(4×1) surface phase, resulted in a severe degradation in the epitaxial quality of the InSb films, compared to those grown on Si(1 1 1)7×7 surface [16]. The degradation is so severe that, for deposition temperatures above 300°C InSb growth is completely suppressed. Sb adsorption on the In-terminated Si(1 1 1) surface replaces the Si–In bonds by Si–Sb bonds, and this replacement is accompanied by a large modification in the bonding nature of the Si surface [13]. The deterioration in the epitaxial growth is related to the In-presence rather than to the structure of In-layer [17]. Moreover, we recently found that Sb effectively agglomerates few nanometer thick In-layer on Si(1 1 1) surface at 300°C (this is the minimum deposition temperature to grow good quality InSb films). Although, we are not sure at present about the In–Sb interface reaction on the H-terminated Si(1 1 1), the above result prompted us to verify the possibility of growing high-quality InSb films on Si(1 1 1) substrates without an In-prelayer. Our preliminary results indicated that growth of epitaxial InSb films on Si(1 1 1)7×7 surface is relatively easy, compared to the growth on Si(0 0 1) substrate [14].

In the present paper, we report the direct heteroepitaxial growth of InSb on Si(1 1 1) substrate without using In-prelayer. The importance of two-step growth to improve the crystalline quality and to achieve higher electron mobility is also detailed. In addition, we discuss the effect of growth temperature on the evolution of surface morphology and crystal quality of the InSb films.