InSb epilayers on GaAs(100) for spintronic and magneto-resistive sensor applications

doi:10.1016/j.physe.2003.08.006

Physica E: Low-dimensional Systems and Nanostructures

Volume 20, Issues 3–4, January 2004, Pages 216-219

https://doi.org/10.1016/j.physe.2003.08.006 Get rights and content

Abstract

Both magneto-resistive sensors and spintronic hybrid semiconductor devices require thin epitaxial layers of high-mobility InSb. Here we study unintentionally doped InSb epilayers grown on semi-insulating GaAs(100) substrates by molecular-beam epitaxy. We have introduced an initial low-temperature growth step extending the work that the NTT group reported in 2000. We find significant improvement in the room temperature mobility for epilayer thickness between 60 and $300 nm$ . The importance of the initial growth step to the epilayer mobility performance is discussed.

Introduction

Recent activities have rekindled interest in semiconductor magneto-resistive (MR) sensors for read heads and other applications [1]. To produce these devices it is desirable to have a material that has a high room temperature (RT) mobility μ (because the geometric magneto-resistive boost is proportional to μ²) and a thin preferably surface-active region (to increase the proximity to the magnetic bit). The fabrication of high mobility, thin InSb epilayers offers a possible route to satisfy these requirements. In addition, this material system is interesting for spintronic applications because of the high spin–orbit coupling. Recent measurement of spin lifetime [2] in n-type degenerate epilayers of InSb are encouraging, suggesting RT spin lifetime of the order of $300 ps$ . For hybrid spintronic devices, where carriers will be injected from a highly spin-polarized magnetic material, there are significant device advantages if the semiconductor epilayer is thin and has high mobility (particularly if Elliott–Yafet [3] is the dominant spin relaxation mechanism).

In the interest of both MR sensors and spintronic applications, we have revisited the study of mobility as a function of epilayer thickness [4]. In order to avoid parallel conduction, semi-insulating GaAs(100) was employed as the substrate for InSb growth by molecular beam epitaxy (MBE).

The main obstacle of acquiring high mobility of the hybrid system comes from the large lattice mismatch (14.6%) between InSb and GaAs. Recently, Kanisawa et al. [5] of NTT in Japan obtained smooth and continuous two-dimensional thin InSb layers down to $30 nm$ by growth on GaAs(111)A substrates (that suppresses initial 3D growth) and by introducing a 3-nm InSb wetting layer grown at 310–325°C. In our study, we have extended the NTT recipe to see if any improvements can be made for growth on GaAs(100) substrates. We demonstrate that the electrical properties appear extremely sensitive to the details of the initial growth step, and improvement in properties is possible particularly for samples between 60 and $300 nm$ thick.

Section snippets

Experimental

The InSb thin films were grown on semi-insulating GaAs(100)-oriented substrates (AXT) in a VG Semicon V80 MBE system. Elemental Sb (7N; UMC) and In (7N; ACROTEC, High mobility grade) were used as source materials from the evaporation of the elements inside normal Knudsen cells. The V/III incorporation ratio was set close to 1, and the sample growth was monitored by Reflection high-energy electron diffraction (RHEED) with an incident angle of 2° throughout this work. For each sample, the GaAs

Results and discussions

Hall measurements were performed between $77 K$ and RT in a magnetic field of $10 mT$ to ensure that a low-field approximation is valid. As is generally applied [5], we use a simple single-carrier single-layer model to determine the RT mobility and carrier concentration. It should be noted that the use of single-carrier single-layer model is only for characterizing the samples. Further investigation for transport properties of InSb layers is outside the scope of this paper and will be discussed

Conclusions

In the present work, we have revisited the problem of producing thin high-mobility InSb films on highly mismatched GaAs(100) substrates, where 3D island growth cannot be suppressed. We have extended a LT/HT growth recipe initially introduced by the NTT group and have greatly improved the electrical properties over a narrow range of film thicknesses. The mobility of a $100 nm$ thick film is increased by 2–3 times, compared with the best previously reported values. This benefit results from the

Acknowledgements

We wish to dedicate this paper to Prof. R.A. Stradling who tragically passed away during the course of this work.

The work is supported by the UK- EPSRC grant GR/R42402 and the EU contract FENIKS: G5RD 2001 00535. We thank QinetiQ for access to processing facilities and Toshiba Research Europe Ltd. for access to magneto-transport facilities.

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InSb epilayers on GaAs(100) for spintronic and magneto-resistive sensor applications

Abstract

Introduction

Section snippets

Experimental

Results and discussions

Conclusions

Acknowledgements

Appl. Phys. Lett.

Phys. Rev. B

Phys. Rev.

Physica Scripta T

Appl. Phys. Lett.

Appl. Phys. Lett.