Elsevier

Applied Surface Science

Volume 440, 15 May 2018, Pages 939-945
Applied Surface Science

Full Length Article
Growth and characterization of InSb on (1 0 0) Si for mid-infrared application

https://doi.org/10.1016/j.apsusc.2018.01.219Get rights and content

Highlights

  • InSb layer was grown on exact (1 0 0) Si using an AlSb/GaSb buffer.

  • Interfacial misfit arrays accommodated lattice mismatch in the buffer.

  • The quality of InSb grown on AlSb surface was higher than on GaSb surface.

  • InSb layer exhibited the highest 300 K mobility of 20,202 cm2/V s.

  • InSb photoconductors on Si was developed and characterized.

Abstract

Monolithic integration of InSb on (1 0 0) Si is a practical approach to realizing on-chip mid-infrared photonic devices. An InSb layer was grown on a (1 0 0) Si substrate using an AlSb/GaSb buffer containing InSb quantum dots (QDs). The growth process for the buffer involved the growth of GaSb on Si using an interfacial misfit array, followed by InSb QDs on AlSb to decrease the density of microtwins. InSb layers were separately grown on AlSb and GaSb surfaces to compare the effect of different interfacial misfit arrays. The samples were characterized using transmission electron microscopy and X-ray diffraction to determine the structural properties of the buffer and InSb layers. The InSb on the AlSb sample exhibited higher crystal quality than the InSb on GaSb sample due to a more favorable arrangement of interfacial misfit dislocations. Hall measurements of unintentionally doped InSb layers demonstrated a higher carrier mobility in the InSb on the AlSb sample than in InSb on GaSb. Growing InSb on AlSb also improved the photoresponsivity of InSb as a photoconductor on Si.

Introduction

The hetero-integration of narrow bandgap semiconductors with (1 0 0) silicon substrates is a fundamental technique for the development of on-chip infrared photonic devices. These devices have a versatile range of uses, from optical communication to emerging on-chip chemical and biological sensors [1]. In particular, devices in the mid-infrared bandgap range (3–8 μm) show great application potential in on-chip optical interconnection [2], thermal imaging and sensing of specific gas molecules (NO, CO, CO2) [3]. InSb is attracting great interest as a material for mid-infrared applications, with a cutoff wavelength of 7.3 μm at 300 K. Heteroepitaxial growth of InSb layers on Si enables the construction of economically efficient on-chip InSb photonic devices, allowing InSb-based photonic devices and Si-based circuits to be monolithically integrated without requiring any bonding process. However, the growth of InSb on (1 0 0) Si substrates is a longstanding challenge due to the relatively high lattice mismatch (19.3%), stemming from the different lattice structures of InSb (zinc-blende) and Si (diamond-like). These differences result in a high density of defects, which suppresses device performance. Moreover, nucleation of InSb on the (1 0 0) Si surface is prohibited because Sb atoms prefer to bond with Si rather than In atoms, resulting in the formation of In metallic islands on Sb-terminated Si surfaces [4]. Therefore, a continuous InSb layer cannot be formed by direct deposition of In and Sb atoms on (1 0 0) Si, and a buffer layer between the InSb layer and the Si substrate is needed.

Mori et al., attempted to grow InSb on Si through a V-grooved (1 0 0) Si substrate, found that InSb grew instead on the (1 1 1) surface [5]. To grow InSb on (1 0 0) Si, a buffer layer was needed. Materials such as Ge, AlSb and GaAs have proved to be effective buffers due to their suitable lattice constants, which are intermediate between InSb and Si [6], [7], [8]. In recent decades, a new approach to the growth of highly lattice-mismatched materials, known as the interfacial misfit (IMF) method, has been developed for cases of heteroepitaxy involving GaSb/GaAs, InSb/GaAs and AlSb/Si [9], [10], [11]. Using this method, a highly periodical IMF array consisting of pure 90° misfit dislocations is formed, which relieves most of the strain energy caused by the lattice mismatch [12], while the threading dislocations arising from the interface are minimal. Compared with 60° misfit dislocations, 90° misfit dislocations are capable of relieving higher strain energies and do not glide to form threading dislocations. This method accommodates the entire lattice mismatch at the interface without a buffer layer; however, carefully controlled growth conditions are important for the formation of the IMF array [10], [13], [14].

In this work, a new buffer structure was proposed and successfully grown using the IMF method, allowing the fabrication of an InSb photoconductor on 0° offcut (1 0 0) Si (exact (1 0 0) Si). The purpose of using 0° offcut (1 0 0) Si due to its totally compatible with standard CMOS fabrication [15]. The formation of an IMF array significantly decreased the buffer thickness and threading dislocation density in the InSb layer. The new buffer structure included two IMF arrays. The first was located at the GaSb/Si interface. GaSb was grown on a Si substrate instead of on the more common AlSb, as AlSb on Si has been reported to have a high surface roughness [16], which can impair the subsequent growth. In addition to the threading dislocations induced by the large lattice mismatch, an anti-phase domain (APD) is the other dominant defect in InSb on a 0° offcut (1 0 0) Si. When a polar III–V semiconductor compound was grown on nonpolar Si, the formation of a monoatomic step on the Si surface caused part of the atoms of the III–V compound to be arranged in opposite order from those in an ideal lattice [17]. Most of APDs annihilate near the III–V/Si interface [18]. In some situations, the APDs result in microtwins which can propagate across the heteroepotaxial structure [19], [20]. Ko et al. suggested that InSb quantum dots (QDs) on an AlSb surface could act as a defect filter to suppress the microtwin associated with APD [21]. Therefore, following the growth of 120 nm GaSb and 80 nm AlSb, InSb QDs were grown on the AlSb surface. A GaSb layer was sequentially grown to cover the InSb QDs. The lattice mismatch between InSb and GaSb was accommodated through the second IMF array, which was separately formed at two interfaces-InSb/AlSb and InSb/GaSb. To investigate the effect of two different interfaces on the quality of InSb layer, two samples were grown on AlSb and GaSb as referred as “InSb on AlSb” and “InSb on GaSb” and their structural, electrical and optical properties were compared.

Section snippets

Experimental procedure

All samples were grown using a solid-state molecular beam epitaxy (MBE) system equipped with antimony (Sb) valved crackers, which provided a Sb2 flux. The growth process was monitored by in-situ reflection high-energy electron diffraction (RHEED). Before growth, the Si substrates were etched with hydrofluoric acid to remove oxides on the Si surface. The substrates were transferred to the MBE chamber and heated to 950 °C for 30 min to remove residual oxides. RHEED showed a clear (2 × 2) pattern,

Structural properties of InSb on Si

Fig. 2(a) and (b) show [1 −1 0]- and [1 1 0]-directional RHEED patterns, respectively, obtained during the growth of GaSb on Si when the GaSb layer thickness was about 40 nm. At both directions, [1/3]-order streaky exhibits, which is different from the reported (1 × 3) RHEED pattern during the GaSb grown on native substrate under Sb overpressure [22]. This (3 × 3) pattern can be attributed to the superposition of two (1 × 3) patterns from two different domains [23]. In this study, exact (1 0 0) Si

Conclusions

In conclusion, we demonstrated the growth of InSb through an AlSb/GaSb buffer on (1 0 0) Si substrates. A GaSb layer of thickness 120 nm was first grown on Si at 430 °C, with an AlSb prelayer to accommodate the lattice mismatch between GaSb and Si. AlSb with a thickness of 80 nm was subsequently grown, and InSb QDs were finally grown on the AlSb surface to suppress microtwins, the success of which was confirmed using TEM. For the top layer of the buffer, two structures were compared. The first

Acknowledgements

This work was supported by Singapore National Research Foundation through the Competitive Research Program (Grant No: NRF-CRP6-2010-4). The authors of this paper would like to express their gratitude to Dr. Tong Jinchao and Mr. Zheng Yi for their assistance with the photoconductor measurement and valuable discussion.

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